>From strauss@astro.Princeton.EDU Wed Sep 17 17:35:28 1997 Subject: Reading for next time, and thinking about term papers Hello all, As Andrea reminded me just as you were all leaving today, I should assign a writing assignment for next time, which I was only able to shout as you were all leaving. We're going to study the nature of stars, and their births and deaths, next time, so you want to read Chapters 4, 5, and 6 from Goldsmith and Owen's book. As you read, scribble down any questions or thoughts you might have, and we can discuss them in class. Of course, feel free to read Chapters 1-3 as well; we covered some of the material there today, although at a somewhat superficial level. You may also be amused to look forward to the first subsection of Chapter 7 of the book; it settles the question of "What is life?" in a rather profunctory way. The first four chapters of Sullivan's book give a more chatty introduction to our subject. There is a nice description of the Copernican Revolution there. I mentioned briefly that each student is required to give a 15 minute presentation in class on either the midterm paper or the final paper (thus these presentations would be on October 22 or December 10, respectively. I would like to have roughly half the students for each. I would like each of you to decide which one you will do your oral presentation by the third class (two weeks from today), as I want you all to start working on this early. Note that you don't have to decide on your paper topics to make the decision when you are going to give your oral presentation! Let me know by e-mail or at class which you choose. OK, now a fun philosophical question for you all to chew on (and indeed, debate, if you'd like, before next time among yourselves or via e-mail; remember you can send e-mail to everyone in the class by sending it to course-frs131-f@lists.princeton.edu): The typical sizes of stars is like the Sun, which has a radius of 700,000 kilometers, while the typical distance *between* stars is roughly 1 light year, or something like 10^{13} kilometers (notice my lame way of writing scientific notation). That is, the separation of stars is something like 10^7 times their typical sizes, which is why stars essentially never crash into each other; they are too far apart. Note that the entire galaxy has a radius of ~40,000 light years, so even when you get used to the distances between stars, the galaxy is a pretty big place. Let's now do the same calculation for galaxies. The typical distance between galaxies is roughly 2 million light years, which is only 50 times the typical sizes of galaxies. Compare with the factor of 10^7 above for stars! But here's the philosophical question: the entire size of the observable universe is about 10^{10} ly, or about 5000 times the typical separation of galaxies. The point of this is that once one gets used to the distance between galaxies, the universe is not all that big a place. Do you agree? Is the universe a small place? (Note: the observable universe refers to that part of the universe which we can observe, given the finite speed of light, and the finite age of the universe (roughly 10^10 years). Light from any galaxies more distance than 10^10 ly has not had time to reach us yet!). -Michael >From jgbeguin@phoenix.Princeton.EDU Wed Sep 17 18:07:48 1997 On the question of the 'size' of the universe at the galaxy, as opposed to stellar, scale: Perhaps I have a pyro streak, but I can't help being fascinated by collisions of heavenly bodies! As Prof. Strauss pointed out, colissions between star are very rare (though I'd love to be there when it DOES happen) since they are so 'small' and distant. I found it interesting, though, that galaxies are much more tightly packed for their size then are stars.. MUCH more! If they are spaced only about 50 times their own size, one would expect more frequent colissions. I recently read an article on galactic colissions which concluded that, generally, big galaxies tend to tear up and/or eat smaller ones, however, most of the stars make it intact and just end up in another galaxy, or a deformed galaxy. Also, I think the fact that galaxies are generally moving away from each other, because of their common origin at the Big Bang, must reduce the number of colissions significantly. Also, relative to their size, they probably just have less time to collide. So basically, I think there is a lot more to take into consideration than size/spacing ratio in determining star vs. galaxy collisions. Any comments/ideas anyone? --Julien ########################## # # # Julien George Beguin # # 91 Blair Hall # # Mathey College # # Princeton University # # Princeton, NJ 08544 # # U. S. A. # # # ########################## # # # Tel. +1 (609) 258-9091 # # JGBeguin@Princeton.edu # # # ########################## >From strauss@astro.Princeton.EDU Thu Sep 18 09:07:25 1997 Subject: Collisions between galaxies Julien is right, collisions between galaxies are indeed much more common than are collisions between stars, and it is now believed that galaxy collisions are a major factor in the evolution of galaxies. Julien is also right that the expansion of the universe causes the rate of collisions to be smaller than it otherwise would be. It also turns out that the most destructive collision from a galaxie's point of view (that is, one that will distort it the most) is not the fast collisions one might find in very dense environments (like a cluster of galaxies) but rather the slow, "gentle" collisions. This is different from collisions between cars! The slower the collision, the more time gravity has to act to distort the galaxies. Maybe for fun, I'll bring in some slides next time of some dramatic galaxy collisions; they are beautiful to look at. Another question for all you to ponder: what are the time scales we're talking about? How long does a collision between two galaxies typically last? You can figure it out in rough numbers, if I tell you that galaxies move relative to one another at speeds of a few hundred kilometers per second. There seem to be some problems with the e-mail list for this class. Are things coming out OK for you guys? Did you all get Julien's e-mail? If not, let me know, and I'll complain to the powers that be that set up this e-mail list. -Michael >From shep@phoenix.Princeton.EDU Thu Sep 18 12:59:48 1997 Subject: Living clay... Some of you expressed some interest in the comments I made about living clay. First, I must apologize that I was a little off in my description. The theory I was aiming for is the Dual-Origin Theory by A. G. Cairns-Smith. The basic premise is that amino acids could easily form, but that the jump from amino acids to complex chains of RNA or DNA was too difficult to occur naturally. Hence, Cairns-Smith argues that clay structures were the first life forms on Earth. Many of you have probably done the chemistry experiment of seeding a super-saturated solution, a large amount of some crystal is dissolved in hot water, after it slowly cools if another crystal is dropped into the solution, the dissolved atoms begin to come out of solution and add onto the crystal. The end result is that the entire beaker quickly forms a huge crystal. This is an example of crystalline growth. In nature, however, this growth is not nearly as perfect. Clays, for instance, consist of layers of oxygen ions seperated by other positive ions. Replacing some or many of these positive ions does not inhibit the growth of the crystal, and, in fact, the changed structure can be passed along to subsequent layers. This process has some similarity to evolution and inheritance. Cairns-Smith goes on to say that these living crystals started to form organic materials to help the crystal grow. However, once the crystals formed organic materails that started reproducing faster than the crystal, the organic molecules took over. Of course, if this theory were correct one would expect to still find crystal life, which they havent, but no one has really looked either. Anyway, I know that it's a bit off the wall, but does challenge some of the standard concepts of life. Thanks. Shep >From strauss@astro.Princeton.EDU Mon Sep 22 14:08:10 1997 Subject: Expanding universe >>>>> "Chen" == Chen Feng Ng writes: > Hi. I have a question. I read that the universe is expanding, and I > wondered if that meant the solar system was also expanding. If the > solar system is expanding at present, I would expect the rate of > expansion to be so miniscule that it would be very hard to detect. > Chen Feng Ng Hi Chen, This is a very good question; indeed, I asked this question of one of the graduate students in her qualifying exam! The observation that the Universe is expanding holds only on very large scales. We observe that on scales somewhat larger than the mean distance between galaxies, that galaxies are systematically moving away from each other. That is, the expansion of the universe becomes apparent on scales larger than, say, 10 or 20 million light years. This can also be understood theoretically, it turns out, from Einstein's General Theory of Relativity, and holds on scales where the approximation that the universe is roughly uniform is valid. Indeed, on scales that large, this approximation does roughly hold. On smaller scales, like that of our solar system, the universe is anything but uniform and smooth, and one does not expect theoretically for expansion to be taking place. Indeed, very careful observations of all sorts confirms our intuitive notion that the solar system is *not* expanding. -Michael From: shahneil Subject: pondering can radio waves be interpreted into images? or can radio waves be manipulated in such a way so they can capture images? -------------------- Neil Pravin Shah 317 Hamilton Hall Mathey College Princeton, NJ 08544 (609) 258-7194 neilshah@princeton.edu >From strauss@astro.Princeton.EDU Tue Sep 23 09:31:54 1997 Subject: Radio waves Hi Neil, The answer is yes; one can certainly transmit images via radio waves. Television is an example of this; the images are indeed transmitted by radio waves. It is not exactly the same frequency as what your radio actually picks up, otherwise radio and television signals would interfere with each other; television is assigned a range of frequencies (and in particular, a narrow range for each channel) distinct from the range that is used by radio stations. The signal from either radio or television is transmitted as a long linear string; for a television signal, the 2-dimensional image is represented as a series of straight lines, which cover the image; this is transmitted fast enough to update the full image roughly 20 times a second, so motion in the image appears continuous. -Michael >From strauss@astro.Princeton.EDU Wed Sep 24 17:14:30 1997 Subject: This and that Hello all, A few things: First, I ordered another copy of Goldsmith and Owen, and five more copies of Sagan, at the U-store; they say that they should receive them in a week or so. Second, let me remind you that you should let me know by next week whether you want to give your oral presentation at the sixth or twelfth class. It would probably be easiest to let me know by e-mail. To sweeten the pot slightly, people doing an oral on the sixth week can turn in their term paper on the seventh week (after the fall break), while people doing an oral on the 12th week must turn in their term paper on the sixth week. Third, let me remind you of the reading for next week (the material in the following should carry us through most of the following week as well, as we've fallen a bit behind our agenda): Goldsmith & Owen, Chapter 11 Sullivan, Chapters 1-6 Sagan, Chapters 1-4 As you read, jot down any questions you might have, and we'll start class next time discussing some of these questions. Then we will finish our discussion of stars: we still need to talk about nuclear fusion, the nature of stars of different mass, and the death of stars. We'll then move on to our own solar system, which will soon lead to discussions of the early Earth and the origins of life here. It is not too early to start thinking about what you want to do your midterm paper on. Take a look at some possible topics listed on the course home page (http://www.astro.princeton.edu/~strauss/life/paper_topics). And come on by my office to discuss what you would like to write about; as I said before, discussing your topic with me is a requirement! I will be out of town Thursday and Friday of this week, but I'm around all of next week. Finally, I would appreciate any feedback you might have on how the class is going? Do you want more discussion and less lecturing? The other way around? Is the material too complicated? Too easy? Let me know, either by e-mail or by coming by my office. To end, here's a philosophical question to ponder and discuss: We showed in today's class that the lifetime of the Sun, 10^10 years, is roughly the same as the age of the Universe as a whole, 1.5x10^10 years. Is that just a wild coincidence? Did it have to come out that way? Let us ask the question a different way: suppose there were a star with a lifetime of 10^7 years; could intelligent life have developed on a planet in orbit around such a star in such a short time? In the next class, we'll discuss the lifetime of other stars, and indeed ask the question of whether such a star could exist. Cheers, Michael From: "Ollie Williams" Subject: Ollie has a question One thing I thought about last class but forgot to ask was this: If we accept that the universe is infinitely large, and that galaxies are spread out throughout this infinite space, how can we really measure the amount of time since the Big Bang? I'm guessing that 15 billion years was calculated by taking the rate at which other galaxies are accelerating away from us, and sort of putting that rate in reverse to find the time when all galaxies were very, very close to each other. My only problem with this is that we can only see part of the universe, the "visible universe," so are we getting 15 billion years from the time when the visible universe was clustered together? If so, this is not necessarily the time when all matter in the total universe was grouped together. And since there are sections of the universe that are infinitely far away (sections we can't yet see), shouldn't the time since the Big Bang really be 10^infinity years ago? Ollie no understand. Sorry if that's confusing. I don't really know how to phrase it any better. I asked a guy at TI that question last night, and he sort of stumbled away confused. Oh well. Ollie ~~~~~~~~~~~~~~~~~~~~~~~~~ * Ollie Williams, Inc. * oliverw@princeton.edu * =A9 Copyright 1997, All Tights Reserved * La Casa de O-Train: * http://www.geocities.com/SoHo/7570 ~~~~~~~~~~~~~~~~~~~~~~~~~ From: Macauley Peterson Subject: Re: Ollie has a question Well, with regard to the 15 billion yrs estimate: I believe that figure was reached from observations of the farthest objects we can see and from the cosmic background radiation. And as far as infinite time goes: if you believe the Big Bang occurred (and certainly most astronomers do at present), then time, in effect, started at the big bang. So even if 15 billion yrs--a number which has shifted back and forth from time to time--is not quite right, time doesn't have to be infinite for infinite space to exist. Still, I agree, it feels like it should. :) -Cauley From: Daria Karp Subject: Re: Ollie has a question Well, I have a thought- If the universe is really infinite, which is a difficult concept for us to grasp, since we live on a planet and even the largest things we can conceive have an "end"- anyway, If our universe is infinite, isn't it possible that in all that space, multiple "big bang"s could occur all the time, in places so distant that we'll never even know? If our infinite universe was "born" 15 billion years ago, is it possible that it was just born into something that already existed? The thing that is most difficult for me to grasp is the concept of infinity. I accept it, but it's still difficult to comprehend. Just like the length of time humans have been on Earth is but a fraction of a percentage of the age of the planet, is it possible that our universe's age is but a fraction of that of what is really out there. Am I getting too far into this?- Because I'm afraid that at a certain point, an understanding of the origins of the universe might have to incorporate a concept of spirituality. However, the concept of God is so subjective that it would definitely be too sensitive to get into. Can anyone conceive of an alternative that would also be able to explain the birth of the universe? I guess that's too big a request, since astronomers still don't know. I'm just interested in hearing other students' ideas. Sorry if I'm being overly inquisitive. This is just a topic that constantly assaults my curiosity. Toodles, Daria dlkarp@.... From: Daria Karp Subject: just one more thought... If the universe is expanding and stars and galaxies are retreating from us at a rate proportional to distance from us, wouldn't our technology have to be increasing at an almost exponential rate to be able to ever catch up to the retreating stars around which other planets with intelligent life might be orbiting? Is travel to other stars ever going to be possible? From: Julien Beguin Subject: Re: Ollie has a question Providing a God as an agent for the creation of the universe solves nothing, since, this done, one must provide an explanation for the God's creation. It simply adds an extra step. If one insists that a God would be self-creating, why not then the universe? Here is my best atempt to explain "creation from nothing": Imagine a graph of a circle -- which is an analogy to our universe. Now imagine that we are points in this circle that retain memories of points directly left of us, in the -x direction, for a short distance. >From this perspective, as we look 'back' in time (to the left) it will apear as if the universe were smaller, and smaller, and at one point in our 'time' did not exist at all! However, the circle is still there, it simply 'starts' at a certain point along the x axis. Furthermore, we might conclude that the size of our universe is as it is because it was a certain different size at a previous point in 'time', i.e. further left. However, in fact, at each point along the x axis a cross section of the circle will have a certain height, or 'size', not because of the 'size' at another point, but because the circle is governed by a single formula: r^2 = x^2 + y^2. In this sense, the universe could be regarded as having some sort of 'governing equation'. Seen as such, a 'sudden burst of creation from nothing' as seen by us, poses no philosophical problems -- just as a circle starting at a certain point on the x axis, where 'before' there was nothing, poses no problem. The only significant questions are "What determines the equation?" (again "God does" will not solve anything here) and "What is the equation?". The latter is almost certainly beyond the realm of human comprehension, in its entirety at least. The former, however, I find rather intriguing. My best guess, at present, is that the 'equation', and consequently the universe, are determined by a 'natural' condition. This may sound like a throwback to the ancient greeks seeking circles as a 'natural' order for heavenly bodies, but, although their application of the idea clearly did not work, I think it has some merit. Basically, I think the universe posesses the properties it does because it can be no other way -- just as a square MUST have four courners. A square without four corners could not exist, not because things without four corners cannot exist, but because such things are not squares. Likewise, the universe, as a universe, cannot exist in any configuration but that it is in, because if it were not, it would not be the universe! Hope you understood what I am trying to say. It is dificult to explain and may sound like be a load of nonsense, but it sums up my current thoughts on the nature of the universe. :O) See y'all Wednesday. --Julien From: Macauley Peterson Your 2nd note is far (infinitely? :)) more easy to address Daria. The stars that we might travel to at some point in the future are all close enough not to be affected by the type of expansion that we observe in the universe as a whole. On small scales, like our immediate neighborhood in the Milky Way, stars are not necessarily getting farther away. Only on the galactic scale would this be a problem. And I don't think we need to worry--"oh damn we won't be able to get to that galaxy"--at present, since we haven't even gotten our act together to go to Mars yet! Cauley >From strauss@astro.Princeton.EDU Tue Sep 30 1:00:30 1997 Hello all, It turns out that our troubles with the e-mail list for FRS 131 were not quite over. I was not included on the list, which means that I didn't receive any of the e-mails that you all sent out over the last week! That has been straightened out now, and I have received the full backlog. Let me respond to some of them here. Shep wrote talking about the Cairns-Smith model of clay-based life. We will talk a little about this when we talk about the origins of life on Earth. This would be a great topic for someone to do for a term paper! Ollie asks how we measure the age of the universe. The explanation he gave is just about right; by seeing how fast galaxies are moving apart, and asking at what time they were on top of one another, one determines the time at which the density of the universe was infinite. The result of this calculation is the 15 billion years I mentioned in class. The exact number is uncertain for a number of reasons: Measuring velocities of galaxies is easy, but measuring their distances (which you also need for this calculation) is *much* more challenging (after all, you can't just put a yardstick down!). Also, the rate of expansion has not been uniform from the beginning, as gravity works against the expansion. Calibrating this effect is quite challenging. Ollie is right; we can only make statements about the expansion of the visible universe; that material within 15 billion light years. By definition, we have no observations of what the expansion is like further away than that. Thus it is possible in principle that on larger scales, the expansion rate of the universe is quite different; one could imagine what are sometimes referred to as a series of "little bangs" popping off in various regions. This gets rather speculative, to put it mildly! Daria had come up with a similar idea in her e-mail. And it is worth repeating the statement that the "Big Bang" is a singularity in the equations which describe the expansion, which means it is a place in which the equations break down. The physicists are no better at describing what "before the Big Bang" means than anyone else; their equations break down, and they are therefore at a loss. Daria's second question was more straightforward, and Cauley's answer was correct. Chen had asked a similar question earlier; see my response to her. The universe is *not* expanding on scales below about 10 million light years, so, in particular, stars in our galaxy are not receding. Even though galaxies are moving away from us, it is still possible in principle to travel to them. The Virgo cluster is about 30 million light years away, and is receding at 1,500 km/s (ballpark numbers; astronomers love to argue over the exact values). If you had a space-ship that could travel at almost the speed of light (of course completely technically impossible now, but we are allowed to dream, no?), and were willing to fly for 30 million years, we would indeed get there. It is receeding from us; in that time we were travelling, it would be 1500 km*pi*10^7 sec/yr*pi*10^7 years = 1.5x10^18 km, or roughly another 150,000 light years further away. So we have to add a mere 150,000 years to our travel plans to get there. No big deal! The distances are vast, but the point is that if you travel fast enough, you can overtake these galaxies in principle, just like you can overtake a train in front of you which is moving away, in a sufficiently fast car. -Michael From: "Ollie Williams" Wed, 1 Oct 1997 16:39:31 Here are two acronyms for star classification I came up with during class but was afraid to contribute: Ollie Broke Another Friend's Great Karaoke Machine On Baywatch All Females Get Kinky Men Food for thought. Ollie From: shahneil Wed, 1 Oct 1997 19:32:24 i'd like to thank ollie for his nmemonic devices. i forgot to ask one of the questions i had from the reading today. sullivan made some mention of the orientation of the planets in the solar system and how they resembled something in music. can someone please explain the link between music and astronomy? another thing that came to mind was having an optional night lab where we could see through the telescopes at princeton. i was wondering prof. strauss if it would be possible for us to have a look at what astronomers see. the reason i'm sending this to the whole class is so we can show prof. strauss who else is interested . well that's all from me, neil -------------------- Neil Pravin Shah 317 Hamilton Hall Mathey College Princeton, NJ 08544 (609) 258-7194 neilshah@princeton.edu From: strauss@astro.Princeton.EDU Thu, 2 Oct 1997 11:41:59 Hello all, The reference to music comes from Johannes Kepler, who was interpreting the planetary data of Tycho Brahe in the 17th century. Kepler determined a series of empirical laws of the planetary motions, which were later shown by Newton to be a direct consequence of his law of gravitation. Kepler was very influenced by the Greek philosophers, especially Pythagoras, who saw a confluence between the harmonies of music and a mathematical description of nature. They believed that the patterns in nature should match musical harmonies. Kepler saw these harmonies in the orbits of the planets, and worked mightily to show that the orbital periods exhibited various simple ratios. They don't really, in practice, although we'll talk briefly about something called tidal locking, which would have made Kepler happy! In any case, you may have heard the phrase, "music of the spheres", which refers to Kepler's work; "spheres" refers to planetary orbits. -Michael From: strauss@astro.Princeton.EDU Thu, 9 Oct 1997 10:29:38 Hello all, First, let me clear up some facts I got mixed up in yesterday's class. I was talking about orbital resonances between Io, Europa, and Ganymede; their orbital periods around Jupiter are 1.769, 3.551, and 7.155 Earth days, respectively, in the ratio 1:2:4. I had gotten the order of these three, and their respective periods, somewhat confused. Here's an interesting thing to think about. We said that Io is close enough to Jupiter that it is strongly stretched by Jupiter's tidal forces. One can imagine that if the tidal forces are strong enough, that they may do more than stretch; they may simply tear the moon apart. So let's do a calculation. Take a moon of radius r in a circular orbit of radius D in orbit around a massive planet of radius R. We will assume that the moon is small, r << D, and r << R. Let us assume that the planet and the moon have the same density, and let us also assume that the moon is held together by its self-gravity. Now consider two mass elements in the moon; one at its center, and one at its far edge (as seen by the planet). They are both pulled by the planet's gravity, the one at the far edge less so (because it is further away). They are held together by the gravity of the moon. When does the tidal force (the difference in force between the two from the planet, which tries to pull them apart) exceed the gravitational force holding them together? I'll let you do the calculation; you should find that this happens when D < 1.26 R. What you have just derived is called the Roche limit; any poor moon that comes wandering too close to the planet's surface is torn to bits by tidal forces. Roche actually originally did a more detailed calculation than this, and found the limit D < 2.44 R (tidal forces cause instabilities in the moon's structure even further out). If you can find a table of the radii of orbits of the moons and rings of the outer planets, check this out. Are there any moons within the Roche limits of these planets? Where do the rings lie? Another question to ponder; *we* certainly are well within the Roche limit of Earth; after all, we sit at just 1 Earth radius from the Earth's center! Why are we not torn to shreds by the Earth's tidal field? Finally, let me mention that there will be a series of talks given by Bob Kirshner on the evening of October 13, 14, and 15 (8 PM each evening), in Dodds Auditorium (in the Woodrow Wilson School, the large modernistic white building on Washington Road and Prospect). The talks are free and open to the public. Bob Kirshner is talking about supernovae, a subject on which he is one of the world's experts. I believe he is planning to pitch the talks at the layman level. He is a *superb* public speaker; he is definitely worth going to hear! For those of you who do go, a trick question: which well-known late-night talk show host does Dr. Kirshner resemble? Indeed, the resemblance is uncanny.... Cheers, Michael From: Julien Beguin Fri, 10 Oct 1997 17:26:15 > Another question to ponder; *we* certainly are well within the Roche > limit of Earth; after all, we sit at just 1 Earth radius from the > Earth's center! Why are we not torn to shreds by the Earth's tidal > field? I think this is because we are held together principally by intermolecular bonds, rather than by gravity. I suppose that if we were held together purely by the gravity which we create, we probably would be torn apart! From: Macauley Peterson Fri, 10 Oct 1997 19:09:00 I think, more likely, it is because the distance between our feet and our heads is not great enough for tidal forces to come into play. If our height were, say, from here to some significant percentage of the moon's orbit, we would have a problem. Actually, we would have quite a few problems! From: Julien Beguin Fri, 10 Oct 1997 22:43:18 Yes but then we would be so massive that our own mass would be the dominant force in holding us together! I think that even a small body, if it is held together only by gravity, will be broken up by tidal forces since the Roche limit does not specify any particular size as a limit, but rather a distance. Of course, in smaller bodies, intermolecular forces will dominate making it harder to break up. Cauley: But the reason that moons feel tidal forces is that one side (the one closest to the planet) feels the pull of gravity more strongly than the far side. This stretching wouldn't occur if the moon had a diameter of only 1.5 meters. That's what I meant. I intended the other problems to be disreguarded in my example. Julien: Yes but this all cancels out since the Rovhe limit does not vary for objects of different masses. It aplies even at small scales. The only difference at small scales is that intermolecular forces are stronger RELATIVE TO the gravitational forces aplying and can therefore hold small objects together bellow the Roche limit From: strauss@astro.Princeton.EDU Date: Mon, 13 Oct 1997 09:52:20 -0400 (EDT) Hello all, On the debate between Julien and Cauley about the effects of tidal forces on us: Although we are only 1.5 meters tall or so, there is a small difference in the gravitational forces on our heads and our feet; our feet are that much closer to the center of the Earth than is our heads. It's a pretty small effect (can you calculate it?). But as Julien points out, we are not held together by gravitational forces. We weigh only 75 kilos or so; for a body this small, gravitational forces are pretty weak! We would be pretty delicate creatures if this were the case! Indeed, it is molecular forces that hold us together, and indeed hold essentially all solid objects together in our everyday world on scales much smaller than the Earth or Moon. By this point, I have heard from most, although not all, of you on what you want to write about for your midterm paper. I have not yet received an outline from any of you yet; please send that along so that I can give comments. Most convenient would be to send it to me by e-mail. On Wednesday, we will first talk about the geologic history of the rocky planets, and then start the discussion of the origin of life on Earth. I thought it would be fun to redo our discussion of the definition of life; reread the first part of the article by Chyba, which I passed out earlier, in preparation for this. -Michael From: strauss@astro.Princeton.EDU Date: Tue, 14 Oct 1997 14:06:13 -0400 (EDT) Hello all, I've made some updates to the syllabus for our course, in particular, I've added suggestions for readings for the next few classes. Tomorrow we will talk about the origin of life on Earth; I'll mostly work from the article by Horowitz that I passed out two weeks ago, with additional material from Goldsmith and Owen. Next week, we will have the oral presentations; in time we have left, we will discuss the effects of meteorite impacts on life on Earth. Sagan's book has the best discussion of this (Chapters 17-18); I will also pass out additional articles if I can dig them up. After the fall break, we will discuss the possibilities of life on Mars. There are good chapters on this subject in all three of our textbooks. In addition, we will have a guest lecture by Tullis Onstott of the geology department here. He is an expert on Mars, and also on life in extreme environments on Earth. He will talk to us about that; in preparation, there are two recent Scientific American articles to read (both available on the Web; you can click on them from the syllabus page), one by Dr. Onstott himself. That should keep you all reading for a while! -Michael From: "Tind S. Ryen" Date: Tue, 14 Oct 1997 15:08:46 -0400 (EDT) Goldsmith and Owen argue in Chapter 11 that temperature differences are the cause for the seperation of rocky and gaseous planets. While it makes sense that the cooler regions around the protostar could form larger bodies, why then are the planets we suspect around other stars so close? For instance, the planet around Beta Pegasi is suspected to be the size of Jupiter, and to have a orbit of only FOUR days... The only reasons I could think of to explain this is that as a protostar Beta Pegasi was significatly cooler than Sol. Or perhaps the star was late in starting nuclear fusion, providing for a cooler region around it? Anyway, I just though I would bounce some of these ideas around. On another subject, I've started the futile task of trying to get information out of CIT. I'm presenting next week, and I would like to use PowerPoint and then get a projector from CIT. Is anyone else interested in something like this? Thanks for the feedback everyone. Later, Shep From: Michael Strauss Date: Thu, 16 Oct 1997 08:40:33 -0400 (EDT) ------- start of forwarded message (RFC 934 encapsulation) ------- Title: Limits of Life on Earth: Are They the Key to Life on Other Plants? New NSF Grants to Foster Answers Date: October 10, 1997 Media contact: October 10, 1997 Cheryl Dybas NSF PR 97-61 (703) 306-1070/cdybas@nsf.gov Program contact: Mike Purdy (703) 306-1580/mpurdy@nsf.gov LIMITS OF LIFE ON EARTH: ARE THEY THE KEY TO LIFE ON OTHER PLANETS? New NSF Grants To Foster Answers From scalding hot places that rival Dante's Inferno to frigid locations colder than the dark side of the moon, scientists taking part in a $6 million National Science Foundation (NSF) research initiative are searching for life forms on Earth that may provide insight about possible life on other planets. The first NSF awards in this initiative -- which is titled Life in Extreme Environments (LExEn) -- involve more than 20 research projects and some 40 scientists who will look at life in Earth's most extreme habitats. "Life flourishes on the earth in an incredibly wide range of environments," explains Mike Purdy, coordinator of the NSF initiative. "These environments may be analogous to the harsh conditions that exist now, or have existed, on earth and other planets. The study of microbial life forms and the extreme environments they inhabit can provide new insights into how these organisms adapted to diverse environments, and shed light on the limits within which life can exist." NSF's directorates of biological sciences; engineering; geosciences; mathematical and physical sciences; and office of polar programs are providing total funding of $6 million to explore the relationships between organisms and the environments in which they exist. A strong emphasis has been placed on environments that are near the extremes of conditions on earth. Funding will also support research about our solar system and beyond, to help identify possible new sites for life beyond earth. Scientists are studying environments such as the earth's hydrothermal systems, sea ice and ice sheets, anoxic habitats, hypersaline lakes, high altitude or polar deserts, and human engineered environments such as those created for industrial processes. Projects involve finding techniques for isolating and culturing microbes found in extreme environments, developing methods of studying these microbes in their natural habitats and devising technologies for recovering non-contaminated samples. -NSF- HIGHLIGHTS OF LExEn PROJECTS ú Hyper-arid deserts are among the most extreme environments on earth. The Atacama Desert in Chile, with its rainless regions, is one such hyper-arid desert here on earth. LExEn grantees Frederick Rainey and John Battista of Louisiana State University will investigate the range of microorganisms living in this hyper-arid desert, with the goal of shedding light on the survival of microorganisms in similar extreme environments elsewhere on earth. ú Recent investigations have identified microbial communities in various crustal environments down to 9,200 feet below the earth's surface. Very few microbial samples exist from deep within continental crust, because coring is expensive. But now Tullis Onstott of Princeton University has uncovered a unique opportunity to study microbial communities at depths more than 10,000 feet below the surface: in the gold mines of South Africa. Reconnaissance samples taken from a hole bored into a uranium-rich, gold-bearing mine in South Africa have shown the presence of intact microbial cells. Onstott will examine the relationship between mineralogy and bacteria living in these deep rocks by conducting intensive research at one particular South African gold mine. ú Microorganisms may lie, Lazarus-like, viable but entombed in ice sheets and ice caps of the Tibetan plateau, the South American Andes, and the north and south polar regions. A project by Lonnie Thompson and Ellen Mosely-Thompson, glaciologists at Ohio State University (OSU), and their colleagues will resuscitate microorganisms from ice cores kept at OSU's Byrd Polar Research Center, and use recovered DNA from the organisms to determine relationships to other organisms, as well as abundance and age. The scientists will assess the longevity of the organisms as well as the diversity of tiny life-forms deposited at the same geographical site thousands or even hundreds of thousands of years apart. The researchers hope to uncover extinct genes or gene fragments to compare with modern counterparts. ú What is the telltale signature of past life in extreme environments? The University of Rochester's Ariel Anbar and colleagues will study whether stable isotopes of key metabolic metals fractionate -- and leave their "John Hancock" -- when the metals are taken up and metabolized by microorganisms. If this is the case, the method could be used to identify traces of life in extreme environments where other "biomarkers," or signs of life, cannot be used. The study will focus on copper and zinc isotopes expected to be abundant when these metals are taken up by microbes in a process catalyzed by enzymes, and iron isotopes expected when iron is reduced in reactions mediated by microbes. ú Many regions of the solar system where life is postulated to exist, such as the oceans of Jupiter's moon Europa, are characterized by pressures far greater than those experienced at earth's surface. Relatively little data exists on the nature of barophilic (high-pressure-loving) life forms, or the pressure boundaries within which life may exist. Douglas Bartlett of the Scripps Institution of Oceanography in La Jolla, California, will conduct research on genetic components associated with survival in high-pressure conditions. In his studies, Bartlett will use so-called hyper-barophiles recently obtained from a high-pressure location at the bottom of the Japan Trench, a deep-sea location where pressures reach many tons per square inch. ú How does one study the ancient climate of Mars? James Kasting of Pennsylvania State University hopes to look back through time and see what the paleoclimate on Mars was like. Early Mars appears to have had a warm and wet climate, but existing climate models have been unable to explain this hypothesis. The answer may lie in methane, which, if added to the Martian paleoatmosphere, may have brought the surface temperature above the freezing point of water early in the planet's history. But where would this methane have come from? Such a source could, in principle, have been provided by bacteria living on the surface of early Mars. ú Water, water, everywhere, and how critical to the existence of life, but is it preserved as liquid beneath the icy crust of Charon, Pluto's moon? Until now, researchers have believed that water may be maintained on planetary surfaces through radiative heating from nearby stars. Douglas Lin from the University of California and coworkers will examine whether a layer of water can persist below the surface of a planet's moon, maintained as liquid by tidal interaction between planet and moon. They will analyze such interaction between Pluto and Charon as well as between Uranus and its "satellites." From: strauss@astro.Princeton.EDU Date: Thu, 16 Oct 1997 09:57:37 -0400 (EDT) Hello all, Just so that it is absolutely clear: those of you who are *not* giving a presentation next week must turn in their midterm papers at that time. Those who are giving presentations may turn in their papers the next time we meet, following the Fall break, on November 5. Most of you have given me outlines for their papers by this point, and I have gotten one first draft for comments. Let me express my willingness (indeed, eagerness) to talk to you about your papers and/or presentation, to read a first draft and give comments, and so on. I am around essentially all the time between now and two weeks from now (at which point I leave for a week of observing in Hawaii, getting back just in time for class on November 5), so please come on by. I am sorry if I sound like a broken record, but please practice your talk beforehand. Fifteen minutes is a short amount of time, and without practice, it is easy to lose a lot of time to getting started, overly long introductions, etc. Take a look at my notes on guidelines for writing the papers and giving the presentations: http://www.astro.princeton.edu/~strauss/life/talks.notes As I mentioned before, we have a quite extensive slide collection here in the astronomy department covering all astronomy topics; you may find it useful to select from this. I can also supply people with overhead transparencies, if they would like to use those. Just let me know. I suggest the following order for the presentations next week: Daria Shep Cauley Julien Neil Kelly Chen Let me know if this causes any problems. Shep asks in his e-mail from a few days ago why giant planets are seen so close to their stars in the planetary systems known outside of our own solar system. We will discuss these planetary systems in some detail (probably on November 12), but the quick answer is that these discoveries have really turned a lot of our basic ideas about how planetary systems form on their head. We'll have a guest lecture from Scott Tremaine, a member of my department, who is researching exactly this question. It is clear that our models for the formation of planets will be undergoing some real revisions in the next few years! -Michael Hello all, As you may know, I am teaching Astro 203, the introductory astronomy course for non-majors, in the Spring. In addition to the standard textbook, I am considering assigning a popular-level book in astronomy, and asking students to write an essay on one of several topics related to the book. The book I have in mind is our text, "Pale Blue Dot", by Carl Sagan. I'd like to get any feedback from you on how you like the book, and its suitability for a large class. Let me know your opinion by e-mail or in person. Incidentally, I am around all day today except for 12-2; feel free to come by if you'd like to talk about your papers and/or presentations. -Michael Hello all, In the issue of Sky and Telescope that arrived in today's mail, there is an entire article devoted to the issue of life on Europa. Julien, I'll bring it with me to the office tomorrow, and you can make a xerox of it if you'd like. The rest of you (who happen not to be writing papers on exactly this subject) can read the article at your leisure; Sky and Telescope is received by the Astrophysics Library. -Michael Hello all, Let me say again that I was very impressed by the quality of all of your presentations today. You did a very good job, and I (and hopefully all of you) learned a lot of new things today. Let me remind you all of my schedule; I am here through next Wednesday, but will be out of town starting next Thursday, returning early in the morning two weeks from today. I will be in e-mail contact while I am gone, if you would like to ask questions about the papers, etc. I think it was Andrea who pointed out that it would be very interesting to read each others' term papers. What do you think? One way this could be done is if you can put your papers on the Web, and then send e-mail around telling people where you can look at it. Alternatively, send it to me (in plain text format), and I can post it on the course Web page. It might be good to share ideas, and perhaps get some discussions going on some of the issues raised. On a similar note, it was a little frustrating today that given the time constraints, I had to cut off the questions and discussions at the end of each of your presentations, just as things were getting interesting. It might be fun to have an e-mail discussion on some of the issues that were raised today. To start things off, let me ask one question based on each of your presentations; perhaps you can all choose one or two to respond to (and of course, if you have more interesting points to raise, please do so!): 1. Daria pointed out that views of the origin of the universe in various mythologies and philosophies from around the world seem to come in two basic forms; either they believe in an eternal, unchanging universe (the Aristotelian view), or they believe in a single creation event, in which some higher being brought the universe into existence. Question: is it fair to divide or categorize a broad range of philosophies this way? If so, does it tell us something basic about human thought processes that so many different cultures have come up with common ideas? (The great philosopher Carl Jung believed that to a certain extent, the unity of myth was indeed something basic to the human psyche). 2. Shep invoked the centrifugal force in his arguments about why molecular cloud cores collapse into a disk, and then said that this force doesn't exist. Can you come up with a rephrasing of his argument that does not invoke any fictitious forces? 3. Cauley discussed the status of missions to Mars. A discussion we only just got started on was the need to send humans there. It would be tremendously expensive. Do you agree with the Sagan quote that Cauley gave, which basically said that the strongest argument for humans going to Mars was to satisfy our need for a frontier? Are there other arguments for Mars? 4. Julien's discussion of what Europan life might be like was fun. He basically said that they would have advanced senses of touch and smell, but be blind. A question: if such creatures were intelligent, would they learn astronomy? Would they be interested in the possible presence of life on the third planet from the Sun? How might they go about trying to determine whether it exists? 5. If I understood Neil's discussion of Jainism, there was almost a need for life elsewhere, because there needed to be at least one enlightened being (I've now forgotten the term Neil used; it started with a Th) somewhere in the universe, and it doesn't not exist on the Earth. Are there other religions that are as so specifically open to the notion of life on other planets? 6. All of the extremophiles that Kelly described were single-celled, and I believe (although am not sure) that all were bacteria. Could there be multi-celled extremophiles? I know that there are a number of interesting macroscopic creatures that live near the thermal deep-sea vents that Kelly talked about; are these extremophiles? Are they special in any specific way? 7. Chen talked about Louis Frank's observations, which seem to imply that comets are crashing into the Earth's surface at the rate of thousands per day. What consequences might this have to our ideas of how the early Earth formed its oceans and atmosphere? Finally, let me remind you of the various reading assignments to be completed by next time: the various articles I've handed out in class, the Mars chapters of our three books, the comet collisions chapter of Sagan's book, and the two Scientific American articles on extremophiles which are on the Web. Hello all, One thing we perhaps do not do enough of in our class is have open discussions, where I am not lecturing, and people have a chance to talk about a variety of things that interest them. It occurred to me that if people are around over the Fall break, and would be interested, we could hold class at our usual time, at our usual place next week (I'd have to check to make sure the room is free), and spend an hour or two just to talk about some of the issues that have come up. One good topic to start things off, for example, might be the question that came up yesterday; is it the role of religion to "fill in the gaps", as it were, that science leaves? Let me know whether having such a discussion interests you. It would of course be strictly voluntary. I'll send around a note in a day or so letting people know if there is enough interest to do this. -Michael From Kelly, November 1: On Wed, 22 Oct 1997 strauss@astro.Princeton.EDU wrote: > To start things off, let me ask one question based on each of > your presentations; perhaps you can all choose one or two to respond > to (and of course, if you have more interesting points to raise, > please do so!): > 6. All of the extremophiles that Kelly described were single-celled, > and I believe (although am not sure) that all were bacteria. Could > there be multi-celled extremophiles? I know that there are a number > of interesting macroscopic creatures that live near the thermal > deep-sea vents that Kelly talked about; are these extremophiles? Are > they special in any specific way? Hi everyone. Hope that everyone had a fun (and relaxing) fall break. As you probably already know from the Scientific American article, there are no multi-celled hyperthermophiles or even hyperthermophilic eukarya. Hyperthermophiles are mostly archea and some are bacteria. There are a bunch of interesting organisms at the bottom of the ocean including tube worms, clams, and shrimps. I think that people even tried to eat the deep sea shrimps, but said they tasted like sulfur. I think I'll end with that great thought. See everyone on Wednesday! Kelly From Michael, November 5 Hello all, First, a reminder that the reading assignment for next week is Chapter 16 of Goldsmith and Owen, Chapter 7 of Sullivan, and the articles I handed out today. One of these articles, by Alan Boss, is written at an advanced undergraduate level, and so may be somewhat more difficult to plow through; don't worry if you don't understand everything! It is not too late to start thinking about your final paper. This should be a bit more substantial than your midterm paper. I would like each of you to choose a topic for that paper by our 9th class (i.e., two weeks from today); as before, you can choose from the list I have on the Web, or make up your own, and of course, please talk to me to discuss your topic and possible reading material. Now for the funny story about the Martian meteorite, which I promised in today's class, but never got to. There is a fellow, Neil Tyson, who is director of Hayden Planetarium at the American Museum of Natural History in New York City, and also is a lecturer in the Astrophysics Department here in Princeton (if you ever get a chance to take a course from him, do so; he is a fantastic teacher!). He found himself in Washington D.C. in early August of last year, in a lobbying effort to raise money from Congress for a new educational initiative at the Planetarium. He had a scheduled meeting with Dan Goldin, NASA's chief administrator, but upon arriving at his door, was told by his secretary that Dan Goldin would be unable to see him, as some rather urgent business had come up (see if you can guess what that urgent business was!). Neil was not about to fly all the way back to New York empty-handed, and was able eventually to talk his way into Goldin's office, where he gave his spiel about his program. He was able to invoke Goldin's interest, he told me, by bringing up the fact that they had both grown up in the Bronx (Neil had done his homework!), and had their first exposure to astronomy in the Hayden Planetarium, and he left with a pledge of Goldin's support for his program. When he got back to the street, his cellular phone rang; it was his secretary, telling him that one of the major news agencies (I don't remember which one) wanted him for an interview for the evening news to give his expert opinion on the discovery of Mars (as head of Hayden Planetarium, Neil is quite a public figure, and often gets called to report on important astronomical discoveries). This was the first that Neil had heard about this discovery. He agreed to do the interview, provided he be given a copy of the MacKay et al article to be published in Science to read, which was being circulated clandestinely via fax all over the country (I doubt that Morris' mistress was responsible for that part of the leak!). The following morning, Neil was in Peyton Hall, handing out copies of this fax to everyone in the department. I think it had been refaxed several times, and was close to illegible, besides which being filled with mineralogical jargon that none of us astronomers knew. Nevertheless, we read it as best we could. That afternoon, President Clinton held his press conference on the White House lawn announcing the discovery, with Dan Goldin by his side. We all watched it together on TV in Peyton Hall. When Goldin spoke, he invoked the nostalgia he felt, remembering the sense of wonder he felt as a kid growing up in the Bronx, visiting the Hayden Planetarium. Neil nearly fell out of his chair! "I gave him that line! I gave him that line!" -Michael Resent-Date: Thu, 6 Nov 1997 16:37:40 -0500 From: "Tind S. Ryen" Hi everyone. I was just wondering what the general consensus of our class was for colonizing Mars? I would venture to say that most of the public would be against the idea. Is that true for anyone in the class? There are some excellent reasons not to go. Even if we do it faster, better, cheaper it's still a lot of money and time. Can we afford to send manned missions to Mars when more and more people fall below the poverty line here on Earth? Will the scientific merits of the mission compensate for it's cost? Just a thought... Shep Resent-Date: Fri, 7 Nov 1997 09:22:12 -0500 From: strauss@astro.Princeton.EDU Shep asks about people's opinions for colonizing Mars. Before asking this question, one has to first ask whether it makes sense, in the near term, to send a manned mission to Mars. What are the rationales for doing so? Some number of years ago, Bush commissioned a study to look into such a mission, and came up with a price-tag of $450 billion (!). Moreover, it was not at all clear what the astronauts would do once they arrived on Mars. I mentioned a book in class, "The Case for Mars", by Robert Zubrin, that argues that a manned mission could be sent to Mars much more cheaply. At times he gets a bit overly optimistic, but estimates that it could be done for as little as "only" $20 billion (when he is less optimistic, he says it should be twice that). That's a lot of money, but a factor of 20 below the original price tag! It is much cheaper, because he plans not to bring fuel for the return trip along, but rather, synthesize it on Mars' surface. And what is Zubrin's motivation for sending people to Mars? To look for life, of course! He argues that robotic missions are just not good enough to search for life; imagine looking for fossils on Earth with a robot. It just doesn't work; you need trained geologists and microbiologists with microscopes, drilling equiptment, etc... Later in the book, he argues that what we *really* need to do is to colonize Mars. He argues that this could pay for itself, by mining Mars to manufacture various materials which could be sent back to Earth. I must say that this part of the book got rather vague. His strongest motivation for the colonization was the frontier argument that came up in class briefly; we need to go to Mars to give us a frontier spirit again. If anyone would like to borrow the book to read, come on by my office, and I'll lend it to you. Like Shep, I would be interested to hear all of your opinions on this. Does a manned mission make sense? Does colonization make sense? Cheers, Michael From: "Chen Feng Ng" Date: Tue, 11 Nov 1997 14:56:23 -0500 Here's a cute quote that was featured in a Calvin and Hobbes comic a long time ago, but this is the guy who said it: One of the surest signs that intelligent life exists in outer space is that none of it has tried to contact us. - Normandy Allen - Chen ~ dona nobis pacem ~ http://www.princeton.edu/~chenng From: strauss@astro.Princeton.EDU Subject: about papers Date: Fri, 14 Nov 1997 10:49:46 -0500 (EST) Hello all, Let me start by saying that I enjoyed reading your papers a lot. You guys really did an impressive job on them. I think that you all would benefit from reading each other's papers. Some of you have written on similar topics; for example, Daria, Andrea, and Neil have all written on various aspects of the interface between religion and science; Scott and Cauley have written on different aspects of the space program; Chen and Joe have written on theories of the origin of life; Julien and Dan have written on the possibilities of life on Europa and Titan, respectively, and so on. Three of you have put your papers on the Web, and I've made links to these off the course home page. I urge all of you to do this. One way to do so is simply to mail me the text of your paper (in ascii, or plain text format; I'm afraid I can't read Word), and I can put them on the Web. Incidentally, feel free to drop by my office any time if you would like to discuss the comments I wrote on your papers. And as I said in class today, also come by to talk about possible subjects for your final paper. Let me give some general comments on the papers which may be of use as you start thinking about writing your final papers. First, I had asked that you start the paper with an abstract; only a few of you actually did so. An abstract is a one- or two-paragraph summary of the entire paper, labelled as such, from which I can see your main points and lines of argument at a glance. Abstracts are standard for scholarly papers in all fields, especially the sciences. I was a little disappointed that essentially none of you ended up using equations in your papers. There were a few cases where you wrote a description of an equation, in English, without giving the equation itself. I had the feeling that you were afraid that including equations was not appropriate for a term paper. If it is appropriate, by all means include equations in your papers! Similarly, some of your papers would have been much improved with the addition of a few hand-drawn diagrams, or figures xeroxed from books or taken off the Web. Some of you filled lengthy paragraphs with verbal descriptions of various things, that would have been much clearer if you could have referred to a figure. However, it is imperative that if you show a figure, that it be explained in full in a caption. If the figure is taken from an external source (i.e., anything other than one you created yourself), the source should be properly cited. A figure without any discussion or description is not very useful. Finally, it is important that when you present results you have learned about in your reading, that you describe them in enough detail, and with enough explanation, so that they are clear to someone who has not read the material. Occasionally, you would state facts out of context, with little enough explanation that I did not know where they came from. I hope these comments are useful. Let me know, of course, if you have questions. Cheers, Michael From: Kelly Yamasato Subject: Papers on the Web Date: Mon, 17 Nov 1997 21:05:43 -0500 Hi guys! I think there were a few people who were planning to send their mid-term papers to Professor Strauss to put on the web but weren't sure how. If you are one of these people and your paper is currently in Microsoft Word, go to "save as" under File and save it in MS-DOS text. Then you can send the paper to Prof. Strauss as an email attachment. Hopefully this should work. I am not very good with computers, but if anyone would like to send me any questions regarding this, I would be happy to try answer them. See everyone Wednesday. Kelly From: Michael Strauss Subject: Hot news about Mars Date: Tue, 18 Nov 1997 09:01:33 -0500 (EST) Subject: EXISTENCE OF MUCH EARLY WATER ON MARS SAID EXPLAINED THE FOLLOWING RELEASE, STRICTLY EMBARGOED CONSISTENT WITH PUBLICATION IN SCIENCE MAGAZINE, WAS RECEIVED FROM THE UNIVERSITY OF CHICAGO, IN ILLINOIS, AND IS FORWARDED FOR YOUR INFORMATION. Steve Maran, American Astronomical Society EMBARGOED: For release Thursday, Nov. 13, 3 p.m. Central Time (4:00 p.m. EST) An explanation for flowing, liquid water on ancient Mars There is ample evidence from photographs- provided by Viking, Mars Pathfinder and Mars Global Surveyor-of deep channels on the surface of Mars presumably cut by flowing liquid water. How could Mars- at Pathfinder's landing site a chilly minus 100 F-once have been warm enough to have liquid water on its surface? The answer, says a University of Chicago climatologist and his French colleague, is reflective carbon- dioxide ice clouds that retain thermal radiation near the planet's surface. The scientists' theory is published in the Friday, Nov. 15, issue of the journal Science. "This is a problem that has perplexed scientists ever since the '70s, when Viking provided the first detailed images of Mars," said Raymond Pierrehumbert, University of Chicago Professor of Geophysical Sciences. "How can you account for Mars being warm enough to have flowing water, especially when the sun was actually fainter early in Mars' evolution?" Pierrehumbert collaborated with French climatologist Francois Forget, from the Laboratoire de Meteorologie Dynamique du CNRS in Paris. Previous models of the atmosphere of ancient Mars have incorporated carbon dioxide in the atmosphere to use effects similar to global warming to heat the planet. "The problem was," said Pierrehumbert, "when you try to put enough CO2 in the atmosphere to warm it sufficiently, the carbon dioxide condenses out. It was thought that the thick clouds that form as a result would reflect sunlight back to space and actually cool the planet. "When we re-examined this, we found that this dry-ice 'blanket' actually warms the planet because it reflects infrared light back to the surface more than it reflects solar radiation outward." The curious property of carbon dioxide ice clouds, as opposed to the water ice clouds found on Earth, is that the particles are large enough to scatter infrared light more effectively than visible light coming from the sun. Ordinary, Earth-type clouds absorb heat from the planet's surface and re-emit it both back to the surface and to outer space, losing half of the heat in the process. "But the carbon dioxide clouds act like a one- way mirror, and, although not a lot of sunlight gets through to the planet's surface, what does reach the planet is converted to heat, which the clouds then reflect back to the surface," said Pierrehumbert. "This mechanism produces a large enough effect that it can, in fact, warm the planet to the point where it is possible to have liquid water." Pierrehumbert said this climate model provides some clues as to the types of life forms that might have evolved on Mars. "If we're going to be looking for analogues of terrestrial life forms on Mars," he said, "then we should be looking for the kinds of organisms that might evolve in extreme environments, like the bottoms of oceans or in caves. "The conditions on early Mars-some four billion years ago-were a little more like the conditions at the bottom of the ocean than like a rainforest. It would have been dark, warm enough for liquid water, but without a large energy source for photosynthesis," he said. Pierrehumbert and Forget's model also extends the habitable zone on extrasolar planets and increases the likelihood that life exists outside our solar system. Previously, scientists thought that only planets orbiting within 1.37 astronomical units (one AU is the distance between Earth and the Sun) of a star could have water above the freezing point. But if the planets have carbon-dioxide ice clouds, they could have liquid water as far away as 2.4 AU. Mars is 1.52 AU from the Sun. Similarly, carbon-dioxide ice clouds could have played a role in warming Earth when the Sun was fainter than it is today, preventing a global freeze that could have kept Earth locked forever in ice. If the Earth had ever cooled to the point where its oceans had all frozen, it would never have warmed up again because too much solar radiation would have been reflected back to space by all of the surface ice. Pierrehumbert and Forget say their model fits well with a theory proposed by Carl Sagan and Christopher Chyba, and published in Science earlier this year, that a methane and ammonia atmosphere warmed early Mars. "The problem with methane," said Pierrehumbert, "is that it breaks down very quickly when exposed to sunlight, so you need a biological engine-life on Mars-to feed the atmosphere as the methane is depleted. Our model provides the starting conditions under which life could have evolved and started the production of methane gas. And once the gas forms, the carbon dioxide ice clouds actually shield the methane from sunlight and keep it from breaking down as quickly." Pierrehumbert and Forget next plan to tackle the problem of what weather might have been like on early Mars, including the possibility of carbon dioxide blizzards and carbon dioxide-ice glaciers. ### Hello all, I have seen the schedule for talks in the Astrophysics department next semester; there are two scheduled speakers of great interest to this course. Mark your calendars! On Tuesday, February 10, at 4:30 PM, Harry McSween will give a talk, Evidence for life in a Martian meteorite. McSween is one of the world experts on meteorites, and in particular, the Martian SNC meteorites. You may remember that we read an article of his about the history of Martian water, a few weeks ago. On Tuesday, April 7, Jill Tarter will give a talk, Project Phoenix: results from SETI observations on the NRAO 140' and future plans She is one of the "big names" in the SETI world, and indeed, her name will come up in class next week, as we talk about some of the SETI searches that are going on. In particular, we will learn about Project Phoenix. It is widely supposed that the character of Eleonar Arroway in the book "Contact" was modelled on Jill Tarter. Both talks will be at 4:30 PM in the auditorium in Peyton Hall, and of course are open to the public. Given your background from your course, I suspect that you all will be able to follow these talks without too much trouble, although you may not understand every detail. -Michael Hello all, I just received in the mail the December '97 issue of Scientific American. In there is an article by Gibson et al entitled, "The Case for Relic Life on Mars". You should all read this article! You can find it on the Web at: http://www.sciam.com/1297issue/1297gibson.html Let me know if you have trouble pointing at this site, and I will xerox it for class on Wednesday. -Michael From: strauss@astro.Princeton.EDU Date: Tue, 2 Dec 1997 21:34:07 -0500 (EST) Hello all, Let me remind you all that I am expecting outlines for the term papers from all of you. Maybe I didn't make this clear, but thus far, I have only gotten a detailed outline from three of you, and some of you are only now deciding what to talk about. This is of course especially important for those of you who are doing oral presentations a week from tomorrow, but is relevant for all of you. If you are thinking of doing this at the last minute, let me point out that it is already the last minute! Needless to say, I am also expecting you all to have done all the reading that I have assigned (now two weeks ago). For all intents and purposes, you should now have read all the way through our three textbooks (although I think I skipped the odd chapter here and there in my assignments), in addition to my various handouts. I have contacted the relevant people at CIT; we will have an LCD projector for your presentations a week from tomorrow, just as we had for the first round of presentations. Please let me know if you need any other audiovisual help. Cheers, Michael Hello all, I hope you all enjoyed today; I certainly did. Neil was in fine form today! If you like his stuff, you should check out the several books that he's written: Merlin's Tour of the Universe, and Universe Down to Earth. He also writes a monthly column for Natural History Magazine. As I mentioned in class, I urge those of you who have checked out books from the library for your term papers, that are likely to be of interest to others, to xerox and/or take notes on those parts you need and return the book so that others can use it. If you do need to hold onto the book for a while, please send an e-mail to the class telling them who they should go bug if they need the book as well! A good general source of references for further reading can be found in the back of each of our textbooks, especially Sullivan's book, whose listing is particularly complete. Incidentally, another source of useful references are all of your midterm papers. I think there are nine of them now on the Web; check them out off the course home page. It is certainly appropriate to use your classmate's midterm paper as a reference in your term paper, if the subject matter matches... Let me clarify that I am not terribly concerned if two people's paper topics overlap. I simply want to avoid two oral presentations on the same topic. Let me suggest the following order for the oral presentations next week: Ollie Joe Scott Andrea Dan Jen Needless to say, it is important for people to show up right on time! In the remaining half of the class after the oral presentations, I'll present a very brief discussion of SETI (I was hoping to do this today, but Neil took longer than expected!), and we'll finish the course with a free-wheeling discussion of all that we've learned. Cheers, Michael Hello all, I should point out that, even more so than your midterm papers, your final papers are covering a broad enough range of material that there is no way that you can hope to cover it all in depth in a 15 minute oral presentation. There is nothing wrong, and indeed I would encourage you to, restrict the topic of your oral presentation to some subset of all you will write about. It is far better to cover such a subset well, then all the material in a great rush; people will get much more out of your talk. -Michael Hello all, I have a tentative date and time for our showing of the movie Contact. It is January 8, at 7:30 PM, in the Peyton Hall Auditorium. The date is tentative, because I haven't yet confirmed it with Eileen Reeves, who is teaching the Freshman Seminar, "Extraterrestrials and Literature". Please let me know if the time will not work with you; it is still quite flexible. Thanks, Michael Hello all, You will all be interested in the following press release. I've read the original articles (in the January 16 issue of Science, full text on http://www.sciencemag.org/content/vol279/issue5349/), and find the case pretty convincing. The first article looks for amino acids in the meteorite (something the original McKay et al paper did not do), and finds them in the abundances, and with the handedness expected if the meteorite has been contaminated with meltwater from the Antartic glacier. Indeed, all the amino acids found were left-handed, as is true for all amino acids in living creatures on Earth. (It is of course possible that life on Mars also has left-handed amino acids). The second paper looked at the isotopic abundance of the carbon in the meteorite. For reasons I didn't fully understand, one does not expect any appreciable amounts of C14 from the Martian surface itself, while, because our atmosphere and biosphere have C14 in them, the presence of C14 indicates terrestrial contamination. They do indeed find C14 in the meteorite. It would be very interesting to hear what the response of McKay et al to this is. There was a sound bite quoted in an article about this in USA Today (not the best place to learn about science!), which implied that they accepted that there was contamination, but said that this did not change their conclusions about Martian life. Hmmmm.... In any case, let me remind you again that there will be a talk on all of this here in Princeton, at which we will hear the latest: February 10 in the Peyton Hall auditorium at 4:30 PM, by Harry McSween, an expert on Martian meteorites. Cheers, Michael THE FOLLOWING RELEASE WAS RECEIVED FROM THE SCRIPPS INSTITUTION OF OCEANOGRAPHY, AT THE UNIVERSITY OF CALIFORNIA, SAN DIEGO, AND IS FORWARDED FOR YOUR INFORMATION. Please note the strict embargo. Steve Maran, American Astronomical Society EMBARGOED BY SCIENCE MAGAZINE FOR RELEASE: 4 p.m. EST Jan. 15, 1998 MEDIA CONTACTS: Scripps Institution of Oceanography, Cindy Clark or Janet Howard, (619) 534-3624 cclark@ucsd.edu; jehoward@ucsd.edu University of Arizona Lori Stiles, (520) 621-1877 lstiles@u.arizona.edu ORGANIC MATERIAL IN MARTIAN METEORITE FOUND TO BE FROM EARTH Organic material contained in a meteorite heralded as bearing signs of previous life on Mars is actually from Earth. Scientists at UCSD's Scripps Institution of Oceanography and the University of Arizona in Tucson report in two separate papers in the Jan. 16 issue of Science that the potato-sized rock was contaminated by the surrounding Antarctic ice in which it was found. The scientists are the first to publish results of tests of organic material contained in the meteorite, named Allan Hills 84001 (ALH84001), since research teams at NASA's Johnson Space Center and Stanford University announced their results in August, 1996. "This is bad news with respect to using these meteorites to assess whether there ever was or is life on Mars," said Jeff Bada, a professor of marine chemistry who headed the Scripps team. "It shows that the meteorites aren't going to give us a definitive answer." Bada's team analyzed amino acids contained within a sample from the meteorite while Timothy Jull's team at the University of Arizona examined the radiocarbon activity of the bulk organics.=20 "What we found was that, yes, there are amino acids in the meteorite at very low levels, but they are clearly terrestrial and they look similar to amino acids we see in the surrounding Antarctic ice," Bada said. "How they got in there is still an open issue." Likewise, Jull's team used 14C and 13C tracers to determine the origin of the carbonate minerals and organic carbon in the meteorite. Their results indicated that the bulk of organic material in ALH84001 is contaminated material it acquired after falling to Earth. "It looks like regular terrestrial organic material," Jull said. "The 14C content of it suggests that there were several episodes of contamination." Scientists at Johnson Space Center and Stanford reported in Aug. 1996 that they had found the first organic molecules thought to be Martian in origin. Called polycyclic aromatic hydrocarbons (PAHS), these organic molecules were found in easily detectable amounts in tiny globs of carbonate within the meteorite. They also noted finding several mineral features characteristic of biological activity and possible microscopic fossils of primitive, bacteria-like organisms inside the meteorite. Their findings were published in the Aug. 16, 1996, issue of Science. The scientists proposed that very primitive microorganisms may have assisted in the formation of the carbonate, and some of the microscopic organisms may have become fossilized, in a fashion similar to the formation of fossils in limestone on Earth. Jull's analysis of isotopes contained in organic material and carbonate from the meteorite, however, indicates the two are of a completely different origin, making a relationship between the two impossible. "The organic material contains 14C and the carbonate doesn't because the carbonate came from somewhere in space, presumably Mars, and the organic material is a recent addition which took place while the meteorite was sitting on the ice," Jull said. "So, there is no connection between the two things." Bada said he chose to focus his analysis on amino acids within the meteorite because, unlike PAHS, they play an essential role in biochemistry. An expert in the analysis of amino acids, Bada used high-performance liquid chromatography to analyze amino acids in the meteorite to determine their "handedness." He found that the bulk of the amino acids consisted of the left-handed forms similar to that seen in the Allan Hills ice in Antarctica where the meteorite was found. Bada said he could not rule out the possibility that minute amounts of some extra-terrestrial amino acids such as right-handed forms of alanine were preserved in the meteorite. "What we and Tim Jull's team have shown is that there is no evidence in our hands that the meteorite contains any compounds that we could definitely trace to Mars except maybe some tiny mysterious component that we don't understand at this point," he said. Bada said scientists will have to wait until a Mars mission scheduled for 2005 to bring back samples from the Martian surface to determine whether life ever graced the planet. "In the meantime, we can throw any kind of analyses that we want to at these meteorites and we are not going to provide an answer one way or another about whether life existed on Mars," he said. Co-authors of the Scripps paper are Daniel Glavin, a Scripps graduate student; Gene McDonald, of NASA's Jet Propulsion Laboratory; and Luann Becker, of the University of Hawaii. Co-authors of the University of Arizona paper are Christopher Courtney, Daniel Jeffrey and Warren Beck, all of the University of Arizona.