Dusty Planetary Systems

The formation of gas-giant planets needs to happen before the primordial gas-rich disk dissipates in ~ 6 Myr, while the formation of terrestrial planets and massive planets beyond the ice line is not limited by the presence of gas in the disk and can continue for approximately 100 Myr; a critical step in this latter process is the formation of planetesimals. Observations with the Spitzer Space Telescope showed that there is evidence that at least 15% of mature stars (10 Myr-10 Gyr) of a wide range of masses (0.5-3 MSun) harbor planetesimal belts with sizes of 10s-100s AU. This evidence comes from the presence of an infrared emission in excess of that expected from the stellar photosphere, thought to arise from a circumstellar dust disk. The reason why these dust disks are evidence of the presence of planetesimals is because the lifetime of the dust grains (< 1 Myr) is much shorter than the age of the star (> 10 Myr); therefore, the origin of these dust grains cannot be primordial but must be the result of on-going dust production generated by the collision, disruption or sublimation of planetesimals like the asteroids, comets and Kuiper Belt objects (KBOs) in our solar system. The discovery of the debris disk phenomenon in 1986, a decade before the identification of extra-solar planets around main sequence stars, provided the first evidence that a critical step in the process of planet formation (the formation of planetesimals) is taking place around other stars. The presence of debris disks (and therefore planetesimals) around stars with a very wide range of spectral types, from M-type to the progenitors of white dwarfs - with several orders of magnitude difference in stellar luminosities - implies that planetesimal formation is a robust process that can take place under a wide range of conditions. The study of debris disks sheds light on the formation, evolution and diversity of planetary systems.


Research Lines

  • Study of debris disks at different wavelengths and its interpretation in terms of the frequency and characterization of planetesimal belts and the frequency and timing of Late Heavy Bombardment-type of events in extra-solar planetary systems (goal of the Spitzer-FEPS Legacy Program, the Herschel-DEBRIS Key Program and one of the core projects of the future SAFARI-SPICA instrument).
  • Study of debris disk structure via high-spatial resolution observations and numerical models of dust dynamics to assess whether the complex morphology observed in some spatially-resolved debris disks (inner evacuated regions, warps, off-centered and/or clumpy rings) could be the result of gravitational perturbations produced by one or more medium- to large-sized planets (goal of the Spitzer-FEPS Legacy Program and one of the core projects of the future SAFARI-SPICA instrument). Because the structure of the debris disk is sensitive to planets with a wide range of masses and semi-major axes, and is independent of the system’s age, it covers a parameter space complementary to that of radial velocity, transit and direct imaging techniques.
  • Study of the link between debris disks and planets via:
    • The statistical analysis of Spitzer and Herschel debris disks surveys.
    • The search for planets in protoplanetary and debris disks with Subaru/HiCIAO SEEDS program.
    • Numerical simulations of planetary systems consisting on giant planets and swarms of planetesimals.
  • Solar system-debris disk connection. The study of dust in the solar system dust is critical for the understanding of the debris disk phenomenon because it can shed light on the dust properties, origin, dynamics, spatial distribution and effect of planets on the disk structure; and vice versa, models and observations of extra-solar debris disks can help us place our solar system into context (ZEBRA mission).
  • Estimates and implications of the presence of planetesimals in interstellar space:
    • Prospects for the future detection of one of these objects entering the solar system as a highly hyperbolic comet.
    • Possibility of the exchange of solid material between planetary systems and implications for lithopanspermia; the exchange is done via a dynamical mechanism that yields very low velocity chaotic escape and capture of planetesimals implying increased transfer probabilities.