Friday 12 December 2014
to 11:30 at
Migo Mueller (SRON, The Netherlands)
Earth is largely covered in water; life as we know it could not exist without it. But where does it come from? How can a differentiated body like the Earth, which was completely molten in the past, have any surface water at all? How can exoplanets have surface water, if any? These questions fascinate scientists and the general public alike.
It's believed that young Earth accreted a “late veneer” of extraterrestrial material as it formed a lasting solid crust. Water and organic molecules were delivered by comets and/or certain chondritic meteorites, with measured isotope ratios (including but not limited to D/H) favoring the latter (Alexander et al., 2012). Water-rich meteorites contain chemically-bound water. Their parent bodies are low-albedo (albedo=reflectivity) asteroids. Interestingly, recent observations directly showed water vapor outgassing from certain low-albedo asteroids; this demonstrates that asteroids can contain water ice in addition to the chemically-bound water considered so far.
I present recent observations, using the Spitzer Space Telescope, to measure asteroid albedos, thereby constraining the water-rich low-albedo population. In particular, we constrained the physical properties of two ultra-small (D<10m) asteroids considered as targets for NASA's Asteroid Retrieval Mission (ARM) concept. Spitzer-IRS observations of the eclipsing binary asteroid system (617) Patroclus show a surface rich in fine-grained silicates, yet the bulk density is that of water ice.
I also present a recently begun PhD project, aiming at modeling the dynamics of water delivery in the Solar System and, by extension, in exoplanetary systems. The main thrust of this work is to define observational quantities that will allow water-delivery models to be tested using JWST, EELT, and Spica. In doing so, we will be guided by the results of Rosetta, Dawn at Ceres, and two sample-return missions to low-albedo near-Earth asteroids: Hayabusa-2 (launch: end Nov 2014) and OSIRIS-REx (launch planned for Sep 2016).