| Description |
In September 2010, 25 years will have passed since the first in-situ encounter of a space probe with a comet. This first visit occurred in September 1985 when the International Cometary Explorer (ICE), passed through the tail of P/Giacobini-Zinner. Up to that point, comet and asteroid scientific observations were always based upon remote sensing be they performed from ground or from space. The next opportunity for a comet encounter arose with the return of Halley.s Comet in 1986, whereby many satellites (Giotto, Vega 1 & 2, Suisei & Sakigake) were launched to perform in-situ observations. The first asteroid flybys, Gaspra & Ida/Dactyl, occurred as part of Galileo.s journey to Jupiter. Since this time, NEAR, DS1, Hayabusa, Rosetta, Deep Impact, Stardust-NExT and Dawn satellites have all been launched with the aim of performing flybys, orbiting & sample return.Remote sensing & in-situ measurements are considered highly complementary in nature: remote sensing shows the global picture, but conversion of measured fluxes in physical quantities frequently depends on poorly constrained model parameters (e.g. dust size distribution or fluorescence efficiencies). In-situ techniques measure physical quantities in a more direct way, but are limited in spatial coverage. The benefit of both combined is that we can compare surface composition, reflectance, albedos & temperatures of in-situ and remote sensing and as a result greatly improve the scientific understanding of the objects in question. This proposal focuses on using the Herschel Space Observatory to remotely observe a select set of in-situ comets/asteroids. The down-selection from 29 asteroids & comets to the final eight was made based upon many criteria, the main one being prioritisation of the most important open scientific issues existing for each of the targets for which the Herschel Space Observatory, its sensitivity & wavelength coverage, could indeed contribute in a highly significant and, in specific cases, conclusive way to their resolution. |
