But comets are this scientist's best friends. With Rosetta, ESA started a new project for a rendezvous mission and they needed the instrument developed for CRAF. That's how my odyssey led me to the Max Planck Institute in Garching. At the same time NASA started its new Discovery program. With Stardust they launched their first dedicated comet mission in February 1999 with my impact spectrometer CIDA (Cometary and Interstellar Dust Analyzer) aboard. On the European side, Rosetta was launched March 2, 2004 on its 10-year journey to comet 67P/Churyumov-Gerasimenko.
Another spectacular phenomenon yet to be attempted was the excavation of material from inside a comet. This happens naturally when ices sublime off a comet’s surface as it orbits close enough to the Sun, but nobody is there to watch it. The goal of NASA’s Discovery mission, Deep Impact, was to learn more about the composition of comet Tempel 1. By releasing a copper impactor into the path of the comet in a controlled manner, scientists would create a crater and get a look inside the nucleus.
The experiment at comet Tempel 1 was a full success and the optical instruments returned so much data that the interpretation has been ongoing. The mass density of the comet nucleus was derived, water ice was seen on the surface for the first time, sublimation of ice grains was documented, and emission of water into the sunlit hemisphere in one direction, and of CO and CO2 in a different direction, was identified. Remote observations of the ejected dust cloud helped begin to identify minerals contained therein. Last not least, the crater phenomena allowed us to assume a 1m crust on the nucleus and icy material below. There were big surprises, too: the dust emitted from the crater was finer than expected and obscured the crater itself, a structure as big as 100 m in diameter.
While scientists studied data from Tempel 1, yet another step in cometary investigations was completed in 2006: Stardust’s sample container with coma dust collected at comet Wild 2 was returned to Earth. For the first time real dust from a real comet was in the hand of scientists. They could now use high-resolution machines to evaluate it, which didn’t even exist at the time of launch in 1999. No wonder results keep coming! It takes time to analyze millimeter-sized samples in subunits of 10 nanometers. Once again, amazingly large grains were found along with highly volatile material. The types of minerals suggest that the grains were formed, or at least heated close to, the Sun and then transported to the outer solar system region, where comets originated. Wow!
With all these missions complete and ROSETTA on its long way to the comet, maybe it was time for me to retire. But with exciting new comet explorations on the horizon, retirement does not come so easy. Scientists found new tasks for both the STARDUST and Deep Impact spacecrafts. The Deep Impact spacecraft goes on as EPOXI to visit comet Hartley-2 in November 2010, and the STARDUST craft, having dropped off its sample container, is voyaging on a second mission to comet Tempel 1 as Stardust-NExT. It plans to complete more surface photography when it flies by in February of 2011, and hopefully with a bit of luck will image the crater that was left there by Deep Impact.