Several more probes have been designed and built to visit comets in the near future.
Stardust, the 4th Discovery mission launched in February 1999, will collect coma samples from the recently deflected comet 81P/Wild 2 on 2 January 2004 and return them to Earth on 15 January 2006 for detailed laboratory analyses. Stardust will be the first mission to bring samples back to Earth from a known comet and also the first to bring back contemporary interstellar particles recently discovered. These samples should provide important insights into the nature and amount of dust released by comets, the roles of comets in planetary systems, clues to the importance of comets in producing dust in our zodiacal cloud as well as circumstellar dust around other stars, and the links between collected meteoritic samples with a known commentary body. Samples are collected in newly invented continuous gradient density silica aerogel. Stardust is facilitated by a magnificent trajectory designed to accomplish a complex and ambitious flyby sample return mission within the Discovery program restrictions. The remaining science payload, which provides important context for the captured samples, includes a time?of?flight spectrometer measuring the chemical and isotopic composition of dust grains; a polyvinylidene fluoride dust flux monitor determining dust flux profiles; a CCD camera for imaging Wild 2 coma and its nucleus; a shared X band transponder providing two?way Doppler shifts to estimate limits to Wild 2 mass and integrated dust fluency; and tracking of the spacecraft’s attitude sensing for the detection of large particle impacts. The graphite composite spacecraft brings the collected sample back to Earth by a direct reentry in a capsule.
Stardust, the fourth NASA Discovery mission, launched on 7 February 1999, now circles the Sun in an orbit that will cause a close encounter on 2 January 2004 with the comet 81P/Wild 2. Stardust will collect coma dust at 150 km from Wild 2’s nucleus and return it to Earth for detailed laboratory analysis on 15 January 2006. Figure 1 shows an artist’s rendition of the Stardust spacecraft encountering the comet Wild 2 with the sample collector fully deployed. The Halley Intercept Mission (HIM) proposed in 1981 for the last comet Halley apparition inspired the near 2?decade quest for this comet coma sample return mission, Stardust.
In addition, along the way to Wild 2, the backside of the Wild 2 sample collector will be used to capture interstellar particles (ISP) as bonus science. Besides the primary sample instrument, Stardust also makes in situ investigations to provide important context to the return samples: a time?of?flight spectrometer, a dust flux monitor, an optical navigation camera, an X band transponder for determining integrated dust flux and an estimate of the mass of Wild 2, and monitoring of spacecraft attitude control disturbances for large particle impacts.
The return of lunar samples by the Apollo program provided the first opportunity to perform detailed laboratory studies of ancient solid materials from a known astronomical body. The highly detailed study of these samples revolutionized our understanding of the Moon and provided fundamental insights into the remarkable and violent processes that occur early in the history of moons and terrestrial planets. This type of space paleontology is not possible with astronomical and remote sensing. Despite these advantages, however, the last US sample return was made by Apollo 17 over 30 years ago! Now, 3 decades later, Stardust is leading a new era of sample return missions, including missions to return samples of solar wind [Burnett et al .,2003], asteroid [Fujiwara et al., 1999], and Mars [Garvin, 2002].
Picture Credit : Google