The Stardust probe is a veteran of space travel and particularly of meetings with comets: launched in 1999, in early 2004 it met with the comet Wild 2 and besides shooting several photos it also took some samples. In early 2006 it returned to the Earth vicinity where it launched the capsule containing the samples.
The mission went so well that the Stardust spacecraft still had a fair amount of fuel so NASA decided to leave it in orbit around the Sun if the opportunity for a new mission should pop up. In 2007 it was in fact decided to use it for the mission Stardust NExT (New Exploration of Tempel) sending it to the comet Tempel 1 for a close encounter.
Comet Tempel 1, whose official designation is 9P/Tempel, was discovered by astronomer Wilhelm Tempel in 1867. It’s part of the Jupiter comets family with the big planet making its orbit unstable with its gravitational influence.
In July 2005 the Deep Impact probe made the first visit to the comet Tempel 1, in recent days the Stardust spacecraft has taken new photos, including the ones of the crater left by the impactor launched from Deep Impact, and made new measurements to improve our knowledge.
After the close encounter of the past few days with the comet, the Stardust spacecraft will keep on taking pictures as long as it’s at a useful distance from it, then it will be really the end of the operations for this old probe that has definitely done its duty.
The importance of the mission isn’t only in our scientific curiosity to improve our knowledge of comets but also for practical reasons that may become extremely important in the future.
First of all a comet such as Tempel 1 with an unstable orbit could one day come dangerously close to Earth: in recent years we’re keeping an eye on asteroids and comets with increasing attention to verify which of them will pass close to Earth. The fact that comets lose material when sufficiently close to the Sun because the water they contain begins to evaporate and / or sublimate makes it more difficult to trace their routes in long term so a better understanding of their nature is useful to predict the best evolution of their orbits.
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In a future prospect of space travels it’s useful to know thoroughly the nature of asteroids and in some ways even more of comets because they contain large amounts of water whose availability may someday make a difference for space missions with astronauts.
Unfortunately too many people think that these space missions are useless: it would be easy to argue that space agencies have little budgets compared to the military but I think it would be important to make people understand their practical importance besides the addition to our knowledge.
Space missions have produced many technological advancements and if one day we’ll finally start moving out of an overpopulated and polluted planet it will also be thanks to a better understanding of comets obtained through probes such as Deep Impact and Stardust.