Launched in 1999, Stardust finished its main mission in 2006, sending a tiny sample of particles from the Wild 2 comet to Earth via a parachute-equipped canister. NASA then recycled the probe, sending it past a comet last month to photograph a crater left by a projectile launched by another space probe.
It accomplished one last experiment on Thursday, firing its thrusters until its last hydrazine fuel was gone. The length of that burn, a little under 2 1/2 minutes, will tell engineers exactly how much fuel was left so they can see how accurate their calculations were. That in turn will help with the design and operation of future probes.