Japan’s Hayabusa2 probe has successfully completed its mission at the asteroid Ryugu and is now on its way home. It’s expected to get here late next year. Space probes don’t often get to come home, so you might wonder why this one is coming back to Earth. The reason is that it’s what’s called a sample return mission – it’s bringing back pieces of the asteroid!
Sample return missions are great, because they give scientists on Earth a chance to examine samples directly. Normally when we send a probe somewhere we have to think in advance of all the tests we want to carry out, and then we only get to choose the most important ones because of limitations of space and weight, and then if the tests fail or the results are inconclusive there’s no way to follow up or try again (at least no cheap way). Being able to get samples into a lab means we can do a lot more science on them! Sending a probe to an object is like sending the lab to the samples; sometimes you really need to bring the samples to the lab instead.
Hayabusa2 isn’t the first sample return mission. The first was Apollo 11, and all the Apollo missions which landed on the Moon brought samples back to Earth. Most sample return missions haven’t involved sending people to collect the samples, though! The Soviet Union’s Luna series of probes were the first robotic sample return missions. The crew of the Mir space station brought back samples of interstellar dust in a material called aerogel. Aerogel was also used by the Genesis probe to sample the solar wind (Genesis crashed on landing, but still produced useful results), and later by the Stardust probe, to sample a comet’s tail. Hayabusa2’s predecessor was also a sample return mission and brought back samples from the asteroid 25143 Itokawa.
The next sample return mission you’re likely to hear about is called OSIRIS-REx. It’s already at 101955 Bennu collecting samples, and will be returning to Earth in 2023.