Space missions meant to return cosmic samples to Earth are expensive, more complicated and riskier than regular robotic missions, but worth it, scientists say.

Recent sample-return missions, like the Japanese Hayabusa asteroid probe that attempted to gather billion-year-old rock from an asteroid's surface, have proven their usefulness, SPACE.com reported Tuesday.

"With a sample-return mission, you have a resource from which you can harvest information for generations," Michael Zolensky from NASA's Johnson Space Center in Houston said. "It is much easier and more efficient to perform analyses on Earth than anywhere else."

Zolensky was a co-investigator for NASA's Stardust mission, the first to return samples from a comet and from interstellar space. He is also a member of the sample-analysis team for the Hayabusa mission.

The Hayabusa probe plunged into Earth's atmosphere over part of the Australian outback June 13, returning after a seven-year journey in which it encountered the asteroid 25143 Itokawa.

A re-entry capsule containing particles was released from the probe about 3 hours before it plummeted to Earth.

Sample returns are costly, scientists admit, but offer advantages over robotic missions that attempt analyses remotely, like recent Mars missions.

"It's an expensive thing to do," Michael Meyer, Mars chief scientist at NASA headquarters in Washington, said. "But there are huge advantages to sample return. You get to interrogate the sample, and when you do experiments here on Earth, you actually pick apart a rock and look at separate minerals. You can't do that on Mars."