Japanese scientists have begun to open the Hayabusa asteroid capsule.
The canister, which returned to Earth on 13 June, is being worked on at the Japanese space agency's (Jaxa) Sagamihara Campus in Kanagawa.
It is hoped the vessel will contain small amounts of dust grabbed from the surface of asteroid Itokawa by a spacecraft in 2005.
Researchers said they had already detected a trace gas in the capsule but had yet to identify it.
"We still don't know exactly what kind of gas it is, but the researchers confirmed a trace of low-pressured gas in the capsule," a Jaxa official told AFP.
One of the scientists' key tasks is to make sure the vessel is handled in perfectly sterile conditions. They have to be certain that any substances they recover are extraterrestrial and not merely Earthly contamination.
It is expected to take at least a week to properly open the capsule to get access to its sample containment box.
Scientists say any residues could give them new insights into the early history of the Solar System and the materials that went into building the planets.
"If the capsule contains fragments of at least 10 microns (thousandths of a millimetre), researchers can make an analysis," the Jaxa spokeswoman said.
The capsule's return two weeks ago marked the culmination of a remarkable seven-year adventure, which saw the Hayabusa mission spend three weeks orbiting asteroid Itokawa and attempt to pluck dust from its surface.
The $200m mission encountered many technical problems, from being hit by a solar flare to experiencing propulsion glitches. But each time an issue came up, the Japanese project team found an elegant solution to keep Hayabusa alive and bring it back to Earth - albeit three years late.
The sample capsule fell safely to Earth in Australia thanks to its heat-shield and a parachute. The main Hayabusa spacecraft, however, was destroyed on re-entry to the atmosphere.