NASA space probe OSIRIS-REx is due to drop a capsule containing a sample from an asteroid over the desert of the US state of Utah on Sunday, in a first for the US space agency.
NASA estimates that the capsule contains about 250 grams of debris collected from the asteroid Bennu about three years ago. The probe is expected to release the capsule about 102,000 kilometres above the Earth's surface.
The capsule, protected by a heat shield, is expected to enter the Earth's atmosphere at around 1442 GMT and, with the help of parachutes to slow its descent, touch down an estimated 13 minutes later.
NASA is targeting a landing zone that measures 58 by 14 kilometres.
Once the capsule lands, it will be taken to NASA laboratories in Texas for examination. A team of around 200 scientists hope to analyse the sample using 60 different scientific approaches.
If everything goes well, it would be the first sample of an asteroid to be successfully brought back to Earth in NASA's history - and probably the largest such sample ever taken.
In 2005, the Japanese space probe Hayabusa managed to land on an asteroid. In 2010, it brought back to Earth the first soil samples ever collected from such an asteroid. Although other probes have flown to asteroids, Hayabusa remains the only probe to bring material back to Earth so far.
OSIRIS-REx (the name is an acronym for "Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer") was launched from NASA's Cape Canaveral Spaceport in September 2016 and arrived at Bennu about two years later.
In October 2020, the probe took a sample from the asteroid during a complicated manoeuvre which lasted several hours.
