The first close-up images of the most distant object ever visited by a space probe have revealed it to be shaped like a snowman.
Ultima Thule is more than 6 billion kilometres from the sun - 44 times further than the Earth - and passed earlier this week by NASA's New Horizons probe.
The first images - taken from 2 million kilometres away - were made up only of pixels, and appeared to show it had a peanut shape.
The latest pictures show not only is it snowman-shaped, it's red like Mars and about as bright as potting soil, NASA scientists said.
"[Ultima's] only really the size of something like Washington DC, and it's about as reflective as garden variety dirt, and it's illuminated by a Sun that's 1900 times fainter than it is outside on a sunny day here on the Earth," said principal investigator Alan Stern.
"We were basically chasing it down in the dark at 32,000mph (51,000km/h) and all that had to happen just right."
The 'head' has been named Thule and the body Ultima.
So far only 1 percent of the data recorded in the fly-by has been downloaded - it'll take 20 months for it all to get here.
Paul Schenk, co-investigator on the agency's New Horizons mission, told RadioLIVE on Wednesday the probe's flyby of distant space rock Ultima Thule - deep in the mysterious Kuiper Belt - has been a great success.
"We've begun the exploration of the outermost part of the solar system - the area that's populated by small, icy bodies out beyond the orbit of Neptune for the first time. We're basically finishing the exploration of the solar system."
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When New Horizons launched in 2006, bound for Pluto, Ultima Thule hadn't even been discovered yet. But after its primary mission of mapping Pluto was complete, scientists aimed it at the newly discovered rock in the far-flung Kuiper Belt, 1.5 billion kilometres beyond the distant dwarf planet.
"We don't have another target identified yet, because it's an area we don't have much data or information on yet," said Dr Schenk.
"If we see another object we can visit, we'll go to it."