The first comet astronomers have seen without a tail could hold clues to how the solar system was formed.
Officially known as C/2014 S3, the comet has been dubbed 'Manx' after the tail-less cat breed.
Manx is made mostly of rock, rather than ice, with between 100,000 and 1 million times less water than other comets. Without water there's nothing for the sun to boil off, so there's no tail.
It's the first rocky ball ever spotted coming in from the Oort cloud, a faraway region of space which astronomers believe is the source of many comets.
If they can work out how it ended up out there, instead of in the asteroid belt with the others, it could reveal more about how the solar system ended up the way it is.
"Depending how many we find, we will know whether the giant planets danced across the solar system when they were young, or if they grew up quietly without moving much," says European Southern Observatory astronomer Olivier Hainaut.
Manx was first spotted in 2014 -- hence its rather boring official name -- but the discovery was only announced at the weekend.