The New Horizons spacecraft has spotted two pairs of small asteroids called 鈥渢ight twins鈥� on the outer edges of our cosmic neighbourhood. These objects may help us understand how planets were formed in the early solar system.
The members of these pairs of asteroids are so close together that we could never tell from any Earth-based telescope that they consist of two separate objects.
鈥淭o make these observations, we had to press the highest-resolution camera on the spacecraft鈥� and the spacecraft itself, to their limits,鈥� said at Johns Hopkins University in Maryland, who presented this work at a virtual meeting of the American Astronomical Society鈥檚 Division for Planetary Sciences on 6 October.
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The two asteroid couples are called 2011 JY31 and 2014 OS393. The spacecraft took hundreds of images of each object, revealing that the asteroids that make up 2011 JY31 are each about 50 kilometres across, and they are separated by a bit less than 200 kilometres. The ones that make up 2014 OS393 are about 30 kilometres across and separated by about 150 kilometres.
New Horizons聽hurtled past Pluto in 2015 and passed close to another distant space rock called Arrokoth in 2019, and continues to explore a region of the solar system called the Kuiper belt. These latest asteroids are part of a population called the cold classical Kuiper belt objects (KBOs), which are some of the most primitive rocks in the solar system.
Including these two sets, we have now observed three cold classical KBOs up close, the third being Arrokoth. 鈥淭wo out of the three are tight twins, which is remarkable and may be telling us something important about the planetesimal formation in the outer solar system,鈥� said Weaver.
Arrokoth appears to have also once been two objects, which fused together in a slow collision. This common property hints that many of the objects in the outer solar system may have started as binaries rather than single large boulders.
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