The asteroid that Japan’s Hayabusa2 spacecraft will meet and land on in 2031 is significantly smaller and rotating much faster than originally believed. These new observations of KY26 were reported on September 18.
The asteroid, known as KY26, was previously estimated by astronomers to be about 30 metres (98 feet) wide and to rotate once every ten minutes, based on brightness observations.
“We found that the object’s reality is completely different from what it was previously described as,” said Toni Santana-Ros, an astronomer at the University of Alicante who is also affiliated with the University of Barcelona and led the asteroid’s studies using the European Southern Observatory’s Very Large Telescope (VLT) in Chile.
However, a new wave of observations from global observatories, including the VLT, combined with radar data, has shown that scientists overestimated KY26’s size and characteristics. KY26 is actually only about 11 metres (36 feet) wide, small enough to fit within the dome of one of the VLT’s eight-metre telescopes. It rotates so rapidly that it completes a rotation every five minutes.
“The smaller size and faster rotation now measured will make Hayabusa2’s visit even more interesting but also more challenging,” said Olivier Hainaut, an astronomer at the European Southern Observatory.
The Japanese Aerospace Exploration Agency’s Hayabusa2 mission is currently on an extended journey that will take it to KY26 in 2031. Its goal is to orbit and land on the tiny asteroid to learn more about its composition and structure. The mission previously rendezvoused with the 900-metre (2,953-foot) wide asteroid Ryugu in 2020 and returned samples to Earth.
“We have never seen a 10-metre (33-foot) asteroid in situ, so we don’t really know what to expect and how it will look,” said Santana-Ros.
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While Santana-Ros is careful to note that a debris pile cannot yet be ruled out, the findings strongly suggest that the asteroid is made of solid rock fragments rather than loose, dusty material. When KY26 arrives, Hayabusa2 will be able to determine its exact composition and structure.
The aim of Hayabusa2 is to collect more information about small asteroids, as these are the most common to strike Earth. But as the VLT’s observations show, we can learn a lot about them without leaving the ground.
“We now know we can characterise even the smallest hazardous asteroids that could impact Earth, such as the one near Chelyabinsk in Russia in 2013, which was barely larger than KY26,” said Hainaut.
Santana-Ros sees even greater potential beyond planetary defences. “Our methods could influence future plans for near-Earth asteroid exploration or even asteroid mining,” he added.
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