An artist’s impression of Japan’s Hayabusa2 space mission touching down on the surface of the asteroid 1998 KY26. New observations with ESO’s Very Large Telescope (VLT)  have revealed that 1998 KY26 is just 11m wide, almost three times smaller than previously thought, and is spinning once every five minutes, which is much faster than expected. The image above shows an updated size comparison between the asteroid and spacecraft. Credit: ESO/ M Kornmesser. Asteroid: T Santana-Ros et al. Hayabusa2 model: SuperTKG (CC-BY-SA).

A new study has revealed the Hayabusa2 space mission’s target asteroid, 1998 KY26, is tinier and faster than thought.

Astronomers have used observatories around the world, including the European Southern Observatory’s Very Large Telescope (ESO’s VLT), to study the asteroid 1998 KY26, revealing it to be almost three times smaller and spinning much faster than previously thought.

The asteroid is the 2031 target for Japan’s Hayabusa2 extended mission. The new observations offer key information for the mission’s operations at the asteroid, just six years out from the spacecraft’s encounter with 1998 KY26.

Astronomer Toni Santana-Ros, a researcher from the University of Alicante, Spain, who led a study on 1998 KY26, said: “We found that the reality of the object is completely different from what it was previously described as.”

The new observations, combined with previous radar data, have revealed that the asteroid is just 11 metres wide, meaning it could easily fit inside the dome of the VLT unit telescope used to observe it.

It is also spinning about twice as fast as previously thought. Santana-Ros added: “One day on this asteroid lasts only five minutes!” Previous data indicated that the asteroid was around 30 metres in diameter and completed a rotation in ten minutes or so. 

Co-author Olivier Hainaut, an astronomer at ESO in Germany, said: “The smaller size and faster rotation now measured will make Hayabusa2’s visit even more interesting, but also even more challenging.”

This is because a touchdown manoeuvre, where the spacecraft ‘kisses’ the asteroid, will be more difficult to perform than anticipated. 

Final target

1998 KY26 is set to be the final target asteroid for the Japanese Aerospace eXploration Agency (JAXA)’s Hayabusa2 spacecraft.

In its original mission, Hayabusa2 explored the 900-metre-diameter asteroid 162173 Ryugu in 2018, returning asteroid samples to Earth in 2020.

With fuel remaining, the spacecraft was sent on an extended mission until 2031, when it’s set to encounter 1998 KY26, aiming to learn more about the smallest asteroids.

This will be the first time a space mission encounters a tiny asteroid — all previous missions visited asteroids with diameters in the hundreds or even thousands of metres. 

Santana-Ros and his team observed 1998 KY26 from the ground to support the preparation of the mission.

Because the asteroid is very small and, hence, very faint, studying it required waiting for a close encounter with Earth and using large telescopes, like ESO’s VLT in Chile’s Atacama Desert. 

Solid chunk of rock

The observations revealed that the asteroid has a bright surface and likely consists of a solid chunk of rock, which may have originated from a piece of a planet or another asteroid.

However, the team could not completely rule out the possibility that the asteroid is made up of rubble piles loosely sticking together.

Santana-Rosa, who is also affiliated with the University of Barcelona, said: “We have never seen a ten-metre-size asteroid in situ, so we don’t really know what to expect and how it will look.

“The amazing story here is that we found that the size of the asteroid is comparable to the size of the spacecraft that is going to visit it! And we were able to characterise such a small object using our telescopes, which means that we can do it for other objects in the future.

“Our methods could have an impact on the plans for future near-Earth asteroid exploration or even asteroid mining.” 

Hainault said: “Moreover, we now know we can characterise even the smallest hazardous asteroids that could impact Earth, such as the one that hit near Chelyabinsk, in Russia in 2013, which was barely larger than KY26.”

The study is published in Nature Communications.