Hayabusa2 reaches tiny 1998 KY26
Japan's Hayabusa2, which brought samples of Ryugu to Earth, is due to reach the tiny asteroid 1998 KY26, only about 11 m across, in July 2031. It will be the first close look at an asteroid that spins once every 5 minutes 21 seconds.
The story
In December 2020 Japan's Hayabusa2 dropped about 5.4 grams of material from the asteroid Ryugu into the Australian desert. Only the sample capsule came down. The spacecraft itself headed back into space and began a second journey on its remaining fuel. Its final target is the asteroid 1998 KY26, which it is due to reach in July 2031.
1998 KY26 is only about 11 metres across, similar to the length of a bus. If all goes to plan, it will be the smallest asteroid ever visited by a spacecraft. It also spins very fast, turning once every 5 minutes and 21 seconds or so. Compared with Earth, which turns once a day, that is an astonishing speed.
Why such a small, fast-spinning object does not fly apart is not yet certain. Scientists see two possibilities. The asteroid might be a single solid block of rock, or it might be made of smaller pieces stuck together by weak forces. Only a close look will show which is true.
The spacecraft has already made one stop along the way. In July 2026 Hayabusa2 swept past the asteroid Torifune, also called 2001 CC21, at about 5 km per second and took pictures. Torifune turned out to be made of two lobes pressed together, about 840 m along its longest side. Hayabusa2 will now fly past Earth in December 2027 and June 2028, using its gravity to steer toward KY26.
Mission goals
Small asteroids far outnumber large ones, and they hit Earth more often. The object that exploded over Chelyabinsk, Russia, in 2013, breaking windows across the city, was about 20 metres across. How an object like that breaks up in the atmosphere depends on how solid it is inside. Yet no asteroid this small has ever been studied up close.
A fast-spinning asteroid is a natural test of strength. A rubble pile is known to fly apart if it spins faster than about once every 2.2 hours, because the spin flings its pieces outward. KY26 spins about 25 times faster than that. Detailed pictures of its surface and shape from Hayabusa2 will give scientists their first real observations for judging how strongly small asteroids hold together.
The quick pass by Torifune also mattered. It showed that a spacecraft can photograph an asteroid's shape and surface while flying past at high speed, without stopping to orbit it. That skill could prove useful when a newly found object must be studied in a short time. The Torifune images also gave the team a chance to check the spacecraft's cameras and navigation before the arrival at KY26.
Mission chronology and background
Hayabusa2 launched in December 2014 and reached Ryugu in June 2018. It touched down on the surface twice, in February and July 2019, to collect samples, left Ryugu in November 2019 and sent its capsule to Earth in December 2020. The samples contained several kinds of amino acids and minerals showing that water once soaked through the rock.
The target for the extended mission was chosen in September 2020. Several candidates were checked to see whether the spacecraft could reach them on its remaining fuel and at a suitable time, and KY26 was selected. The deciding factor was that its orbit is close to Earth's, so getting there did not require a large change in speed.
1998 KY26 was discovered on 28 May 1998 with the Spacewatch telescope at Kitt Peak in Arizona. When it passed near Earth that June, radar observations first confirmed its rapid spin. At the time some scientists suggested it might be rich in water, but later observations showed this was not the case. Recent observations suggest instead that its surface is made of bright, almost white rock.
Other milestones of this mission
Where to see it — sky and simulator
1998 KY26 is far too small and faint for amateur telescopes, and Hayabusa2 cannot be seen from the ground either. News of the mission comes through JAXA's Hayabusa2 pages and press releases, and images of the asteroid are expected around the time of arrival. The NowSky simulator does not include Hayabusa2's path, so it does not replay this journey.
The journey since the capsule drop in December 2020 can be laid out in order: the pass by Torifune in July 2026, the Earth flybys in December 2027 and June 2028, and the planned arrival at KY26 in July 2031. Each pass by Earth uses its gravity to shift the orbit a little, until it finally meets the orbit of KY26. Switching on asteroids in the orbit view shows the orbit of Ryugu, the asteroid Hayabusa2 visited earlier.
FAQ
How big is 1998 KY26?
Recent observations put it at about 11 metres across, roughly the size of a bus, spinning once every 5 minutes 21 seconds. It was once thought to be about 30 metres wide, but observations published in 2025 showed it is smaller.
Will it bring back another sample?
No. The sample capsule was already sent to Earth in 2020, so this visit will not return samples. Its main work is to take close-up pictures and measure the asteroid's shape and spin.
When does it arrive?
It is due to arrive in July 2031, after passing Earth twice for gravity assists, in December 2027 and June 2028.
Why this asteroid?
It could be reached on the remaining fuel, and no asteroid this small has ever been studied up close. Its very fast spin also makes it a natural test of how strongly small asteroids hold together.
Related
- OSIRIS-APEX arrives at Apophis
- DART — humanity moves an asteroid
- Apophis flyby (2029)
- Earth — object index
- The Sun — object index
Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.