Hayabusa2 plans to land on an asteroid that's only 36 feet wide and 3.5 million miles away

Hayabusa2 is heading toward an asteroid so small that it is basically the size of the spacecraft. New observations show that asteroid 1998 KY26 is far tinier and spins far faster than scientists thought.

The mission is on course for a rendezvous in 2031, after delivering samples of asteroid Ryugu to Earth in December 2020. Those plans come from JAXA’s official mission overview.

This work was led by Toni Santana-Ros of the University of Alicante. His team’s results now set the stage for how operations must be planned six years out.

Small asteroids are not just curiosities. They are the size class most likely to affect daily life if one ever hits Earth, and they tell us how larger bodies are built and break apart over time.

Details of asteroid 1998 KY26

New peer reviewed analysis indicates that 1998 KY26 is roughly 36 feet (11 meters) across and completes one rotation every 5.3516 minutes. That is about one third the size and twice the spin rate of earlier estimates.

Its surface reflects a lot of sunlight, meaning it has a high albedo and likely comes from a particularly bright class of asteroids.

A surface this reflective does not rule out a loose structure, but it hints at an enstatite-rich makeup that is different from the darker rubble piles we have visited before.

“We found that the reality of the object is completely different from what it was previously described as,” said Santana-Ros.

Landing challenge for Hayabusa2

A 5-minute spin means the surface speed and lighting change rapidly. Touchdown becomes harder, because a probe must match motion and complete tasks in very short windows.

“The smaller size and faster rotation now measured will make Hayabusa2’s visit even more interesting, but also even more challenging,” said Olivier Hainaut of the European Southern Observatory (ESO).

The asteroid is faint, so the team timed their campaign for a favorable, close pass and combined light and radar data.

A lightcurve is the measured change in brightness over time, and by inverting those patterns across many viewing angles, researchers solved for the period and likely shape.

The best fit period is 5.3516 minutes, with a retrograde spin axis and an irregular, slightly elongated body. The radar data, reinterpreted with the new period, point to the smaller size and agree with the optical results.

What the surface may be like

High reflectivity and bright asteroid colors suggest a crust that is rich in enstatite, yet the structure could still be a loose aggregate.

Cohesion of a few to a few dozen pascals could hold a small rubble pile together, even at this spin rate.

On other small bodies, boulders can be fragile and porous. Independent work on Bennu, another near-Earth asteroid, shows boulders with unexpectedly low strength

This is an important clue for how tools and touch-and-go tactics might behave on similarly small targets.

Implications for planetary defense

Objects this size are not rare, but landing on anything that small has never been conceived or attempted.

NASA’s analysis of the 2013 Chelyabinsk airburst puts that impactor near 60 feet (18 meters) across, with consequential energy release in the atmosphere, and with no warning before entry.

The agency’s technical report documents the event’s size and speed.

Better characterization of 10 to 60 foot (3 to 18 meter) objects helps refine risk models and response plans. It also sharpens predictions of how near-Earth object populations evolve under subtle forces.

At this size, sunlight can gently push on the orbit over years through the Yarkovsky effect, the tiny recoil from heat emitted after the surface warms.

Knowing the spin axis and surface properties cuts uncertainty and improves long-term trajectory predictions.

A fast rotator also constrains what shapes can survive. Loose material migrates, cavities matter, and equators may accumulate fines while poles stay bare.

Hayabusa2’s challenge with 1998 KY26

Operations teams prefer slow, predictable surfaces. Here, windows are measured in seconds, not minutes, and instrument exposures must adapt to a moving target.

Landing may still be possible with a “kiss” style maneuver if navigation and timing are tuned.

Even without touchdown, a close escort would deliver the first up close look at a decameter scale asteroid, which is a valuable outcome on its own.

Ground-based observing will not add much before arrival because the target is too faint for most of the decade. Mid-infrared snapshots with JWST could still pin down size and thermal behavior years in advance.

The mission team has time to test playbooks in simulators and to define clear go, and no go criteria for any contact attempt. That breathing room matters when fuel and time are tight at the end of a long journey.

It shows that careful timing with large telescopes can pull reliable physics from a target the size of a house.

It also shows that cross checking old radar with new spin data can unlock size, shape, and surface reflectivity without a spacecraft on site.

That kind of groundwork pays off in terms of safer operations and sharper science. It also builds tools we can use on the next small, fast object we discover on a hurried pass.

The study is published in Nature Communications.

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