JAXA’s Hayabusa2 spacecraft touches down on the tiny asteroid 1998 KY26 on this artist’s impression of their 2013 rendezvous. New information present the asteroid is roughly the identical dimension because the spacecraft itself. Credit score: ESO/M. Kornmesser. Asteroid: T. Santana-Ros et al. Hayabusa2 mannequin: SuperTKG (CC-BY-SA)
The latter encounter simply bought slightly extra fascinating, although, as astronomers introduced right now they’d found that 1998 KY26 is each smaller and rotating extra shortly than preliminary observations indicated. In actual fact, it’s so small that it’s roughly on par with the scale of Hayabusa2 itself.
Small world
Primarily based on information taken by a number of ground-based telescopes throughout 1998 KY26’s latest shut strategy to Earth final 12 months and printed right now in Nature Communications, astronomers have now decided it’s simply 36 ft (11 meters) throughout. That’s roughly the width (not the size) of a doubles tennis court docket. It’s additionally one-third the scale of earlier estimates, which had pegged it at almost 100 ft (30 m) in diameter.
In accordance with JAXA, the Hayabusa2 spacecraft bus (the primary physique of the craft) measures 5.2 ft by 3.2 ft by 4.1 ft (1.6 m by 1 m by 1.25 m). Together with its photo voltaic panels, Hayabusa2 is almost 20 ft (6 m) throughout.
“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!” mentioned examine first creator Toni Santana-Ros, of the College of Alicante, Spain, in a press launch.
What’s extra, 1998 KY26 is spinning twice as quick as beforehand believed: It makes a full rotation each 5.4 minutes, fairly than the beforehand measured worth of about 10 minutes.
These could be nothing greater than staggering stats if not for one factor: Whereas Hayabusa2 will merely fly by 2001 CC21, it’s aiming to briefly contact down on 1998 KY26 in an analogous method to its actions at Ryugu. On 2,960-food (900 m) Ryugu, which spins as soon as each 7.6 hours, that was a difficult however achievable maneuver. On tiny, fast-spinning 1998 KY26, it’s going to be a very completely different ballgame.
“The smaller size and faster rotation now measured will make Hayabusa2’s visit even more interesting, but also even more challenging,” mentioned European Southern Observatory (ESO) astronomer and examine co-author Olivier Hainaut.
This composite picture from the Gemini South Telescope exhibits asteroid 1998 KY26 (circled) as a single level, whereas background stars seem as coloured strains of dots. Credit score: Worldwide Gemini Observatory/NOIRLab/NSF/AURA/T. Santana-Ros
Measuring asteroids
Why have been our earlier estimates up to now off?
Figuring out the sizes and shapes of asteroids is difficult. Historically, astronomers observe the asteroid — which seems as only a tiny level of sunshine, even with highly effective telescopes — because it strikes by way of the sky, monitoring delicate adjustments in brightness over time, known as a light-weight curve. Astronomers search for repeating patterns within the gentle curve, which permits them to map out completely different areas of the asteroid because it spins and decide how shortly it completes a full rotation. In addition they estimate its form based mostly on the sunshine curve and calculate its sized from the quantity of daylight it displays — brighter asteroids are assumed to be greater, and fainter ones assumed to be smaller.
However this system isn’t good and the extra observations astronomers can take, the higher. 1998 KY26 orbits the Solar as soon as each 1.4 years at a mean distance of about 114 million miles (183 million km), largely exterior Earth’s orbit (though it does briefly cross our orbit as soon as throughout every of its orbits). In accordance with the paper, since its discovery in 1998, 1998 KY26 by no means bought brighter than magnitude 24 — some 10,000 instances fainter than Pluto is at present. That made it troublesome to review, however in spring 2024, 1998 KY26 handed near Earth at about 12 instances the space of the Moon, making it seem brighter and ripe for detailed statement.
Telescopes resembling ESO’s Very Massive Telescope and the U.S.’s Gemini, SOAR, and Víctor M. Blanco 4-meter Telescope, all in Chile, all peered on the house rock because it handed. The brand new gentle curves measured the asteroid’s spin because it was illuminated by the Solar from a number of completely different angles, which allowed a clearer image of 1998 KY26’s form and dimension. The brand new views revealed a smaller, faster-spinning asteroid than beforehand assumed — and, based mostly on this new information, one which displays far more daylight than beforehand assumed as effectively. Astronomers are actually classifying it as an Xe-type asteroid, the one class identified to mirror such a excessive quantity of daylight.
In comparison with Hayabusa2’s earlier toughdown goal Ryugu, 1998 KY26 is a few 81 instances smaller and spins virtually 88 instances quicker. Credit score: ESO/M. Kornmesser. Asteroid fashions: T. Santana-Ros, JAXA/College of Aizu/Kobe College
Solutions await
The asteroid’s small dimension and quick spin even have implications for its construction. Ryugu, for instance, is what astronomers name a rubble pile asteroid, made up largely of amassed smaller bits of particles held collectively by gravity. However what about 1998 KY26, which is smaller and spins a lot quicker than Rygu? Might it even maintain on to rubble on its floor because it spins, fairly than flinging it out into house?
Astronomers say sure, however additionally they can’t rule out the chance that 1998 KY26 is a single, stable rock throughout, both. If it’s the latter, it could have as soon as been a bit of a bigger physique that was thrown out throughout a collision. We’ll solely be capable of inform which state of affairs is right as soon as Hayabusa2 will get there. “We have never seen a 10-meter-size asteroid in situ, so we don’t really know what to expect and how it will look,” mentioned Santana-Ros.
In accordance with the paper, ground-based telescopes will be unable to acquire any additional information on 1998 KY26 earlier than Hayabusa2’s go to in 2031. Nonetheless, the James Webb Area Telescope would possibly be capable of take a peek in March 2028 and January 2029, providing an opportunity to verify the present dimension estimate and maybe give clues to the asteroid’s temperature and density.
Understanding 1998 KY26 represents a precious alternative to be taught extra concerning the roughly 39,000 identified asteroids whose orbits strategy Earth’s. Whereas 1998 KY26 is just not itself thought-about a hazard, there are 2,508 at present identified objects that do have orbits that convey them shut sufficient to our planet to boost issues. And, in line with the examine, asteroids the scale of 1998 KY26 “are the most common objects that could cause critical effects on human activities if they impact the Earth.”
The latest measurements reveal the power of present know-how to characterize such small asteroids, bolstering future planetary protection efforts as we search to know the objects — significantly the small, stealthy ones — that populate our planet’s native neighborhood.
