Hayabusa2’s 2031 goal is similar measurement as its spacecraft customer

Following its profitable assortment of fabric from the asteroid 162173 Ryugu in 2019, the Japan Aerospace Exploration Agency’s (JAXA) Hayabusa2 spacecraft swung by Earth to drop off its valuable cargo in December 2020. But at the same time as scientists proceed to poke, prod, and zap grains of Ryugu to unlock their secrets and techniques, Hayabusa2 has been redirected to rendezvous with two extra asteroids: 2001 CC₂₁ subsequent yr and 1998 KY₂₆ in 2031.

The latter encounter simply obtained a bit extra attention-grabbing, although, as astronomers introduced in the present day they’d found that 1998 KY₂₆ is each smaller and rotating extra rapidly than preliminary observations indicated. In reality, it’s so small that it’s roughly on par with the scale of Hayabusa2 itself.

Small world

Based on information taken by a number of ground-based telescopes throughout 1998 KY₂₆’s latest shut method to Earth final yr and printed in the present day 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 courtroom. It’s additionally one-third the scale of earlier estimates, which had pegged it at almost 100 ft (30 m) in diameter. 

According to 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). Including 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!” stated examine first writer Toni Santana-Ros, of the University of Alicante, Spain, in a press release.

What’s extra, 1998 KY₂₆ is spinning twice as quick as beforehand believed: It makes a full rotation each 5.4 minutes, quite than the beforehand measured worth of about 10 minutes.

These could be nothing greater than staggering stats if not for one factor: While Hayabusa2 will merely fly by 2001 CC₂₁, it’s aiming to briefly contact down on 1998 KY₂₆ in the same 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 completely totally different ballgame.

“The smaller size and faster rotation now measured will make Hayabusa2’s visit even more interesting, but also even more challenging,” stated European Southern Observatory (ESO) astronomer and examine co-author Olivier Hainaut.

Measuring asteroids

Why had been our earlier estimates thus far off? 

Determining the styles and sizes of asteroids is hard. Traditionally, astronomers observe the asteroid — which seems as only a tiny level of sunshine, even with highly effective telescopes — because it strikes by means 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 totally different areas of the asteroid because it spins and decide how rapidly it completes a full rotation. They additionally estimate its form primarily based on the sunshine curve and calculate its sized from the quantity of daylight it displays — brighter asteroids are assumed to be larger, and fainter ones assumed to be smaller. 

But this system isn’t good and the extra observations astronomers can take, the higher. 1998 KY₂₆ orbits the Sun as soon as each 1.4 years at a mean distance of about 114 million miles (183 million km), principally exterior Earth’s orbit (though it does briefly cross our orbit as soon as throughout every of its orbits). According to the paper, since its discovery in 1998, 1998 KY₂₆ by no means obtained brighter than magnitude 24 — some 10,000 occasions fainter than Pluto is presently. That made it tough to check, however in spring 2024, 1998 KY₂₆ handed near Earth at about 12 occasions the gap of the Moon, making it seem brighter and ripe for detailed remark. 

Telescopes akin to ESO’s Very Large Telescope and the U.S.’s Gemini, SOAR, and Víctor M. Blanco 4-meter Telescope, all in Chile, all peered on the area rock because it handed. The new gentle curves measured the asteroid’s spin because it was illuminated by the Sun from a number of totally different angles, which allowed a clearer image of 1998 KY₂₆’s form and measurement. The new views revealed a smaller, faster-spinning asteroid than beforehand assumed — and, primarily based on this new information, one which displays far more daylight than beforehand assumed as properly. Astronomers at the moment are classifying it as an Xe-type asteroid, the one class recognized to mirror such a excessive quantity of daylight.  

Answers await

The asteroid’s small measurement and quick spin even have implications for its construction. Ryugu, for instance, is what astronomers name a rubble pile asteroid, made up largely of accrued smaller bits of particles held collectively by gravity. But what about 1998 KY₂₆, which is smaller and spins a lot quicker than Rygu? Could it even maintain on to rubble on its floor because it spins, quite than flinging it out into area? 

Astronomers say sure, however additionally they can’t rule out the likelihood that 1998 KY₂₆ is a single, stable rock right through, both. If it’s the latter, it could have as soon as been a chunk of a bigger physique that was thrown out throughout a collision. We’ll solely be capable to inform which state of affairs is appropriate 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,” stated Santana-Ros.

According to the paper, ground-based telescopes will be unable to acquire any additional information on 1998 KY₂₆ earlier than Hayabusa2’s go to in 2031. However, the James Webb Space Telescope would possibly be capable to take a peek in March 2028 and January 2029, providing an opportunity to verify the present measurement estimate and maybe give clues to the asteroid’s temperature and density. 

Understanding 1998 KY₂₆ represents a precious alternative to study extra in regards to the roughly 39,000 recognized asteroids whose orbits method Earth’s. While 1998 KY₂₆ is just not itself thought-about a hazard, there are 2,508 presently recognized objects that do have orbits that deliver them shut sufficient to our planet to lift considerations. And, in keeping 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 display the power of present know-how to characterize such small asteroids, bolstering future planetary protection efforts as we search to grasp the objects — significantly the small, stealthy ones — that populate our planet’s native neighborhood.