JAXA’s Fleet of Mini-Robots Lands on a World Stuffed with Surprises
Within the early hours of 22 February, gentle was simply starting to brighten the campus of JAXA’s Institute of House and Astronautical Sciences (ISAS) in Kanagawa, Japan. It ought to have been a quiet time, however the Hayabusa2 management room was full of individuals. We had been about to land on an asteroid.
Greater than 340 million kilometers (210 million miles) away from us, our spacecraft hovered solely meters above asteroid 162173 Ryugu, ensuring of its focusing on. Then, like its namesake peregrine falcon, Hayabusa2 descended and snatched a pattern. Once we acquired the pictures from the landing, we had been shocked to see a darkish stain over the pattern web site. Ryugu was already the darkest world ever visited; our transient landing had left it darker.
Mission to a NEO
Close to-Earth objects (NEOs) like Ryugu are thought to have as soon as been a part of bigger our bodies that orbited within the asteroid belt between Mars and Jupiter. Collisions between asteroids and the push from photo voltaic radiation can transfer these our bodies onto barely completely different trajectories. These small modifications can have orbital dynamics results, similar to an in depth strategy to Mars that drastically modifications the asteroid’s orbit in order that it approaches the orbit of Earth as a NEO.
The Hayabusa2 mission is analyzing Ryugu’s composition via distant commentary. These information, along with the examination of returned samples, ought to give us clues to this asteroid’s parentage. We will use this historical past to map the motion of water and organics via the photo voltaic system and to the terrestrial worlds. Whereas returning a pattern is a difficult and dangerous endeavor, the analyses that may be carried out in a laboratory again right here on the bottom drastically outstrip something that may be achieved in house.
The predecessor of Hayabusa2—the spacecraft Hayabusa—returned to Earth with a pattern from an S-type asteroid, 25143 Itokawa, in 2010 (see The Planetary Report 30, no. Four). Ryugu is a C-type, or carbonaceous asteroid, a categorization for primitive asteroids which can be anticipated to include carbon-rich materials. One concept for a way Earth turned liveable means that our younger planet was pelted with meteorites from asteroids like Ryugu. These delivered water and easy organics that shaped our seas and triggered the beginning of biology.
Testing this speculation drives the science behind Hayabusa2. If samples from asteroid Ryugu are discovered to include hydrated (waterbearing) minerals or natural compounds that match these on Earth, then C-type asteroids could also be a key element to forming a livable world.
The Hayabusa2 asteroid explorer mission launched on three December 2014. Some 1,302 days later, the spacecraft arrived at its vacation spot. On 27 June 2018, the spacecraft thrusters fired to take care of a continuing place 20 kilometers (12 miles) from the asteroid on a line between Earth and Ryugu. That is our “dwelling place,” the place we carry out nearly all of our distant observations. Our devices revealed a brand new world that shocked the entire group.
Ryugu is roughly 1 kilometer (zero.6 miles) throughout and is formed like a spinning high (or abacus bead), with a thick equatorial ridge. Some of the visually hanging options is a 290-meter-diameter crater that straddles the equator, which we named Urashima. Urashima is the title of a personality in Japanese legend who traveled to a dragon’s underwater palace, Ryugu citadel, and introduced again a treasure field.
The highest form was a shock. Quickly rotating our bodies expertise a centrifugal drive that’s the identical outward push you’re feeling on a merry-go-round. This could push materials towards the equator to create the bulging form of a spinning high. Nonetheless, Ryugu rotates solely as soon as each 7.6 hours, which is just too gradual for reshaping by centrifugal drive to happen. If rotation is the reason for the highest form, then the asteroid should have been spinning sooner prior to now.
Seen via the 7 completely different filters on the telescopic optical navigation digital camera, Ryugu seems homogenous in coloration, with a slight blue tinge to the equatorial ridge. The colour homogeneity is per the speculation that Ryugu shaped from fragments of a bigger asteroid that turned nicely blended as they coalesced. After it shaped, the floor of Ryugu was weathered by radiation and light-weight from the Solar, cosmic rays, and collisions with micrometeorites. This house weathering tends to make a floor darker and redder. When unfastened materials slides down the slope of the steep equatorial ridge, the slides expose brisker materials, providing a possible rationalization for the ridge’s bluer hue.
The anticipated collisional historical past for NEOs meant that we anticipated that Ryugu would have a “rubble-pile” construction: somewhat than a coherent physique, it’s fabricated from rocks held loosely collectively by the asteroid’s gravity. We had anticipated to see a floor pitted with craters and boulders, interspersed with flatter areas and lined with a layer of finer-grained regolith. Nonetheless, we had been shocked to search out that Ryugu seems to have virtually no fine-grained regolith. A worldwide have a look at Ryugu exhibits a homogeneous unfold of boulders bigger than eight meters, whereas nearer inspection reveals a excessive density of boulders about 1 meter in measurement. The biggest boulder, 130 meters throughout and named Otohime Saxum, sits close to the south pole.
Itokawa (the vacation spot of Hayabusa) additionally had a floor lined in boulders. Nonetheless, this asteroid had a flat plain with a width of about 50 meters lined with roughly centimeter- sized grains of regolith. We had anticipated an analogous open house on Ryugu, and its absence made touchdown a critical problem.
Roving an asteroid
Hayabusa2 has Four various kinds of floor operations. The spacecraft carried three rovers, a European- constructed lander, and a Small Carry-on Impactor (SCI) for producing a synthetic crater to reveal subsurface materials. The spacecraft itself additionally wanted to the touch the floor to collect materials.
After virtually 2 months of distant observations, the Japanese and worldwide group members of the Hayabusa2 Joint Science Staff gathered at ISAS to decide on touchdown websites. Information from optical navigation cameras and a laser altimeter had been used to create a three-d mannequin of the asteroid to information the choice. Issues similar to floor temperature, native slope, and boulder density had been main elements for the touchdown web site choices, which additionally needed to be safely separated in distance in order to not intervene with each other.
The day of intense dialogue resulted in selecting websites on the asteroid’s northern aspect for the rovers, the southern aspect for the lander, and near the equator for landing. The websites had been additionally separated in longitude across the asteroid.
A few month in a while 21 September, Hayabusa2 descended to a low altitude of about 55 meters over Ryugu’s floor and separated 2 of the rovers, MINERVA-II-1A and -1B, later named HIBOU and OWL. They had been designed to check movement in a low-gravity surroundings. On Ryugu, there may be not sufficient friction for wheels to roll.
The rovers due to this fact have an inside weight that rotates and rebounds to create a drive that hops the rover throughout the floor. The rovers are photo voltaic powered and autonomous, hopping when their batteries are sufficiently charged. Cameras and thermal sensors ship information again to Hayabusa2, offering a close-up have a look at the rugged panorama.
HIBOU and OWL transmitted information for 113 and 10 Ryugu days respectively after which went quiet. They might have moved right into a shadowed area on the asteroid floor and should have been unable to recharge their batteries. It might be potential to regain contact with one or each because the Solar shifts on Ryugu’s floor later within the 12 months.
On three October, Hayabusa2 descended as soon as once more to deploy the Cell Asteroid Floor Scout (MASCOT) lander. The German (DLR) and French (CNES) house businesses offered this highly effective, shoebox-sized laboratory. The lander was outfitted with Four devices to picture the floor, measure floor temperature and any magnetic subject, and analyze the floor composition. Powered by a lithium battery, MASCOT was designed to final about 16 hours, or 2 asteroid days. It exceeded this expectation by working for 17 hours, and the outcomes are at the moment being analyzed by the European group.
The unique plan was for Hayabusa2 to gather a pattern on the finish of October 2018. Nonetheless, with the floor being extra treacherous than anticipated, we determined to postpone that with a purpose to additional analyze a protected approach to function the landing. On the finish of 2018, everybody on the group celebrated with a limited-edition “landing beer,” created by the Yatsugatake Brewery in Kiyosato. As Japan welcomed within the new 12 months, we started preparations for descending.
To verify the approach for landing and to analyze the panorama in additional element, we carried out three rehearsal descents in September and October 2018. In the course of the third rehearsal, Hayabusa2 descended to an altitude of 12 meters and dropped a goal marker, a extremely reflective, baseball-sized object. A flashlight on the spacecraft can illuminate the marker whereas optical navigation cameras take pictures. The reflective floor makes the marker simple to identify. The spacecraft can monitor the marker’s place and use that to navigate exactly throughout landing.
The high-resolution rehearsal photos revealed precisely how difficult Ryugu’s terrain could be for sampling. Though the boulder density was decrease within the chosen touchdown web site than elsewhere on the asteroid, the flat space we lastly chosen for touchdown was solely about 6 meters throughout. This was far smaller than the 100-meter flat area required by our unique landing plan.
Landing was scheduled for about eight:00 a.m. Japan time on 22 February (23:00 UTC on 21 February), with the descent towards the floor starting the morning earlier than.
Because the sampler horn touched the floor, Hayabusa2 fired a 5-gram tantalum bullet alongside its sampler horn and into the asteroid. This was designed to interrupt up bigger boulders and stir the floor materials to permit a portion to stand up contained in the sampler horn and into the pattern container. Shortly after the spacecraft started to ascend, Hayabusa2 decelerated in order that any materials caught within the inverted tooth of the horn tip could be lifted into the container. At 11:20 a.m. (02:20 UTC), the primary of the three chambers (“room A”) throughout the container closed. We had been happy that we had collected our first pattern.
In March, Hayabusa2 ready to make use of its Small Carry-on Impactor (SCI) to generate a synthetic crater at a web site about 100 levels east of the primary landing level.
The SCI is a cylindrical container containing 9.5 kilograms (21 kilos) of explosive. When detonated, the explosion quickly accelerates a 2-kilogram (Four.Four-pound) copper plate on the bottom of the SCI to a pace of about 2,00zero meters per second. The plate strikes the asteroid to freshly expose subsurface materials. This new crater will enable us to see materials unaltered by house weathering, confirming if the blue tinge on the equatorial ridge is certainly from a less-weathered floor.
The SCI experiment labored as deliberate on 5 April. Earlier than the SCI detonated, Hayabusa2 started an evacuation trajectory that took the spacecraft behind the asteroid and out to an altitude of about three,500 meters in the mean time of the explosion. We didn’t wish to get hit by any escaping particles from the impression!
As this text goes to press, we’re deciding whether or not to gather a second pattern from a area near the crater or from a second web site on the asteroid. This second pattern will doubtless be our final since by July, Ryugu can be nearing the perihelion of its orbit, and its floor will develop into too heat for landing operations.
Hayabusa2 will then proceed to look at Ryugu remotely till the tip of the 12 months and return to Earth with the samples on the finish of 2020. It will be a busy few years!