For those of you who’ve been asking, I think the best way to keep up with the Hayabusa2 mission to asteroid Ryugu is via Twitter, @haya2e_jaxa. The news continues to percolate via websites and various publications, with a sustained ripple when the spacecraft successfully tested its sample mechanism and touched down on the asteroid. I’ll remind you too that the mission team now offers updated systems information in English on its Haya2NOW page for obsessives like me who want a really fine-grained look at what’s going on.
Hayabusa 2 is once again at what JAXA calls its ‘home position’ about 20 kilometers above the asteroid as the multi-part sample selection process continues. JAXA’s news release on the touchdown was to the point:
National Research and Development Agency Japan Aerospace Exploration Agency (JAXA) executed the asteroid explorer Hayabusa2 operation to touch down the surface of the target asteroid Ryugu for sample retrieval.
Data analysis from Hayabusa2 confirms that the sequence of operation proceeded, including shooting a projectile into the asteroid to collect its sample material. The Hayabusa2 spacecraft is in nominal state. This marks the Hayabusa2 successful touchdown on Ryugu.
But really, Twitter carries the excitement of the mission via tweets like these:
[TD1-L08E1] 2/22 at 8:42 JST. The following has been confirmed at Gate 5:
・Projectile was command to fire.
・Spacecraft state is normal.
Based on this, we determined touchdown was successful! A detailed analysis will now be done.
— HAYABUSA2@JAXA (@haya2e_jaxa) February 22, 2019
and photos like the one below, which was sent out to thank worldwide supporters for their thoughts and encouragement. Look at the size of the Hayabusa2 team! Congratulations to all of you.
Upon touchdown within the 6-meter circle selected on the asteroid, the spacecraft fired a tantalum ‘bullet’ into the surface to drive particles outward that the sampling instrument could collect. The craft then rose again, as vividly attested in the photo below, where its shadow is obvious. Two more samples are to be taken before Hayabusa 2 departs the asteroid, the final sampling involving a larger crater deliberately blasted into the asteroid to probe sub-surface materials.
Image: Image captured roughly 1 minute after touchdown at an estimated altitude of about 25m (error is a few meter). The color of the region beneath the spacecraft’s shadow differs from the surroundings and has been discolored by the touchdown. At the moment, the reason for the discoloration is unknown but it may be due to the grit that was blown upwards by the spacecraft thrusters or bullet (projectile). The photograph was taken with the Optical Navigation Camera – Wide angle (ONC-W1) on February 22, 2019 at an onboard time of around 07:30 JST. (Credit: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu, AIST.)
You may recall that the original first sample collection was scheduled for last October, but had to be delayed because the surface of the asteroid turned out to be rougher than expected. JAXA has been operating two small robotic rovers — MASCOT and MINERVA-II — on the surface, which produced the information that centimeter-sized gravel and larger were to be found there. As the agency reported online, a key question was whether the material was fine enough be released from the asteroid during the sampling events planned, which is why an artificial gravel experiment was performed in Tokyo at the end of December.
Image: Target simulating the surface of Ryugu (Credit: JAXA, University of Tokyo).
As JAXA went on to report:
In the ground test performed during the initial development, even large rocks with similar strengths to carbonaceous chondrite meteorites were crushed when a projectile made of metal (tantalum) with a mass of 5g was injected at about 300 m/s. It was confirmed that material formed from the resulting small pieces could be gathered by the sampler. So in this test, it was predictable that the bullet would crush material that it struck, but what would be the behavior of the gravel surrounding the focus of the shot?
From the results of the experiment, the fragments of gravel that were crushed were released into the surrounding gravel where they collided like billiards to break up the material. The resulting sample amount exceeded the initial assumption that would be released from the surface (Figure 4).
While the diameter of the collision site (crater) made by the impact of the projectile is smaller than when compared to that in a fine regolith layer, it was a sufficient size in comparison with the inner diameter of the open tip of the sampler horn.
The plan is for Hayabusa2 to depart Ryugu in December of this year, with return to Earth toward the end of 2020. Assuming a successful sample return, Hayabusa2 will mark the first time samples from a C-type (carbonaceous) asteroid — the most common, constituting 75% of those known — have been returned to Earth. Naturally we’ll also keep an eye on OSIRIS-REx and its operations at 101955 Bennu, another carbonaceous asteroid, for both sample returns should give us a window into early building blocks of our planet. The OSIRIS-REx sample return is scheduled for 2023.