The sensitivity of Hayabusa2's LIDAR must be adjusted on a case-by-case basis for a wide variety of conditions around Ryugu. The spacecraft can automatically do this on the fly, but on 16 May, some "noise data" got factored into the adjustment and knocked the LIDAR out of calibration. Upon noticing an altitude discrepancy, Hayabusa2 immediately backed itself away from the surface.
I'm not entirely sure what "noise data" means, but Ryugu is very dark, which messes with the LIDAR and caused a similar glitch last year. In any case, JAXA says they "found [an] adjustment method that could reliably prevent noise mixing. This will be adopted from now on." With this fix in hand, Hayabusa2 descended to Ryugu on 30 May for a second try, and this time, it was successful!
JAXA, Chiba Inst. of Tech
Hayabusa2 second target marker drop
Hayabusa2 drops its second marker on asteroid Ryugu from an altitude of about 10 meters on 30 May 2019. These images were taken from altitudes between 10 and 40 meters.
In my last update I also noted that JAXA was considering collecting the second sample from a region called S01, which is close to, but still a few tens of meters away from the artificial crater Hayabusa2 created using its copper impactor. Scientists believed that a sample from S01 should still contain some subsurface Ryugu material excavated during the impact. Here's a handy map:
JAXA, Tokyo University, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, Aizu University, AIST
Hayabusa2 second touchdown candidate sites
This image, taken before Hayabusa2's SCI operation, shows where the artificial crater was formed, and circles several nearby second touchdown candidate sites.
But wait—why wouldn't they sample directly from the crater itself, to guarantee they get some subsurface material? The reason was that the terrain in that area looked a little too dicey to bring the spacecraft, which spans 6 meters across its solar panels, in for a touchdown.
However, during the aborted touchdown operation on 16 May, mission managers collected some new up-close imagery of the area around the crater, and decided they might be able to sample from it after all! Here's a panorama I made using 2 of the new images Hayabusa2 captured in that area:
JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu, AIST (Panorama by Jason Davis / The Planetary Society)
Hayabusa2 SCI artificial crater site
This panorama of Ryugu's surface near the artificial SCI crater was created using 2 images captured by Hayabusa2 at heights of 500 and 600 meters on 16 May 2019 during an aborted target marker drop attempt. The SCI crater can be seen as a dark splotch in the upper right.
The team liked what they were seeing well enough to drop the second target marker directly in C01, an area that includes the artificial crater:
While the target marker could not be dropped during the PPTD-TM1 operation, we were able to image around the artificial crater at low altitude. As a result, the "PPTD-TM1A" operation will drop a target marker in the CO1 area between May 28 - 30. https://t.co/i7f106Yblbpic.twitter.com/UJlw16hgxh
So what happens now? JAXA’s latest press briefing says they will make a decision on whether to proceed with a second sampling by mid-June. The touchdown itself would be performed "between the end of June and start of July." As I explained in my last update, Hayabusa2 is almost out of time to collect a second sample, because Ryugu is approaching perihelion, which is causing the asteroid’s surface temperature to rise. JAXA now says they have until late July to collect a sample; that's a couple weeks longer than their previous estimates.