The Japanese Hayabusa-2 spacecraft will touch down on and grab a sample of asteroid Ryugu today. You can watch it live here starting at 3:45 p.m. Central Time this afternoon (Feb. 21). The whole sequence, from touchdown and sample retrieval to ascending back into orbit, will take about 2½ hours. For updates in case plans change, check the Hayabusa Twitter site.
Hayabusa 2 touchdown — live streaming starts 3:45 p.m. CST today Feb. 21; 6:45 a.m. Tokyo time (JST) Feb. 22
This will be the second time Japan has attempted to sample an asteroid. On Nov. 19, 2005, during the first Hayabusa mission, the spacecraft attempted its first touchdown on asteroid Itokawa. After contact, the probe was supposed to fire a small projectile at the surface; dust and bits of rock kicked up by the impact would be collected in a canister for the flight home. But on the way down a sensor detected an obstacle. The probe reacted by placing itself in “safe mode” which prevented the firing device from working. Fortunately, it did touch down for about 30 minutes, disturbing the surface enough for a bit of dust to waft upward into a collection canister. The minute particles finally made back to Earth for analysis in June 2010. If you’re a qualified scientist you can request a study sample from NASA here.
Assuming all goes well, Hayabusa 2 will take a pinch of Ryugu this afternoon from a chosen site marked with a reflective target that was dispatched to the surface earlier. As I write, scientists at the Japan Aerospace Exploration Agency (JAXA) are painstakingly guiding Hayabusa to the surface.
Once it lands on Ryugu — a tiny body just 3,000 feet (914 meters) across and located 170 million miles (274 million km) from Earth — a device will shoot a bullet made of the metal tantalum into the gravelly surface at 985 feet per second (300 m/s). Scientists had hoped for a dustier surface, but it turned out to be so rocky they had to perform new tests firing into gravel in the lab to make sure particles would be released and travel into the canister. It worked! It helps that the gravity of the asteroid is so slight that even modest fragments will blast off from the impact.
Once the sample has been retrieved and sealed in the canister, the probe will back off from Ryugu and return to orbit. At least two more sampling attempts from other parts of the asteroid will be made before Hayabusa 2 departs in December this year and returns to Earth in December 2020.
UPDATE 6:30 p.m. CST: The landing and sample retrieval was a success!