Jason DavisSep 22, 2018

Japan's Hayabusa2 spacecraft successfully drops rovers on asteroid Ryugu

Two small spacecraft the size and shape of cheese wheels have made history by sending home pictures of their successful landing on an asteroid.

The probes, collectively named MINERVA-II1, were dropped from Japan's Hayabusa2 spacecraft Friday onto asteroid Ryugu from a height of about 60 meters. Both landed successfully and are transmitting images and data, and at least one is autonomously hopping around the surface as designed. 

Though small in stature compared to rovers like NASA's SUV-sized Curiosity on Mars, the MINERVA-II1 probes can move, which classifies them as rovers. They are the first-ever rovers to be deployed on an asteroid. 

Image from MINERVA-II1 Rover-1B
Image from MINERVA-II1 Rover-1B This color image, taken immediately after separation from Hayabusa2, was captured by MINERVA-II1 Rover-1B on September 21 at around 4:07 UTC. The surface of Ryugu can be seen in the lower right. JAXA

Hayabusa2, which arrived at Ryugu in June, began the deployment sequence Friday by leaving its "home" position 20 kilometers above the kilometer-wide asteroid. As the spacraft moved closer, it sent home images in real-time, and its shadow appeared on Ryugu like a TIE fighter from Star Wars

Hayabusa2 shadow selfie (closeup)
Hayabusa2 shadow selfie (closeup) Hayabusa2 sees its shadow from an altitude of about 80 meters during operations to release the two MINERVA-II1 rovers on September 21. JAXA

Hayabusa2 successfully deployed the two rovers at 4:06 UTC, but their fate was not initially clear. Voltage levels on the rovers dropped as Ryugu, which makes a full rotation period every 7.6 hours, turned away from sunlight, indicating the spacecraft were most likely safe on the surface.

On Saturday, JAXA released images taken by the rovers. Two were captured immediately after separation, and in one, the Hayabusa2 mothership is visible as a blur of light with ghostly solar panels. 

Minerva-II1 Rover-1A picture 1
Minerva-II1 Rover-1A picture 1 This color image, taken immediately after separation from Hayabusa2, was captured by MINERVA-II1 Rover-1A on September 21 at around 4:08 UTC. The surface of Ryugu can be seen at the bottom. JAXA

The rovers are designed to autonomously hop around the surface without human intervention using small, rotating motors. Thanks to Ryugu's weak gravity, they can stay afloat for 15 minutes, and move 15 meters in any direction. One image from Rover 1-A was apparently captured mid-hop, after it had already begun to explore the surface.

MINERVA-II1 Rover-1A Picture 2
MINERVA-II1 Rover-1A Picture 2 This image was captured by MINERVA-II1 Rover-1A on September 22 at around 2:44 UTC. The image was captured mid-hop after a successful landing. JAXA

MINERVA stands for the "MIcro Nano Experimental Robot Vehicle for Asteroid, the second generation," and is the successor project to a similar rover that flew aboard the first Hayabusa spacecraft that visited asteroid Itokawa. That MINERVA rover missed the asteroid's surface and tumbled into deep space after deployment in 2005.

Another rover named MASCOT is scheduled to be deployed in October, and a third MINERVA rover, MINERVA-II2, is expected to land next year. The primary goal of Hayabusa2 is to collect a sample from the surface, as early as October, for return to Earth in 2020.

MINERVA-II1 rovers
MINERVA-II1 rovers A rendering of MINERVA-II1 rovers 1A (back) and 1B exploring Ryugu. JAXA
Hayabusa2 shadow selfie (wide)
Hayabusa2 shadow selfie (wide) A wider view of Hayabusa2's shadow on asteroid Ryugu, during MINERVA-II1 deployment operations Sept. 21. JAXA

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