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Two rovers sent to the surface of an asteroid by a Japanese spacecraft have landed successfully, a thrilling moment in the history of space exploration.
Called Rover 1A and 1B, together known as Minerva II-1, the two rovers were released by the Japan Aerospace Exploration Agency's (JAXA) Hayabusa-2 spacecraft on Friday 21 September. Following a descent lasting several hours they successfully touched down, with confirmation arriving today.
"Both rovers are confirmed to have landed on the surface of Ryugu," the Hayabusa-2 team posted on Twitter. "They are in good condition and have transmitted photos & data. We also confirmed they are moving on the surface."
Each tiny rover weighs about 1 kilogram (2 pounds), and they're designed to hop across the surface of the asteroid. They were carried to Ryugu, located about 280 million kilometers (175 million miles) from Earth, by Hayabusa-2 after launching in December 2014.
Earlier on Friday the team had shared a rather stunning image showing the shadow of the spacecraft on Ryugu. Following the separation, Hayabusa-2 raised its altitude to several kilometers above the asteroid.
In late June 2018 Hayabusa-2 arrived at Ryugu, which measures about 1 kilometer (0.6 miles) across. The spacecraft will remain here until December 2019, mapping the surface of the asteroid and performing a slew of scientific investigations. This includes sending four landers to the surface of the asteroid, with Minerva II-1 being the first of the landing attempts.
Early on Friday, reaching a distance as low as 55 meters (180 feet) from the asteroid, the spacecraft released these first two landers. The successful landing means they are the first movable rovers ever to be deployed on an asteroid.
The rovers will "hop" across the surface by spinning a mass inside of them. This transfers momentum, which causes them to tumble or jump across the surface. Each movement must be carefully controlled so the landers don’t accidentally jump too high and escape the asteroid’s gravity.
This is because the gravitational pull of the asteroid is incredibly weak. While on Earth they weigh a kilogram, on Ryugu each lander has a relative mass of less than a quarter of a gram. Each hop can reach a distance of several meters, moving at up to 9 centimeters (3.5 inches) per second.
On board each rover are cameras that will send back images from the asteroid. They also contain sensors that will measure the surface temperature at different locations. The images and data will be sent back to Hayabusa-2, which will relay the information to Earth.
Here's how the rovers move across the surface
Hayabusa-2 is the successor to the Hayabusa mission, which visited the asteroid Itokawa in the early 2000s. This spacecraft also attempted to deploy a lander, called MINERVA, but it failed and was lost on its way to the asteroid.
That first mission did manage to return a tiny sample of the asteroid to Earth, though, despite the system designed to collect material mostly failing. Hayabusa-2 will attempt to better this, using an impactor to hit the surface and form a crater. The spacecraft will then try to scoop up material from the crater.
As mentioned Hayabusa-2 also has two other landers, the Mobile Asteroid Surface Scout (MASCOT) and Rover 2, also part of the Minerva-II mission. The former will be released at the start of October, and the latter next year.
But for now, we have the very exciting news that these first two landers have been successful. The drama has been somewhat comparable to the Philae landing on Comet 67P back in November 2014, the first-ever landing on a comet. Now all eyes are on Rovers 1A and 1B.
