On a primitive piece of space rock more than 100 million miles (160 million kilometres) from Earth, two tiny robotic explorers took their first cautious "hops" this weekend - the first movements made by any human-made spacecraft across the surface of an asteroid.
The twin rovers were deposited Friday atop the half-mile-wide asteroid Ryugu by their parent spacecraft, the Japanese space agency's Hayabusa 2.
The next day, JAXA shared an impressionistic image of the landing site: the craggy dark stone of the carbon-rich Ryugu lit by a brilliant beam of light from the sun.
Photo taken by Rover-1B on Sept 21 at ~13:07 JST. It was captured just after separation from the spacecraft. Ryugu's surface is in the lower right. The misty top left region is due to the reflection of sunlight. 1B seems to rotate slowly after separation, minimising image blur. pic.twitter.com/P71gsC9VNI— HAYABUSA2@JAXA (@haya2e_jaxa) September 22, 2018
The rovers - dubbed Rover-1a and Rover-1b - are each roughly the size and shape of a cookie tin.
Solar-powered internal rotors loft them in the asteroid's low gravity, allowing them to propel themselves across its surface to snap photographs and take temperature data.
"I cannot find words to express how happy I am," project manager Yuichi Tsuda said in a statement after the rovers' safe arrival was confirmed.
In the coming months, the MINERVA-II rovers will be joined by two more landers. Hayabusa 2 will also smash the asteroid with explosives to blast away part of its surface, exposing underground material that the spacecraft will collect and eventually send back to Earth.
If all goes to plan, it will be the first mission to return a sample from a C-type asteroid, which are often compared to time capsules from the earliest days of the solar system, more than 4 billion years ago.
Ryugu is named for a magical palace at the bottom of the sea where a fisherman is given a mysterious box in a popular Japanese folk tale.
"The Hayabusa 2 will also bring back a capsule with samples," JAXA explained in a news release announcing the asteroid's name, "thus the theme of 'bringing back a treasure' is common."
The space agency also noted that Ryugu is thought to contain water - making it an appropriate namesake of an underwater palace.
Hayabusa 2 will stay at Ryugu until late 2019, when it will depart with its collected samples and set course for Earth. JAXA hopes to receive the samples the following year.
In labs on Earth, scientists will assess the asteroid fragments to understand the processes that allowed planets to form from the swirl of gas and dust that surrounded the primitive sun.
They will compare the rocks to meteorites and to samples collected by other missions, including NASA's OSIRIS-Rex, which is slated to arrive at the asteroid Bennu in 2020.
"By studying asteroids, we learn more about the early solar system and more about life itself," the 'Science Guy' and Planetary Society CEO Bill Nye tweeted as the rovers made their descent Friday.
"It is amazing to be a human living at this moment in the history of space exploration."
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