Over the weekend, a pair of robots, each about the size of a frying pan, tumbled out of a spacecraft and landed on the surface of another world.
The robots are part of a Japanese mission to visit an asteroid, collect some of its rocky material, and then return it to Earth. In late 2014, Japan launched the Hayabusa2 spacecraft bound for Ryugu, a small asteroid that measures slightly more than half a mile and orbits near Earth. The spacecraft caught up with Ryugu in June after a three-year chase. Then, last week, it cozied up to the asteroid, coming within several hundred feet of its rocky surface, and dropped the two bots.
Their successful deployment is a very impressive achievement. It’s not easy to land something on such a fast-moving, faraway object; a similar attempt on a comet in 2014 ended with a robot becoming permanently wedged in a dark crevice. But perhaps the most striking part of the maneuver is in the photographs of the landing.
The two Japanese robots have captured Ryugu in incredible detail. The images reveal a richly textured surface, with rocks of all sizes jutting out into the darkness of space:
From this vantage point, Ryugu doesn’t look like a hazy space rock floating hundreds of millions of miles away. It looks comfortingly familiar, like a rocky outcrop you might stumble across while hiking on Earth.
The images are unlike the majority of previous observations of asteroids. For many decades, other spacecraft and telescopes have shown asteroids as tiny specks of light, or fuzzy blots, or hazy lumps of smooth rock. My personal favorite description of one picture, from 1989, reads: “The slightly elongated smudge in this image is the asteroid.”
Telescope technology has vastly improved in the more than 200 years since asteroids were first discovered, but today, only the most powerful telescopes can resolve distinct features on the surface of the objects. The best way to photograph an asteroid is to visit, or at least fly past.
In 1991, the Galileo spacecraft buzzed past the asteroid Gaspra on its way to Jupiter. NASA engineers used data from the spacecraft to stitch together an image of the asteroid, which The New York Times described as “the first close-up photograph ever made of a rocky asteroid hurtling through the solar system.” This was the photo:
Galileo was about 10,000 miles from the asteroid when its camera pointed toward Gaspra. The Times referred to the composite photo as “a sharp portrait” of an asteroid, and, indeed, it was at the time.
The Hayabusa2 mission will produce many more close-up images in the coming weeks, thanks to the two robots. JAXA, the Japanese space agency, calls them rovers, but that’s a bit of a misnomer. The robots don’t have any wheels, which wouldn’t be efficient in Ryugu’s low-gravity environment. Instead, the bots are designed to push themselves around, and will quite literally bounce around the surface.
As the mission provides us with more close-up views of Ryugu, it will also deliver an unprecedented look at the solar system’s ancient past. Scientists believe that asteroids like Ryugu are remnants of the system’s creation about 4.5 billion years ago. The rocks have remained mostly unchanged since then, which means they still contain the materials—a mix of rock, minerals, and organic compounds—that coalesced to form the planets.
The Hayabusa2 spacecraft will soon attempt to excavate some of that history. The probe will fire a projectile at Ryugu to create a crater and expose long-buried material, and then dip its instruments inside to collect some samples before heading back to Earth. Like the two robots, Hayabusa2 has cameras on board. Our views of an asteroid are bound to become sharper still.
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