NEW JERSEY (NYTIMES) - After a perplexing failure last month, the National Aeronautics and Space Administration's (Nasa) latest Mars rover, Perseverance, was able to drill a sample of rock on Wednesday (Sept 1).
The rover took pictures of the rock in the tube and sent the images to Earth so that mission managers could be sure they had not come up empty again. Then Perseverance will seal the collection tube and put it away in its belly.
The success, visible in images posted online on Thursday, is most likely a relief to scientists working on the mission.
"You can see a beautiful rock core," geochemistry Professor Kenneth A. Farley, from the California Institute of Technology and the project scientist for Perseverance, said in an e-mail on Thursday morning.
One of the key tasks for Perseverance is to collect rocks and soil that will eventually be brought back to Earth by another mission so that scientists can exhaustively study them using state-of-the-art instruments in their laboratories, the way they have with moon rocks from the Apollo and Soviet missions of the 1960s and 1970s.
And yet, on Aug 6, the first time that Perseverance drilled, collected and sealed a rock sample, everything appeared to go flawlessly - except the tube was empty.
"It was definitely a bit of despair," Prof Farley said in an interview before the latest drilling attempt. "Everybody was so ready to declare victory. And then somebody said, 'Yeah, here's a picture, there's nothing in the tube'. It was very deflating."
The rover used its cameras to look around and see if the rock core had somehow dropped to the ground. But there was no sign of it. The rock sample had, it seemed, vanished.
The greatest worry was that Perseverance's intricate drilling mechanism had suffered a crippling malfunction and that it would not be able to collect any samples at all. But after reviewing the data, the engineers and scientists concluded it was the rock, not the rover, that was to blame.
"The rock simply wasn't our kind of rock," Ms Jennifer Trosper, the mission's project manager, wrote in a Nasa blog post on Aug. 19. The rover's systems had performed as expected - "quite well, as a matter of fact", Ms Trosper wrote - but the rock was too fragile.
"The act of coring into it resulted in the rock breaking apart into powder and small fragments of material, which were not retained in the tube due to their size," Ms Trosper said. She added that despite numerous tests on Earth, "we had not encountered a rock in our test suite that behaved in quite this manner".
Prof Farley concedes that there were warning signs that the August rock might not have been the best one to try first. Its brown colour indicated rust, it contained salts and it was full of holes.
Rust, salts and holes meant the rock had been sitting in a lake or groundwater for a very long time. That was potentially a fantastic scientific find. The mineralogical changes caused by water could illuminate billions of years ago when Mars was wet and habitable.
But a rusty, salty rock filled with holes could also be very crumbly. "We learned a lesson," Prof Farley said.
The operation was not a complete loss. The tube has no rock or soil, but it does contain sealed, uncontaminated Martian air, something the scientists had planned to collect at another time.
For the second drilling attempt, the rover drove about 400 yards onto a ridge slightly higher than the surrounding landscape, "and we selected the hardest looking rock you could find up there", Prof Farley said. This boulder, nicknamed Rochette, survived through the ages and was not eroded away by the winds, strong evidence that it is not crumbly.
The boulder looks like a piece of a hardened lava, which can be precisely dated. Thus, scientists will be able to determine how old this boulder is, and it helps pin down the ages of lower, older layers.
"This was a high-value target," Prof Farley said.
It will be more than a decade before Prof Farley and other scientists can get their hands on it. Perseverance at some point will probably drop the hermetically sealed tubes on the Martian surface, to await pickup by a future rover, still on the drawing board.
That rover will take the rock samples to a small rocket that will launch the samples on a trip back to Earth, but they will not arrive until the 2030s.
Perseverance will continue exploring a 45km-wide crater named Jezero, especially an ancient, dried-up river delta along the western rim. The rover is accompanied by a small robotic helicopter named Ingenuity that was added to the mission to test the ability to fly through the thin air of Mars.
While Nasa had planned to leave Ingenuity behind after a series of test flights, it proved so successful that the helicopter continues to follow along with Perseverance, acting as a scout of the terrain ahead. And it is improving the rover's scientific mission, too.
The scientists had intended to visit a site that looked striking in images taken from orbit. "Then we looked at the helicopter images," Prof Farley said, and were less impressed.
"We will save a bunch of time by not driving over there," he said.