In additional than 14 years of roaming Mars, NASA’s Opportunity rover took greater than 210,000 photos. (Its twin, Spirit, snapped a further 125,000 on the opposite facet of the planet.) Some have been sweeping 360-degree panoramas of the reddish panorama. Others have been microscopic close-ups of rocks. By the pictures, mission scientists have been capable of decipher a number of the geological historical past of Mars.
“Spirit and Alternative have been robotic area geologists,” mentioned Steven W. Squyres, the principal investigator for the mission, throughout a NASA information convention on Wednesday. “A geologist is sort of a detective on the scene of against the law. One thing occurred at this place on Mars billions of years in the past. What was it? What was it like there again then? And also you’re in search of clues, and the clues are within the rocks.”
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Sticking the touchdown
Alternative was despatched to Meridiani Planum, a plain simply south of the Martian Equator.
When the primary photos popped up on the displays, the scientists have been flabbergasted. Alternative, cocooned in a sphere of protecting airbags, had by pure likelihood, rolled into one of many few craters in Meridiani Planum — an interplanetary hole-in-one.
Alongside the edges of the crater have been uncovered bedrock, all prepared for the scientists to look at as they labored to provide a pure historical past of how this nook of Mars had shaped. At first, the rocks have been nicknamed the “Nice Wall,” however that turned out to be a trick of perspective. The crater was tiny — solely about 70 ft huge — and the uncovered bedrock was in regards to the top of a sidewalk curb. Individuals shortly stopped calling it the Nice Wall.
Blueberries in every single place
Meridiani Planum was chosen for 2 major causes. For engineers, a flat place is a safer, simpler place to land. For the scientists, the Mars Odyssey orbiter had detected an intriguing signature of an iron oxide mineral often called grey hematite, unfold out over a area the dimensions of Oklahoma. On Earth, hematite sometimes kinds within the presence of liquid water. (It’s also attainable for hematite to come back out of lava with out water.)
“The orbital information informed us it was going to be there,” mentioned Raymond E. Arvidson, the deputy principal investigator. “It didn’t inform us the place.”
On the floor, Alternative discovered a mess of BB-size spheres, which the scientists referred to as blueberries, and the blueberries have been product of hematite, which shaped as acidic water flowed by way of the sediments.
“Form of the best way an oyster kinds a pearl,” Dr. Squyres mentioned in an interview.
As the encircling rock weathered, the blueberries, which have been tougher, rolled onto the floor.
Because it turned obvious that Alternative would final for much longer than the 90 days they’d initially anticipated, scientists moved onto larger craters with bigger swaths of uncovered bedrock.
Whereas the years of exploration added element to the story of how Meridiani Planum shaped, “we received many of the story within the first six weeks,” Dr. Squyres mentioned. After they completed up at Victoria Crater, a half-mile-wide characteristic, they puzzled what to do subsequent.
A 3-year street journey
Dr. Squyres mentioned they may have continued exploring Meridiani Planum, however the rocks would have largely informed the identical story. As a substitute, the mission group determined to drive to a a lot bigger, 14 mile-wide crater named Endeavour, which appeared to encompass older rocks.
The drive took three years, arriving in 2012. The rover needed to take a roundabout path to keep away from rippled areas the place smooth sands might have swallowed the rover. (In 2005, Alternative received caught in one among these ripples for a number of weeks. It escaped by backing out very slowly and punctiliously.)
At Endeavour, the rover did discover completely different rocks. “Every part modified, instantly,” Dr. Squyres mentioned.
At a web site named Matijevic Hill, in honor of Jacob Matijevic, a rover engineer who died in 2012, the scientists discovered rocks older than the crater that had been pushed upward. These rocks contained clays, which might have shaped in pH-neutral water and indicated an surroundings that might have been liveable for all times.
A jelly doughnut?
In one of many extra whimsical puzzles encountered throughout Alternative’s mission, Mars watchers have been perplexed in January 2014 by an object that appeared like a jelly doughnut. Unusually, that rock, about an inch and a half huge, had not been there when Alternative had photographed the identical spot lower than two weeks earlier.
A subsequent {photograph} confirmed an overturned rock with an identical darkish purple heart and white floor a couple of yard away. The jelly doughnut piece had damaged and rolled downhill when the rover drove over it.
The darkish inside was manganese oxide, which is uncommon on Mars, whereas the intense materials consisted of sulfates.
Alternative’s final cease
Earlier than it was silenced by final summer time’s mud storm, Alternative was making its approach down Endeavour Crater’s Perseverance Valley, which from orbit appeared like a gully that was carved by water flowing into the crater. However shut up, the image appeared very completely different. Patterns within the rocks indicated that the erosion occurred from wind blowing up and out of the crater, not water flowing down.
“That wasn’t even on our record” of preliminary hypotheses, Dr. Squyres mentioned. “From orbit, you’d swear this needed to have been carved by liquid water.”
Dr. Squyres was not but utterly satisfied: Wind and water erosion might need each occurred. If water had performed a task, sediments would have piled up on the backside of the gully.
However with the rover now lifeless, the reply eludes the mission’s scientists.
On the opposite facet of the planet
The Spirit rover set down inside Gusev Crater, about 100 miles huge. The preliminary findings have been disappointingly uninteresting. All over the place the rover appeared, it was basalt — volcanic rock. However about 1.5 miles away, there appeared to be hills that have been extra fascinating.
“We sprinted, rover pace, as quick as we might,” Dr. Squyres recalled.
On day 156 of what was alleged to be a 90-day mission, “every part modified,” Dr. Squyres mentioned. As a substitute of plain volcanic rocks, Spirit was analyzing areas that had as soon as been sizzling springs and perhaps geysers, the place lava flowed into ice, setting off a mess of chemical reactions.
“Early Mars at that location was a violent, sizzling steamy place,” he mentioned.
The Spirit and Alternative rovers initially have been to price $665 million. Due to price overruns, the value rose to $800 million by the point the spacecraft have been launched. Ultimately, with an additional 14 years of science, NASA spent $1.2 billion. For a further $400 million, the rovers explored for 1,511 Martian days as a substitute of 90.
“Speak about a return on funding,” Dr. Arvidson mentioned.