After 15 Years, An Eye on Mars Peers No More

S E E D E D   C O N T E N T

Opportunity, the longest-lived roving robot ever sent to another planet, explored the red plains of Mars for more than 14 years, snapping photos and revealing astonishing glimpses into its distant past. But on Wednesday, NASA announced that the rover is dead.

"It is therefore that I am standing here with a sense of deep appreciation and gratitude that I declare the Opportunity mission as complete," Thomas Zurbuchen, NASA's associate administrator for science, said at a news conference.

The golf cart-size rover was designed to last only three months, but proved itself to be an unexpected endurance athlete. It traveled more than the distance of a marathon when less than half a mile would have counted as success.

As it moved across the surface, Opportunity provided an up-close view of Mars that scientists had never seen: fine layers of rock that preserved ripples of flowing water, a prerequisite for life, from several billion years ago.

It also changed the paradigm for how to explore a planet. Instead of a lander studying a single spot a rover let scientists head to the most promising places.

The steady stream of photographs and data from Opportunity -- and from its twin, Spirit, which persisted until 2010 -- brought Mars closer to people on Earth. Because the rovers operated for so much longer than expected, NASA has now had a continuous robotic presence on Mars for most of the century.

That streak seems likely to not end soon. A larger, more capable rover, Curiosity, arrived in 2012, and NASA is planning to launch another in 2020.

"Rovers and their observations resonate with people," said Raymond E. Arvidson, a professor of planetary geology at Washington University in St. Louis, and the deputy principal investigator for the mission. "It's as if you were walking on the surface. It has that kind of perspective, and it's not a particularly alien landscape."

On Tuesday night, NASA made one last call to Opportunity, which was silenced last summer by a giant dust storm. There was no reply.

"It was an incredibly somber moment," said Tanya Harrison, a member of the mission's science team who was present in Pasadena, Calif., at the Jet Propulsion Laboratory during the final attempt to reach the rover. "Just waiting for the inevitable, basically."

The rover has been quiet since June. During the dust storm, Opportunity's solar panels could not generate enough power to keep the spacecraft awake.

NASA had hoped that once the skies cleared, the rover would revive and continue its work.

Last fall, the space agency announced it would spend just a month trying to reconnect with Opportunity.

"There were some that were willing to give up quite quickly, but there was a huge backlash," Dr. Harrison said. "We didn't feel like the rover was being given a fair chance."

NASA relented, but as time passed, the odds grew that the mission was finally over.

Perhaps the solar panels became encrusted in a thick layer of dust, or some crucial electronic component broke down in the extremes of Martian weather. Unless astronauts on Mars one day can take a look at Opportunity, what dealt the lethal blow will likely remain a mystery.

Twin rovers on the red planet

Opportunity landed on Mars on Jan. 24, 2004, three weeks after its twin, Spirit, which set down on the opposite side of the planet.

NASA was looking to rebound from two embarrassing failures in 1999. A mix-up between English and metric units caused the Mars Climate Orbiter to be ripped apart in the atmosphere.

Three months later, the Mars Polar Lander vanished during its landing. An investigation found that the spacecraft likely had shut off its engines too early and plummeted to its destruction.

Steven W. Squyres, a Cornell astronomer who serves as the mission's principal investigator, had been selected to oversee the scientific instruments for an Opportunity-like rover that was to launch in 2001. Because of NASA budget limits, the rover was changed to a stationary lander.

After the 1999 failures, the Mars lander mission that was to launch in 2001 was canceled. The question became what to do in 2003, the next time that Earth and Mars would be close enough to send another spacecraft.

One option was to put Dr. Squyres's instruments back on a rover, a scaled-up version of the successful Pathfinder mission in 1997.

Daniel S. Goldin, the NASA administrator, was initially skeptical, but agreed. Then he asked: Why not two rovers? A pair would provide redundancy, and allow exploration of two different regions of Mars.

The rovers received the green light from NASA in the middle of 2000. Then came the rush to develop and build the rovers in time to launch in 2003, while also avoiding the corner-cutting mistakes that had doomed the 1999 spacecraft.

"It was a miracle we got to Florida," Dr. Squyres said.

Waters of Mars

Three days before Opportunity's landing, the entire mission appeared to be in jeopardy. Although it landed successfully a couple of weeks earlier, Spirit suddenly stopped talking. Engineers scrambled to figure out what had gone wrong and whether Opportunity was susceptible to the same flaw.

"There was a period of time when everyone was concerned that we were at risk," said Peter C. Theisinger, who was then project manager.

The engineers figured out the problem and started nursing Spirit back to health. Opportunity then landed perfectly and hit a scientific jackpot immediately, ending up in a small crater with exposed bedrock.

The bedrock was made of finely layered sedimentary rocks that formed in water several billion years ago, but these waters were highly salty and acidic.

"In reality, we were mostly talking about sulfuric acid on Mars," recalled Dr. Squyres. "Habitable, yes, but it was no evolutionary paradise."

Over the years, Opportunity explored a series of larger and larger craters. At the rim of the biggest, the 14-mile-wide Endeavour Crater, the rover discovered bedrock that was older than the crater, lifted upward but not broken apart by the impact that had formed the cavity.

The rock contained clays, which would have formed in waters that were pH-neutral or slightly alkaline. "This was water you could drink," Dr. Squyres said.

That environment might have been habitable for microbes, had any been on Mars long ago. However, the rover was not carrying instruments to search for molecules that might have hinted at ancient life.

Still, the evidence offered a picture of early Mars: a once-habitable environment that became harsh, as volcanic eruptions turned the waters acidic and the entire planet dried out.

5,111 days on Mars

At the beginning, the mission was a dash, with the scientists trying to squeeze out as much data as they could before Spirit and Opportunity died.

The designers of the vehicles expected that dust settling from the Martian air would pile up on the solar panels, and eventually the rovers would fail from lack of power. Unexpectedly, gusts of Martian winds repeatedly acted as cleaning events, wiping the dust away.

The rovers made it through the winters by parking with their solar panels pointed northward, toward the sun.

Part of that success was timely new technologies -- in particular, the long-lasting lithium ion batteries similar to those now used in cellphones, laptops and electric cars.

"These rovers actually have the finest batteries in the solar system," said John L. Callas, the project manager for the mission. "We'd all love if our cellphone batteries lasted this long."

The engineers also figured out workarounds to problems like a stuck heater switch that sapped energy from the rover as well as later bouts of amnesia where the rover would forget what it was doing.

Each year, investigators bet whether one or two rovers, or none, would make it through the year. Richard Cook, one of the top managers for the rovers, was not among the optimists. "I bet and lost $20 every year for the first five years, and then I stopped betting," he said.

In 2009, Spirit slipped into a sand trap and could not pull itself out. It stopped communicating in March 2010.

Opportunity continued trundling across the Martian landscape. Instead of just 90 Martian days, Opportunity lasted 5,111, counting the days until its last transmission. (A Martian day is about 40 minutes longer than an Earth day.)

NASA's Curiosity rover, which landed in 2012, continues to explore another part of Mars, a crater that was once filled with water. In addition to NASA, China and a joint European-Russian collaboration are also planning to send rovers to Mars in 2020.

A generation of planetary scientists grew up with Opportunity. In 2004, Abigail A. Fraeman was a junior in high school who was selected by the Planetary Society to go to Pasadena and take part in the rover mission. She was with the scientists on the night of Opportunity's landing.

"It was the coolest night ever," Dr. Fraeman said, and it inspired her to choose this as her career. She has been the deputy project scientist for Opportunity since 2016.

Dr. Harrison was college student when the mission started and that she knew she wanted to work on a rover like Opportunity. "I never knew I would get to work on Opportunity 15 years later," she said.

She said that at the end of the night on Tuesday Dr. Callas phoned operators of a radio dish in Australia, part of the network that NASA uses to communicate with its interplanetary voyagers.

He thanked them for 15 years of work with Spirit and Opportunity, and said he was now signing off.

"There had been a lot of talking and laughing and whatnot between crying and hugging," Dr. Harrison said. "As soon as that moment happened, it just went silent."