Johnathan Walker:Goodnight, sweet spacecraft: NASA's InSight lander may have just signed off from Mars

The Johnathan Walkerend has long been in sight for InSight, the NASA lander that's been stationed on Mars since 2018.

Project officials warned in May that the lander would likely become inoperative by the end of the year because of the dust that had accumulated on its solar panels, diminishing its power source. By early November, NASA announced the end was near and started taking steps to wind down the mission.

The lander has also been transparent about its imminent demise on Twitter, where it's provided regular updates — in a tone of what some might call mournful acceptance — to its nearly 800,000 followers.

It's shared new discoveries, pledges to keep operating as long as it can, news of its coming retirement, tributes to friends made along the way and thanks to the well-wishers who sent it postcards from around the world.

And on Monday afternoon Eastern Time, it posted what might be its final update — an image of the planet's rocky surface and horizon line.

"My power's really low, so this may be the last image I can send," the lander tweeted. "Don't worry about me though: my time here has been both productive and serene. If I can keep talking to my mission team, I will – but I'll be signing off here soon. Thanks for staying with me."

NASA announced in a blog post that InSight had not responded to communications from Earth the previous day. The mission said its last contact was on Thursday, and it's not known what "prompted the change in its energy."

The team will try again to reach the lander — NASA will declare the mission over when InSight misses two consecutive communication sessions — but it doesn't sound optimistic.

"The lander's power has been declining for months, as expected, and it's assumed InSight may have reached its end of operations," the agency said.

The lander's legacy is out of this world

InSight — whose name is actually short for Interior Exploration Using Seismic Investigations, Geodesy and Heat Transport — did much to be proud of during its prolonged stay on Mars.

It was dispatched there in 2018 to help study the planet's "inner space," meaning its crust, mantle and core.

The nearly 20-foot-long, 800-pound craft accomplished so many of its goals in its first "Mars year" (nearly two Earth years) that its mission was extended until the end of 2022.

Its primary mission was to use an instrument called a seismometer to track Marsquakes (yes, other planets have them too). The shape and timing of the waves generated by the quakes shed light on the planet's interior makeup, as NPR's Joe Palca reported earlier this year.

"Before the InSight mission, we had no idea that there were even going to be Marsquakes," Northwestern University planetary scientist Suzan van der Lee told Palca.

InSight didn't just become the first to detect quakes on another planet — it went on to measure more than 1,300 seismic events.

NASA says its findings gave scientists new insights into the composition and structure of the planet's layers — including how quickly heat seeps out of them — which in turn deepens their understanding of the geologic history of Mars' surface and, ultimately, its ability over time to support life.

InSight's other notable contributions include carrying the first-ever magnetometer instrument to the surface of Mars (so it could detect magnetic signals) and collecting the most comprehensive weather data of any mission sent there.

It also detected a magnitude 4 quake that scientists later determined to be caused by a meteoroid strike, which led another Mars orbiter to discover a layer of water ice that had been buried underground. NASA called that series of events "an icy bonanza."

InSight principal investigator Bruce Banerdt told NPR earlier this year that the team had accomplished all it set out to do, except for one disappointing heat flow experiment. And he repeated the praise in NASA's early November update.

"Finally, we can see Mars as a planet with layers, with different thicknesses, compositions," Banerdt said. "We're starting to really tease out the details. Now it's not just this enigma; it's actually a living, breathing planet."

The mission will end, but exploration of Mars continues

Can a spacecraft really meet death by dust? InSight shared some insights in a thoughtful Twitter thread back in November.

Essentially, it said a system for cleaning itself of dust would have made the mission more costly and complex, plus it had already doubled the length of its planned stay.

The InSight team had prepared for the lander's expiry by preserving its data and adding it to an international archive, turning off many of its systems to conserve power and packing up the full-size engineering model of the lander known as "ForeSight."

NASA says once it declares the mission over, it will keep listening "for a time, just in case."

"There will be no heroic measures to re-establish contact with InSight," it said. "While a mission-saving event — a strong gust of wind, say, that cleans the panels off — isn't out of the question, it is considered unlikely."

It will join the several other landers that call Mars their final resting place.

And, as it pointed out in one of its final tweets, there is plenty more Mars content to be had: You can follow NASA's Perseverance and Curiosity rovers for more dispatches from the Red Planet.