Dust is gathering on its panels, obfuscating them from the life-giving light of the sun. Assuming that a dust devil won’t soon whizz by and blow some of that dust off, and presuming a dust storm doesn’t add more of that rust-hued volcanic confetti to the solar panels, it’s looking increasingly likely that this summer will be the moment it drifts into an endless slumber.

“It looks like in the summer time frame — late-spring, early-summer — is when it becomes impossible to power the seismometer, at least power around the clock,” says Bruce Barnerdt, principal investigator of the InSight mission. InSight’s engineers may be able to pull a rabbit out of the proverbial hat at the last minute, giving the lander a little more juice. But in just a few months, InSight probably won’t be able to conduct any more scientific inquiries — and soon after, the spacecraft itself will be drained of power.

Some are expressing their bewilderment on social media. This is NASA we’re talking about here. They seriously couldn’t think of a way to get rid of something as simple as dust building up on the lander’s solar panels? Why not use a little blast of compressed gas, or even a brush?

The thing is, NASA and every single scientist and engineer working on or with InSight did see this coming. In an ideal universe, InSight would be invulnerable; it would be an eternal fountain of Martian marvels. But like all of us mortal surface dwellers, death is a sad certainty, even for robots on another world. InSight’s hourglass is almost empty, and with its demise, room will be made for its descendants.

InSight was always destined to die.

Most uncrewed missions to other worlds focus on several key fields of study. What is its surface geology like? What’s the deal with its climate? Where’s its water? Is any of it habitable? Did it once contain life? Are there any little critters still calling this corner of the cosmos home? These are, of course, questions of the utmost necessity, the answers to which have existential implications for us back home. But if we ever hope to truly understand the way worlds work, we need to look under the hood. A planet’s vast, layered, complicated geologic engines drive almost everything that happens on the surface, from the state of the climate to the scale and rhythm of its volcanism.

A humming engine keeps a world alive, geologically speaking. And the components of that engine tell us how worlds are put together, and how they may one day lose their spark and die.

The only planetary engine scientists have seen in reasonable detail is Earth’s. The passage of seismic waves through Earth’s interior — whose speed and trajectories vary depending on the material they pass through during their voyage — has been used to map out its subterranean labyrinths in remarkable detail. We live atop a churning ocean of rock and metal and time, filled with molten mountains and iron serpents that continuously crack, crush, and forge the crust we all live on. There is so much we have yet to learn about what goes on down there.

During the Apollo era, several seismometers were placed on the lunar surface — and with the help of both natural moonquakes and some artificial ones created by falling spent rocket boosters, we heard our natural satellite ring like a large bell, revealing some of its internal layering. And although the images procured by this seismic sleuthing were nowhere near as granular as those produced back on terra firma, they were still far better than anything obtained from any other world.

Mars, a smaller and rockier cousin to Earth, has long intrigued planetary scientists. It was once far more waterlogged than at present, perhaps a tad warmer, and it likely had a thicker atmosphere as well as more profuse and frequent volcanic activity. Now it’s an irradiated desert. Working out what caused this sort of transformation seems like a good idea, and one major piece of the puzzle is hiding within its interior. What is Mars’s planetary engine like? What are its individual components made of?

Enter: InSight. Landing on Mars’s Elysium Planitia on November 26, 2018, it is set to work. And instead of sniffing the skies or cracking open rocks to see their mineral makeup, it used its array of gadgets to seek answers below the red-tinted soil: a heat probe, to work out how toasty or not the engine was today; a radio science experiment to determine how the planet wobbles on its axis as it orbits the Sun, which can be used to size up the engine’s components; and the pièce de resistance, a highly sensitive seismometer that can use marsquakes to map out Martian layer cake.

During InSight’s two Earth-year mission — roughly one single Martian year — the mission’s multitude of scientific objectives were completed. The one major hiccup came with measuring the flow of heat through the planet: the lander’s heat probe couldn’t punch itself into the ground and get operational thanks to some surprisingly incorrigible soil. Fortunately, the robot’s seismometer, using a quirk of physics, came to the rescue and provided an alternative way to determine this heat flow — at the same time that it identified a major site of seismic activity on Mars, heard the possible whispers of magma shifting beneath it, and providing the first-ever map of the insides of another planet.

“A seismometer is a very, very complex instrument. And the whole idea that you can shoot it off from a rocket on Earth, have it go through the atmosphere of Mars at supersonic speed, touch down and then have it couple to the surface…I mean, we don’t even drop seismometers out of airplanes on Earth,” says Tom Wagner, a program scientist at NASA’s Planetary Science Division. “It’s an amazing feat of engineering and science.” And it’s ensured that InSight has been “a success, by any measure.”

Instead of ending the mission back in December 2020, as scheduled, NASA opted to keep the party going, extending operations for another two years. But judging by the amount of dust that has gathered on its wing-like solar panels, InSight looks unlikely to make it to the year’s end.

It is understandable that curious members of the public want to know why nothing was done to prevent this dust build-up in the first place, says Simon Stähler, a seismologist at ETH Zürich in Switzerland and member of the InSight science team. After all, other space missions have lasted well beyond their original timelines. NASA’s Opportunity rover provides one of the most remarkable examples of this sort of persistence. It landed on Mars in 2004 as part of a pair of rovers, both on a quest to find geologic signs of ancient water. It was supposed to last 90 days. Instead, it lasted for almost 15 years. It took a colossal dust storm, one that smothered its solar panels, to finally kill it off.

“This maybe creates the perception that every space mission is basically designed to last until somebody shuts it off,” says Stähler—or at the very least gives the impression that InSight succumbing to dust after just three or four years is a relative disappointment.

So why has InSight’s end arrived so seemingly soon? Part of it is down to luck: the chaos of the Martian desert has dumped far more dust on its solar panels than its winds have decided to remove. The other half of the equation, though, provides the answer to the question many are asking: why not simply manufacture a way for the lander itself to blow that pesky dust away?

NASA picks its missions in a variety of ways, one of which is through the Discovery program. These are (for space missions) relatively low-cost affairs, coming with cost caps of roughly $600 million, with a narrow range of science objectives. Teams of scientists propose various mission concepts, and, through a grueling series of stages, a winner is chosen every few years. InSight is part of the Discovery program, meaning that it had something of the order of $600 million to use. And that, says Wagner, also the NASA’s Discovery Program lead, means you can’t do everything you’d want to do.

No matter how much funding a space mission is given, when designing it, “you have to make all kinds of compromises all the time,” says Barnerdt. “If one mission doubles its budget, something else has to go away.” So when it came to designing InSight, the team had to demonstrate as best it could that this future lander would achieve all its scientific objectives — all of which revolve around seeing into Mars — without going over budget. And it turns out that solar panels are a lot cheaper than using a Perseverance rover-style nuclear battery, something known as a radioisotope thermoelectric generator, or RTG.

“NASA is able to produce one RTG per decade, roughly,” says Stähler, each costing about $100 million. They used to be easier to make, but since the end of the Cold War, the supply of free plutonium from the production of nuclear weapons has effectively run dry. Adding one to InSight’s design would have likely prevented it from ever becoming a reality during the Discovery program decision process.

Could the design have included something as simple sounding as a brush to clean the solar panels? Sure—but these solar panels are remarkably thin, and a brush could feasibly damage them. And it wouldn’t be as straightforward as adding a brush to InSight’s toolkit either. That would have taken a lot more time and money to rigorously test to make sure nothing would go wrong during the mission. Mission engineers don’t like to complicate things by adding potential points of failure. At one point, someone on InSight’s science team wondered if the lander’s somewhat stumpy arm could prod the solar panels, or perhaps scrape off some dust. “The engineers laughed at us,” says Stähler.

On occasion, says Barnerdt, he does second-guess the design choices on InSight. Maybe, just maybe, they could have somehow got a brush or something onto the lander without unnecessarily risking the lander’s safety or breaking the bank. But at the end of the day, InSight was designed to accomplish several very specific things within two Earth-years, something that tried-and-tested solar panels would permit within the budget set. It succeeded, and every mission that comes after will stand on its scientific shoulders.

And this year, it’ll give up the ghost. If that makes you, a keen observer of space missions, sad, pour one out for the mission team. For these scientists and engineers, it’s almost akin to losing an old friend. Although InSight’s specific design came about in 2006, the idea of having one or several geophysical observatories to chart out Mars’s planetary engine crystallized in the 90s. To see that lofty goal be attained, then to watch the instrument slowly die in a lonely alien desert, is both surreal and melancholic.

“I’m completely emotionally attached to this thing. It’s really been a part of my life for almost 30 years,” says Barnerdt.

“To think that it’s all going to come to an end in a matter of months…I actually try not to think about it very much, but when I do it really does make me sad.”