A respectable moon, Ganymede, creeps out from behind Jupiter’s shadow. Credit: NASA/JPL-Caltech
Delete Your Orbit is a recurring column on NOW.SPACE that provides well-informed, but alarmingly petty analyses of various objects in our universe.
At first glance, Jupiter’s moon, Metis, might look like a good choice for the discerning hipster interested in having an obscure moon as their favorite space object. It’s the closest known moon to the surface of Jupiter, which is a cool bit of trivia, I guess. It’s weird looking, if that’s what you are into. Best of all, nobody has heard of the place. Astronomers didn’t even know about it until 1979!
And I hear you! It looks like it could have a good underdog story going on. I mean—and I am not joking here—this Ansel Adams-caliber masterpiece is the best image of Metis that exists right now:
Think it’s that kinda moonish-looking thing in the middle? Think again! It’s that diffuse blob on the right. No disrespect intended, Galileo. Credit: NASA/JPL-Caltech
Grotesque, I know. Metis’ darkly dismal surface is probably full of craters (based on the clearer pics of the nearby larger moons)—a harsh reminder of what life is like that close to the largest planet in the solar system.
Its long side (yes, it’s absurdly oval-shaped) measures in at a whopping 60 km in length. It has so little mass, in fact, that an object traveling 80 km/s or less could launch material into space and past its orbit simply by crashing into its surface. That’s good news, since the only thing you’d want to do if you accidently landed there is blast away ASAP, given the intense radiation you’d be subjected to.
Metis, to be clear, is the deformed shard of a once-marginally noteworthy moon collision that has been further warped by Jupiter’s intense gravity. Some astronomers actually use the scientific term “collisional shards” instead of “moons” to describe it and other similar objects. These might be valid excuses for some, but not for me. To put it mildly, Metis is an aggressive affront to the ideal Platonic sphere we have come to expect from the cosmos.
My main beef, though, is that it is a depressing place even to think about. In fact, I would argue, Metis will spend its severely limited remaining days in this universe as a potent symbol of existential futility. Its very existence (and, one might ironically argue, its only claim to fame) is merely to provide its Jovian overlord with a constant supply of material for its inner main ring.
Metis and the other inner moons of Jupiter in relation to its alleged ring structure. Credit: NASA/JPL-Caltech
To this end, tiny space stuff repeatedly pounds into Metis, and these tiny impacts launch dust from the Metisian surface into Jupiter’s main ring. Without this steady supply of new material, Jupiter’s main rings would cease to exist. This is because ring material (dust and small rocky stuff) has a pretty short lifespan due to the repeated pulverizing forces it experiences. One cannot help but note, at this juncture, that Jupiter, beloved as it may be, is not really known for its easily visible ring structures.
Still, it is Metis’ comically low mass that allows it to play this role at all. It’s so easy to get stuff off its surface and into space that the moon pretty much turns into that character Pig-Pen from the cartoon Peanuts, circling around Jupiter in a dusty haze every 7 hours. (Fine, its orbit is blazingly fast; I’ll give it that).
Metis’ spirit animal. Credit: Charles M. Schulz
Forget about Metis.
The thing is, it’s not really all that good at making rings begin with. Though early studies guessed that Metis and its nearby partner Adrastea, were the primary contributors to Jupiter’s main ring, later studies showed that they contribute only a paltry third of the material. A third! To add one final note of futility to the whole process, Metis not only helps (a bit) with replenishing the rings, it also plays a role in destroying them, too—its close path through the ring disturbs and deflects the stuff that is already placed there. Talk about futility.
So here we have a weird-looking hunk of rock whose sole purpose is to be slowly and literally worn apart to create a ring that nobody can see anyway. And here’s the kicker! It’s so close to Jupiter that it’s slowly but inexorably marching toward the day when its orbit decays and it crashes into Jupiter itself. Every one of Metis’ passing orbits is as futile as its effort to maintain Jupiter’s practically invisible ring system.
These are not the stories I want to think of when I look up to the night sky. Do yourself (and everyone else) a favor: Forget about Metis. If something reminds you of this soon-to-be-forgotten space relic, just remember that Pluto has an entire region that looks like a heart. Because Pluto is a champion.
TL;DR: Metis, a grotesque and deformed shard of rock masquerading as a Jovian moon, is a dangerous existential crisis just waiting to happen.