Star Bound №9: Reaching for Pieces of the Past
Checking in on NASA’s Lucy Mission
To the extent the American media reports on space at all, the big boys — NASA and SpaceX, Musk and Bezos, Starliners and Crew Dragons — get the big press. That’s understandable. Crewed missions are sexy. Giant rockets stir the imagination. And NASA’s plan to get us back to the Moon by way of the Artemis project is exciting, though it’s certainly taking longer than advertised.
Lost in the propwash of these splashy crewed missions are some very interesting — and somewhat quirky — science expeditions. Of course, any flight into space is to some extent a science mission, since we’re still learning on the job. But the little sojourns I’m talking about are different. They’re all about discovery. And one of the most interesting of them was launched from Kennedy Space Center in October of 2021, when the probe NASA calls Lucy set off to study Trojans.
You heard me. Trojans. More specifically, Trojan asteroids. An asteroid, of course, is a space object that is way smaller than a star, smaller than a planet (though there’s some gray area here), and larger than, well, a pebble. There are millions of asteroids in our solar system. Occasionally one will pass uncomfortably close to Earth. But by far the majority of them stay in their lane, orbiting the sun just as we do, and not of particular interest.
Among the solar system’s millions of asteroids, though, is a subset that scientists are keen to study. They are the “Trojan” asteroids, space objects that are caught in the competing gravitational pulls of the sun and a planet and which consequently share the orbital path of that planet, locked in a more or less permanent space race in which the positions never change. So far, we’ve seen these sorts of asteroids only in our own solar system, though they may exist in others as well.
The first Trojan asteroid was observed in 1906 near the planet Jupiter. We now know that Jupiter has many thousands of Trojans. In fact, there are two groups, or “swarms,” of them. One occupies space about 60 degrees in “front” of Jupiter’s orbital path, and the other group moves through space around 60 degrees behind the giant planet. The asteroids in the “forward” position bear the names of famous Trojan heroes, while those in the rear are named after Greeks. Earth has two Trojans, both of which orbit “ahead” of us; interestingly, the existence of the second of these asteroids was only confirmed a couple of months ago. Neptune, Mars, Uranus, and Venus also have Trojans.
Lucy will visit the Jovian Trojans. The spacecraft, which looks like two giant pinwheels (its solar arrays) attached to a large R2D2 that’s wearing a Japanese samurai hat over its face to avoid sunburn, is some forty-eight feet long. On its way to Jupiter, the probe will first fly by the solar system’s main asteroid belt, between Mars and Jupiter, where it will visit a small inner-belt asteroid in 2025. Then it will head toward Jupiter, with the plan for it to reach the Jovian “forward” Trojans in 2027, and to make it to the others in 2033. Built by Lockheed Martin and launched atop a United Launch Alliance Atlas V rocket, Lucy is powered by eight MR-103J thrusters and six MR-106L thrusters, all manufactured by Aerojet Rocketdyne, and carries a suite of instruments that will allow it to study asteroid features, surface temperature, and composition.
After observing the Trojan asteroids, Lucy will take up a position in Jupiter’s L5 Lagrange point and be available (it is hoped) for further studies, though none are currently planned. Lucy is currently over 50 million miles from Earth, and seems to be functioning well, with the exception that one of her solar arrays failed to deploy properly. Engineers at NASA are working to fix the problem, and to determine if the mission can proceed with this one slightly sub-optimal array. So far, indications are that the mission can proceed, though the matter is not yet settled.
Asteroids are a subject of interest these days at least in part because they may contain, or be made of, substances that are valuable here on Earth. Famously, one asteroid, 16 Psyche, is suspected to be made of iron and nickel in amounts that could be worth a trillion dollars on Earth. No such claims are made at present for Jupiter’s Trojans. Nevertheless, some may contain ice that could be harvested for consumption or commercial use in space. And because astronomers believe these Trojans were trapped in their orbits at or near the formation of our solar system, all of them are artefacts of deep time that may be able to help us understand how our local planetary neighborhood was platted and what it’s made of. As NASA puts it, Jupiter’s Trojans are “time capsules from the birth of our Solar System more than 4 billion years ago, [and] thought to be remnants of the primordial material that formed the outer planets.”
It is the notion of Jupiter’s Trojans as developmental artefacts that gave the mission its name. “Lucy” is the moniker given the collection of bone fragments found by paleontologist Donald Johansen in Ethiopia’s Afar Valley in 1974. This tiny constellation of splintered calcium indicates that proto-humans like Lucy probably learned to walk upright before the rapid expansion of brain size that eventually made us human — an important clue in understanding evolution. Not coincidentally, the name of the “main belt” asteroid that Lucy will visit in 2025 is “52246 Donaldjohanson,” after the famous archeologist. Fossils on Earth, fossils in space: it’s a neat conjunction.
Another little quirk of the Lucy mission: it carries a sort of “greeting card” bearing messages from various earthlings, including all four Beatles and Yoko Ono, Martin Luther King, Jr., Amanda Gorman, and Carl Sagan. The thoughts are harmless enough, and it’s an amusing callback to the plaques and golden records sent into interstellar space in the Seventies on the Pioneer 10 and Voyager missions, when we were eager to post Tinder profiles of ourselves for the galaxy to see. Since Lucy will almost certainly never leave our solar system, it’s unclear who the messages are meant to reach. Future earthlings, perhaps? Or settlers on one or more of Jupiter’s moons? No matter. Lucy has set out for the future to tell us about our past. The science just keeps coming — and it’s weirder than we ever thought.
For more information about Lucy and her mission, check out https://www.nasa.gov/mission_pages/lucy/main/index
