NASA’s Lucy mission prepares to fly near Trojan asteroids
Lucy’s mission It gets its nickname from the fossilized partial skeleton of early human ancestors, Australopithecus afarensis, discovered in 1974, that changed ideas about human origins and evolution. The research team hopes that this planetary science spacecraft will do what that skeleton did to palaeoanthropology, by giving us insight into the formation and evolution of our solar system.
In the early days of the solar system, debris orbited in a compact disc around a young sun. Bits and motions of matter gathered together, condensed into snow, and matured into the ordered planets we see today. Asteroids are basically a discard pile that process. “They’re the remnants of this very early time before planets appeared,” says Tom Statler, a Lucy program scientist at NASA.
He likens the study of asteroids to hierarchical research – if, in this metaphor, the pyramids are Jupiter, Saturn, Uranus, and Neptune, and the Trojan asteroids are the material from which they are built. You can only learn so much about how those great structures look from the final triple product. Find the abandoned building area, and you can infer more about its origins. “The objects that eventually became Trojans formed throughout the outer solar system and were moved and locked up where they are now,” Statler says. “Trojans are some leftover food that was washed up and left there.”
And although our planet is rocky, and not a gas giant, studying exoplanets will give us information about how it formed. “It has become clearer and more obvious that no planet evolves in isolation from others,” Statler says. “The Earth is what it is because the Solar System is what it is… To understand Earth, we need to understand how other planets formed and evolved.”
Lucy will rely on three main tools: L’LORRI, L’TES, and L’Ralph. The prefix “L” indicates that they are part of Lucy’s mission, since all of them are based on devices that have been ported before. LORRI and Ralph were instruments aboard the New Horizons mission to Pluto and the Kuiper belt. “Lori” then means “Lucy Lowry,” says Michael Vincent, assistant director of the Division of Space Operations at the Southwest Research Institute. OTES was part of the OSIRIS-REx spacecraft to asteroid Bennu, and was launched in part from an instrument called TES, which had previously flown aboard the Mars Global Surveyor spacecraft. “The devil we knew was what we wanted to hold on to,” Vincent says. (Also, one of the scientists on the expedition has a French background and was, as Vincent laughs, “trying to classify the place.”)
LORRI is basically a great camera, sharp enough to take clear pictures of a 200-foot crater from 600 miles away, and map it to reveal the history of the asteroid. He can also search for rings and satellites, and will help Lucy navigate toward asteroids. After all, choosing which far point to target is not easy. “This stuff isn’t that big out there, and we’re going to have a hard split,” Vincent says.
L’TES works kind of like the offline thermometers you might know from Covid-19 checks, but instead of pointing it toward the forehead, the instrument points to a spot on an asteroid and measures its temperature by detecting infrared radiation coming from who-is. “Over time, you sort of build up an overall picture by sweeping over different surfaces,” Vincent says. Their goal is to measure “thermal inertia,” or how fast or slow an asteroid’s parts are heating up or cooling — an indication of the materials an asteroid is made of. Sand, for example, holds heat differently than rocks, which you might have noticed if you had walked a long distance on the beach at sunset.