Jupiter’s asteroids could teach us about the solar system’s past

Imagine Jupiter and its small asteroids as a cosmic Halloween backdrop on the front porch of the solar system. The planet itself – swirling, stormy, the largest in the solar system – is the Pumpkin, while its accompanying tiny asteroids look like funky gourds, one group in front and one behind. The pumpkin and these gourds have been displayed like this for billions of years, linked by a quirk of gravity, tracing the same loop around the sun.

Earlier this month, NASA launched a spacecraft named Lucy to admire this fall space exhibit. Spacecraft have visited Jupiter before, but none have ever gone to closely inspect the planet’s smaller asteroids. However, after half a century of exploring most major planets and moons, NASA is beginning to extend its reach to smaller, more specialized objects most people have never heard of. Everyone knows Jupiter the pumpkin, but who has heard of these original shaped water bottles? So far, the mission hasn’t gone exactly as planned (more on that later), but NASA seems confident that the spacecraft will one day reach these distant, mysterious objects.

Astronomers have known about asteroids for some time. A German astronomer discovered the first in 1906, and over the years, as telescopes became more sophisticated, astronomers found many more. They started naming objects after the characters of the most famous battle in Greek mythology, the Trojan War: Achilles, Agamemnon, Hector. Asteroids, which now number in the thousands, are known as Trojan horses.

The Trojan asteroids are larger than the last asteroid visited by NASA last year. But they’re still small on a cosmic scale, and especially compared to Jupiter: most known Trojans are about the size of a small US state, while more than 1,300 Earths could fit inside interior of Jupiter. Trojans are dark, with matte surfaces that reflect very little sunlight. The gravitational forces of the Sun and Jupiter keep the Trojans where they are; one set always stays in front of the planet on its path around the sun, and the other always trails behind. And the Trojans could be the most related asteroids in the solar system: “Like a cold winter morning [when] it takes a lot more energy to get out of your bed, asteroids don’t want to use the energy to get away either,” Sierra Ferguson, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, told me.

But much about asteroids is still unknown. We’ve had pictures of Jupiter for decades, but even to powerful space telescopes like Hubble, Trojans only appear as specks of light. From the ground, astronomers observe the Trojans through “occultations,” an inadvertently creepy term for an astronomical phenomenon that involves light and shadow. Sometimes a Trojan asteroid briefly passes a distant star in Earth’s field of view and casts a shadow on our planet for only a few seconds. Astronomers are fanning out around the world, trying to watch the star temporarily fade as the asteroid passes. “If you have enough of these telescopes spread over a large enough area,” says University of Arizona scientist Alessondra Springmann, “you can actually get a silhouette of the asteroid by tracking how long it takes to the star for weak.”

The Lucy mission aims to transform these blurry silhouettes into textured worlds. The spacecraft will visit seven Trojan horses over the next 12 years, study their composition and other properties, and check to see if any of them have their own small moon, or even a delicate set of rings. There’s also the very real possibility of the team stumbling upon something they never imagined. In 2019, when another NASA spacecraft visited a nearby asteroid, scientists discovered that the rock was ejecting hundreds of gravel-sized pieces into space, a scenario no one on the team has ever seen. predicted.

Trojans, no matter how small, could reveal big truths. Scientists believe these asteroids are remnants of the early solar system, bits that weren’t swept up to create planets and moons. That’s why the team named the mission Lucy, after the famous skeleton of a human ancestor that archaeologists discovered in Ethiopia in 1974. Just like Lucy the fossil has given us new insights into human evolution. , astronomers hope that Lucy the spacecraft will provide information on the formation. of the solar system.

This is because astronomers now believe that some of the outer planets – Saturn, Uranus and Neptune – did not form where they are now, but were instead born much closer. They came to this conclusion about 15 years ago, after astronomers around the world kept finding Jupiter-sized exoplanets orbiting very close to their suns. Such a configuration implied that the exoplanets had migrated. Maybe the same thing happened in our own solar system? Scientists say that in the beginning, Jupiter and the other major planets jostled around the solar system, swinging their gravity. Jupiter must have picked up asteroids that were far beyond Neptune, where many other space rocks reside, and brought them closer to the sun. Nature smoothed some rocks into planets and moons, but left those asteroids untouched, suspended in the invisible amber of the universe.

Lucy will look for signs of this ancient stampede in Trojans, Andy Rivkin, a planetary astronomer at the Johns Hopkins Applied Physics Laboratory in Maryland, told me. Astronomers understand certain minerals well enough to know where they should appear in the solar system, based on their distance from the heat of the sun. Lucy’s instruments could detect some substances that one would expect to find somewhere as far away as Neptune’s orbit, but not near Jupiter’s current orbit – an indication that the asteroids did indeed come from the cold reaches .

But first, Lucy has to sit up. After the spacecraft launched into space, it struggled to deploy one of its two giant decagonal solar panels, which when deployed resemble intricate spider webs. The wobbly solar panel still hasn’t fully deployed, and engineers don’t yet know why. Lucy will fly farther from the sun and for longer than any other solar-powered spacecraft in history, and she needs all the sunlight she can get. Engineers are currently analyzing the data and trying to find a fix. They could try deploying the panels again in mid-November, NASA said yesterday, or maybe just leave them as they are. If all goes well, Lucy will head into one of the most delightful displays in the solar system, finally allowing us to admire the calabash-shaped asteroids that follow Jupiter, our big fat pumpkin of a planet, around the sun .

Arline J. Mercier