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


Imagine Jupiter and its small asteroids as a cosmic Halloween setting on the front porch of the solar system. The planet itself – swirling, stormy, the largest in the solar system – is the pumpkin, while the tiny asteroids accompanying it resemble funky-shaped gourds, one group in front and the other behind. The pumpkin and these gourds have been on display like this for billions of years, bound by a whim 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 been to closely inspect the planet’s small asteroids. After half a century of exploring most of the major planets and moons, NASA is beginning to expand its reach to smaller, more specialized objects that most people have never heard of. Everyone knows about Jupiter the pumpkin, but who has heard of these awesomely shaped gourds? So far, the mission hasn’t gone exactly as planned (we’ll talk about that later), but NASA seems confident that the spacecraft will one day reach these distant and mysterious objects.

Astronomers have known asteroids for some time. A German astronomer discovered the first in 1906, and over the years, as telescopes became more sophisticated, astronomers have found many more. They began to name the objects after characters from the most famous battle in Greek mythology, the Trojan War: Achilles, Agamemnon, Hector. Asteroids, which number in the thousands today, are collectively known as Trojans.

The Trojan asteroids are larger than the last asteroid visited by NASA last year. But they are still small on a cosmic scale, and especially compared to Jupiter: most known Trojans are about the size of a small American state, while more than 1,300 Earths could fit inside. 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 ahead of the planet on its path around the sun, and the other always lags behind. And Trojans could be the most well-known asteroids in the solar system: “Like a cold winter morning [when] it takes a lot more energy to get out of bed, asteroids also don’t want to use the energy to move away, ”Sierra Ferguson, a planetologist at the Southwest Research Institute in Boulder, Colorado, told me.

But a lot of things about asteroids are still unknown. We’ve had photos of Jupiter for decades, but even for powerful space telescopes like Hubble, Trojans only appear as points of light. From the ground, astronomers observe Trojans through “occultations,” an inadvertently spooky-sounding 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 over our planet for just a few seconds. Astronomers are deployed around the world, trying to watch the star temporarily fade away as the asteroid passes. “If you have enough of these telescopes spread out over a large enough area,” says Alessondra Springmann, a scientist at the University of Arizona, “you can actually get a silhouette of the asteroid by tracking how long it takes to get there. ‘star for weak. “

The Lucy mission aims to transform these fuzzy silhouettes into textured worlds. The spacecraft will visit seven Trojans over the next 12 years, study their composition and other properties, and see if any of them have their own little moon, or even a delicate set of rings. There’s also the very real chance that the team will stumble upon something they never imagined. In 2019, when another NASA spacecraft visited a nearby asteroid, scientists discovered that the rock was throwing hundreds of pieces of gravel on its own into space, a scenario no one on the team had predicted.

Trojans, no matter how small, could reveal great truths. Scientists believe these asteroids are remnants of the early solar system, pieces that weren’t swept away to create planets and moons. This is 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 information about human evolution. , astronomers hope that Lucy the spacecraft will provide information about the formation of the solar system.

This is because astronomers now believe that the outer planets – Jupiter, Saturn, Uranus, and Neptune – did not form where they are now, but rather arose much further into the solar system. They came to this conclusion about 15 years ago, after astronomers around the world continued to find Jupiter-sized exoplanets orbiting very close to their suns. Such a configuration implied that the exoplanets had migrated inward from the far reaches. Perhaps the same has happened in our own solar system? Scientists say that in the beginning, the large planets jostled each other around the solar system, causing their gravity to oscillate. Jupiter must have carried asteroids that were coasting 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 she left these asteroids untouched, hanging in the invisible amber of the universe.

Lucy will be looking for signs of this ancient Trojan horse rush, 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 sun’s heat. Lucy’s instruments could detect some substances that you would expect to find somewhere as far as Neptune’s orbit, but not near Jupiter’s current orbit, an indication that the asteroids have indeed come from the cold regions of the Earth. outside.

But first, Lucy has to stand up. After launching the spacecraft into space, it struggled to deploy one of its two giant decagonal solar panels which, when deployed, look like intricate cobwebs. The wobbly solar panel still hasn’t deployed and engineers don’t yet know why. Lucy will fly farther from the sun, and longer, than any other solar-powered spacecraft in history, and he needs all the sunlight he can get. Engineers are currently analyzing the data and trying to find a fix. They could try to deploy the panels again in mid-November, NASA said yesterday, or maybe just leave them as is. If all goes well, Lucy will slip into one of the most beautiful spectacles in the solar system, finally letting us admire the gourd-shaped asteroids that follow Jupiter, our great pumpkin of a planet, around the sun.

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