NASA’s Lucy mission lifts off to unlock the mysteries of the solar system

Beyond the main asteroid belt, alongside the gargantuan planet Jupiter, hundreds of thousands of unexplored worlds, each less than 220 kilometers in diameter, hold precious secrets about the birth of our solar system.

A new NASA mission called Lucy launched Oct. 16 from Cape Canaveral, Florida, to embark on a journey to study these asteroids, known as Jupiter Trojans. During the 12-year, four-billion-mile journey, Lucy will periodically dive into two swarms of asteroids that lead and follow Jupiter as it orbits the sun, flying by a total of seven Trojans, as well as an eighth bonus asteroid in the main belt, between Mars and Jupiter.

“Lucy will explore a region of our solar system that has never been explored before,” said Adriana Ocampo, Lucy program manager at NASA Headquarters in Washington, DC, during an Oct. 14 press briefing.

Jupiter’s Trojans have not been seen in more detail than mere specks of light in the night sky; Lucy will fly within 600 miles of them. Along the way, the mission will set the record for the most asteroids visited by a single spacecraft.

Lucy will hit her first target, the main-belt asteroid, in 2025, then depart for the Trojans, which she will explore in a series of flybys from 2027 to 2033. Spacecraft data, detailing the color of the asteroids , composition, density and craters, should help researchers determine when and where each formed in the solar system.

The mission – only the tenth to venture to Jupiter – will also inform simulations of the early solar system, helping to reveal how our neighborhood around the sun came to be.

Fittingly, “Lucy” was inspired by the famous fossil of the same name, a 3.2 million year old skeleton of an ancestral cousin of modern humans. In a sense, Jupiter’s Trojans perform the same role as these iconic bones: to preserve remnants of a distant past that scientists can use to make sense of our present.

“These things are really the fossils from which the planets formed,” said Hal Levison, principal investigator of Lucy and a researcher at the Southwest Research Institute in Boulder, Colorado, during a press conference on October 13. “If you want to understand where the solar system is coming from, you have to go to these little bodies.”

A flight for the ages

Lucy’s mission relies on a complex trajectory that places the spacecraft in a six-year orbit around the sun. After a series of flybys of Earth to use our planet’s gravity for extra punch, Lucy will fly past main-belt asteroid 52246 Donaldjohanson, a 2.5-mile-wide world named for the paleoanthropologist who discovered Lucy’s fossil.

The spacecraft will then pass through the main Trojan swarm in 2027, flying through five Trojans in one go. On the next pass, in 2033, it will dive into the trailing swarm, where it will pass Patroclus and Menoetius, a binary asteroid system.

The intricate path Lucy will make through the solar system has been painstakingly mapped out by Lockheed Martin’s Brian Sutter, the spacecraft’s mission architect. “Brian’s role isn’t just a scientist, he’s an artist,” says Levison.

Although the Jupiter Trojans occupy two fairly narrow bands of the solar system, they are extremely varied in color, size, and certain aspects of their orbits, ranging from gray to deep, muted red, and they vary from less from six-tenths of a mile wide to about 70 miles wide.

Some of these asteroids look like other types of small bodies scattered throughout the solar system. The grayish Eurybate, for example, resembles asteroids found orbiting in the main belt just beyond Mars. The slow-dancing pair of Patroclus and Menoetius, on the other hand, closely resemble the binary systems of the Kuiper Belt, a region beyond Neptune’s orbit.

“We designed our mission to investigate the diversity of objects in this population,” Lucy’s deputy principal investigator, Cathy Olkin, also of the Southwest Research Institute, said during an Oct. 12 press briefing.

Lucy’s team had to build a spaceship capable of making the four billion kilometer journey. At its furthest, Lucy will be more than half a billion miles from the sun, where sunlight is only a few percent of what we get on Earth. So Lucy needs massive solar panels: The spacecraft’s twin solar panels carry nearly 8,000 individual solar cells, spread over an area as large as three and a half parking spaces. At Trojan distances, these huge arrays will only generate about 500 watts of power, less than average microwave uses.

During flybys, Lucy will approach within 600 miles of her target asteroids at speeds of nearly 15,000 miles per hour, requiring her instruments to be mounted on an extremely precise gimbal. During Lucy’s closest approach to each target, her higher-resolution camera, called the LORRI, will be able to capture surface features as small as 24 feet in diameter.

“The kind of data you can get up close, both for geology and composition, is not something you can replicate by just seeing it as a point of light,” says Andy Rivkin, an expert in small bodies at the Johns Laboratory for Applied Physics at Hopkins University.

Asteroid armies flanking Jupiter

Astronomers estimate that several hundred thousand Jupiter Trojans orbit alongside the gas giant. Since 1906, when the first Trojan Jupiter was discovered, astronomers have located nearly 11,000 of these objects. More than half of them have been discovered since 2010, thanks to steadily improving telescope readings scanning the night sky.

The asteroids were named after the warriors who fought in the Trojan War: the Greek heroes for the asteroid swarm leading Jupiter and the Trojan heroes for the rear swarm. As astronomers prepare to discover hundreds of thousands more Trojans over the next decade, The IliadThe well of names is finally exhausted.

Today, the new Jupiter Trojans are named after modern Olympic athletes. In 2020, Lucy’s team announced that they had discovered a small object orbiting one of Lucy’s flyby targets, Eurybates. The smaller object, now called Queta, is named after Mexican track and field athlete Norma Enriqueta Basilio Sotelo, the first woman to light the Olympic cauldron.

For decades, these asteroids were thought to be mere remnants of the formation of Jupiter’s largest moons. But over the past 25 years, scientists have realized that Jupiter’s Trojans could provide major clues to our solar system’s chaotic youth.

The first days of chaos

Astronomers know from ground-based telescopes that Jupiter’s Trojans come in a variety of colors, suggesting they’re not all made of the same materials. Yet somehow, this jumble of small bodies ended up settling into extremely stable – and hard-to-reach – orbits alongside Jupiter.

“Since they share the same orbit of Jupiter, they are kind of like witnesses to everything that happened with Jupiter,” says Simona Pirani, a postdoctoral researcher at the University of Copenhagen who studies the early formation of the solar system. . And unraveling the story of Jupiter, the largest planet, is crucial to the story of the entire system.

In 2005, Levison and his colleagues at the Observatoire de la Côte d’Azur in Nice, France, published an influential hypothesis – now called the Nice Model – that proposed an era of chaos in the solar system’s youth.

In the Nice model and other similar scenarios, the solar system started out with many more small bodies than it has now, and Jupiter, Saturn, Uranus, and Neptune migrated inward as they formed. initial. After they became large planets, the gravitational dances of the gas giants with tiny “planetsimals” shifted their orbits bit by bit, until they slipped into an unstable configuration.

Suddenly, the giant planets are thought to have rocketed off to their present positions, scattering many small bodies out of the solar system and mixing up some of the remaining ones. Some theories even suggest that a fifth gas giant could have been ejected from the solar system around this time, adding to the chaos.

Jupiter may have captured its Trojan asteroids during all the fuss, many of which likely formed beyond Neptune. In the years since the Nice Model was first published, theorists have updated it to try to explain even more unusual features of Trojans. Others have tested whether some of Jupiter’s Trojans could have been captured even earlier in the solar system’s formation, perhaps even when a baby Jupiter was only the size of Earth.

But to test these theories about the formation and evolution of the solar system, scientists need to visit Jupiter’s Trojans up close.

“I can’t wait to find something I didn’t expect,” says Levison. “There is no doubt!”

This story has been updated to reflect the successful launch of NASA’s Lucy spacecraft.

Arline J. Mercier