The most mysterious asteroids in the solar system
They are trapped.
Two swarms of curious and diverse space rocks – called Trojan asteroids – are constantly traveling around the sun, one in front of the gas giant Jupiter and the other behind. Jupiter and the Sun’s gravity have combined to lock Trojans into this unchanging orbit. Asteroids cannot leave. This is one of the main reasons why Trojan meteorites probably don’t land on Earth, which means we don’t have any samples of these distant, still largely mysterious objects.
But planetary scientists are keenly interested in the history of Trojan horses. They suspect that these icy rocks are captured relics from the formation of our solar system around 4 billion years ago. If so, Trojans are the smallest building blocks of planets. They can help us understand how Earth and other planets came into being.
“This is the first recognition of the Trojan swarms.”
“If we want to understand ourselves, we have to understand these little bodies,” Hal Levison, a planetary scientist who leads the unprecedented mission to investigate Trojans, told Mashable.
The mission, named “Lucy” after the ancient remains of a fossilized human skeleton, will visit six different Trojan asteroids during its 12-year mission. It launched in 2021. “This is the first recognition of Trojan horse swarms,” Levison said.
An illustration of the six different Trojan asteroids and one main-belt asteroid that the Lucy mission will visit
Credit: NASA/Goddard Space Flight Center Conceptual Image Lab
Learn more about space rocks and asteroids on Mashable:
Captured Cosmic Capsules
A looming question is how primordial chunks of our early solar system became trapped in swarms around Jupiter. A main theory (based on simulations of planet formation) is that in the nascent solar system, the now distant giant planets (Jupiter, Saturn, Neptune, and Uranus) were closer to the sun, instead of the intensely icy distant worlds that they are today. Meanwhile, smaller icy objects – the Trojans – formed beyond the planets in the outer realms of our solar system.
But about 880 million years after the solar system was formed, it underwent dramatic changes for reasons still under investigation. The large planets became violently unstable, Levison explained, and reoriented further from the sun. This created an opening for outer objects (Trojans) to eventually be propelled close to Jupiter by gravitational force.
“That’s when we think the Trojans got stuck,” Levison said.
Since then, they have been orbiting in swarms around Jupiter. They are believed to be pristine remnants of the solar system from billions of years ago. And that’s what makes them so valuable.
Planets grow by countless collisions, accumulating in the larger worlds we see today. Untarnished Trojans are the type of smaller, rocky, icy objects believed to have helped make planets. These are various “fossils” from the formation of planets, Levison pointed out. If we want to know how the Earth formed to become the habitable, cloudy, lush world we know today, we need to know what, exactly, formed it.
Trojans hold these clues. We just have to get there.
An animation of Trojan asteroid swarms (green) orbiting the sun. Credit: CAS Astronomical Institute / Petr Scheirich / NASA
The Deep Space Mission
The Lucy spacecraft, fitted with two huge solar panels, is nearly 52 feet wide. To fuel his journey to the realm of Jupiter, hundreds of millions of miles from the sun, he needs to collect Sunlight Bounties.
Most of the 12-year mission will involve traveling to and around the Trojans in a serpentine loop journey. The craft will not take any samples, but will rush for a few close flybys of the asteroids. In total, the mission will closely observe the rocks with a multitude of different cameras for approximately 24 hours. The craft, with vast distances to cover, will transport through space and zoom in on these objects.
“We won’t be able to blink,” Levison said.
“We’re not going to be able to blink.”
Lucy’s powerful cameras, including a spectrometer that can see what asteroids are made of, will observe the composition, mass and geological history of rocks. They will see how freezing Trojans are and how different they are from each other. Planetary scientists already know that some are dark red and resemble some of the extremely distant objects found today on the outskirts of the solar system, beyond Neptune.
Levison expects to be surprised by what Lucy throws back at him. The mission will give scientists unprecedented insight into how our solar system and humble blue planet evolved and matured into the eight-planet realm we see today. “I can’t wait to see what mysteries the mission will uncover!” Bill Nelson, NASA Administrator said in a press release.
On a winding tour of the solar system, Lucy will fly past her first Trojan in 2027 and her last in 2033.
“We’re going to visit a lot of these things,” Levison said.
The path of the Lucy spacecraft (in green) to visit the two Trojan asteroid swarms
Credit: Southwest Research Institute