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Second asteroid ever to share Earth’s orbit is a big one

Parts of our solar system are rich with asteroids, like the Jupiter Trojans where thousands of asteroids share the orbit of Jupiter. Asteroids cluster here due to the gravitational interactions between Jupiter and the sun, creating a stable orbit called a Lagrange point. There have also been asteroids discovered sharing the orbits of Venus, Mars, Uranus, and Neptune. But very few asteroids have been found that share the orbit of Earth — just two have been discovered to date — and astronomers have recently confirmed the existence and size of one of these rare Earth Trojans.

The asteroid, called 2020 XL5, was first discovered in 2020 using the Pan-STARRS1 survey telescope in Hawai‘i. Recent research has found that it is a big one, at 0.73 miles across, making it three times as large as the other known Earth Trojan, called 2010 TK7. It is the orbit of these asteroids, sharing the orbit of Earth, which makes them special and gives them the name of Trojans. “Trojans are objects sharing an orbit with a planet, clustered around one of two special gravitationally balanced areas along the orbit of the planet known as Lagrange points,” explained one of the researchers, Cesar Briceño, in a statement.

Artistic impression of an asteroid in the foreground with the Milky Way and a bright star in the background.
Using the 4.1-meter SOAR (Southern Astrophysical Research) Telescope on Cerro Pachón in Chile, astronomers have confirmed that an asteroid discovered in 2020 by the Pan-STARRS1 survey, called 2020 XL5, is an Earth Trojan (an Earth companion following the same path around the Sun as Earth does) and revealed that it is much larger than the only other Earth Trojan known. NOIRLab/NSF/AURA/J. da Silva/Spaceengine Acknowledgment: M. Zamani (NSF’s NOIRLab)

When researchers first spotted 2020 XL5, they weren’t sure if it was actually a Trojan asteroid or whether it was merely crossing over the orbit of Earth. Observations with the 4.1-meter SOAR (Southern Astrophysical Research) Telescope on Cerro Pachón in Chile confirmed its orbit, and also found out about its size. Other instruments also confirmed its orbit and found that it is a C-type asteroid, meaning it contains a lot of carbon.

There might be many Earth Trojans, but one reason they are so rarely identified is that they are hard to spot, because they can only be seen at sunrise or sunset. Even 2020 XL5 will not always stay in its current orbit, as over thousands of years gravitational forces will pull it out of orbit and send it off into space.

The discovery of Earth Trojans is important because asteroids are typically extremely ancient, so studying them can help us learn about the early solar system. And finding asteroids orbiting near Earth may make them easier to visit.

“If we are able to discover more Earth Trojans, and if some of them can have orbits with lower inclinations, they might become cheaper to reach than our Moon,” said Briceño. “So they might become ideal bases for an advanced exploration of the Solar System, or they could even be a source of resources.”

The research is published in the journal Nature Communications.

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