In this illustration, the asteroid is at the bottom left. The two bright spots above it on the left are the Earth (right) and the Moon. The sun appears at the top right.

NOIRLab / NSF / AURA / J. da Silva / Space Engine

Scientists may have just identified the top of cosmic matter. It is an asteroid that crosses the universe with the Earth and the story of its discovery is a masterpiece of cinema.

The science saga begins in December 2020. A routine study of the sky designed to detect asteroids threatening to crash on our planet, a slight spot appeared – a formation that struggles to signal a little “I’m here” to astronomers. For four months, researchers used powerful telescopes, such as the Southern Astrophysical Research Telescope in Chile, to observe the space fragment, trying to figure out what it is, where it is and why it is there.

They slowly realized that the signal was emitted by an asteroid with almost a mile called 2020 XL5, but the location and knowledge of the rock remained a mystery. He was treading too close to the sun, a huge obstacle to ground-based telescopes. And so an idea was born.

Researchers speculate that if the 2020 XL5 signal is difficult to see now, it may have been just as faded in past sky research. Maybe it was missed. Of course, after searching the 2012-2016 archives of the Dark Energy Survey and the Victor M. Blanco 4-meter telescope, the quiet space rock reappeared.

Its existence has been neglected for almost a decade.

“Suddenly we had 10 years of data on this object,” said Tony Santana-Ross, a planetary scientist at the Institute of Space Sciences at the University of Barcelona and the University of Alicante. “It simply came to our notice then. I mean, now we’ve suddenly realized that we can do a really solid analysis. “

In an article published Tuesday in the journal Nature Communications, Santana-Ross and fellow researchers concluded that 600 years ago, 2020 XL5 was captured at the 4th point of Lagrange on Earth – an area of ​​stability in the orbit of our planet, strung along with its gravity and solar. They say the cosmic piece will remain there for approximately 4,000 years.

Surprisingly, the positioning of the 2020 XL5 considers it an terrestrial Trojan or asteroid satellite on our planet that travels right next to us. This is the second earthly Trojan horse ever found. It is also the largest, standing three times larger than the first, 2010 TK7.

But most importantly, it proves that things lurk in L4.

“Hayabusa2 from the Japanese agency passed through point L5, and Osiris-Rex from NASA passed through L4,” Santana-Ross explained. “They tried to find objects inside these points and could not find them.”

While the 2010 TK7 is also around L4, Santana-Ros said it is considered an exotic anomaly. “Now,” he added, “we know there are at least two of them.


This is where the 2020 XL5 will appear in the sky from Cerro Pachón in Chile, while the asteroid orbits the point of Lagrange Earth-Sun 4, also known as L4. The arrows show the direction of its movement. The SOAR telescope appears at the bottom left.

NOIRLab / NSF / AURA / J. da Silva

Space bases and asteroid mining

Due to the gravitational balance found at all points of Lagrange, dust, asteroids and random galactic objects can easily get stuck there. In fact, these anchor points are so fixed that NASA’s James Webb Space Telescope and ESA Gaia surveyor are currently located on L2.

Approaching L4 and L5, Santana-Ross said the space objects living in these pockets are especially special because they follow a galactic plane easily accessible from a human spaceship.

“The expensive part of a rocket is to change its inclination and go into the orbital plane of an asteroid,” Santana-Ross said. “But if it’s close to our orbital plane, then it will be cheaper to get to these bodies than to get to the moon, for example.”

Things floating in these orbits could be ideal for astronauts’ science bases, alien telescopes, or even considered candidates for asteroid mining. “I would say that in the next few decades, if we find more of these objects, they will probably be number one for NASA, ESA, all space agencies,” Santana-Ross said.


Lagrange points are places in space where the gravitational forces of two massive bodies, such as the sun and the planet, balance, making it easier to orbit a low-mass object, such as a spaceship or an asteroid. This diagram shows the five Lagrange points for the Earth-Sun system. Note: The size of the Earth and the distances in the illustration are not to scale.

NOIRLab / NSF / AURA / J. da Silva

Earth Trojans against Jupiter’s Trojan horses

If all this moves your memory of NASA’s Lucy mission, which launched last year to Jupiter’s Trojan asteroids, you’re not alone. In summary, some of Jupiter’s asteroids, the Trojans of Jupiter, are considered primary. This means that they have existed since the beginning of time.

In green you see the leading and subsequent swarms of Trojans on Jupiter. Lucy is on her way.


NASA is interested in learning about them because they are essentially remnants of the building blocks of our solar system. However, the two earthly Trojans are not so ancient.

“Both are transient asteroids or asteroids of transient origin, which means they haven’t been there forever or since the formation of Earth,” Santana-Ross said.

However, the research team says that the very existence of these terrestrial Trojans in L4 is enough to call this an important scientific discovery. Then they say that scientists need to start thinking about pointing their telescopes at L4 and inventing missions to study our solar system.

Webb and Gaia, for example, cannot observe these points because they were created to peer into deep space, not our solar system. As an example, Webb needs to be super cool because of its infrared image processors, so pointing it at the sun would interfere with the survey data.

“[L2] “It’s a great place to be if you want to watch in the direction of a galaxy or even other galaxies,” Santana-Ross said. “But if you want to watch the sun, it’s a terrible place.”

We hope to see some focus of the solar system in the coming years – and trace the asteroid’s path to great space discoveries.