Saturday, February 24

A Trojan asteroid will accompany the Earth for 4,000 years

On December 12, 2020, the Pan-STARRS1 survey telescope detected the asteroid 2020 XL5 from Hawaii (USA), and that same month it began to study, but the object was very faint and approached the Sun in the field of view , which made it difficult to observe.

In order to determine which asteroid it was and its orbit, an international team of astronomers followed it at the beginning of 2021 with three telescopes: one from the Optical Ground Station (OGS) that the European Space Agency has on Mount Teide (Canary Islands), the Lowell Discovery in Arizona (USA) and the SOAR operated by the NOIRLab of the National Science Foundation (NSF) in Chile.

Asteroid 2020 XL5, with a diameter of 1.2 km, is the second Earth Trojan. It arrived 600 years ago and is located at the Lagrange point L4, where it will remain for four millennia.

“With these data we were able to better determine its orbit and carry out a search in archives, finding 14 undetected observations of 2020 XL5 between 2012 and 2019, therefore we had more than a decade of observations!” Toni Santana-Ros from SINC points out. the University of Alicante and the Institute of Cosmos Sciences of the University of Barcelona, ​​”and this allowed us to confirm that it will be a Trojan asteroid of the Earth for more than 4,000 years”. The results are published this week in the journal Nature Communications.

Trojan asteroids are small objects that share an orbit with a planet and remain stable about 60° ahead or behind the main body. For example, Jupiter has more than 5,000 known Trojan asteroids – the mission Lucy NASA will explore some of them – and Venus, Mars, Uranus and Neptune have them too.

Second terrestrial Trojan asteroid

In the case of Earth only one was known, 2010 TK7less than 400 meters wide, and although a previous study already pointed out that 2020 XL5 was the second, is now confirmed “and we are sure that it will remain in L4 for 4,000 years”, says Santana-Ros. Afterwards he will be disturbed by gravitational forces and will escape to wander through space.

Lagrange or L points are gravitationally balanced regions around two massive bodies, such as the Sun and a planet. The Earth-Sun system has five, and the Trojan asteroids may be at L4 and L5, although the two detected so far accompanying Earth have been seen at L4.

The second terrestrial Trojan asteroid is three times larger than the first. The diameter of 2020 XL5 is about 1.18 kilometers, according to the authors, who also propose that it is from type cthe most common in the solar system, very rich in carbon and generally dark.

“The SOAR data allowed us to carry out a first analysis photometric of the object, revealing that it is probably a type C asteroid with a size greater than a kilometer,” says Santana-Ros, “although these are preliminary conclusions that must be confirmed with new observations, because we also do not know its rotation period and its shape, that could also modify these results.

Possible origin in the asteroid belt

Regarding the origin of 2020 XL5, it is surely the main asteroid belt, from where it could have been ejected after an interaction with Jupiter. “But we don’t have enough information to confirm this with any certainty either,” acknowledges the astronomer.

It is possible that 2020 XL5 and 2010 TK7 are not alone: ​​there could be many more terrestrial Trojan asteroids that have not been detected until now, due to the fact that they appear very close to the Sun.

According to scientists, the two Earth Trojan asteroids discovered so far may not be alone: ​​there could be many more that have gone undetected because they appear so close to the Sun, making observations difficult. In fact, their searches are done near sunrise or sunset, with the telescopes positioned close to the horizon.

“If we could discover more terrestrial Trojans, and some had orbits with lower inclinations, it could be cheaper to reach them than our Moon”, says another of the authors, Cesar Briceño from NOIRLab, “therefore, they could become bases ideal for advanced exploration of the solar system, or even to constitute a source of resources”.

Some early or primordial Solar System Trojans, orbiting at L4 or L5 in their planet’s system with the Sun, offer information about how the planet formed. Knowing how many objects there are in these regions, their size and mass, helps astronomers to delimit the evolution models of the solar system.

“Unfortunately, the two known terrestrial Trojan asteroids are temporary objects,” says Santana-Ros. “In the case of 2020 XL5 was captured at the L4 point approximately 600 years ago, it is not a primordial object, but it can be useful to better understand the dynamics of these bodies and help discover new ones. Its exploration would not be justified, but it can be a good passing or overflight object in a mission with other objectives”.