Thanks to data from the Soar telescope, an observatory in which Brazil is a majority partner in Chile, researchers have confirmed that Earth has an asteroid 1.2 km in diameter that follows the planet in its orbit around the Sun.
Much has been said about the libration (or Lagrangian) points of a system like the Earth-Sun, now that the James Webb Space Telescope has settled into one of them, L2, located 1.5 million km from Earth, following the planet on its ride through the solar carousel. But two other points of the same type, L4 and L5, are exactly in the Earth’s orbit, 60 degrees from the planet, one ahead and one behind.
They serve, like the others, as a kind of natural parking lot, in which the gravity of the two stars (Sun and Earth, in this case) is counterbalanced to stabilize objects located there. It goes for ships, like the Webb, and also for asteroids, which, when they stop there, are called Trojans.
The term was originally used to describe the boulders that lie at points L4 and L5 of the Jupiter-Sun system, accompanying the giant planet in its orbit. But in theory any world with enough mass can have them. In fact, there are Trojans associated with all gas giants and almost all rocky ones (only Mercury has not had at least one such object discovered).
The first terrestrial Trojan to be found was 2010 TK7, detected, guess what, in 2010. The second, now detailed, was spotted a decade later, when the Pan-Starrs telescope in Hawaii discovered 2020 XL5. But at the time of its discovery, it was possible that it was just a passing asteroid, not a Trojan.
However, a search of archival images from DECam, camera of the Dark Energy Survey project, revealed the object’s position at various times between 2012 and 2019. Earth – and will do so for at least another 4,000 years, until it is gravitationally disturbed and takes another path.
Soar data in particular allowed us to estimate the size and composition of 2020 XL5. It is a C-type asteroid, rich in carbon, and its diameter is large. At 1.2km, it is triple the size of the 2010 TK7. Both are located at L4, a Lagrangian point that travels ahead of Earth in its orbit. In L5, which follows the planet’s path around the Sun, they still haven’t found anything.
The result was published in the journal Nature Communications and may be just one more in a list: it is quite possible that Earth has other Trojans waiting to be discovered. Mars, while much smaller, has at least nine (and possibly 14, if we count objects not yet officially listed as Trojans). It makes it easier, in this case, to be close to a large repository, the asteroid belt.
This column is published on Mondays, in Folha Corrida.
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Source: Folha
