The Moon may have a long-lost “twin” in orbit around Mars


Scientists studying an asteroid trailing behind Mars have found that the large space rock has the same chemical signature as the Moon, suggesting that this relic fragment may be a “twin” smaller than the lost kilometer of our closest celestial neighbor. .

Loitering 60 degrees forward and behind Mars along its orbit is a family of asteroids known as Trojans.

Along with Mars, these small rocky worlds can also be found by the thousands crowding around Jupiter and Neptune within gravitational “safe havens” known as Lagrange points.

Scientists think that the Trojans may have attached themselves to Martian orbit just as the planets ended up in their final configuration, so their primitive nature makes them ideal objects for studying the early evolution of the Solar System.

Furthermore, all Trojans in a Lagrange 5 (L5) orbit around Mars have the same ancestors and belong to the same group known as the Eureka family.

Members of the Eureka family contain a lot of olivine; a magnesium-iron silicate mineral that is common in the earth’s subsoil. I mean, anything but a rogue rock.

Known as 101429, this particular object has come to the attention of scientists as its mineralogical composition is not the same as other L5 Trojans.

After using spectroscopy to study the chemical content of 101429, a team led by Christou Apostolos at the Armagh Planetarium and Observatory (AOP) found that this imposter is rich in orthopyroxene, a mineral that ranges from pure magnesium silicate. (MgSiO3) to pure ferrous iron silicate (FeSiO3) – and has more in common with areas of the lunar surface than its fellow L5 inhabitants.

“The early solar system was very different from the place we see today,” says Apostolos. “The space between the newly formed planets was full of debris and collisions were the order of the day. Large asteroids – we call these planetesimals – were constantly hitting the Moon and other planets. “

How the Moon formed is a matter of debate, but many scientists think that a Mars-sized object collided with a proto-Earth ejecting substantial material that eventually collected and melted into a ‘ orbits our planet to form the Moon.

This is known as the giant impact hypothesis, and a fragment of such a collision may have reached the orbit of Mars when the planet was still forming and trapped in its Trojan clouds, says Apostolos.

However, Apostolos and the team say, there is a possibility that 101429 is just another asteroid, similar perhaps to ordinary chondrite meteorites, which have become lunar-like in composition through millions or billions of years of spatial alteration.

Alternatively, the object came from Mars itself. “The 101429 spectrum shape tells us it’s rich in pyroxene, a mineral found in the outer layer or crust of planet-sized bodies,” says the team leader.

“Mars, like the Moon and Earth, was hit by impacts early in its history, one of which was responsible for the gigantic Borealis Basin, a crater as wide as the planet itself. Such a colossal impact could easily have sent 101429 en route to the planet’s Lagrangian point L5, “Apostolos points out.

The true origins of 101429 are still undetermined, but its identification is important as it could teach scientists how to find Earth Trojans, if they exist.

So far, Mars is the only terrestrial planet known to host Trojans, but if others are found in the inner Solar System, and if they once belonged to the Earth, then they should stand out for their unusual composition.

These small yet undiscovered asteroids may have to wait until Vera C. Rubin’s Observatory begins operations in 2022.

Although the Rubin Observatory is set to probe the nature of dark matter and dark energy, it will also conduct the most ambitious investigation of the solar system to date.

Rubin is expected to discover about ten times the number of asteroids currently known to help scientists gain new insights into how planets are formed and how our Solar System has evolved over its history.

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