The asteroid Trailing Mars is perhaps the long-lost twin of our …

Representation of the planet Mars and its retinue of Trojans orbiting the Lagrange points L4 and L5. The dashed curve traces the orbit of the planet. In L5, the asteroid 101429 is represented by the blue dot, the asteroid Eureka and its family are represented in red and amber respectively. Photo credit: Armagh Observatory

An international team of planetary researchers led by AOP astronomers has found an asteroid behind it Mars with a composition very similar to that of the moon. The asteroid could be an ancient fragment of debris that dates back to the gigantic influences that shaped the moon and other rocky planets in our solar system such as Mars and Earth. The research that was published in the journal Ikarusit also has an impact on the search for such primordial objects which are connected to our planet.

Trojans are a class of asteroids that follow planets in their orbits, just as a flock of sheep might follow a shepherd trapped in “safe havens” 60 degrees in front of and behind the planet (Figure 1). They are of great interest to scientists because they represent the material remnants of the formation and early development of the solar system. Several thousand of these Trojans exist along the giant planet’s orbit Jupiter. So far, astronomers have only discovered a handful of Mars Trojans that are closer to the sun, the planet closest to Earth.

Reflectance spectrum of asteroid 101429 from data obtained from the Very Large Telescope at the European Southern Observatory in Chile and the NASA Infrared Telescope Facility in Hawaii. This is plotted on a spectrum of an area around Littrow Crater near the Apollo 17 moon landing site obtained from the Mauna Kea Observatory in Hawaii. Photo credit: Armagh Observatory

Where could such an unusual object come from? One possibility is that 101429 is just another asteroid, similar to common chondrite meteorites, that acquired its moon-like appearance through eons of solar exposure, a process known as space alteration.

Alternatively, the asteroid may resemble the moon because it comes from the moon. Dr Apostolos Christou, AOP astronomer and lead author of the article, explains: “The early solar system was very different from today. The space between the newly formed planets was full of debris and collisions were frequent. Large asteroids, which we call planetesimals, kept hitting the moon and other planets. A splinter from such a collision could have reached the orbit of Mars while the planet was still forming and was trapped in its Trojan clouds. ”

A third, and probably more likely, scenario is that the object came from Mars itself. Dr. Christou points out: “The shape of the spectrum 101429 shows that it is rich in pyroxene, a mineral found in the outer layer or crust of planet-sized bodies. Mars, like the moon and the earth, was struck by shock at the beginning of its history. One of them 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 L5 Lagrange point. “Indeed, a few years ago, a Martian origin was proposed for the Trojan brothers of 101429, a group of Trojans collectively known as the Eureka family (Figure 1). These asteroids are also of unusual composition, but while 101429 is pyroxic, these asteroids from the Eureka family are primarily olivine, a mineral found deep within a planet’s mantle.

101429 and his brothers also have something to teach us about how to find Earth’s Trojans, if they exist. Previous work by the team had shown that solar radiation slowly causes debris in the form of stone or pieces of urban blocks of these asteroids to emerge from Trojan clouds on Mars. If the terrestrial Trojans were to resemble Mars, the same mechanism would serve as a source for small asteroids near the Earth, which are distinguished by their unusual composition.

Finding these objects could prove to be the task of the Vera C. Rubin Observatory, which is ready to begin the most ambitious study of the solar system ever. Rubin is expected to discover about ten times more asteroids than currently known. Together with the GAIA satellite, which already overlooks the sky from point L2 Earth-Sun-Lagrange, it offers us perhaps the best short-term views. Trojans track down debris on Earth.

Reference: “Composition and origin of the Trojan asteroids L5 of Mars: results of the spectroscopy” by Apostolos A. Christou,
Galin Borisov. Aldo Dell’Oro. Alberto Cellino and Maxime Devogèle, 1. August 2020, Ikarus.
DOI: 10.1016 / j.icarus.2020.113994
arXiv: 2010.10947

Acknowledgments: The resources and facilities to support this work have been provided by the UK Council for Science and Technology Institutions, the Northern Ireland Department of Communities and THE, the European Organization for Astronomical Research in the Southern Hemisphere.