Asteroid Trailing Mars is possibly the long-lost twin of our …

Depiction of the planet Mars and its retinue of Trojans orbiting around Lagrange points L4 and L5. The dashed curve traces the planet’s orbit. At 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 astronomers at the AOP has found an asteroid that is after it Mars with a composition very similar to that of the moon. The asteroid could be an ancient piece of debris that dates back to the gigantic influences that shaped the moon and the other rocky planets in our solar system like Mars and Earth. The research that was published in the journal Ikarusalso has an impact on finding such primordial objects that are connected to our own planet.

Trojans are a class of asteroids that follow planets in their orbits much like 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 material remains of the formation and early development of the solar system. Several thousand of these Trojans exist along the orbit of the giant planet Jupiter. So far, astronomers have only discovered a handful of Mars Trojans that are closer to the sun, the planet next 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 against a spectrum of an area around Littrow Crater near the Apollo 17 landing site on the Moon, obtained from the Mauna Kea Observatory in Hawaii. Photo credit: Armagh Observatory

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

Alternatively, the asteroid can look like the moon because it comes from the moon. Dr. Apostolos Christou, AOP astronomer and lead author of the paper, 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 – we call these planetesimals – kept hitting the moon and the other planets. A splinter from such a collision could have reached Mars’ orbit while the planet was still forming and 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 101429 spectrum 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 earth, was hit by shocks 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 on its way to the planet’s L5 Lagrange point. “In fact, a few years ago, a Martian origin was proposed for the Trojan siblings 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 Eureka family asteroids 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 the Earth Trojans, if they exist. Previous work by the team had shown that solar radiation causes debris in the form of stone or city block-sized pieces of these asteroids to slowly emerge from the Trojan clouds on Mars. If the Earth Trojans were to resemble Mars, the same mechanism would serve as a source for small near-Earth asteroids, which are distinguished by their unusual composition.

Finding these objects could turn out to be the job of the Vera C. Rubin Observatory, which is poised to begin the most ambitious study of the solar system yet. Rubin is expected to discover about ten times as many asteroids as currently known. Together with the GAIA satellite, which already overlooks the sky from the L2 point Earth-Sun-Lagrange, it offers us possibly the best short-term views. Trojans track down debris on Earth.

Reference: “Composition and origin of the L5 Trojan asteroids of Mars: Results from 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 on Science and Technology Institutions, the Northern Ireland Department for Communities and THE, the European Organization for Astronomical Research in the Southern Hemisphere.