Study reveals details of “golf ball asteroid”

Asteroids come in all shapes and sizes, and now astronomers at the Massachusetts Institute of Technology (MIT), IEEC-UB, and other institutions have observed an asteroid so heavily cratered that they are dubbing it the “golf ball asteroid.”

The asteroid is named Pallas, after the Greek goddess of wisdom, and was originally discovered in 1802. Pallas is the third largest object in the asteroid belt, and is about one-seventh the size of the Moon. For centuries, astronomers have noticed that the asteroid orbits along a significantly tilted track compared with the majority of objects in the asteroid belt, though the reason for its incline remains a mystery.

In a paper published in Nature Astronomy, researchers reveal for the first time detailed images of Pallas, including its heavily cratered surface.

The researchers suspect that Pallas’ pummeled surface is a result of the asteroid’s skewed orbit. While most objects in the asteroid belt travel roughly along the same elliptical track around the Sun, Pallas’s tilted orbit is such that the asteroid has to smash its way through the asteroid belt at an angle. Any collisions that Pallas experiences along its way would be around four times more damaging than collisions between two asteroids in the same orbit.

“Pallas’ orbit implies very high-velocity impacts,” says Michaël Marsset, the paper’s first author and a postdoc in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “From these images, we can now say that Pallas is the most cratered object that we know of in the asteroid belt. It’s like discovering a new world.”

“A violent history”

The team, led by principal investigator Pierre Vernazza from the Laboratoire d'Astrophyisque de Marseille in France, obtained images of Pallas using the SPHERE instrument at the European Southern Observatory’s Very Large Telescope (VLT), an array of four telescopes, each with an 8-meter-wide mirror, situated in the mountains of Chile.

The team obtained 11 series of images over two observing runs, catching Pallas from different angles as it rotated. After compiling the images, the researchers generated a 3D reconstruction of the shape of the asteroid, along with a crater map of its poles, and parts of its equatorial region.

A researcher from the Institute of Space Studies of Catalonia (IEEC) at the Institute of Cosmos Sciences (ICC, UB), Toni Santana-Ros, coordinated the photometric follow-up of Pallas during the project’s first year. The team processed the light-curve data, which was then used by another group to build a 3D model of the asteroid. “Combining both adaptive optics and the 3D shape model provides information about certain areas of the object that might remain non-visible in the optical images,” Santana-Ros explains. “Furthermore, using the model together with the images allows making an enlargement of the object, and then we can measure certain aspects such as its radius or density. For instance, we have obtained an accurate value for Pallas’ density, which was still under debate”. Santana-Ros is currently a postdoc researcher in the Solar System & Minor Bodies group at ICC (IEEC-UB).

In all, the research identified 36 craters larger than 30 kilometers in diameter — about one-fifth the diameter of Earth’s Chicxulub crater, the original impact of which likely killed off the dinosaurs 65 million years ago. Pallas’ craters appear to cover at least 10 percent of the asteroid’s surface, which is “suggestive of a violent collisional history,” as the researchers state in their paper.

To see how violent that history likely has been, the team ran a series of simulations of Pallas and its interactions with the rest of the asteroid belt over the last 4 billion years — about the age of the solar system. They did the same with Ceres and Vesta, taking into account each asteroid’s size, mass, and orbital properties, as well as the speed and size distributions of objects within the asteroid belt. They recorded each time a simulated collision produced a crater, on either Pallas, Ceres, or Vesta, that was at least 40 kilometers wide (the size of most of the craters that they observed on Pallas).

They found that a 40-kilometer crater on Pallas could be made by a collision with a much smaller object compared to the same size crater on either Ceres or Vesta. Because small asteroids are much more numerous in the asteroid belt than larger ones, this implies that Pallas has a higher likelihood of experiencing high-velocity cratering events than the other two asteroids.

Marsset’s co-authors include collaborators from 21 research institutions around the world. This research was supported, in part, by NASA, the French Ministry of Defense, Aix-Marseille University, and the European Union’s Horizon 2020 research and innovation program.

This article is based on a news that originally appeared on MIT News.

Links

– IEEC
– ICCUB
– Solar System & Minor Bodies Group

More information

This research is presented in the paper “The violent collisional history of aqueously evolved (2) Pallas”, by Michaël Marsset et al., that was published in the journal Nature Astronomy on 10 February 2020.

The Institute of Space Studies of Catalonia (IEEC  — Institut d’Estudis Espacials de Catalunya) promotes and coordinates space research and technology development in Catalonia for the benefit of society. IEEC fosters collaborations both locally and worldwide and is an efficient agent of knowledge, innovation and technology transfer. As a result of over 20 years of high-quality research, done in collaboration with major international organisations, IEEC ranks among the best international research centers, focusing on areas such as: astrophysics, cosmology, planetary science, and Earth Observation. IEEC’s engineering division develops instrumentation for ground- and space-based projects, and has extensive experience in working with private or public organisations from the aerospace and other innovation sectors.  

IEEC is a private non-profit foundation, governed by a Board of Trustees composed of Generalitat de Catalunya and four other institutions that each have a research unit, which together constitute the core of IEEC R&D activity: the University of Barcelona (UB) with the research unit ICCUB — Institute of Cosmos Sciences; the Autonomous University of Barcelona (UAB) with the research unit CERES — Center of Space Studies and Research; the Polytechnic University of Catalonia (UPC) with the research unit CTE — Research Group in Space Sciences and Technologies; the Spanish Research Council (CSIC) with the research unit ICE — Institute of Space Sciences. IEEC is integrated in the CERCA network (Centres de Recerca de Catalunya).

Images

PR_Image1: Pallas
Caption: Two views of the asteroid Pallas, which researchers have determined to be the most heavily cratered object in the asteroid belt. 
Credit: Image courtesy of the researchers.

Contacts

IEEC Communication Office
Barcelona, Spain
Rosa Rodríguez Gasén
E-mail: comunicacio@ieec.cat 

Institute of Cosmos Science
Institute of Space Studies of Catalonia
Barcelona, Spain
Toni Santana-Rosa
Postdoctoral researcher
E-mail: tsantanaros@icc.ub.edu