Asteroids

Meet Pallas, the Asteroid That Used to Be a Planet (But Now Looks Like a Golf Ball)

Posted by Jason Major on
3D model of Pallas made from SPHERE image data. Credit: ESO/M. Marsset et al./MISTRAL algorithm (ONERA/CNRS)

No, it’s not a golf ball fished out of the lake; this is an image of Pallas, the third most massive object in the main asteroid belt after Ceres and Vesta. New 3D models made from observations taken with the SPHERE instrument on ESO’s Very Large Telescope show details of Pallas like never before possible, revealing an extensively-cratered surface reminiscent of… OK yes, the dimples on a golf ball. (I like to think Al Shepard would have approved.)

These new images show that the surface of Pallas displays very interesting topographic features suggesting a violent collisional history. Numerous large craters are found in both hemispheres of Pallas, forming a surface resembling a golf ball. The bright spot which appears in the southern hemisphere of Pallas (right image) is also very reminiscent of the salt deposits on Ceres. Credit: ESO/M. Marsset et al./MISTRAL algorithm (ONERA/CNRS)

From ESO on Feb. 24, 2020:

A new study led by Pierre Vernazza (Laboratoire d’Astrophysique de Marseille, France) conducted using ESO facilities has observed the asteroid Pallas for the first time at extremely high angular resolution. The asteroid could be successfully observed in such great detail thanks to the Adaptive-Optics (AO)-fed SPHERE imager on the Very Large Telescope (VLT).

German astronomer Heinrich Wilhelm Matthäus Olbers first discovered Pallas on 28 March 1802. Named for the Greek goddess Pallas Athene, the asteroid — along with many other asteroids discovered in the 19th century — was initially classified as a planet. As time passed and technology improved, Pallas was later reclassified as an asteroid. Today it is famous for being the third-largest asteroid in the Solar System, with an average diameter of 512 km [318 miles]. Source/read more: Golf Ball World | ESO

It’s thought that Pallas’ golf ball-esque dimpling is caused by heavy cratering events it repeatedly experiences as it passes though the plane of the main asteroid belt during its 4.6-year-long orbit around the Sun. According to an article from MIT:

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, much like cars on a race course, 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. 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.”
— Michaël Marsset, lead author and a postdoc in MIT’s Department of Earth, Atmospheric and Planetary Sciences