New photos that have been released show the heavily-cratered Pallas and why it’s been nicknamed the “golf ball asteroid”. It actually does look like a golf ball because countless impacts created many craters on its surface that were probably caused by its highly unusual orbit.
In order to study the asteroid’s surface and shape, scientists used the Spectro-Polarimetric High-contract Exoplanet Research (or SPHERE) imager on the Very Large Telescope that’s located in the Atacama Desert in Chile.
By studying eleven pictures taken of the surface of Pallas, scientists found a large amount of craters that measured between 18.5 and 75 miles wide (Pallas’ diameter averages around 318 miles). In fact, it’s been impacted so many times that it has approximately twice as many craters as the largest asteroid Ceres and around three times as many as the second-largest asteroid Vesta.
According to the researchers (their paper can be read here), the two huge craters on Pallas, which are located near the south pole and by the equator, show that the asteroid was hit in a sideways impact with projectiles that measured between 37 and 65 miles in diameter. The impact near the equator was so strong that it could have possibly created a “family” of several hundred smaller craters that measure less than 12 miles in width.
Miroslav Broz, who is an astronomer at Charles University in the Czech Republic as well as a co-author of the study, told Space.com, “We performed numerical simulations to determine the most probable age of the family, which is 1.7 billion years, and this should correspond to the surface age of Pallas, or at least a substantial part of it.”
According to the researchers, since Pallas travels through space in a tilted and elongated orbit, that’s probably why it is being impacted by objects at an exceptionally high speed of around 25,725 mph compared to the average speed of approximately 12, 975 mph. Pallas’ odd orbit and fast impacts would explain why it is so heavily cratered. Pictures of Pallas can be seen here.
The researchers found another interesting fact about Pallas. They created a 3D model of the asteroid and discovered that it is denser than Ceres but less dense than Vesta which indicates that it has a much bigger rock to ice proportion than Ceres. It also indicates that Pallas has a composition that is quite similar to a type of meteorite that’s called CM chondrite. Chondrites are meteorites that are composed of small round shaped pellets that are called chondrules and they are created when droplets of molten minerals cool off very fast while in space. This new information suggests that the interior of Pallas was never hot enough to create a silicon-heavy rocky core with a water-rich mantle so it probably contains a mixture of ice and rock instead.