Astronomers have found a lot of asteroids, but you would not recognize the vast majority of them from stars in a photograph of the night sky. Even astronomers do not recognize them. He has to take more pictures in a row – then the asteroid will shift towards the starry background.
Some asteroids were touched by radar, some were visited by spacecraft. Overall, we have a more detailed idea of only a handful of them. However, terrestrial astronomy is not completely toothless. Technology is improving.
Two years ago, we wrote about great photographs of the asteroid Hygiea, which was viewed by the SPHERE instrument on the VLT telescope of the European Southern Observatory in Chile. In fact, it was a more extensive work, in which Czech scientists from Charles University also took part.
An international team of scientists has now presented images of 42 of the largest asteroids in the main belt, located between Mars and Jupiter. If you think the number can’t be random, you think so. The press release was issued on the 42nd anniversary of the publication of Adams’ book The Hitchhiker’s Guide to the Galaxy.
And it’s a number that is in a way groundbreaking. So far, we have had more detailed images of only three asteroids in the main belt – the Dawn spacecraft visited Cerera and Vesta, the Rosetta Lutetia spacecraft.
The researchers took pictures between 2017 and 2019. Most of the 42 objects in their sample are larger than 100 km – the team obtained images of 20 of the 23 objects larger than 200 km that move in the belt.
Two main groups
The two largest objects he examined were Ceres and Vesta, which average about 940 and 520 kilometers, respectively. The smallest asteroids are Urania and Ausonia, each only about 90 kilometers in size.
By reconstructing the shapes of the objects, the team found that the observed asteroids are mainly divided into two groups. Some are almost perfectly spherical, such as Hygiea and Ceres, while others have a more strange, “elongated” shape, with their undisputed queen being the “dog bone” asteroid Cleopatra.
This is not surprising. The heavier the object, the rounder it is. Because of this, it is the “roundness” of the object that is used to define the dwarf planets. If we know the shape and size of the body better, we can more easily calculate its density, which is an important data for the study of asteroids.
The lowest density is the asteroid Sylvie (1.3 grams per cubic centimeter), which is approximately the density of coal. Psyche and Kalliope have the highest density – 3.9, respectively. 4.4 grams per cubic centimeter, which is more than the density of a diamond (3.5 grams per cubic centimeter). The planet Psyche is going to visit the probe of the same name. It is an interesting target that consists largely of iron.
Astronomers will be able to view even more asteroids in even finer detail with the upcoming ELT telescope, which is built close (as the crow flies) to the VLT.
ELT allows us to study objects with a diameter of 35 to 80 kilometers and on their surface they will see craters with a size of approximately 10 to 25 kilometers.