Astronomers have found many asteroids, but most of them are indistinguishable from stars in a photo of the night sky. Even astronomers do not recognize them. He needs to take more pictures in a row – then the asteroid will shift into a stellar background.

Some asteroids have been touched by radar, while others have been visited by space probes. Overall, we have a more detailed idea of ​​just a few of them. However, Earth astronomy is not entirely toothless. Technology is improving.

Two years ago We wrote The SPHERE instrument on the VLT Telescope at the European Southern Observatory in Chile about the best photographs of the asteroid Nokia Hygia. In fact, it was a more elaborate work attended by Czech scientists at Charles University.

An international team of scientists has now presented images of 42 large asteroids in the main belt between Mars and Jupiter. If you think the number is not random, you think so. The press release comes on the 42nd anniversary of the publication of Adams ‘The Hitchhikers’ Guide to the Galaxy.

That’s a shattering number in a way. So far, we have only received more detailed images of the three asteroids in the main belt – the Dawn spacecraft visited by Serra and Vesta, and the Rosetta Lutetia spacecraft.

The researchers took pictures between 2017 and 2019. Most of the 42 objects in their sample were more than 100 km long – the team captured images of 20 of the 23 objects larger than 200 km moving on the belt.

Two main groups

The two largest objects he studied were 940 and 520 km, respectively, with the average Ceres and Vesta. The smallest asteroids are uranium and ozone, each about 90 km in size.

By reconstructing the shapes of objects, the team found that the observed asteroids were mainly divided into two groups. Some are spherical, such as Hygiene and Ceres, while others have a more bizarre “elongated” shape, and their undisputed queen is the “dog bone” asteroid Cleopatra.

This is not surprising. The heavier the object, the rounder it is. For this reason, it is the “circle” of the object used to define dwarf planets. If we know the shape and size of the body well, we can more easily estimate its density, which is important data for the study of asteroids.

The lowest density is Sylvie (1.3 g per cubic centimeter), which is the density of coal. Psych and kalliope have the highest concentrations – 3.9, respectively. 4.4 grams per cubic centimeter, which is more than the density of a diamond (3.5 grams per cubic centimeter). Psyche is going to visit the planet of the same name. This is an interesting target that contains large amounts of iron.

Astronomers can see even better asteroids with the upcoming ELT telescope built near VLT (like a raven flying).

ELT allows us to study objects with a diameter of 35 to 80 km, with craters about 10 to 25 km in size on their surface.