22.09.2017 change 22.09.2017

Vesta - the most massive asteroid under the Sun - on ice

Photo: Elizabeth Palmer & Essam Heggy; Vesta - blue highlighted are the areas where a smoother surface and increased hydrogen presence have been observed. Photo: Elizabeth Palmer & Essam Heggy; Vesta - blue highlighted are the areas where a smoother surface and increased hydrogen presence have been observed.

Under part of the surface of Vesta, the most massive asteroid in the solar system, ice is hidden, according to new research. And it is due to that ice that the surface of Vesta is unevenly covered by traces of cosmic collisions. That is worth knowing if you want to calculate the age of the surface of celestial bodies.

Astronomers who calculate the age of the surface of celestial bodies take into account its "roughness" at different scales (from centimetres to hundreds of kilometres) - how heavily it is cratered and marked with traces of smaller asteroid impacts. The more such traces of cosmic collisions, the more likely it is that the surface is older and the celestial body has drifted longer in outer space. This age estimation does not work well on objects such as the Earth, which have not only the atmosphere, but are also tectonically active. But, for example, the age of the Moon or Mars can be estimated by analysing their craters and traces of cosmic crumbs.


However, it appears that one must be careful when estimating age. An example is Vesta - an asteroid whose different parts are rough to a varying extent. Part of the asteroid is smoother - its roughness is in the order of centimetres and decimetres. Studies have shown that this may be related to ice, which is probably hidden under the surface of the asteroid. Probably it is the ice that makes the traces of cosmic collisions look different. Research has shown that the presence of water (in this case frozen) on asteroids is nothing special. This is the conclusion of the study by Elizabeth Palmer and the team. The results have been published in "Nature Communications" (http://nature.com/articles/doi:10.1038/s41467-017-00434-6). Co-author of the publication is Prof. Włodek Kofman from the French institute IPAG (CNRS) and the Warsaw Space Research Centre of the Polish Academy of Sciences.


Vesta is the most massive asteroid in the belt between Mars and Jupiter. Its average diameter (Vesta is not spherical, but rather ellipsoidal) is about 525 km (6 times less than the Moon\'s diameter). The asteroid core is composed iron and nickel, and on the surface there is a basalt regolith (loose, weathered rock). Vesta was studied by the NASA Dawn mission, which orbited Vesta in 2011-2012. These data were used by the authors of the publication in Nature Communications.


Prof. Włodek Kofman said in an interview with PAP that neutron and gamma spectroscopy allowed to determine the elemental composition of the asteroid to the depth of one meter. It has been shown that hydrogen is present below part of the asteroid surface. "It is probably ice" - said Prof. Kofman. The recently published study suggests that smoother surface is associated with the presence of larger amounts of hydrogen. "The presence of ice could have transformed the surface of the celestial body" - commented the researcher. He explained that under the influence of collisions with other asteroids or cosmic crumbs, the ice under the surface melts. It flows to the surface and changes the appearance of the surface of the asteroid (makes it smoother). Then the water crystallizes again under the surface, or it changes into steam and escapes from Vesta.


Professor Kofman explained that asteroid research may answer the question of where the water on Earth came from. "There are hypotheses that water - our source of life - came from asteroids" - said the scientist. He added that asteroid research may also help understand how the Solar System was formed and how it will change. Scientists also want to know the mineralogical composition of asteroids so that they can use these resources in the future. Researchers can also, based on research, prepare better simulations of asteroid motion. They also want to learn more about how to protect Earth from accidental collisions with asteroids in the future.


West aspires to the title of the largest asteroid in the solar system. However, there are a few "buts". The largest and most massive object in the asteroid belt is Ceres (950 km diameter). But - formally - it is not an asteroid, but a dwarf planet. However, in the solar system, Vesta is undoubtedly an asteroid with the greatest mass (about 2.5x10^20 kg). The asteroid Pallas is less massive. As for dimensions, the two objects are neck and neck. However, they have rather irregular shapes, so the answer to the question of which of them is bigger is not quite obvious.

PAP - Science and Scholarship in Poland, Ludwika Tomala

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