Comet picture.
March 28, 2021
Most comets live beyond the orbit of Neptune and move in elliptical orbits with significant eccentricity. At the end of the 20th century, relatively small bodies were discovered within the orbit of the main asteroid belt with visual characteristics reminiscent of comets - comas, gas or dust tails.
In 2006, the British-American astronomer David Jewitt suggested calling these bodies "main-belt comets" or "MBC objects" (from the English main-belt comets). The orbital period of such a comet around the Sun is 5-6 years. By 2006, only a few of these sites had been reliably confirmed. The term "comet of the main belt" implies that these comets must necessarily exist only within its limits and have a predominantly icy composition. However, the discovery of new objects of this type suggests that this is not always the case. Therefore, they are also called "active asteroids".
The first active asteroid was discovered in 1979. At first it was discovered as an asteroid, but already in 1996, astronomers Eric Elst and Guido Pissaro, observing this object at the La Silla Observatory in Chile, saw a cometary tail when the asteroid was near perihelion. In 2001, the picture repeated itself. The asteroid has been showing cometary activity for 5 months. So the asteroid 7968 Elst-Pizarro received the cometary name - 133P / Elst-Pizarro.
In 1999, as part of a project to search for near-Earth asteroids at the Lincoln Laboratory in the United States (abbreviation LINEAR), cometary activity was discovered near the asteroid (118401) LINEAR, so the object was named after this project. In 2005, the active asteroid 238P / Read was discovered, in 2008 - P / 2008 R1 (Garradd), in 2010 - P / 2010 R2 (La Sagra). In December 2010, cometary activity was detected near asteroid 596 Scheila in the main belt, but, despite the official dual status, according to the rules of the International Astronomical Union, all such objects in the databases pass as asteroids.
Until recently, the "comet" theory of the formation of water on Earth was very popular. According to this hypothesis, water on Earth appeared as a result of bombardment by comets arriving from the outer regions of the solar system. However, according to recent studies, the water of classical comets has almost 3 times more deuterium than the water of the Earth. It is possible that the main belt comets served as a source of water on Earth.
Related article:
Degenerate comets
https://orbiterchspacenews.blogspot.com/2021/03/degenerate-comets.html
ROSCOSMOS Press Release: https://www.roscosmos.ru/30494/
Images, Text, Credits: ROSCOSMOS/Moscow Planetarium/Orbiter.ch Aerospace/Roland Berga.
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