The Hubble Orbital Observatory received the first photographs of the comet from the most distant approaches to the solar system, approaching the Sun for the first time in its history, the space telescope website reports.
“Comet K2 is now so far from the Sun that its gas tail cannot be the product of ice evaporation from its surface. We assume that it arose as a result of the evaporation of frozen gases, which are present only on those comets that have never climbed into the solar system before. That is why it is so special and important to us,”said David Jewitt of the University of California at Los Angeles, USA.
The solar system, in addition to eight "real" planets, Pluto and several dozen dwarf planets, is inhabited by countless asteroids and comets, small rocky and icy celestial bodies. Most of the asteroids we know "live" in the inner part of the solar system, in the main asteroid belt between the orbits of Jupiter and Mars, and comets - in the so-called Oort cloud on its outskirts.
This "cloud", consisting of comets and other "ice" bodies, is located at a distance of 150 - 1.5 thousand astronomical units, the average distance between the Earth and the Sun, from our star. Scientists consider it a kind of dump for "building materials" thrown out of the solar system during its formation, and are actively studying its inhabitants in the hope of uncovering the riddle of the birth of the Earth and other planets.
Comet C / 2017 K2, as noted by Jewitt, "lives" on the outskirts of this cloud - the farthest point of its orbit is at a fantastic distance of a trillion kilometers from Earth, about 7200 astronomical units. Scientists believe that a few million years ago, K2 began its first trip to the Sun, and now it is at a distance of 3.6 billion kilometers from the star.
The first hints of its existence were discovered in May 2017 by another telescope, Pan-STARRS-1, an automated "asteroid hunter", and scientists had to use the power of the Hubble in order to get the first pictures of such a distant object.
Having discovered it, Jewitt and his colleagues examined the archives of photographs of the part of the sky where it is located, and found that the comet began to show activity four years ago, just before scientists did not notice it because of its dimness and great distance from the Earth.
How did Hubble and Pan-STARRS-1 find it? The fact is that this comet has two unusual features. Its orbit is tilted to the plane of the solar system by about 80 degrees, and it has a bright gas and dust tail about 128 thousand kilometers long, despite the fact that it is now located between the orbits of Neptune and Uranus.
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As the pictures and measurements of the Hubble showed, this tail has an unusual chemical composition - it does not consist of water vapor, like the gas envelope of other comets, but oxygen, nitrogen, carbon dioxide and carbon monoxide. All of this material turns to ice in the cold Oort cloud, and evaporates after the comet first penetrates the warmer outskirts of the solar system.
“Billions of years ago, these substances were present on all comets, but they gradually evaporated from the surface of those celestial bodies that periodically approach the Sun and inhabit the vicinity of Jupiter. Therefore, it seems to me that K2 is the most primitive comet that we have ever been able to discover,”continues Juitt.
The journey of C / 2017 K2 is not over yet - the comet will approach the Sun for another five years - in December 2022 it will reach the orbit of Mars and begin to move in the opposite direction. This time, Juitt concludes, will be a golden era for planetary scientists, as they will have the first real opportunity to study the composition of the "pure" primary matter of the solar system by observing the tail of a given comet.