Hills cloud

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The Hills Cloud (also Inner Oort Cloud or Inner Comet Cloud) is a hypothetical collection of comets in the inner areas of the Oort Cloud . If it does exist, it will likely start in about 250 astronomical units (AU) and go up to about 1500 AU.

history

In the 1980s, astronomers first suspected that there might be an area within the Oort cloud where most of the comets are concentrated. In 1981, the astronomer Jack G. Hills set up the theory of the Hills cloud, since most of the observed comets in the Oort cloud have their main axis in a region that lies in the inner region of the cloud.

model

The Hills cloud presumably contains around 20 trillion comets, up to ten times more than the rest of the Oort cloud. According to this model, most of the comets that come into the inner solar system would come from the Hills cloud, which in turn would supply the outer regions of the Oort cloud with comets. Since a large number of comets crash into the sun or leave the solar system due to external influences, the Oort cloud should actually no longer exist. This "supply" of comets would solve this problem.

Oort Cloud and Kuiper Belt

properties

The exact mass of the Hills cloud is unknown; it is estimated to be 13.8 Earth masses. One possible origin is the close encounter between the sun and another star, which can lead to a restructuring of the Oort cloud.

Possible objects of the Hills cloud

Sedna

The minor planet Sedna would be the largest known celestial body in the Hills cloud. It has an extremely eccentric orbit, the closest point of orbit leads Sedna 76 AU to the sun, while the furthest point of orbit is 936 AU away. To be an object of the Kuiper belt, even its innermost orbit point is too far away, after all, the classic Kuiper belt ends in 50 astronomical units. However, it is not far enough away to belong to the classic Oort cloud. Belonging to the Hills cloud is possible. External interference from another planet is also conceivable. Then Sedna would be an outwardly scattered object of the Kuiper belt.

Sedna's orbit is well within the Oort cloud.

2012 VP 113

2012 VP 113 is a smaller celestial body with a similar orbit to Sedna. However, here the aphelion is even further away from the Sun, which is why it could even be a captured interstellar object.

C / 2007 E2 (Lovejoy)

C / 2007 E2 (Lovejoy) is a comet whose affiliation has also not yet been clearly established. It may be an object from the Hills cloud.

There are other smaller comets whose orbits are similar to those of Sedna and other proposed Hills cloud objects.

literature