The prevalent concept has it that every 100 million years or so, stars come close enough to our solar system for them to crash on the multitude of objects in the Oort cloud and place them on a course towards our planetary system. But a team of Swedish researchers argued that the rate of the star-created comets is not as high as that generated by the gravitational influence of the Milky Way galaxy itself on the Oort objects.

The star comets are the more-than-half-a-century old brainchild of Jan Hendrik Oort, who theorized on the existence of the colossal cloud some 100,000 AU (astronomical units – the distance between the Earth and the Sun) away from the Earth back in 1950. Oort estimated that the roaming stars crossing through the cloud would send a large group of comets in this direction, some of them getting close enough in order to be observed from the Earth.

 

But Hans Rickman from the Uppsala Astronomical Observatory in Sweden claims that the comets observed today were set on their course a long time ago, and stellar impacts alone cannot account for their rate. "The comets we see now could be from a stellar passage hundreds of millions of years ago," shared the scientist, cited by Space. The team devised a computer simulation model that mimics the behavior of about a million objects in the Oort cloud.

 

Their conclusion is that this process of dislodging the Oort objects from their regular route and sending them towards far places is also a great deal due to the work of the galaxy's gravity. "The general picture spawned by our results is that injection of comets from the Oort Cloud is essentially to be seen as a teamwork involving both tides and stars," reads their paper.

 

But it is very hard to infer the results of past comet collisions on the Earth's surface or predict future ones. Although the results and ratio of comet impacts should be more obvious than those of asteroids (given that comets' velocity is higher), erosion and aging effects, as well as the fact that the impactor vaporizes upon collision left little associated marks on the terrestrial surface for proper studies.