When do comets come

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Astronomers call these short period comets, since they orbit the Sun relatively often. I should be in my third robot body by then.

The long period comets are much more mysterious. These objects come out of nowhere, pass through the inner Solar System or smash into the Sun, and then zip back out into deep space.

Now, where do they come from? The Dutch astronomer Jan Oort calculated that there must be an even vaster cloud of ice even farther out beyond the Kuiper Belt — between 5, and , astronomical units from the Sun. The layout of the solar system, including the Oort Cloud, on a logarithmic scale.

Credit: NASA Like, the Voyager 1 spacecraft, which is the most distant and fastest object ever sent out by humanity, will still need about years to reach the edge of the Oort Cloud. Astronomers think that occasional gravitational nudges in the Oort Cloud cause these long period comets to fall down into the inner Solar System and make their rare appearances. It could take a comet like this hundreds of thousands or even millions of years to complete an orbit around the Sun.

This is a great example of a long-period comet, which is visiting our neighbourhood for the first time in the 4. This is the dimmest, farthest comet ever discovered, first seen when it was out beyond the orbit of Saturn. This cloud of material around the comet is probably the sublimation of frozen volatile gases, like oxygen, nitrogen, carbon dioxide and carbon monoxide.

Astronomers think it started to become active about 4 years ago, and they just discovered it now. We can barely detect comets outside the orbit of Saturn, not to mention hundreds of times farther than that. In order to interact with the Oort Cloud, astronomers have calculated that a star needs to get within about 6.

Based on data gathered by the Gaia spacecraft, astronomers charted out the motions of , stars in our vicinity of the Milky Way in the next 5 million years or so. Of those stars, 97 will come within 15 light-years of the Sun, and 16 will get closer than 6.