Shut Encounters of the Stellar Form



31 December 2014

Poster for the 1951 movie *When Worlds Collide*.
Paramount Photos
Poster for the 1951 film When Worlds Collide.

A star generally known as HIP 85605 is on a collision course with our photo voltaic system. Not a collision course as in Armageddon, or When Worlds Collide, however quite on a path to come back inside 0.04 parsecs of the Solar. That may appear shut, however that may make it greater than 8,000 instances extra distant than Earth at its closest strategy (8,000 AU). Distant Eris is barely 100 AU by comparability. On condition that stellar distances are sometimes measured in gentle years, and this encounter can be solely 50 gentle days away, that’s remarkably shut by astronomical requirements. This shut encounter gained’t happen for an additional 400,000 years or so. At present HIP 85605 is about 16 gentle years away, so now we have time to plan for its go to. Nevertheless it does elevate an fascinating query as to how such an in depth encounter may have an effect on our photo voltaic system.

One factor we all know for positive is it gained’t considerably have an effect on planetary orbits. By pc simulations of the photo voltaic system, we discover that orbits of the internal planets stay secure over billions of years even with stellar interactions as shut as 0.01 parsecs. Essentially the most outer our bodies akin to Pluto and Eris are much less secure, however on the entire planetary orbits are secure in opposition to all however practically direct stellar hits.

The place issues get much less sure is how a stellar encounter would have an effect on our bodies within the Oort cloud. Though we all know the Oort cloud exists, we aren’t positive about its dimension. The everyday estimate is that the outer Oort cloud is between 20,000 and 50,000 AU from the Solar. In that case HIP 85605 would really transfer by means of the Oort cloud, which might critically disrupt the icy our bodies inside it. Some can be flung out of the photo voltaic system ceaselessly, whereas others can be thrown towards the internal photo voltaic system. This might trigger a dramatic enhance within the variety of comets crossing Earth’s orbit. This uptick would occur over a million-year time scale, however that’s pretty quick on geologic scales. What that may imply for all times on Earth isn’t totally clear.

It’s estimated that about 40 stars have made a “shut” encounter with the Oort cloud over the past 20 million years, and it has been proposed that cycles of cometary impacts as a consequence of such collisions may have led to local weather variation and extinction occasions on Earth. However the proof for such a connection isn’t very sturdy. There isn’t a powerful correlation between affect occasions and extinction occasions, the nice dinosaur affect not withstanding.

Given the lengthy historical past of life on Earth, it isn’t doubtless that such shut stellar encounters have an enormous have an effect on on the photo voltaic system and life on Earth.

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