Is Earth Overdue For a Run-In With a Giant Comet?

December 24, 2015 | Joanne Kennell

Giant comet
Photo credit: European Space Agency/Flickr (CC by SA 2.0)

The comet’s debris, several kilometers wide, could smash into Earth.

There are many things in this vast and mysterious universe that can cause an end to our existence on Earth.  From gamma-rays to magnetic field reversals, and black holes to aliens, the list of potential threats grows longer and longer — and now there is another.  Giant comets.

Over the last two decades, a team of astronomers from Armagh Observatory and the University of Buckingham discovered hundreds of giant comets orbiting in the outer planetary system, and they are more dangerous to life on Earth than asteroids.

These giant comets, nicknamed centaurs, have unstable orbits as they cross the paths of Jupiter, Saturn, Uranus and Neptune, meaning that the strong gravitational fields of the large planets deflect the comets towards Earth every once in awhile.  Thanks by the way, planets.

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Centaurs are generally 50 to 100 kilometers (31 to 62 miles) wide or larger, and just one of these comets contains more mass than all Earth-crossing asteroids found to date combined.  That is terrifying.  Calculations show that centaurs will enter the inner solar system on a path towards earth once every 40,000 to 100,000 years.  Although most of the comet will vaporize and break into larger fragments while approaching close to the Sun and entering Earth’s atmosphere, the size of these comets will inevitably result in debris making surface impacts.

“The disintegration of such giant comets would produce intermittent but prolonged periods of bombardment lasting up to 100,000 years,” the research team wrote in the Royal Astronomical Society journal, Astronomy and Geophysics according to Yahoo News.

You may be wondering when the last time one of these centaurs made an appearance here on Earth.  According to researchers, a giant comet impacted Earth around 30,000 years ago, and most likely had debris ranging from the size of dust to several kilometers across.  Are you familiar with the mass extinction of the dinosaurs 65 million years ago?  Well it may have in fact been caused by one of these centaurs and not an asteroid after all — but that is just speculation.

Most of the research done on potential Earth-colliders has focused on objects in the asteroid belt found between Mars and Jupiter, however this research suggests we need to expand our view.  According to Professor Bill Napier of the University of Buckingham, “In the last three decades we have invested a lot of effort in tracking and analysing the risk of a collision between Earth and an asteroid. Our work suggests we need to look beyond our immediate neighbourhood too, and look out beyond the orbit of Jupiter to find centaurs. If we are right, then these distant comets could be a serious hazard, and it's time to understand them better.”

Well, if the researchers calculations are correct, we still have at least 10,000 years before we have to really start worrying about these centaurs.  That gives humanity plenty of time to figure out how to blow them up before they get too close.

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