Near-earth-objects. These are the asteroids and comets scientists know about in our general neighborhood. A few of them recently zipped past Earth.

The haunting Halloween dead comet.

Halloween NEO

And more recently, asteroid 1998 WT24.

asteroid 1998WT

But one group of astronomers from the UK are highlighting another potential danger. They are called centaurs. Imagine a super-sized comet. Each one measures between 30 to 60 miles across with some even larger. If you put every single asteroid that crossed Earth’s orbit together, a single centaur would still have more mass.

Where are centaurs? They lie in the outer solar system crossing the orbits of Neptune, Uranus, Saturn and Jupiter. Because of these planets’ gravity, their orbits are often unstable. Researchers believe the potential is there for one of these comets to ricochet towards the inner solar system. And Earth.

Check out this image.

centaur orbit paths

See the yellow lines? Those are called trans-Neptunian objects, or TNOs. They always stay beyond the orbit of Neptune. It’s the red lines we are talking about. There are 22 centaurs shown in the image. About 400 have been discovered so far. You can see how unstable the orbits are as they move through the orbits of the outer planets. The gravity of the outer planets could push these comets towards Earth. The good news is this same gravitational interaction can also throw them out of the solar system.

Professor Bill Napier underscores the importance of taking a closer look at centaurs: “In the last three decades we have invested a lot of effort in tracking and analysing the risk of a collision between the 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.”

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Let’s look at the bright side. Calculations show centaurs will be deflected onto a path that crosses the Earth’s orbit about once every 40,000 to 100,000 years. But, the team of astronomers believe that any centaur deflected towards Earth would break apart into smaller, but still large fragments. These pieces could range in size from specks of dust to chunks of rock miles across.

“The disintegration of such giant comets would produce intermittent but prolonged periods of bombardment lasting up to 100,000 years,” the astronomers wrote in their paper.

The astronomers speculate that “specific episodes of environmental upheaval around 10,800 BCE and 2,300 BCE,” indicate the arrival of a centaur around 30,000 years ago. And there is support for this model. Guess the age of sub-millimeter craters seen in lunar rocks gathered during the Apollo program? Nearly all are younger than 30,000 years. That points to a surge in the amount of dust in the inner solar system during this period.

Should we be worried?

You have to remember, we are talking about space. These things take time. Will a centaur hit Earth tomorrow? Probably not. But that doesn’t mean we shouldn’t be taking a closer look at them. Plus, there is good news. Some of these centaurs will eventually be tossed from our solar system.

You can read the entire paper talking about centaurs and the threat they pose.

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