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Giant Comets Could Endanger Life on Earth

By David Reneke

Giant comets could endanger life on Earth, and there is new evidence of water in the Moon’s interior.

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Astronomers have warned that the discovery of hundreds of giant comets in the outer planetary system over the past two decades make these objects a much greater hazard to life than asteroids. These centaurs appear as pinpricks of light in even the largest telescopes because they are so distant from the Earth. Saturn’s 200 km-wide moon Phoebe seems likely to be a centaur that was captured by that planet’s gravity at some time in the past, so until spacecraft are sent to visit other centaurs our best idea of what they look like comes from images obtained by the Cassini space probe orbiting Saturn. NASA’s New Horizons spacecraft, having flown past Pluto earlier this year, will conduct an approach to a 45 km-wide trans-Neptunian object at the end of 2018.

Centaurs move in unstable orbits crossing the paths of the massive outer planets Jupiter, Saturn, Uranus and Neptune. The planetary gravitational fields can occasionally deflect these objects towards the Earth.

Centaurs are typically 50–100 km across, or larger, and a single such body contains more mass than the entire population of Earth-crossing asteroids found to date. Calculations of the rate at which centaurs enter the inner solar system indicate that one will be deflected onto a path crossing the Earth’s orbit about once every 40–100,000 years.

Known severe upsets of the terrestrial environment...

The full text of this article can be purchased from Informit.