Tag Archives: comet

Giant Comets Pose Threat To Life On Earth

Huge comets called centaurs deserve greater recognition as potential destroyers of life on Earth, according to a team of astronomers from the Armagh Observatory and the University of Buckingham. Measuring 50 to 100 kilometers (30 to 60 miles) across, these enormous masses of ice and rock have been identified in their hundreds over recent decades in the trans-Neptunian region the area beyond Neptune, which is the outermost planet in the Solar System.

However, these centaurs can make their way towards the inner planets as their orbits become deflected by the gravitational fields of Neptune, Uranus, and Saturn. Publishing a review of their research in Astronomy and Geophysics,the team estimates that centaurs are likely to cross the Earths orbit every 40,000 to 100,000 years.

Depending on the size, composition, and distance of a given comet, its effects on terrestrial ecosystems are likely to be highly variable. Because centaurs are thought to be unstable, the authors expect the majority of these effects to be caused by dust and other small fragments that result from the disintegration of the comets.

They estimate that a single centaur measuring 100 kilometers (60 miles) could contain about 100 times the mass of all the Earth-crossing asteroids detected to date. This translates to an awful lot of dust, leading the researchers to suggest that comets of this size could fill the Earths atmosphere with tiny particles, reducing the amount of sunlight that can pass through to roughly the level of moonlight, for up to 100,000 years. This, they say, would put an end to commercial agriculture.

A map of the Solar System, showing the orbits of several planets. In red are the orbits of 22 centaurs. In yellow are the orbits of 17 trans-Neptunian objects. Duncan Steel/Royal Astronomical Society

Additionally, larger fragments which could extend for several kilometers in length may generate catastrophic impacts, similar to that which is believed to have led to the extinction of the dinosaurs. According to the report, several such collisions may have occurred in the past, with the authors citing craters in the Gulf of Mexico, Ukraine, Siberia and Chesapeake Bay as likely candidates for centaur impact sites.

Given the probability of a centaur crossing Earths orbit at some point in the future, and the sheer volume of debris caused by the disintegration of these comets, the team claims that some level of impact is inevitable, although the nature and extent of the effects are likely to depend on various factors.

At present, attempts to quantify Earths risk of being affected by a collision are centered around NASAs Spaceguard initiative, which seeks to map up to 90 percent of near-Earth objects (NEOs) larger than 1 kilometer (0.6 miles). This programfocuses mainly on the asteroid belt that sits between Mars and Jupiter, although Professor Bill Napier, who helped to conduct this research, is now calling for the scope of this search to be extended to the outer reaches of the Solar System.

Our work suggests we need to look beyond our immediate neighborhood and look out beyond the orbit of Jupiter to find centaurs, he said in a statement. If we are right, then these distant comets could be a serious hazard, and it’s time to understand them better.

Read more: http://www.iflscience.com/space/giant-comets-pose-potential-threat-earth

Comet, Earth and Mercury Seen Together in Rare Video

A new video from a NASA spacecraft studying the sun has captured an unexpected sight: a wandering comet posing with the planets Earth and Mercury.

The cosmic view comes from one of NASA’s twin Stereo spacecraft that constantly watch the sun for signs of solar flares and other space weather events. It shows Mercury and Earth as they appeared with the Comet Pan-STARRS, a comet that is currently visible from the Northern Hemisphere during evening twilight.

The probe captured the video of Comet Pan-STARRS, Earth and Mercury together while observing the sun from March 9 to March 12.

According to a NASA description, the video “shows the comet and its fluttering tail as it moves through space.” The Earth appears as a bright stationary object on the right side of the video, while Mercury is visible as a moving light on the left side.

The sun is actually out of the frame in the Stereo-B spacecraft’s video, but its solar wind is visible as a stream of material, NASA officials explained. Meanwhile, the view of Comet Pan-STARRS from space is giving scientists a wealth of data to review, they added.

“Comet scientists say the tail looks quite complex and it will take computer models to help understand exactly what’s happening in STEREO’s observations,” agency officials said in a video description. “The comet should remain visible to the naked eye through the end of March.”

Comet Pan-STARRS is currently visible to stargazers in the Northern Hemisphere just after sunset. To see the comet, look low on the western horizon just after the sun has gone down. Comet Pan-STARRS can appear as a bright head with a wispy trail, weather permitting, though some stargazers have said the bright evening twilight can make spotting it tricky.

The Comet Pan-STARRS was discovered in June 2011 by astronomers using the Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) in Hawaii. The comet’s official name is C/2011 L4 (PANSTARRS).

Scientists estimate that Comet Pan-STARRS takes more than 100 million years to orbit the sun once. The comet crossed into the Northern Hemisphere evening sky last week after months of being visible to observers in the Southern Hemisphere.

NASA’s twin Stereo A and B spacecraft (the name is short for Solar TErrestrial RElations Observatory) observe the sun in tandem to provide unparalleled views of how material from solar eruptions makes its way to Earth. The spacecraft launched in 2006 and are part of a fleet of sun-watching spacecraft that monitor solar storms.

Comet Pan-STARRS is one of several comets gracing the night sky in 2013. Pan-STARRS was joined by the Comet Lemmon earlier this year when both were visible together in the Southern Hemisphere sky. Later this year, the sungrazing Comet ISON could put on a potentially dazzling display when it makes its closest approach to the sun in late November.

Homepage image courtesy of Astronomy Education Services/Gingin Observatory

This article originally published at Space.com
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Read more: http://mashable.com/2013/03/15/comet-earth-mercury-video/