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Saturday 17 December 2011

Roll up roll up, see the amazing death defying comet!

Image left: The brilliant twin tails, one of dust the other of ions, of comet west. Image courtesy of John Laborde.

Comets[1], wandering escapees from the protoplanetary disk that formed our solar system almost 5 billion years ago, usually lead a solitary existence: They move silent and almost invisible out beyond the ice giant Uranus and Neptune [2]. Only occasionally does one break ranks with its fellows and come hurtling into the inner solar system. It does not do this willingly, it must be pushed or pulled by the gravity of some other body. When that happens the comets frozen surface boils away into space, subsurface pockets of more volatile material explode through its skin as jets, and the comet briefly develops a tenuous atmosphere of gasses, called a coma [3]. This coma is shed and renewed as the black (comets are usually covered in a crust of pitch black hydrocarbons) ice ball hurtles inwards, leaving behind tails of dust and gas that catch the sunlight and can be a spectacular display if Earth is in the right position.

Image right: despite their brilliant tails the cores of comets are actually grey to black in colour, as demonstrated by comet Halley here. Image courtesy of ESA.

Other exceptions may be hiding amongst the ranks of D-class asteroids [4]: Volatile rich, covered in hydrocarbon molecules, these may be the burnt out cores of comets gathered along the outer edge of the asteroid belt. They resemble the bizarre Tagish lake meteorite [5], which still poses many mysteries to science: Odd hollow organic globules [6], nano-diamonds, buckyballs and compounds called pyridine carboxylic acids [7]. Some of these odd objects seem not to be so burnt out, and are referred to as main belt comets [8].

And sometimes a comet does not just hurtle sun wards. Sometimes, as if it has lost its way from the safe cool depths, a comet flings itself into the solar systems central inferno [9]. This is what astronomers thought would happen to comet Lovejoy this week. It has been tracked by the Solar Dynamics Observatory (SDO [10]), a spacecraft who's main mission is to study the sun itself. But this was too juicy to miss, so they got the doomed comet in one corner of the spacecrafts eye and are posted updated photos as they got them. They even ran those images together into a time lapse movie of what we all expected to be comet Lovejoys final moments.... enjoy:

Video above: Comet Lovejoy approaches the sun with its tail rippling in the solar winds. Courtesy of JPL/NASA.
You can see the comets tail twitching and kinking in the blasts of plasma from the Suns surface! But it turns out the snowball thrown into hell did have a chance after all......

Video above: Comet Lovejoy takes a seemingly fatal plunge into the sun, only to emerge from the other side hours later! Courtesy of JPL/NASA.

Despite passing just 120,000km from the suns surface, and despite the solar behemoth tearing off part of its tail, the enigmatic comet has proved to be made of stern stuff; tearing past the surface of the sun at incredible speeds and back out the other side. At the size of two football fields it is hardly an obvious challenger to the Suns 3 light second wide majesty, yet this underdog has at least survived to tell the tale. Others have not been so lucky: Another comet met a truly spectacular demise at the suns hands in may of this year:

Video above: A comet dies spectacularly as it careens into the Sun. Image courtesy of JPL/NASA.

Now Lovejoys (presumably) melted and altered surface will take a story of peril and fire surmounted back into to cool of deep space....and perhaps one day we will catch up with it to read that story in greater detail.

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