Comets have fascinated human beings for longer than recorded history. They are beautiful, unpredictable and not well understood. The Greeks thought of them as stars with long hair. The Chinese kept records of comets dating from 1600 BC.
It wasn’t until 1705 that scientists realized that some comets orbit the sun on a regular timetable. Edmund Halley suspected that the comet sightings of 1456, 1531, 1607, and 1682 were, in fact, the same comet cycling through the inner solar system on a regular, and predictable basis. He correctly predicted the comet would return again in 1758 and it did. That comet now bears his name – Halley’s Comet. (By the way, Halley’s Comet is due to return again in July, 2061).
Comets are small objects composed of rock, dust and ice that orbit the sun. Some have referred to them as the “dirty snowballs” of the solar system. Their orbits can range from a few years to several million years and are subject to change as they interact with the gravitational pull of other objects in the solar system – most notably Jupiter. As they approach the sun, comets heat up and water vapor and other gasses vent from the surface and interior forming a thin atmosphere and often a tail.
Ten years ago, the European Space Agency launched a robotic spacecraft called Rosetta – after the Rosetta Stone, the slab bearing the same decree in three languages that was the key to understanding Egyptian hieroglyphs.
Over the past decade, Rosetta has photographed two asteroids but that was only a sidebar to it’s primary mission which begins today. Rosetta has reached it’s final objective – a comet called 67P/Churyumov–Gerasimenko.
“Chury” is an oddly shaped object about two and a half miles long and two miles wide. It looks like two rocks glued together.
Today, Rosetta fired it’s thrusters to place the spacecraft into orbit around the comet.
Rosetta will study the comet from as close as half a mile, as Churyumov–Gerasimenko zips around the sun over the next year. In November, it will launch a lander called Philae. Upon landing, Philae will fire two harpoons into the surface to secure itself to the comet. Philae is packed with instruments to provide a huge amount of data on Chury.
No one knows what will happen as the comet approaches the sun. Will Rosetta and Philae keep working? Will they be damaged by the debris blown off the surface and venting out of the interior of the comet as it nears the sun?
Only time will tell, but it ought to be interesting.
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Tags: 67P/Churyumov–Gerasimenko, Chury, Comet, dirty snowball, ESA, Halley's Comet, Philae, Rosetta