The European Space Agency's Rosetta probe is orbiting a comet that, at this writing, is about 250,000 miles from the sun and moving closer. Once the probe's Philae lander is deployed - it's scheduled to land Nov. 12 - it will become the first manmade object to make a controlled landing on a comet.

Rosetta spent a little more than 10 years traveling to intercept Comet 67P and began orbiting it at an altitude of 31 miles on Sept. 10. It's just a few miles above the comet now and preparing to land.

The comet is 2.5 miles by 2.8 miles in size and was discovered in 1969 when two Ukrainian astronomers spotted it on photographic plates. It was probably larger then - since its discovery, the comet has made about six orbits around the sun and some mass is sloughed off by the sun's heat every time a comet makes a pass. Its tight orbital period of about 6.5 years provides a good opportunity for a more relaxed planning and inspection timeline.

In keeping with an Egyptian naming theme, the Rosetta probe's lander is named after Philae Island in the Nile River where an obelisk was discovered and used with the Rosetta Stone to decipher Egyptian hieroglyphics.

Once the lander touches down, it will spend about a week studying the comet and will transmit images from the surface so that scientists back on Earth can determine what the comet is made of.

Here's what they know so far: it's icy and it stinks. A mass spectrometer on the Rosetta probe has been analyzing gases being burned off of the comet as it moves into the sun's heat. It has detected hydrogen sulphide, ammonia and formaldehyde, with traces of hydrogen cyanide and methanol. If Comet 67P were on Earth where the scent could be experienced, instead of the vacuum of space, a dog would smell something like rotten eggs, cat urine, a horse stable and bitter almonds. The comet's odor wouldn't be strong enough for a human to smell, even close-up.

Scientists say that Comet 67P wasn't expected to release this many molecules yet, and as it gets even closer to the sun it should release even more complex ones in greater numbers.

Comets are an enticing study subject because they may have been the first solid objects to come out of the solar nebula 4.5 billion years ago when our solar system was born. A concentration of interstellar dust and hydrogen gas called a molecular cloud was the solar system's birthplace. Our proto-sun formed in the hot dense center, and the rest of the cloud formed a swirling disk called the solar nebula.

Matter on Earth and throughout the solar system has evolved since then, but it may still be in its original state inside a comet, offering a glimpse back in time to when the solar system formed. Comets also may have played a role in creating our atmosphere, possibly as carriers of the water and complex molecules necessary for life on Earth.

Keep up with the Rosetta mission by visiting http://rosetta.esa.int.

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