Wednesday, April 21, 2010

Ten Things You Don’t Know About Comets

From Discover's Bad Astronomy blog is a list of 10 things you may or may not know about comets.

1) The actual solid part of a comet is tiny. The actual solid part of a comet is tiny.

2) Comets are dirty snowballs. In general, comet nuclei are mountain-size dirty snowballs: rock, dust, gravel and other bits of stuff all mixed up with frozen gases and of course lots and lots of water.

3) Comets spend most of their lives looking pretty much like asteroids. They tend to have long, elliptical orbits. The farther they are from the Sun, the slower they travel, so really they might spend 99.9% of their lives far, far from the heat of our nearest star in temps so cold that even water freezes harder than rock.

4) Every time a comet comes near the Sun, it dies a little bit. Some comets are held together by the frozen gases. As one of these passes the Sun, that gas blows away, and the comet loses some of its structural integrity. Eventually, if it’s mostly gas, it’ll disintegrate.

5) Comets can have two tails. In fact they can have lots of tails. The dust tail can be broken up into several straight features called dust striae, possibly due to large pieces of the comet breaking off and forming their own tails.

6) Comets spawn meteor showers. Millions of tons of material blowing off a comet every time it passes the Sun. If a comet’s orbit intersects the Earth
the Earth can plow through this debris which burns up in our atmosphere, and we get a meteor shower.

7) Comets are potentially more dangerous than asteroids. They can come from deep, deep space, falling all the way from beyond Neptune’s orbit. They pick up a lot of velocity, and some can be moving at 70 km/sec (40 miles/sec) this speed makes them pound for pound 10 times more energetic than asteroids.

8) Seven comets have been visited by spacecraft. So far.

9) The best comet hunter of all time is SOHO. The Solar and Heliospheric Observatory.

10) Some comets can be seen in daylight. If a comet gets close enough to the Earth, or close to the Sun at the right angle, it can become bright enough to be seen even during the day.

Of course the article has LOTS more data than I put here. Click the article title to go to the complete Discover entry

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