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Jupiter and the Great Black Spot
In the Sikhote-Alin Mountains of Eastern Russia, around 10:30 in the morning on February 12, 1947, a huge iron meteorite entered Earth's atmosphere. Traveling at 31,000 miles per hour and having a mass of around seventy tons, the meteorite was reportedly brighter than the sun. It must have been quite a freakish sight, watching a huge fireball streak across the sky. The meteorite, being approximately 93% iron, was magnetic and hopefully did not give off any alien radiation.
A similar event happened recently on our gas giant neighbor, Jupiter. Just hours after this observer was peering through the 14-inch UNH telescope at Jupiter, an amateur astronomer in Australia discovered that the gas giant had acquired a black scar. On July 19, 2009, Jupiter was hit by something big--an alleged comet which no one had predicted. Jupiter rotates so fast (it takes just under ten hours for one rotation) that the impact must have happened sometime between when I saw it and when Anthony Wesley found the black scar.
The recently improved Hubble Space Telescope--courtesy of STS-125--quickly trained its cameras on the impact which occurred in the gas giant's south polar region. Hubble's sharp images, taken with the new Wide Field Camera 3, revealed a plume of debris expanding across Jupiter's atmosphere. Astronomers are estimating that the mark left by the impact is about the size of the Pacific Ocean.
The impact greatly resembled Jupiter's collision with comet Shoemaker-Levy 9 exactly fifteen years ago in 1994. That comet was torn into twenty-one fragments by Jupiter's strong gravitational field, and it is that same force which actually captures small solar system bodies, preventing them from coming towards the earth… or flinging them towards us.
A near-miss occurred in 1770 when comet Lexell passed within about a million miles of Earth after Jupiter sent it flying towards us. But perhaps we can forgive Jupiter for that incident because after the comet passed around the sun and back towards the gas giant, the comet disappeared. It is suspected that Jupiter's gravity sent comet Lexell away.
So, in light of all this activity, will an object hit the earth? I, for one, am not worried about an impact, and I will not worry about it unless total destruction of our planet was imminent. Then I would be concerned about the fate of the earth. But there is no reason to live in fear of a negligible threat.
Really large, devastating impacts occur on Earth only once every few hundred million years and even small impacts do not occur very often. Chances are not favorable that something could hit the earth within one's lifetime. Although Jupiter experiences impacts, such an occurrence is much less likely to happen to the earth because the gas giant has a very large gravitational field and magnetic field. It probably attracts small solar system bodies right to it.
However, the earth is much smaller and does not exert as much attractive forces on other objects in the universe, unless the object is headed straight towards our planet. Of course, we can do research and try to learn as much as possible about asteroids and comets in order to prepare ourselves in case of an emergency.
* To find the latest information on asteroids and comets, visit the JPL's asteroid watch.
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