Even with weathering and erosion, there is a good statistical sampling of impacts on the land area of earth. We can infer impact probabilities for the Earth from evidence in-hand. The oceans toss a bit of uncertainty into the mix. Jupiter doesn't retain impact scars long; the atmosphere sweeps away the evidence in a matter of days or weeks. Events such as these can help bolster models of Jovian impact frequencies, but probably have little or no effect on the numbers as far as earth goes. Kim is right- if you're a planet, your location in the solar system largely determines just how vulnerable you are to impacts. Jupiter and the outer planets are the size they are because they have been exposed to a much greater inventory of raw materials, either by initial accretion from the solar nebula, or later impact. On Wed, Jul 22, 2009 at 9:53 PM, Kim <kimharch@cut.net> wrote:
David has a valid question and though I'm no expert, I'll try to answer to the best of my limited knowledge.
Jupiter would have a much higher probability of large impacts due to: (1) Its much larger mass makes it quite literally a bigger target. (2) Its position closer to the source of most comets, i.e. the Oort cloud and the Kuiper belt, makes it more likely to encounter such objects.
Probabilities and averages don't give a true picture of what could happen. For example, I'm always annoyed at the nightly TV weather forecasts when they use the term "normal" to describe the average temperature for a given day. A temperature a few degrees above or below the average is not abnormal. Similarly, when we predict impacts that may occur on average, say, every 1000, 10,000 or 10 million years, it is no predictor of a non-average impactor. We are simply a random target for whatever may come our way. The interesting coincidences of this latest Jupiter impact are just that, coincidences, and are no predictor of what may occur to Earth today, tomorrow, next year, or next millennium.
Hope this helps, but I hope more that I'm not way off base.
Kim
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto: utah-astronomy- bounces@mailman.xmission.com] On Behalf Of BAXTER J DAVID Owner Sent: Wednesday, July 22, 2009 9:52 AM To: Utah Astronomy-Digest Subject: [Utah-astronomy] Asteroid or Comet Collision With Earth Probability
Jupiter had major collisions with a comet 10 years ago this week. This week Jupiter had another major collision, probably from a comet. With this interesting fact in mind, is there a higher probability, than what is commonly given, that Earth could have a major impact from a comet or asteroid? Within the past ten years, Earth has also had a couple of lunar distance close calls with asteroids that were not detected until they where very close, by astronomical standards.
Sincerely,
J. David Baxter
baxman2@q.com
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