Astronomy Question: Asteroid Impacts
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Russ writes: Dear Astronomer, I have only the most rudimentary understanding of Astronomy having never been very proficient in the sciences area. However I am writing a fiction novel and I have found myself at an impasse regarding factual data in astronomy. In part of my novel (a work in progress) I would need to know the following information:
1. How long would it take an asteroid of sufficient size and mass to travel from the region of Saturn to Earth and ultimately impact and destroy the majority of life on earth?
2. What size (miles wide), mass, and speed would be sufficient to extinguish life on earth?
3. Do Jupiter and larger planets like Saturn usually pull threatening large bodies such as asteroids and comets into their gravitational pull and save Earth from impact?
4. Is there any theoretical way that may become available in the future of repelling such threatening bodies?
5. How often would you say threatening bodies of sufficient size come close enough to realistically threaten Earth.
I am sorry there are so many questions, but I am very ignorant in these areas, and even though the book is a book of fiction (and I think a good idea), I would like the information written in it to at least be close to actual factual astronomy data. I would be so very grateful if you could answer these questions. That way I can continue on with the book. Sorry if the questions seem silly, but it is all part of the story plot.
Great set of questions Russ! There’s a lot of information to cover, so click the “read more” link below:
I’ll answer the questions about “Near-Earth Objects” as they are called, in order. The answers appear in italics, after the question.
The main asteroid belt lies between Mars and Jupiter, however you can look up information on “Centaurs” which are found between Jupiter and Neptune. You can read more about asteroids in general at: http://nineplanets.org/asteroids.html My research shows velocities between 11km/sec and 25km/sec. Assuming the average speed (18km/sec or 65,000 km/hr) and a straight path at a distance of 1.4 billion km between Earth and Saturn, about 2 1/2 years. Sorry for the large error bars on that data!
Chicxulub crater is one of the largest impact craters on Earth, widely theorized to be the impact responsible for the “K-T” extinction event 65 million years ago which wiped out nearly all life on Earth. The impactor is believed to be about 10km in diameter and formed a crater just under 200km in diameter. You can also read more about “Meteor Crater” in Arizona which is a 1.2km wide crater formed from a 50 meter diameter 150,000 ton object which hit the Earth at over 13km/sec. Even an asteroid of 1-2km diameter would produce a life-altering impact.
Generally speaking, yes. We’ve actually witnessed Jupiter acting like a shepherd. One notable occurrence was when Comet Shoemaker-Levy 9 collided with Jupiter in July 1994. Shoemaker-Levy 9 was travelling at over 50km/sec and left visible scars in the Jovian atmosphere, some larger than Earth!
If you’ve ever seen movies like “Armageddon”, you know that theories on deflecting incoming threats range from almost-possible to downright absurd. What it boils down to is the amount of time we have before the asteroid reaches Earth. There have been a few “surprise” asteroids that have come close to Earth with only a few days notice and were large enough to destroy a good sized city.
Without getting into a lot of complex equations, the basics are: You can move an asteroid a tiny amount over a large amount of time MUCH easier than trying to move the asteroid a large amount in a short amount of time. Some techniques include “painting” the object to change the pressure from solar radiation, or using a small “tug” craft to gently nudge the object over time. Something to consider: “Blowing up” an incoming asteroid is nearly as disastrous as the impactor itself hitting Earth. If the asteroid didn’t re-assemble itself, you’d end up with a far larger path of destruction.
A general “rule of thumb” is that the larger the impactor, the more rare the impacts are. Technically speaking Earth is constantly bombarded by dust grain sized impacts. As mentioned earlier, the last “life-killer” (over 10km diameter) impact was 65 million years ago, and smaller impacts around 1km in diameter are thought to happen roughly every half million years.
Currently the IAU Minor Planet Center tracks objects such as asteroids, comets and other such objects in the solar system. You can read more on what the MPC does at: http://www.minorplanetcenter.net/iau/mpc.html
Ray Sanders is a Sci-Fi geek, astronomer and blogger. Currently researching variable stars at Arizona State University, he writes for Universe Today, The Planetary Society blog, and his own blog, Dear Astronomer
2012-12-04 08:06:12
Source: http://www.dearastronomer.com/2011/06/13/asteroid-impacts/
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