Archive for August 4th, 2009

Comets, asteroids, and craters, oh my!

by Treloar Bower, Curator of Education

The news is buzzing lately with images of an Earth-sized “scar” in the atmosphere of Jupiter that an amateur astronomer from Australia spotted recently. NASA even oriented the Hubble telescope, which underwent repair in May, to take a look even though it’s not slated to be back online quite yet.

Photo credit: NASA, ESA, and H. Hammel (Space Science Institute, Boulder, Colo.), and the Jupiter Impact Team

Photo credit: NASA, ESA, and H. Hammel (Space Science Institute, Boulder, Colo.), and the Jupiter Impact Team

The massive scar in Jupiter’s clouds was likely caused by an asteroid or comet. Interestingly, that object was probably only about 50 to 100 miles in diameter. The scar is much, much larger than the object that actually made impact. Why is that? The force of the impact of the object against the gas planet caused debris and what scientists call ejecta to shoot away in all directions from the point of impact. Essentially, the speed and direction of an object (or derivation of momentum with respect to time) at impact influences how big crater will be. In the case of a gas giant planet like Jupiter, we see a scar in the atmospheric gases. The greater the force of impact, the greater the field of debris and ejecta will be.

We illustrate this phenomenon here at the Museum in a cool activity we do with our visitors as part of our Virtual Space Community partnership with Space Center Houston. We create a model planetary surface in a pan by layering flour under a thin layer of cocoa powder. By dropping rocks or beads from varying heights into the flour, we can see the size of the debris and ejecta field caused by the impact of our “asteroid” or “comets.” The flour under the cocoa powder shoots out on all directions. We can see it across the surface of our planet and in a “cloud” over our planet.

Our atmosphere protects us from most asteroids and comets because they usually burn up in our atmosphere — but some do make it to the surface. We call them meteorites and they are spherical in shape because of the forces acting on them as they travel through the atmosphere rounds off their uneven surfaces. The Earth’s moon, lacking an atmosphere, has been, and will continue to be, impacted by objects of all shapes and sizes. No atmosphere, no rounding. Some night when the moon is visible, take a pair of binoculars and look for the irregularly shaped scars of asteroids and comets that have hit the moon over many millennia.

August 2009

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