Asteroids have been in the news lately and now one of their icy relatives, Comet Hartley 2, is making a big splash in the astronomical and spaceflight communities – including our very own University of Maryland (UMD). This comet will not be a crowd pleaser as Comet Hale-Bopp was back in the late ‘90’s as it will be barely visible in the night sky. But that doesn’t mean it will not be of immense historical and scientific importance.
Comets are the left over debris, along with asteroids, from the formation of our solar system 4.5 billion years ago. These two classes of solar system objects are thought to be related as comets and asteroids can exhibit characteristics indicative of one another. Some asteroids could be "dead" comets in that they have lost all of the volatile and icy material that makes up comets while some comets are covered with significant layers of dust. Just recently two asteroids were found to contain water, a major component of comets.
Comet Hartley 2 is a small comet as its' nucleus (the actual body of the comet) is less than a mile across. The coma (the gaseous envelope created by outgassing of volatiles and dust from the nucleus caused by heating from the Sun) is rather large and very active. The coma is expected to increase in size and activity in the coming days, just in time for NASA/UMD's Deep Impact/EPOXI spacecraft cameras to capture it all up close.
This is the spacecraft's second flyby of a comet as it flew by and also impacted Comet Tempel 1 with a launched 800 pound copper impactor on July 4th, 2005. This was a spectacular mission and marked the first time in history that humanity had impacted a cometary body. Much was learned about the composition of a comet 's nucleus as large amounts of water and dust made up the debris ejected as a result of the impact.
Because there was so much debris from the impact the spacecraft’s cameras could not record the resulting crater and view the exposed sub-surface material. This was a disappointment as one of the mission objectives was to see how large the resulting crater was and to examine the crater’s internal and external structure. The images that were obtained were impressive in their detail.
Read More About Deep Impact: http://deepimpact.umd.edu/gallery/index.html
Comet Hartley 2 is currently visible in binoculars and telescopes from dark sky sites and from NASA/UMD's Deep Impact/EPOXI spacecraft. The comet will be closest to the Earth on October 20th at a distance of only 11-million miles - close indeed – and may get to naked eye visibility away from city lights. The Moon will be getting brighter in the sky as well which will make the comet harder to see.
But the nearly Full Moon will not be an issue for NASA/UMD's Deep Impact/EPOXI spacecraft as the intrepid cometary explorer will flyby Comet Hartley 2 at a distance of only 435-miles on November 4th. The flyby will only be the 5th time humans have flown by a cometary nucleus. The others were Comets Halley, Borrelly, Tempel 1, and Wild 2. When you consider that there are billions, if not trillions of comets in the solar system, there is much we need to learn.
The spacecraft’s cameras will remain pointed at the comet’s nucleus during the flyby and will be exposed to impacts from the gas and dust making up the coma. This was not done in the Deep Impact mission. The resulting images are expected to be unprecedented in their detail and may allow us to see actual jets of material spewing forth from visible structures.
Read More About Deep Impact/EPOXI: http://science.nasa.gov/science-news/science-at-nasa/2010/15oct_epoxi/
Asteroids and comets pose an impact threat to our planet so the more we learn about them the better we can defend ourselves against the threat they pose.
SkyGuy in VA
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