Arecibo gives comet some radar love

Bad Astronomy
The entire universe in blog form
Oct. 29 2010 10:42 AM

Arecibo gives comet some radar love

Using a giant radio telescope like a cop's radar gun, astronomers have made some pretty cool images of the nucleus of the comet Hartley 2:

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

arecibo_hartley2

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Hartley 2 is a comet that is currently very close to the Earth as these things go: last week it passed us at a distance of about 18 million km (11 million miles). Astronomers took advantage of the close pass to ping the comet with radar pulses. By timing exactly how long it took the pulses to go from the telescope to the comet and back to Earth, they can create a map of the comet's shape and other characteristics -- something like how dolphins and bats use echolocation to map their surroundings... though, as Emily Lakdawalla at The Planetary Society Blog explains, it's a bit more complicated.

From the images, it looks like the nucleus -- the solid, central part of a comet -- is highly elongated, about 2.2 km (1.4 miles) in length, and rotates once every 18 hours. We've only seen a handful of comets up close, and in general the nuclei are potato-shaped, so this one fits that description. The image has a scale of about 75 meters per pixel.

These observations were made to help out the EPOXI space mission, which will pass just 700 km (420 miles) from the nucleus of Hartley 2 on November 4. That means we'll be getting some really cool close-up images and data from the comet very soon! Stay Tuned.


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