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The Sciences

What 50 AU looks like

Bad AstronomyBy Phil PlaitAugust 2, 2005 4:48 AM

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Note added August 9, 2005: This entry was part of the Tangled Bank carnival of science blogs at Creek Running North

. In my last blog entry I showed a picture of what I thought was one of the two (now three, actually) objects recently discovered lurking in the outer solar system. We observed it using GORT, a telescope my group built to look for galaxies and such. Well, Logan and I observed the field again on Saturday, a day after the first observations, and -- lo and behold -- one of the "stars" had moved! And it was the very one I figured must be 2003 EL61, the 70%-of-Pluto-sized iceball orbiting the Sun at 50 AU, 50 times the Earth-Sun distance, or roughly 7.5 billion kilometers (4.5 billion miles) out. Here are the two images, side-by-side:

As Galileo said, "And yet, it moves." You can see how far the dinky little thing moved in a single day. Pretty cool. By the way, as before, I didn't do the best job processing the images, so there are still leftover bits and pieces of things in the images. EL61 is marked in both. Take a look at that image. That object orbits the Sun, so slowly it takes 375 or so years to complete one circuit. The surface temperature is something like -400 Fahrenheit. The surface itself is probably frozen nitrogen, oxygen, and methane, colored a dirty dark red from organic compounds made by the interaction of feeble UV light from the distant Sun with those simple chemicals. It has a moon, which circles it once every 49 days. And even then, it's not all that strange-- there are probably millions of objects out there just as icy, just as dark, and just as lonely. There are a lot of worlds in this solar system of ours, a lot of territory to discover and explore.

el61_july292005_thumb.jpg

el61_july302005_thumb.jpg

Image of EL61 from July 29, 2005

Image of EL61 from July 30, 2005

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