What 50 AU looks like

Contributed by
Aug 1, 2005

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:

Image of EL61 from
July 29, 2005
Image of EL61 from
July 30, 2005

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.

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