You gotta love the Hubble Space Telescope. There it is up there, looking out across the deeps of space and time, spotting shreds of galaxies as they formed some 300,000 to 500,000 years after the Big Bang, and then it turns around and gives us a view of a little shard of a world called Sedna. This place, smaller than the Moon, smaller than Pluto, lies about 90 times the distance between the Earth and Sun, out in a region of the solar system called the Kuiper Belt. It’s a leftover bit of ice (mostly) from the formation of the solar system some 5.5 billion years ago. It’s so dim and small that HST’s image is one pixel across. But, it’s an informative pixel!

For instance, it tells us that (so far) HST hasn’t spotted a companion to this planetoid, although the astronomer who discovered it on March 15, 2004, calculated its spin rate (it’s “day”) and determined that it should have a moon of some kind. The fact that it doesn’t illustrates one of those wonderful “non-results” that tells us valuable information. Science is replete with stuff like this — what looks like a non-result actually helps us put limits on an object’s actions or size or mass or other characteristic. It reminds me of the observation run I did in Hawaii where we studied Comet Hale-Bopp in late 1996. We thought we might be able to spot a plasma tail forming earlier than might be expected. However, when we examined the data, we found no evidence of the plasma tail, which told us that even with a comet of that size, it had to be close enough to the Sun (essentially within about 2 to 2.5 AU of the Sun) before its plasma tail would form. It helped us nail down parts of a descriptive theory we were formulating about how and when and why these glowing tails form when they do as a comet approaches the Sun during its orbit.

Astronomers will keep studying Sedna, and in fact, they have looked at it with other telescopes since its discovery. Expect to see a few more announcements about this frigid world at the frontiers of the solar system!