We know the planets close to the sun, and our closest neighbors, but few people know of the other big red hunk of matter orbiting the sun. The most distant known object in the solar system is Sedna, and astronomers hope that it's a sign of things even farther out.

At the center of the solar system is the sun. It took a bit of bother settling that fact, but settle it we did. What's out closest to the edge? Astronomers think that it's the icy Oort Cloud of objects, which keeps sending comets into the inner solar system. But what have they actually seen? About eight billion miles out, they've spotted a planetoid that they've dubbed Sedna. Sedna is 800-1100 miles in diameter, or roughly half the size of the moon. It's so far out that the sun, from a person on Sedna's perspective, would be no larger than a particularly big star - about the size of a pinhead.


Sedna is red, like Mars, which speaks to an interesting composition, but scientists are mainly interested in it because its position might tell us something about the Oort Cloud and the history of life on Earth. The Oort Cloud should be about ten times farther out than Sedna, but Sedna might have started out as material from the cloud. The planetoid, they think, was either nudged inward or conglomerated billions of years ago when a single rogue star swooped distressingly close to the sun. Its gravity would have pulled in some of the materials from the cloud to comparably close orbit, and sent a lot of comets hurtling towards the Earth. The impacts might have set life on Earth back quite some time. Who knows what might have sprung up on Earth if Sedna, and its companions, had stayed out with the Oort.

In short, Sedna might have been as cuddly as its namesake. Sedna, in Inuit mythology, got into a fight with her father. He took her out to sea in his kayak, and threw her overboard. She clung to the side, and he chopped off her fingers to dislodge her. Her fingers became seals, walruses, and whales, and she became a mighty, and feared, sea goddess. In many variations of the story she then used the sea to drown her father. In mythology, no one ever decides to hug it out. Then again, very few huggers get planets named after them. It's a trade-off, really.

Image: R. Hurt (SSC-Caltech), JPL-Caltech, NASA

Via Nasa twice.


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