What else is out there?

Byline: The Register-Guard

The discovery of a planet-like object far beyond the orbit of Pluto makes our solar system seem a bigger, more complicated place. It underlines the fact that our understanding of even our little corner of the universe is incomplete, calling into question NASA's decision to cancel maintenance of the Hubble Space Telescope.

The Hubble telescope didn't spot what astronomers are calling a planetoid. This dark little world - about 8 billion miles from the sun, and slightly smaller than Pluto - was detected by a telescope on Earth. Yet it was just a few weeks ago that Hubble's latest triumph, the discovery of the most distant known galaxy, was announced. The space telescope continues to be the most productive scientific instrument ever built, and could be enlisted to provide clearer images of the newly found planetoid and, perhaps, other objects like it.

The discoverers have proposed calling the planetoid Sedna, after the Inuit creator of Arctic sea creatures. Sedna is currently 86 astronomical units from the sun - one unit being the distance between the sun and the Earth. Already the most distant object known to travel around the sun, Sedna's orbit might carry it as far as 900 astronomical units from the center of the solar system.

Sedna's discovery comes at a time when a pair of robotic rovers are searching for, and finding, evidence that Mars was once a watery planet. It comes at a time when astronomers are finding scores of small moons in orbit around Saturn and Jupiter. It comes when Pluto's status as a planet is being challenged - perhaps it ought to be regarded as more like Sedna than the inner eight planets. The solar system, it turns out, can still yield many surprises.

Faraway objects such as Sedna reflect little light, making their detection extremely difficult. The region beyond the realm of the nine planets might be home to many more planetoids - a smaller and closer one, called Quaoar, was discovered two years ago. The objects are raising new questions about the structure of the solar system, the quantity of matter in the universe, the origins of comets and the nature of planets.

The Hubble Space Telescope can help answer those questions. As NASA makes plans for responding to President Bush's call for manned missions to the moon and beyond, it should not drop its highly successful program of exploration through observation. There's more to the universe, and even our solar system, than was once suspected.