Newest, Smallest Member of the Solar System

Astronomers have spotted an object only 3,200 feet across, orbiting the sun 4.2 billion miles away. 

It's probably pretty unremarkable.  There are probably countless balls of ice and rock much like it, out in the Kuiper Belt beyond the named planets.

The real story is how they found it with the Hubble telescope.  It's only about a hundredth as bright as the dimmest stars the Hubble can see.

Instead of looking for Kuiper Belt Objects through the telescope itself, Hilke Schlichting of Caltech and her fellow researchers culled through data recorded by the Hubble's Fine Guidance Sensors, three instruments that help point the telescope.  They happen to be very sensitive, taking readings 40 times per second to make sure the telescope isn't turning relative to the stars.

If the Kuiper Belt — which includes Pluto and Charon — is crowded with other, smaller bodies, the researchers figured the sensors would detect them when they passed in front of distant stars, briefly blocking their light.

So they looked — through four years of data, 12,000 hours of it, as the Hubble locked on to 50,000 different guide stars near the ecliptic, that vast plane in which most of the objects in the solar system orbit. They report their results in today's edition of the journal Nature.

In all that time, they say the sensors saw one star wink out.  Just one.  For three tenths of a second.  That was the newly-found object. From the way it interfered with the waves of light from the star far beyond it, they extrapolated its likely size and distance. There's more HERE.Why didn't they find more?  The sensors worked fine.  The researchers suspect there’s so much celestial junk in the outer solar system that the pieces are crashing into each other, breaking into ever-smaller pieces, too small even to be detected by the Hubble’s sensors.  They say they’ll keep looking — at much more than four years of data.(Top: Artist's conception by G. Bacon, Space Telescope Science Institute. Middle: Hubble telescope as seen by the crew of the space shuttle Atlantis in May 2009. (NASA))