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Smallest Kuiper Belt object discovered by Hubble
Posted: December 17, 2009

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The Hubble Space Telescope has detected a cosmic iceberg a mere 975-metres across floating through the Kuiper Belt of comets 6.76 billion kilometres away from the Sun. It’s the smallest and dimmest object ever found in the Kuiper Belt, and is evidence that cometary bodies are ground down by collisions with other objects over billions of years in the far reaches of the Solar System.

An artist’s impression of the frozen comet moving in front of the star. As it did, it caused a 0.3 second blip in the star’s light (yellow line). Image: NASA, ESA, and G. Bacon (STScI).

The previous smallest icy object in the Kuiper Belt to have been discovered was 48 kilometres across, about 50 times larger than this new object, so this is a huge jump in scale, especially when you consider that this chunk of ice is an incredibly faint 35th magnitude, far too faint to be seen directly by Hubble. Instead, a team led by Hilke Schlichting of the California Institute of Technology used the innovative technique of studying the measurements made by Hubble’s three Fine Guidance Sensors.

The Fine Guidance Sensors help keep Hubble pointing in the right direction, whatever it is looking at. They pinpoint stars, measuring their location and triangulating to ascertain where the telescope is looking. In doing so, they make precise measurements of a given star’s light 40 times per second. Schlichting’s team suspected that if any unseen Kuiper Belt objects passed in front of one of these stars, it would create a dip in starlight and a diffraction effect as the starlight bent around the object.

Schlichting and her colleagues had the daunting task of sifting through four and a half years of Fine Guidance Sensor measurements, incorporating 50,000 guide stars, as they searched for any millisecond blips in starlight. All their hard work paid off – in all the observations, one single 0.3-second blip was spotted, even if the body doing the occulting was too faint to be seen. From the length of the blip its distance could be estimated, and from the magnitude of the blip the objects diameter could be calculated.

“I was very thrilled to find this in the data,” says Schlichting. Buoyed by their success, the team now plan to extend their search through Fine Guidance Sensor measurements all the way back to when Hubble was launched in 1990.

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!


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