Hubble Finds Smallest Kuiper Belt Object Ever Seen

December 16, 2009
This is an artist's impression of a one-half-mile-diameter Kuiper Belt Object (KBO) that was detected by NASA's Hubble Space Telescope. The icy relic from the early solar system is too small for Hubble to photograph. The object was detected when it passed in front of a background star, temporarily disrupting the starlight. Credit: NASA, ESA, and G. Bacon (STScI)

( -- NASA's Hubble Space Telescope has discovered the smallest object ever seen in visible light in the Kuiper Belt, a vast ring of icy debris that is encircling the outer rim of the solar system just beyond Neptune.

The needle-in-a-haystack object found by Hubble is only 3,200 feet across and a whopping 4.2 billion miles away. The smallest Kuiper Belt Object (KBO) seen previously in reflected light is roughly 30 miles across, or 50 times larger.

This is the first observational evidence for a population of comet-sized bodies in the Kuiper Belt that are being ground down through collisions. The Kuiper Belt is therefore collisionally evolving, meaning that the region's icy content has been modified over the past 4.5 billion years.

The object detected by Hubble is so faint — at 35th magnitude — it is 100 times dimmer than what Hubble can see directly.

So then how did the space telescope uncover such a small body?

In a paper published in the December 17th issue of the journal Nature, Hilke Schlichting of the California Institute of Technology in Pasadena, Calif., and her collaborators are reporting that the telltale signature of the small vagabond was extracted from Hubble's pointing data, not by direct imaging.

Hubble has three optical instruments called Fine Guidance Sensors (FGS). The FGSs provide high-precision navigational information to the space observatory's attitude control systems by looking at select guide stars for pointing. The sensors exploit the wavelike nature of light to make precise measurement of the location of stars.

Schlichting and her co-investigators determined that the FGS instruments are so good that they can see the effects of a small object passing in front of a star. This would cause a brief occultation and diffraction signature in the FGS data as the light from the background guide star was bent around the intervening foreground KBO.

This is an artist's impression of a small Kuiper Belt Object (KBO) occulting a star. NASA's Hubble Space Telescope recorded this brief event and allowed astronomers to determine that the KBO was only one-half of a mile across, setting a new record for the smallest object ever seen in the Kuiper Belt. Credit: NASA, ESA, and G. Bacon (STScI)

They selected 4.5 years of FGS observations for analysis. Hubble spent a total of 12,000 hours during this period looking along a strip of sky within 20 degrees of the solar system's ecliptic plane, where the majority of KBOs should dwell. The team analyzed the FGS observations of 50,000 guide stars in total.

Scouring the huge database, Schlichting and her team found a single 0.3-second-long occultation event. This was only possible because the FGS instruments sample changes in starlight 40 times a second. The duration of the occultation was short largely because of the Earth's orbital motion around the Sun.

They assumed the KBO was in a circular orbit and inclined 14 degrees to the ecliptic. The KBO's distance was estimated from the duration of the occultation, and the amount of dimming was used to calculate the size of the object. "I was very thrilled to find this in the data," says Schlichting.

Hubble observations of nearby stars show that a number of them have Kuiper Belt-like disks of icy debris encircling them. These disks are the remnants of planetary formation. The prediction is that over billions of years the debris should collide, grinding the KBO-type objects down to ever smaller pieces that were not part of the original Kuiper Belt population.

The finding is a powerful illustration of the capability of archived Hubble data to produce important new discoveries. In an effort to uncover additional small KBOs, the team plans to analyze the remaining FGS data for nearly the full duration of Hubble operations since its launch in 1990.

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4.3 / 5 (6) Dec 16, 2009
The website should maybe try not to display a photorealistic "artist's impression" of what an object may look like beside a headline such as "Hubble Finds Smallest Kuiper Belt Object Ever Seen." Really, I'll believe the Hubble can do *anything*. I'm that gullible.
3.2 / 5 (5) Dec 17, 2009
Just be thankful the artist didn't draw wings on it to illustrate it "flying around the Solar System"...

Looking at the photo more carefully, it's clear from the shadows that we live in a binary system.
3.7 / 5 (3) Dec 17, 2009
Monitoring stars for unpredicted sporadic occultations makes 'searching for a needle in a haystack' the preferred work of pessimists.

Did we get anything more than the occultation data - any temperature, spectra, signature that could be used for future searches? Was this an accidental discovery while searching for more exo-planet evidence?

As for the comments about the 'realistic' artists impressions, I agree they do cause far too much confusion as they attempt to convey the idea.

Even if we were to travel as close as the images portray, direct sunlight would be so weak that the asteroid's surface would require artificial illumination. Hence, the image gives a very false impression.

However, the 'binary system' comment was from someone that may not have read the article properly. The point is that the asteroid was detected while it passed infront of a star not of our solar system.

NASA public relations need to make their media 'smarter' to avoid confusion and criticism
4.6 / 5 (5) Dec 17, 2009
What I find interesting is that this discovery was made from navigational data from Hubble not telescopic data. Someone could have easily said this was just old junk data and deleted it. Its impossible to say when someone will have a bright idea that can produce a nugget of knowledge by data mining an old archive. This is maybe an argument for never deleting anything.
5 / 5 (2) Dec 17, 2009
It would be nice to be able to put upper and lower limits on the number and size of KBOs ,but I expect more observations would be needed.
5 / 5 (1) Dec 17, 2009
More than just a lower limit on the size of Kuiper Belt Objects was obtained. The discovery paper by Schlicting et. al. describes several parameters characterized by this discovery here: .
not rated yet Dec 17, 2009
However, the 'binary system' comment was from someone that may not have read the article properly. The point is that the asteroid was detected while it passed infront of a star not of our solar system.

Quite right. Sorry, I should not have been commenting that late at night. The star behind it looked too large and close to be anything but ours.

I still stand by my assertion that we're lucky nobody put wings on it, though.
not rated yet Dec 17, 2009
An excellent balance of detail and concepts. The second picture tells the story. But really, ditch the first picture.

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