Hubble Finds Smallest Kuiper Belt Object Ever Seen

NASA announced that its Hubble Space Telescope has discovered the smallest object ever seen in visible light in the Kuiper Belt. It is a vast ring of icy debris, encircling the outer rim of the solar system just beyond Neptune, and it is located 4.2 billion miles away from us. This newly found ring might help astronomers learn more about the Kuiper Belt.
: 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. (Source:  NASA, ESA, and G. Bacon)
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. (Source: NASA, ESA, and G. Bacon)

The tiny object – sized at roughly 3,200 feet – is much smaller than the previous object titled as the “smallest object ever seen”, having dimensions some 50 times smaller. Its importance is that it’s the first observational evidence for similar sized objects in Kuiper Belt; scientists estimate that these are being ground down through collisions. Therefore, they conclude that Kuiper Belt has been evolving and modifying for over more than 4.5 billion years.

Hilke Schlichting of the California Institute of Technology and her collaborators have reported the detection of this object in the December 17th issue of the journal Nature. According to their paper, their achievement was accomplished using indirect imaging. This feat is amazing since NASA’s Hubble Space Telescope usually sees objects only 100 times brighter, and even then it is done via direct observation; the newly detected object is so faint that it’s ranked at 35th magnitude.

The Kuiper Belt is a region of the Solar System beyond the planets extending from the orbit of Neptune. It is similar to the known asteroid belt, although it is far larger—20 times as wide and 20–200 times as massive. Like the asteroid belt, it consists mainly of small bodies, or remnants from the solar system’s formation. While the asteroid belt is composed primarily of rock and metal, the Kuiper belt objects are composed largely of frozen volatiles (termed “ices”), such as methane, ammonia, and water.

The detection utilized three optical instruments installed on Hubble. They are called Fine Guidance Sensors (FGS), and they provide high-precision navigational information to the space observatory’s attitude control systems by looking at select guide stars for pointing. The sensors’ special attribute, which enabled this research, is the ability to exploit the wavelike nature of light, thus making precise measurement of stars’ location.

The research conducted was based on data collected from FGS observations during 4.5 years. In total, Hubble had 12,000 hours in which it had imaged a strip of sky within 20 degrees of the solar system’s ecliptic plane; the reason is that there resides the majority of Kuiper Belt Objects (KBOs). According to the team, they analyzed approximately 50,000 guide stars.

Thanks to the gigantic size of the database, the team of astronomers found a single 0.3-second-long occultation event; it is short because of the Earth’s orbital motion around the sun. The success of capturing occultation event is possible thanks to the FGS instruments’ ability to sample changes in starlight 40 times a second.

In order to estimate the distance between Earth and the KBO, the team assumed the KBO was in a circular orbit and inclined 14 degrees to the ecliptic. Then, they used the amount of dimming to calculate the size of the object. “I was very thrilled to find this in the data,” says Schlichting.

In their study, the researchers predict that in several billions of years the debris will collide, grinding the KBO-type objects down to even smaller pieces. The supporting evidence is Hubble’s observations of nearby stars, showing that a number of them have Kuiper Belt-like disks of icy debris encircling them. These disks are the remnants of planetary formation.

In addition to studying Kuiper Belt, the study’s findings help to demonstrate the advantages behind this powerful database, created by archiving Hubble’s data. Future researches might use it to produce important discoveries. When asked about their future intents, the team announces a plan to uncover additional small KBOs by analyzing the remaining FGS data.

TFOT has covered other exciting events captured by the Hubble Space Telescope, such as a rare Jupiter collision, the merging of galaxies, and the imaging of the atmosphere of a planet orbiting another star. Another related TFOT story is the Reclassification of Pluto, located in the Kuiper Belt.

For more information about the smallest Kuiper Belt object ever seen, see Hubble’s website.

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