Today on SPACE.com -- Tuesday, July 3, 2001
NEWSALERT: Tuesday, July 3, 2001 @ 1600 GMT
The latest news from Astronomy Now and Spaceflight Now
National Optical Astronomy Observatory
Tucson, Arizona
"This object is intrinsically the brightest Kuiper Belt Object found so far," says Lowell Observatory Director Robert Millis, leader of the survey team. "The exact diameter of 2001 KX76 depends on assumptions that astronomers make about how its brightness relates to its size. Traditional assumptions make it the biggest by a significant amount, while others make it larger by at least 5 percent."
Assuming a reflectivity (or albedo) of 4 percent, 2001 KX76 would have a diameter of approximately 1,270 kilometers (788 miles), bigger than Ceres, the largest known asteroid. For comparison, Pluto's moon Charon has an estimated diameter of 1,200 kilometers (744 miles). Earlier this year, a Kuiper Belt Object (KBO) called 20000 Varuna was announced with an estimated diameter of 900 kilometers, based on a calculated reflectivity of 7 percent. Applying this albedo to 2001 KX76 gives it a diameter of roughly 960 kilometers (595 miles).
2001 KX76 was discovered in the course of the Deep Ecliptic Survey, a NASA- funded search for KBOs being conducted by the Lowell-MIT-LBT team using the National Science Foundation's telescopes at Kitt Peak National Observatory near Tucson, AZ, and Cerro Tololo Inter-American Observatory in Chile. The team spotted 2001 KX76 in deep digital images of the southern sky taken with the 4-meter Blanco Telescope at Cerro Tololo on May 22 by James L. Elliot of MIT and Lawrence H. Wasserman of Lowell Observatory.
2001 KX76 is currently at a distance of just over 6.4 billion kilometers (4 billion miles) from the Sun. Its orbit is inclined by approximately 20 degrees with respect to the orbital plane of the major planets, but the detailed shape of its orbit remains uncertain. Available evidence suggests that the newly discovered KBO may be in an orbital resonance with Neptune, orbiting the Sun three times for each time that Neptune completes four orbits.
The brightness and colors of 2001 KX76 have been measured by Elliot, Susan Kern, and David Osip, all of MIT, with the Raymond and Beverly Sackler Magellan Instant Camera (MagIC) on the 6.5-meter Magellan Telescope at Las Campanas Observatory in Chile. The object has a distinctly reddish color typical of many primitive bodies in the outer Solar System.
"2001 KX76 is so exciting because it demonstrates that significant bodies remain to be discovered in the Kuiper Belt," Millis explains. "We have every reason to believe that objects ranging up to planets as large or larger than Pluto are out there waiting to be found. Until the Kuiper Belt has been thoroughly explored, we cannot pretend to know the extent or the content of the Solar System."
The existence of the Kuiper Belt was postulated by J. A. Fernandez and by M. Duncan, T. Quinn, and S. Tremaine in the 1980s to explain the origin of short-period comets. These comets move around the Sun in the same direction as the planets, and are found in orbits that are tipped only modestly with respect to the ecliptic plane. These researchers showed that short-period comets could not have originated from the more distant spherical Oort Comet Cloud as originally believed. They predicted that a second, more flattened reservoir of "proto-comets" must lie beyond the orbit of Neptune.
The first Kuiper Belt Object was found in 1992 by David Jewitt and Jane Luu of the University of Hawaii. Since then, astronomers have found over 400 KBOs, but tens of thousands likely remain to be discovered. These objects are believed to be remnants from the formation of the Solar System, and consequently are among the most primitive and least-evolved objects available for study by planetary astronomers.
About one-quarter of the known KBOs have been found by the Deep Ecliptic Survey Team. Other members of the team are Marc Buie of Lowell and Mark Wagner of the Large Binocular Telescope Observatory on Mount Graham, AZ. The Deep Ecliptic Survey was recently awarded formal survey status at the National Optical Astronomy Observatory (NOAO), assuring that this reconnaissance of the outer Solar System will continue for the next three years.
Much more precise measurement of KBO diameters will be possible with NASA's upcoming Space Infrared Telescope Facility (SIRTF) mission, due for launch in 2002. Kitt Peak and Cerro Tololo Inter-American Observatory are part of NOAO, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the National Science Foundation.
The survey team's research is supported by the NASA Planetary Astronomy Program through grants to Lowell Observatory, Flagstaff, AZ, and MIT in Cambridge, MA.
NOAO is operated by the Association of Universities for Research in Astronomy (AURA), Inc. under cooperative agreement with the National Science Foundation.
IMAGE:
The May 22, 2001, discovery image for the large Kuiper Belt Object 2001 KX76
was produced by combining two exposures from the 4-meter Blanco Telescope at
CTIO in such a way that moving objects appear as red-colored pairs of images.
2001 KX76 is the bright red-cyan pair of dots at the center of the picture.
Non-moving objects, such as stars and galaxies, appear white in the picture.
Credit: Deep Ecliptic Survey Team/NOAO/AURA/NSF
ROYAL ASTRONOMICAL SOCIETY
31st March 1998
But rather like the curious incident of the dog that famously did nothing in the night-time [in the Memoirs of Sherlock Holmes] it is the fact that the team DID NOT find more objects that may prove to be a highly significant clue as astronomers probe the mysteries of these outer reaches of the solar system. Based on present ideas about how Kuiper Belt objects formed, astronomers expected to be finding these faint objects at even greater distances. Since they did not, those ideas may need to be revised. It may be that the average size of the KBOs is smaller the farther away they are, so the most distant ones were too faint even for this survey. Or it might be that the objects actually discovered mark the outer edge of the Kuiper Belt.
These latest results will be presented at the National Astronomy Meeting at the University of St Andrews on Tuesday 31st March by Dr Alan Fitzsimmons of Queen's University Belfast on behalf the team, which also includes Miss Edel Fletcher (Queen's University of Belfast), Dr Mike Irwin (Royal Greenwich Observatory) and Professor Iwan Williams (Queen Mary & Westfield College London).
Hardly any previous searches have been targeted on objects as faint and as small as those the UK team were looking for when they made the observations in November 1997. They used the 2.5-metre Isaac Newton Telescope on La Palma to image the sky for 7 nights, searching a total area slightly smaller than that covered by the full Moon. On the telescope they had a new, sensitive, wide-field camera built by the Royal Greenwich Observatory. The new camera can see five times as much sky as the one previously used.
During each night they stared continuously at different patches of sky for up to four hours at a time. In each patch of sky several thousand distant stars and galaxies could be seen. However even these images were not sensitive enough to record the solar system objects the team were seeking. So they combined the images by computer in a way that eliminated all stars, galaxies and nearby asteroids and revealed only faint solar-system objects at large distances from the Sun.
Two new objects were discovered. One is roughly 150 km in diameter, while the other is only 110 km across. Both appear to be around 45 times further from the Sun than the Earth. At this distance, the smallest object was forty million times fainter than the faintest stars that can be seen by eye on a dark night. They are so faint that it is not worth taking up all the telescope time needed to track them in the future, and it is very unlikely they will ever be seen again.
SKY & TELESCOPE NEWS BULLETIN
JUNE 6, 1997
The following text is extracted from 1996 TL66: a new type of transneptunian object
PRESS INFORMATION SHEET:
1996 TL66 was first imaged last October by Jane Luu, Harvard-Smithsonian Center for Astrophysics, and Dave Jewitt, University of Hawaii, during an observing run with two of Jewitt's students on the 2.2-m telescope the University of Hawaii maintains on Mauna Kea. At first, and as the result also of follow-up observations with the Smithsonian Astrophysical Observatory's 1.2-m telescope in Arizona a month later, it appeared probable that the object was a "plutino", one of two main classes of object hitherto identified in the Kuiper Belt (an extensive swarm of icy bodies, presumably proto-comets, identified in recent years as orbiting the sun beyond the orbit of Neptune).
"Plutinos", meaning "little Plutos", is a generic name given to the class of Kuiper Belt members with orbits that come very close, and sometimes even cross, the orbit of Neptune. Despite their often extreme proximity to Neptune's orbit, the plutinos do not in fact have the possibility of encountering Neptune itself, because the periods of revolution about the sun of the plutinos and Neptune are precisely in a ratio of three to two. This means that, after three revolutions of Neptune and two of a plutino (about 500 years), the relative positions of the objects in their orbits repeat, and this cycle does not give the bodies an opportunity to pass within 10 or more astronomical units of each other. Although the cycle may break down eventually, it seems likely that it will continue to repeat for perhaps tens or hundreds of millions of years, thereby preventing devastating encounters between a plutino and Neptune. Pluto, a 2400-km object discovered in 1930, has been known since 1964 to exhibit precisely this type of motion, and it should therefore be considered as the first known member of the Kuiper Belt; the second member of the group would then be Pluto's satellite Charon, discovered in 1978 and having about half the diameter of Pluto.
The plutinos contrast with what may be called the "cubewanos", in recognition of their prototype 1992 QB1, also discovered by Jewitt and Luu. Cubewanos, which comprise perhaps 60-70 percent of the known objects in the Kuiper Belt, travel in orbits that are substantially more nearly circular and closer to the plane of Neptune's orbit than the plutinos. And whereas the plutinos orbit the sun at an average distance of 39 astronomical units, cubewanos have average distances over the range 42-46 astronomical units. They are therefore well beyond Neptune at all times.
After Carl Hergenrother measured 1996 TL66 with the Arizona telescope in December, continuing calculations by Brian Marsden showed that the supposition that 1996 TL66 is a plutino had to be incorrect. At this stage it became evident that the orbit had to be substantially larger and more elongated than that of a plutino. Nevertheless, the orbit's precise character was unclear, something that needed to be settled with further observations. Unfortunately, 1996 TL66 was by then starting to sink into the evening twilight, and no time had been allocated for follow-up in January on any of the suitable professional telescopes. It was at this stage that the help of an amateur astronomer, Warren Offutt, was solicited. At his observatory 1000 meters up in the mountains near Cloudcroft, New Mexico, Offutt has a well-equipped 0.6-meter telescope and electronic imaging device. He was already known by then as the only amateur in the world to have observed a member of the Kuiper Belt (other than Pluto) using amateur equipment, so it seemed likely that he would be able to obtain some measurements that would clinch the situation before 1996 TL66 was lost to view. Offutt was happy to oblige and obtained critical observations on January 10 and 11, thereby providing confirmation of the developing suspicions concerning the 1996 TL66 orbit.
Are there other objects like 1996 TL66? The ease with which it was found, at the start of new wide-field survey, suggests that there are. Furthermore, some of its colleagues may already have been inadvertently detected. For every two Kuiper Belt candidates that are discovered, typically one is lost. Out of the 40 or so Kuiper Belt candidates known, four of those lost possibly do have some of the characteristics of 1996 TL66, notably, indications that their orbits are quite highly inclined to that of Neptune. Perhaps 10 percent of what we think of as the Kuiper Belt may therefore belong to this "scattered" population.
So what is 1996 TL66? Physically, it is probably much the same as the other icy bodies out there, including Pluto. Dynamically, some of the Kuiper Belt objects, perhaps principally the plutinos, form the reservoir that eventually yields the typical short-period comets that at their most distant are near the orbit of Jupiter. If, eventually, the accumulated gravitational attractions of Neptune, Uranus, Saturn and Jupiter conspire to dislodge a plutino, a plutino can be dragged into the vicinity of those planets, to spend then perhaps another million years in a very unstable dynamical situation, bouncing back from one planet to another. This is known as the "centaur" stage, something currently being exhibited by seven known objects. The first of these, named Chiron following its discovery in 1977, does sometimes exhibit a coma or tail and is the largest object known to do so. Eventually, Jupiter wins, sending an object in toward the orbits of Mars and the earth. About a hundred of these short-period comets are known, all of them considerably smaller than Chiron but thereby indicative of the large number of smaller centaurs and plutinos that must exist. In very general terms, 1996 TL66 could be considered in the same category, perhaps also to move up the centaur route-- or once to have been a centaur. Perhaps, indeed, it is destined to move farther out than it is now. Perhaps it is on its way out toward the Oort Cloud. The Oort Cloud of comets surrounding the solar system at a distance of some 20 percent of the nearest star is believed mainly to represent icy bodies ejected from the vicinity of Uranus and Neptune. As many as a trillion proto-comets seem to exist in the Oort Cloud, drawn out from a planar to a near-spherical collection as the result of the gravitational effects of passing stars and giant molecular clouds. To gather a trillion comets takes a long time, and most of the formation of the Oort Cloud must have taken place long ago. The existence of 1996 TL66, and presumably of other bodies in its class, indicates that the process of maintaining the Oort Cloud may still be going on at some small level.
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