Encyclopedia of the Solar System 2nd ed

Kuiper Belt Objects: Physical Studies 607

FIGURE 3 The motion of a Solar System object relative to the background stars and galaxies. Two 300-sec images of the

Centaur 1994 TA taken with the Keck 10-m telescope and a CCD camera in October 1998. The image on the right was

taken about an hour after the image on the left. Because of the Earth’s and 1994 TA’s revolution about the Sun, 1994 TA

moves relative to the fixed pattern of background stars and galaxies. Such motion is how we discover KBOs and Centaur

objects; however, the motion complicates physical studies of a known KBO or Centaur when the image of the KBO or

Centaur comes close to an image of a background star or galaxy.

The IAU names KBOs and Centaurs the same way it names
asteroids. Upon discovery, an object is given a preliminary
designation consisting of a four-digit number indicating the
year of discovery, a letter to indicate the half month of
discovery, another letter to indicate the order of discov-
ery within the half month, and another number to indicate
the number of times the second letter was repeated within
the half month period. For example, the provisional name
of the KBO 2002 LM 60 tells us the object was discovered
between June 1 and 15 of 2002. After the orbit of a KBO
about the Sun becomes well enough known that it isn’t likely
to be lost, the KBO is given a number. It can take obser-
vations over several years to establish a good orbit for a
KBO. The number of 2002 LM 60 is 50,000. No other So-
lar System object has the number 50,000. After an object
receives a number, it receives a name. For example, 2002
LM 60 is known as Quaoar. In this case, the same KBO has
three names. After an object has a number and name, it’s
rarely called by its provisional name. If a KBO or Centaur
object has a number or name, we know that its orbit about

the Sun is well established and there is very little chance of

losing it.

3. Databases of Known Objects

The IAU maintains an Internet listing of known KBOs and

Centaurs as well as elements that describe their orbits about

the Sun. In addition, the IAU, Lowell Observatory, and

NASA’s Jet Propulsion Laboratory in Pasadena, California,

provide Internet tools that enable observers to figure out

where to point telescopes to see a specific KBO or Centaur

object on a specific night. Links to these tools are given in

Table 1.

4. Dynamical Classes

It is possible to divide KBOs into dynamical classes. This

section provides a brief discussion of the classes and likely

TABLE 1 KBO and Centaur Internet Tools

Institution Web Address

Lowell Observatory http://asteroid.lowell.edu/cgi-bin/koehn/asteph

NASA/JPL http://ssd.jpl.nasa.gov/?horizons

IAU http://cfa-www.harvard.edu/iau/MPEph/MPEph.html