EXPLORE


JOINRENEWJOIN

Messages from Earth
  

Space Topics: Trans-Neptunian Objects

(15760) 1992 QB1

First Discovered Kuiper Belt Object (After Pluto)

Until the discovery of (15760) 1992 QB1, the Kuiper belt only existed in theory. Though there were many reasons to expect a swarm of icy bodies similar to the asteroid belt orbiting beyond Neptune (i.e. "transneptunian"), Pluto was the only outer solar system object known until August 1992. In data from the University of Hawaii 2.2-meter telescope, Dave Jewitt and Jane Luu discovered 1992 QB1, the first known Kuiper belt object (KBO). Since then more than a 1,000 transneptunian objects have been discovered, making this distant region of space the subject of much scientific research.

Basic Facts

Diameter: unknown, probably 100-200 kilometers (about 1% of Earth, 10% of Pluto)
Mass: unknown
Bulk density: unknown, probably about 2 grams per cubic centimeter (roughly half-rock, half-ice)
Average orbital radius: 43.7 astronomical units (semi-major axis)
Orbital eccentricity: 0.06 (nearly circular)
Orbital inclination: 2.2 degrees
Orbital period: 289 years
Rotational period: unknown

In the few years following the discovery of 1992 QB1, other objects were discovered on similar orbits: nearly circular orbits never coming close to Neptune. Initially, these objects were classified as "cubewanos," from the name Q-B-1. Now, these objects are typically known as classical Kuiper belt objects. Like 1992 QB1, most classical KBOs appear very red. The color is thought to be caused by complex organic molecules (hydrocarbons) called "tholins" that have formed into a reddish sludge, similar to the dark orange smog in Titan's atmosphere (but in solid, not gaseous, form).

Many scientists predicted the existence of these objects before the discovery of the KBOs. Both Kenneth Edgeworth in 1949 and Gerard Kuiper in 1951 proposed the existence of a transneptunian disk of objects, sometimes called the Edgeworth-Kuiper belt. (These were hypothesized as the source of short-period comets at around the same time as Jan Hendrik Oort's 1950 proposal that long-period comets came from a distant cloud, now called the Oort cloud.) Scientists knew that short-period comets were in orbits that could not have lasted since the beginning of the solar system. They also realized that comets should quickly die out and become dormant, yet many active short-period comets were known, so they suggested that perhaps a distant asteroid-like belt was the source of these recent comets. With the discovery of hundreds of KBOs, we have realized that Kuiper and others were right: short-period comets are continually supplied from an outer solar system filled with small icy worlds like the prototypical 1992 QB1.