Planetoids Beyond Pluto

The doppler effect
Quaoar is about 4 billion miles away from Earth, well over a billion miles farther away than Pluto. Earth as seen by the departing Voyager spacecraft as it departed the solar system: a tiny, pale blue dot.
Credit: NASA

Six years ago, then NASA Associate Administrator Wesley Huntress, Jr., stated , “Wherever liquid water and chemical energy are found, there is life. There is no exception.” Few opportune years like 2004 have presented astrobiology with as many remarkable vistas and fresh perspectives on this fundamental triad of water, chemical energy and life.

Consider this year’s accomplishments of those dedicated to searching for life in the universe.

Landing on Mars not once, but twice. Then finding evidence for water on opposite sides of the red planet. Picking up what appears to be methane signals in the martian atmosphere, one of the residues that might prove one day to be the product of underground biology. Scientists began to discuss seriously what colonization strategies make sense.

Setting off to explore the even richer atmosphere of the Earth-like moon, Titan. Spiraling into orbital capture around Saturn and photographing its majestic rings.

Flying through the tail of a comet and heading home after collecting the first extraterrestrial samples from such dusty iceballs. Launching the Deep Impact probe to smash into a comet and watch how the dust and ice get kicked up.

Filling the astronomy catalogs with well over a hundred new planets, including what may prove to be the first visible exoplanet. Finding some nearby candidates that might occupy temperate locations or safely orbit Sun-like stars.

Witnessing the once-per-century passage of our neighboring Venus across the face of the Sun. The MESSENGER probe took off on its decade long tour of the inner solar system to orbit Mercury.

Discovering the largest planetoids beyond Pluto among those outer nurseries where only comets visit.

The editors of Astrobiology Magazine revisit the highlights of the year and where possible point to one of the strongest lineups ever for beginning a new turn of the calendar. Between the marathon still being run by the twin Mars rovers and the expected descent to Saturn’s moon, Titan, next year promises no letdowns.

The artist’s rendition shows “Quaoar” in relation to other bodies in the solar system, including Earth and its Moon; Pluto; and Sedna, a planetoid beyond Pluto that is the largest known object beyond Pluto.
Image Credit: NASA/JPL-Caltech

Number six on the countdown of 2004 highlights was detection of planetoids beyond Pluto.

In December, David Jewitt (University of Hawaii) and Jane Luu (MIT Lincoln Lab) presented the first high quality spectrum of a bright Kuiper Belt Object (50000) Quaoar beyond Pluto. What they found was the signature of potential volcanic heating, since the ice spectrum showed signs of a crystallizing and not amorphous process at work on the icy planetoid. The surface temperature of Quaoar is only 50 K (-220 C) and, at these low temperatures, the thermodynamically preferred form of ice is amorphous (meaning “structureless”: the water molecules freeze where they stick in a jumbled pattern). The data show that the ice on Quaoar has at some time been raised in temperature above 110 K, the critical temperature for transformation from amorphous to crystalline.

Two ways to heat the ice are 1) to form it at temperatures above 110 K, presumably beneath the frigid surface, and then somehow expose it to view from Earth. Warm ice could be excavated by impact from deeper layers, or blown onto the surface by low-level cryovolcanic outgassing through vents. 2) Ice on the surface could be heated above 110 K by micrometeorite impact. The timescale for this “back-conversion” of crystalline to amorphous ice is uncertain but probably on the order of 10 Myr for the surface ice. 10 Myr is effectively “yesterday” compared to the 4500 Myr age of the solar system. This means that whatever process emplaces the crystalline ice (basically either impact gardening or cryovolcanic outgassing) has been active in the immediate past and, indeed, is probably still active. While the interpretation remains speculative, the good news is that the researchers are, for the first time, able to take useful spectra that reveal unexpected and intriguing properties of the surface of distant Quaoar.

Quaoar’s “icy dwarf” cousin, Pluto, was discovered in 1930 in the course of a 15-year search for trans-Neptunian planets. It wasn’t realized until much later that Pluto actually was the largest of the known Kuiper belt objects. The Kuiper belt wasn’t theorized until 1950, after comet orbits provided telltale evidence of a vast nesting ground for comets just beyond Neptune. The first recognized Kuiper belt objects were not discovered until the early 1990s.

This hard-to-pronounce planetoid was named after a creation god of the Tongva native American tribe, the original inhabitants of the Los Angeles basin. According to legend, Quaoar, “came down from heaven; and, after reducing chaos to order, laid out the world on the back of seven giants. He then created the lower animals, and then mankind.”

What Next?

– Mars Reconnaissance Orbiter (MRO) launch, Mars Orbiter to collect high-resolution, 1-meter, images in stereo-view of Mars
– European Venus Express, Venus Orbiter for two-year nominal mapping life [486 days, two Venus year]

New Horizons, Pluto and moon Charon flyby, mapping to outer solar system cometary fields and Kuiper Belt
Dawn, Asteroid Ceres and Vesta rendezvous and orbiter, including investigations of asteroid water and influence on meteors
Kepler, Extrasolar Terrestrial Planet Detection Mission, designed to look for transiting or earth-size planets that eclipse their parent stars [survey 100,000 stars]
Europa Orbiter, planned Orbiter of Jupiters ice-covered moon, Europa, uses a radar sounder to bounce radio waves through the ice
– Japanese SELENE Lunar Orbiter and Lander, to probe the origin and evolution of the moon

– Japanese Planet-C Venus Orbiter, to study the Venusian atmosphere, lightning, and volcanoes.
– Mars Scout mission, final selections August 2003 from four Scouts: SCIM, ARES, MARVEL and Phoenix
– French Mars Remote Sensing Orbiter and four small Netlanders, linked by Italian communications orbiter

BepiColumbo, European Mercury Orbiters and Lander, including Japanese collaborators, lander to operate for one week on surface
Mars 2009, proposed long-range rover to demonstrate hazard avoidance and accurate landing dynamics

Related Web Pages

2003: Year in Review
Solar System Exploration Survey
Mars Express
Saturn Cassini
Venus Occultation

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