December 31, 2004

Top Space Stories of 2004: Beyond Pluto

Counting down the top ten astrobiology stories for 2004 highlights the accomplishments of those exploring Mars, Saturn, comets, and planets beyond Pluto. Number six in this countdown was the discovery of potential heat sources for ice beyond Pluto, an important finding if water is considered the key ingredient to understanding biological probabilities elsewhere in the solar system.

Astrobiology Magazine -- 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


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