Panel Majority Agrees: Our Solar System Is Special

All five observational and theoretical planetary scientists on a panel last week agreed that our solar system is a special place, reports Space.Com.  At the 5th annual Isaac Asimov Memorial Panel Debate, held at the American Museum of Natural History, the topic was “whether our solar system is special, why it looks the way it does, and how others thus far detected differ.”  All five panelists concluded that, because of the approximately 150 extrasolar planets detected so far, none of which resemble Earth, solar systems like ours may be rare in the universe.  Neil deGrasse Tyson of the Hayden Planetarium moderated the event that was attended by about 700 people.

1. Paul Butler is co-discoverer of two thirds of known extrasolar planets.  He has found that most have eccentric orbits, meaning that earthlike planets in such systems would likely be destroyed or ejected.  “I think with the data at hand,” he said, “we can say that our solar system is rare.  Eccentricity dominates.”
2. Scott Tremaine (Princeton) and Peter Goldreich (Caltech), both astrophysicists, have calculated that large planets like Jupiter can migrate inward and outward in planetary systems.  Many of the observed extrasolar planets are Jupiter-class objects found in Mercury-range orbits.  Earth-like planets would have little hope of survival in such systems.
3. Fritz Benedict (U of Texas) noted that many host stars emit huge flares that would quickly sterilize Earth-like planets.  He remarked,“The older I get, the less likely it seems to me there’d be a bunch of places like our solar system.” 
4. Margaret Turnbull (Carnegie Inst. of Washington) felt that more observations will be needed to consider our solar system special.  But she noted that close-in planets would most likely be tidally locked to the star, turning one side into a dry desert and the other into a freezing wasteland.  Liquid water on the surface of such a world would be impossible.

The first extrasolar planets were detected indirectly in the 1990s.  Prior to that, most scientists assumed that other solar systems would resemble ours, with rocky planets close in and gas giants farther out.  “But what they discovered were solar systems unlike ours with big Jupiter-like planets close to their host star,” wrote Sara Goudarzi for Space.com.  The question now is why ours is so different, and just how rare it will turn out to be as discoveries continue.
    A contrasting view was reported in National Geographic News.  A computer study shows that a “Goldilocks zone” of habitability could exist in many of the known extrasolar systems.  No earthlike planets have been found in them, though, and indeed could not be detected with current technology.  “It’s still philosophical at this point, but I’m an optimist,” said James Kasting, member of a JPL team building the Terrestrial Planet Finder for launch a decade away.  In contrast to the Space.Com article that emphasized the uniqueness of Earth gauged from observations, NG optimistically titled its report, “Many ‘Earths’ Are Out There, Study Says.”

This is why observational science is necessary and important; it keeps speculation in check.  Poor Dr. Tyson (would-be heir apparent to Carl Sagan–see 09/29/2004 entry) must rue the fact that the stubborn data are, so far, contrary to his master’s fresco of our Earth as “an ordinary planet around a humdrum star, lost in a galaxy, tucked away in a forgotten corner of the universe in which there are far more galaxies than people.”  The search is in its early stages, but the data so far appear statistically significant.
    This story provides additional support for the “Privileged Planet” hypothesis (see 06/24/2004 and 08/01/2004 entries, book at PrivilegedPlanet.com and film at Illustra Media).  Back in the early 1980s when Carl Sagan’s Cosmos series was the biggest thing on PBS, inspiring a cult following, most scientists accepted as an article of faith that Earth-like planets were common in the universe.  Five scientists is a small sample of the set of all astronomers, but that all of them on this panel, each professionally involved in the search for extrasolar planets, would be forced by the data to conclude “there’s no place like home,” is also statistically significant.