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Moon systems, not planets, may be place to find life
Alien life might be both and easier and more interesting to find through a new strategy, a study suggests
Feb. 19, 2008
Special to World Science
Many scientists in
search of alien life pursue the obvious strategy: look for potentially habitable planets.
But a new study suggests another plan might work as well or better,
and perhaps yield more intriguing results. Artist's
concept of a moon near a Jupiter-like planet. (Courtesy NASA/JPL) Send us a comment
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it to a friend
Astronomers should study giant planets that, while uninhabitable, lie in areas suitably warm for
life, the authors say. These may turn out to have moons—some of which might indeed support life.
One advantage of this approach, the researchers
argue, is that big worlds are far easier to find than the small, Earth-like ones on which
most habitable-planet searches focus. Unlike the Earth-like
breed, several suitably warm giants, dubbed “temperate Jupiters,” have been reported found already.
Such bodies can “act as ‘sign-posts’ for future studies looking for potentially habitable worlds,” said
the University of Florida’s Scott Fleming, lead author of
the study.
If their moons do harbor life forms, these might even be more interesting
in some ways than their planet-dwelling counterparts.
For instance, if one moon of a distant “Jupiter” had life, so might others, as they would all lie in the same general temperature zone. If advanced enough, the inhabitants might even regularly exploit the proximity among moons to travel or communicate among them. Or, bizarre evolutionary experiments might arise when meteors randomly
plop small organisms from one moon onto another.
On the other hand, a large percentage of moons may be hostile to life, for instance because they’re too small to hold atmospheres. But given appropriate conditions, life, travel and communication among a
“temperate Jupiter’s” moons “would indeed be very possible,” said Fleming,
a doctoral student. His research on detection of “temperate Jupiters,” with colleagues
at the Space Telescope Science Institute in Baltimore and at
other institutions, is to appear in a future issue of the journal
Monthly Notices of the Royal Astronomical Society. The
paper is also online here.
One “temperate Jupiter” reported found last year orbits the star HD 75898, which is visible with binoculars in the faint northern constellation Lynx. Technology
used to date has generally been incapable of finding moons of such
planets. But Fleming said this could change next year with the launch
of a NASA satellite, Kepler: its instruments can detect both
Earth-sized planets and moons, which would reveal themselves through
their gravitational pulls on the planets. But there are concerns
that Kepler’s mission will be too short to find many moons, Fleming
added.
Jupiter-like planets, regardless of temperature zone, are considered uninhabitable themselves, in part because they’re made completely of gas.
Yet if our Solar System is any guide, they’re rich in moons. Jupiter has 61 known moons. These range from the biggest known—about Mercury’s size, some 5,300 km (3,300 miles) wide—to chunks 2 km (1.2 miles) across, too small to even pull themselves into round shapes with their gravity. Saturn, which is
a bit like a somewhat smaller Jupiter with rings, has 31 known moons, in a similar size range. In fact,
most planets in our system have moons, so astronomers suppose
the same would be true elsewhere.
Any residents of a Jupiter-like planet’s moon might find that travel to other moons is rather easy compared to interplanetary travel. The smaller size of moons greatly reduces the energy requirements. For instance, it takes less than one-twentieth the energy to leave our moon
as it does to leave Earth. As for communications among moons—it would take about three minutes for radio or light waves to travel between the two furthest-apart of Jupiter’s moons.
Residents of a multi-lunar system, Fleming said, could literally
all tune in to the same radio station.
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In search of places where alien life may lurk, many scientists pursue the obvious strategy: looking for potentially habitable planets. But some astronomers say another plan might work as well or better: study giant planets that, while uninhabitable, lie in areas suitably warm for life. These may well turn out to have dozens of moons—some of which might indeed support life. Giant planets are also far easier to find than the small, Earth-like ones on which many searches for signs of habitability have focused. Unlike these, several of the suitably warm giants, dubbed “temperate Jupiters,” have been reported found already. Such bodies can “act as ‘sign-posts’ for future studies looking for potentially habitable worlds,” said University of Florida astronomer Scott Fleming. If life forms inhabit their moons, these might even be more intriguing than planetary creatures. For instance, if one moon of a distant “Jupiter” had life, so might others, as they would all lie in the same general temperature zone. If advanced enough, the inhabitants might even regularly exploit the proximity among moons to travel or communicate among them. Or, bizarre evolutionary experiments might arise when meteors randomly drop small organisms from one moon on another. On the other hand, many moons may be hostile to life, for instance because they’re too small to hold atmospheres. But given appropriate conditions, life, travel and communication among a temperate Jupiter’s moons “would indeed be very possible,” said Fleming. His research on detection of “temperate Jupiters,” with colleagues, is to appear in a future issue of the research journal Monthly Notices of the Royal Astronomical Society. One “temperate Jupiter” already reported found orbits the star HD 75898, which is visible with binoculars in the faint northern constellation Lynx. Jupiter-like planets, regardless of temperature zone, are considered uninhabitable themselves, in part because they’re made completely of gas. Yet if our Solar System is any guide, they’re rich in moons. Jupiter has 61 known moons. These range from the biggest known—about Mercury’s size, some 5,300 km (3,300 miles) wide—to mere chunks 2 km (1.2 miles) across, too small to even pull themselves into round shapes with their gravity. Saturn, which is like a somewhat smaller Jupiter, has 31 known moons, in a similar size range. In fact, every planet in our system has moons, so astronomers assume most others would also. Any inhabitants of a Jupiter-like planet’s moon might find that travel to other moons is rather easy compared to interplanetary travel. The smaller size of moons greatly reduces the energy requirements. For instance, it takes less than one-twentieth the energy to leave our moon than it does to leave Earth. As for communications among moons—it would take about three minutes for radio or light waves to travel between the two furthest-apart of Jupiter’s moons. An open question is whether current technology is adequate to find moons in alien solar systems. “Not easily,” Fleming said. The European Space Agency recently planned a project to do just that, though; but it was canceled in 2003 for lack of funds. Dubbed Eddington, the mission involved first finding planets around other suns, then detecting details of the planets’ motions that would betray the gravitational tug of moons.