Planet-hunters
set for big bounty By
Helen Briggs
Science reporter, BBC News, Boston Rocky
planets, possibly with conditions suitable for life, may be more common than previously
thought in our galaxy, a study has found. New
evidence suggests more than half the Sun-like stars in the Milky Way could have
similar planetary systems. There
may also be hundreds of undiscovered worlds in outer parts of our Solar System,
astronomers believe. Future
studies of such worlds will radically alter our understanding of how planets are
formed, they say. New
findings about planets were presented at the American Association for the Advancement
of Science (AAAS) in Boston. Nasa
telescope Michael
Meyer, an astronomer from the University of Arizona, said he believed Earth-like
planets were probably very common around Sun-like stars. "Our
observations suggest that between 20% and 60% of Sun-like stars have evidence
for the formation of rocky planets not unlike the processes we think led to planet
Earth," he said. "That is very exciting." Mr
Meyer's team used the US space agency's Spitzer space telescope to look at groups
of stars with masses similar to the Sun. They
detected discs of cosmic dust around stars in some of the youngest groups surveyed.
The dust is believed
to be a by-product of rocky debris colliding and merging to form planets. Nasa's
Kepler mission to search for Earth-sized and smaller planets, due to be launched
next year, is expected to reveal more clues about these distant undiscovered worlds.
Frozen worlds
Some astronomers
believe there may be hundreds of small rocky bodies in the outer edges of our
own Solar System, and perhaps even a handful of frozen Earth-sized worlds.
Speaking
at the AAAS meeting, Nasa's Alan Stern said he thought only the tip of the iceberg
had been found in terms of planets within our own Solar System. More
than a thousand objects had already been discovered in the Kuiper belt alone,
he said, many rivalling the planet Pluto in size. "Our
old view, that the Solar System had nine planets will be supplanted by a view
that there are hundreds if not thousands of planets in our Solar System,"
he told BBC News. He
said many of these planets would be icy, some would be rocky, and there might
even be objects with the same mass as Earth. "It
could be that there are objects of Earth-mass in the Oort cloud (a band of debris
surrounding our planetary system) but they would be frozen at these distances,"
Dr Stern added. "They
would look like a frozen Earth." Goldilocks
zone Excitement
about finding other Earth-like planets is driven by the idea that some might contain
life or perhaps, centuries from now, allow human colonies to be set up on them.
The key to this
search, said Debra Fischer of San Francisco State University, California, was
the "Goldilocks zone". This
refers to an area of space in which a planet is "just the right distance"
from its parent star so that its surface is not-too-hot or not-too-cold to support
liquid water. "To
my mind there are two things we have to go after: we have to find the right mass
planet and it has to be at the right distance from the star," she said. The
AAAS meeting concludes on Monday. | 
