Bonanza of new solar systems found
Pastor Dale Morgan
Bonanza of new solar systems found*
* From correspondents in London
* May 29, 2007
PLANET-SEEKERS who have spotted 28 new planets orbiting other stars in
the past year say earth's solar system is far from unique and there
could be billions of habitable planets.
The most recent planet discoveries bring the number of known exoplanets
- planets outside our solar system - to 236, the researchers told a
meeting of the American Astronomical Society in Honolulu today.
"We are beginning to see that our home is not a rarity in the universe,"
said Geoffrey Marcy, a professor of astronomy at the University of
California Berkeley, who led the team.
"We are easily able to detect giant planets like Jupiter and Saturn
around other stars. Most orbit far from the star like our own Jupiter
and Saturn orbit from the sun," Prof Marcy said. "It's a common
structure among planetary systems."
New techniques allow astronomers to detect planets that are not enormous
although earth-sized objects cannot yet be seen, said the researchers,
who have posted details of their findings on the internet at
http://exoplanets.org.
Four of the systems also have multiple planets, like earth's own with
its sun, eight planets (Pluto was demoted from planet status) and
smaller orbiting objects.
"We are finding that most stars have not just one planet but when we
find one there is a second or a third or a fourth," Prof Marcy said.
"The ... attribute which really has us the most excited is this new
planet which we found three years ago," Prof Marcy said.
The Neptune-like planet orbiting the star Gliese 436 has intrigued
scientists because it appears to be covered with water - albeit
rock-hard, hot water in a most un-earthlike chemical state because of
the intense pressures on the planet.
Earlier this month, Swiss and Belgian researchers imaged the star as
this planet crossed between it and the earth. The tiny change in the
star's light gave them the planet's diameter and density.
"From the density of two grams per cubic centimetre - twice that of
water - it must be 50 per cent rock and about 50 per cent water, with
perhaps small amounts of hydrogen and helium," Prof Marcy said.
"Now we are very sure it has a rocky core and this giant thick envelope
of water," he said. "This is why we are jumping out of our clothes. It
is the first time we have determined the structure of one of these
extrasolar planets. It is rocky like earth but it has a lot of water,
which is the essential ingredient for life."
This is almost certainly happening over and over again, Prof Marcy said.
Scientists had theorised this for decades but now the hard evidence is
starting to pour in.
"Our Milky Way galaxy has 200 billion stars. I would estimate that 10
per cent of them, perhaps, have planets that are habitable," Prof Marcy
said.
"There are hundreds of billions of galaxies, all of which are more or
less like our Milky Way Galaxy, which is tens of billions of planets
like our own."
There is one unusual property to our solar system: the nearly circular
orbits of the planets, which gives a consistent dose of radiation from
the Sun.
Other solar systems seen so far are not usually like this.
"Most of the planets are not in circular orbits around the host star but
in elongated ones called elliptical orbits," Prof Marcy said.
"We enjoy nearly constant temperatures throughout the year," he said.
"If the earth got too close to the Sun, the earth would heat up, the
water would boil off and that would be bad."
Too far, and it would freeze.
"An elongated orbit could not sustain life," Prof Marcy said.