"The sun and Earth is
not a rarity," said Geoffrey Marcy, professor of astronomy at
UC-Berkeley, estimating that there may be at least 20 million to 30
million solar systems within the Milky Way galaxy. "A family of planets
orbiting a single star is a very common occurrence."
If that is the case, then the likelihood of other Earth-like planets becomes greater.
The newly found planets, reported Monday at the semiannual meeting of
the American Astronomical Society in Honolulu, increase to 236 the
number of known planets outside our solar system, called "exoplanets."
Several of these exoplanets are members of multiple-planet systems.
The discovery of these planets suggests that some other solar systems
may share some of the same features as ours. Like Venus, Earth and
Mars, some planets have rocky interiors and watery surfaces. Close to
the star, those planets are warm. Yet others, like Jupiter, Saturn and
Uranus, are cold gas giants, distant from the star.
"It is heart-warming that other planetary systems have an architecture
that is very reminiscent of our solar system - multiple planets, some
with rocky cores and watery envelopes," Marcy said.
Indirect evidence
Scientists can't see a planet directly; rather, they infer its
existence from the wobbling and dimming of a star as the planet passes
by. But this information can offer enough mathematical detail to create
an accurate picture.
For example, the team also described new details about one specific exoplanet, discovered two years ago.
This planet, which
circles the star Gliese 436, is thought to be half rock, half water.
Its rocky core is surrounded by an amount of water compressed into a
solid form at high pressures and low temperatures. It makes a short,
2.6-day orbit around Gliese 436. Based on its radius and density,
scientists calculate that it has the mass of 22 Earths, making it
slightly larger than Neptune.
"The profound conclusion is, here we've found yet another type of
planet that is already represented in our solar system," Marcy said.
The Planet Search team is headed by Marcy; Paul Butler of the Carnegie
Institution of Washington; Debra Fischer of San Francisco State
University; and Steve Vogt, professor of astronomy at UC-Santa Cruz.
They worked with an Anglo-Australian Planet Search team.
The results were reported at the meeting by UC-Berkeley postdoctoral
fellow Jason T. Wright and John Asher Johnson, who also has a doctorate.
