Milky Way's Planets exceeds 100 billion by TechLegacy


									         Milky Way's Planets exceeds 100 billion

Planets orbiting other stars may be a dime a dozen in the Milky Way, but
cheap hardly means boring.

From a new pair of planets like Tatooine of "Star Wars" fame, each with its
own pair of suns, to a trio of small rocky planets zipping around a red-dwarf
star, the cosmos presents a breathtaking plethora of planetary systems. A
new estimate suggests that the Milky Way's population of planets exceeds
100 billion.

These are among the planet-hunting highlights from this week's winter
meeting of the American Astronomical Society in Austin, Texas.

The ultimate goal is to find Earth-size planets orbiting in a star's habitable
zone -- the place where a planet, with the right atmosphere, can host water
as liquid, ice, and gas on its surface.

While no Earth-scale planets in this Goldilocks zone have yet appeared,
"these latest observations make it extremely likely that Earth-scale planets
in the habitable zone exist, probably in large numbers," says Philip Armitage,
an astrophysicist at the University of Colorado at Boulder.

Three results highlighted at the meeting speak volumes about how far
researchers have come in the 16 years since astronomers detected the first
exoplanet orbiting a sun-like star.

Between 600 and 700 extrasolar planets have been confirmed, depending on
which online catalog keeps tally. NASA's Kepler mission has accounted for 35
of these, with another 2,326 "planet candidates" awaiting evaluation.

Yet this number pales beside an estimate offered by a research team that
presented its results at the meeting and in the Jan. 12 issue of the journal

Based on a six-year survey of stars using a technique known as gravitational
lensing, in which an intervening star's gravity magnifies the light from a star
far behind it, the team estimates that 17 percent of all stars in the galaxy
host a planet of Jupiter's mass or greater. About 52 percent of stars host
Neptune-class planets, while 62 percent host so-called super Earths.

Given the trend toward higher numbers of lower-mass planets, "statistically,
every star in the galaxy should have at least one planet, and probably
more," according to Kailash Sahu, a researcher a the Hubble Space
Telescope Institute in Baltimore and a member of the research team.

What might some of those planetary systems look like? How about Tatooine?
Data from NASA's Kepler mission have revealed two new systems in which a
planet is orbiting a binary star.

Kepler scientists unveiled the first such system in September. But it was
unclear then how many such systems might lurk in the Milky Way.

With two more in the can, "we know that it is possible, if not probable, that
there are at least millions in the galaxy," William Welsh, a researcher at San
Diego State University and a member of the Kepler team, said in a
statement. The results also appear in the Jan. 12 issue of Nature.

Both planets are about Saturn's size. One of the two, Kepler 34-b, orbits its
pair of stars once every 289 days. Meanwhile, the stars eclipse one another
every 28 days. Kepler 35-b's stars are a bit smaller, eclipsing each other
every 21 days. The planet orbits its twin suns every 131 days.

Such systems would keep organisms on their evolutionary toes. Seasons
would repeat several times a year. And the planets would be subject to
swings from hot to cold – a function of ever-changing distances as their
gravitational fields interact.

The potential effects of these changes on an organism's evolution "is a
fascinating topic that we are just beginning to explore," Dr. Welsh notes.

Another team reported discovering the smallest planets yet confirmed. One
is roughly the size of Mars. The other two are smaller than Venus. All three
orbit a dim red-dwarf star some 130 light-years from Earth. The star is only
about 70 percent larger than Jupiter.

The planets are orbiting too close to the star to fall within its habitable zone.
But the find is intriguing, nonetheless.

Red dwarfs represent some 80 percent of all the stars in the galaxy, says
John Johnson, an astronomer at the California Institute of Technology and a
member of the team reporting the discovery. If the discovered planets are
any indication, he notes, red dwarf stars throughout the galaxy could be
"swarming with little habitable planets."


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