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100 Billion Alien Planets

From: "Edward Gehrman" <egehrman.nul>
Date: Thu, 3 Jan 2013 14:46:08 -0800
Archived: Fri, 04 Jan 2013 09:48:56 -0500
Subject: 100 Billion Alien Planets

Source: msnbc.msn.com



100 Billion Alien Planets

Our Milky Way galaxy is home to at least 100 billion alien
planets, and possibly many more, a new study suggests.

"It's a staggering number, if you think about it", lead author
Jonathan Swift, of Caltech in Pasadena, said in a statement.
"Basically there's one of these planets per star."

Swift and his colleagues arrived at their estimate after
studying a five-planet system called Kepler-32, which lies about
915 light-years from Earth. The five worlds were detected by
NASA's Kepler Space Telescope, which flags the tiny brightness
dips caused when exoplanets cross their star's face from the
instrument's perspective.

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100 billion alien planets fill our galaxy: study Never-before-
seen stage of planet birth Need a launch pad? NASA sells off
shuttle facilities ..The Kepler-32 planets orbit an M dwarf, a
type of star that is smaller and cooler than our sun. M dwarfs
are the most common star in the Milky Way, accouting for about
75 percent of the galaxy's 100 billion or so stars, researchers

Further, the five Kepler-32 worlds are similar in size to Earth
and orbit quite close to their parent star, making them typical
of the planets Kepler has spotted around other M dwarfs. So the
Kepler-32 system should be representative of many of the
galaxy's planets, scientists said.

"I usually try not to call things 'Rosetta stones,' but this is
as close to a Rosetta stone as anything I've seen", said co-
author John Johnson, also of Caltech. "It's like unlocking a
language that we're trying to understand =E2=80=94 the language of
planet formation."

Kepler can detect planetary systems only if they're oriented
edge-on to the telescope; otherwise, the instrument won't
observe any star-dimming planetary transits. So the researchers
calculated the odds that an M-dwarf system in the Milky Way
would have this orientation, then combined that with the number
of such systems Kepler is able to detect to come up with their
estimate of 100 billion exoplanets.

The team considered only planets orbiting other types of stars.
So the galaxy may actually harbor many more planets than the
conservative estimate implies =E2=80=94 perhaps 200 billion, or about
two per star, Swift said.

The new analysis confirms three of the five Kepler-32 planets
(the other two had been confirmed previously). The Kepler-32
worlds have diameters ranging from 0.8 to 2.7 times that of
Earth, and all of them orbit within 10 million miles of their
star. For comparison, Earth circles the sun at an average
distance of 93 million miles.

Because the Kepler-32 star is smaller and less luminous than our
sun, the five planets are likely not as heat-blasted as their
tight orbits might imply. In fact, the outermost planet in the
system appears to lie in the habitable zone, a range of
distances that could support the existence of liquid water on a
world's system.

The new analysis also suggests that the Kepler-32 planets
originally formed farther away from the star and then migrated
closer in over time, researchers said.

Several pieces of evidence point toward this conclusion. For
example, the team estimated that the five Kepler-32 worlds
coalesced from material be squeezed into the small area
circumscribed by the planets' current orbits, researchers said.

"You look in detail at the architecture of this very special
planetary system, and you're forced into saying these planets
formed farther out and moved in", Johnson said.

The new study was published Jan. 2 in The Astrophysical Journal.

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