[meteorite-list] So many parent bodies, so few samples

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Mon, 11 Jun 2007 15:52:49 -0400
Message-ID: <iu9r63tvtistji30r8jlkr9n7neujmksh0_at_4ax.com>

http://www.space.com/scienceastronomy/070611_mm_planet_floodgates.html

Trickle of Planet Discoveries Becomes a Flood
By Jeanna Bryner
Staff Writer
posted: 11 June 2007
07:10 am ET

Alien worlds, once hidden from knowledge, are now being discovered in droves,
stunning astronomers with their unique features and sheer numbers. The
discoveries are so common that more and more don't even get reported outside
scientific circles.


Take the announcement at the end of May of a massive planet, dubbed TrES-3, that
zips around its star in an amazingly rapid 31 hours, giving the planet a 1.3-day
year. Astronomers issued a press release, but you might not have heard about it
because the discovery was so overshadowed by other planet announcements and
barely received news coverage.


"It's pretty routine now," said Alan Boss, a planet formation theorist at the
Carnegie Institution of Washington. "Most planets that are found are not deemed
worthy of a press release because they are sort of becoming 'one more planet.'"


The total is now more than 200 extrasolar planets confirmed. And this is the tip
of the iceberg in planet finds. Astronomers have more tools than ever, and
technology is so advanced that planet discovery has become almost mundane.


The regularity of planet finds, luckily, is buffered by the wild variety in the
discoveries themselves, including the following contrasts: nascent worlds of
just a million years versus those that are billions of years old; hot gas giants
and icy Neptune-like orbs; planets that whip around their parent stars with
cosmic speed and others that seem to creep at a slug's pace; and planets
orbiting double-stars, red-dwarf stars and even so-called failed stars.


Transit technique


Astronomers spotted TrES-3 as part of the Trans-atlantic Exoplanet Survey while
looking for transiting planets, or those that pass directly in front of their
home star with respect to Earth. It was detected with a network of telescopes in
Arizona, California, and the Canary Islands. When TrES-3 coasted in front of its
home star, the telescopes picked up a slight dimming of the star's light, by
about 2.5 percent. The scientists used the dimming to estimate the planet's
mass, size and other properties.


It is located 800 light-years away in the constellation Hercules about 10
degrees west of Vega, one of the brightest stars in the summer skies of the
northern hemisphere.


"It is also a very massive planet-about twice the mass of the solar system's
biggest planet, Jupiter-and is one of the planets with the shortest known
periods," said a co-discoverer of TrES-3 Georgi Mandushev of the Lowell
Observatory in Arizona.


The giant orb orbits so close to its parent star, about 50 times closer than
Earth is to the Sun, the astronomers estimate its temperature soars to about
1,500 degrees Kelvin.


Stellar wobbles


While the "transit method" provides astronomers with the best indirect
information about an exoplanet, so far only about 20 transiting planets have
been spotted.


That's why the most successful (based on the number of planet finds) teams have
relied on the so-called wobble method, or radio-velocity technique.


"The radial-velocity teams are the most successful," Boss told SPACE.com. "They
are a victim of their own success. They are able to get more and more telescope
time, because they can prove to the assignment committees that give out the time
that 'if you give us so many more nights we can probably find you so many more
planets,'" Boss said.


He added, "The key bottleneck for finding more planets is simply more time on a
telescope."


The firsts and superlatives


In addition to finding new worlds, the burgeoning field has achieved many
firsts.


In 2001, a team led by David Charbonneau of the Harvard-Smithsonian Center for
Astrophysics used the Hubble Space Telescope and NASA's infrared-detecting
Spitzer Space Telescope to detect for the first time the atmosphere of an
extrasolar hot Jupiter called HD 189733b.


Another hot Jupiter, Upsilon Andromeda b, revealed for the first time an
exoplanet with a temperature variation across its surface: One side has
temperatures rivaling those found deep in a volcano while the other face could
plunge below freezing.


Superlatives abound as well, with discoveries gaining fame as the windiest,
tiniest, most massive and fastest orbiter.


Shortest orbital period in catalog: HD 41004 B b completes a full orbit in 1.328
days.

Longest orbit: HD 154345 b takes 13,100 days to orbit its parent star.

Lightest planet: Gliese 581 C weighs just five Earth masses.

Planet organizer


In an effort to keep track of the rapidly increasing list of exoplanets, a group
of astronomers published a catalog of nearby exoplanets within 652 light-years
of Earth in a 2006 issue of the Astrophysical Journal, though they realize
updates will be a must on a routine basis.


"Without question, the catalog presented here will become out of date before it
is printed," the researchers say in the published report of the catalog.


But with such a huge sample of relatively nearby planets, theorists now have the
chance to test out their theories in the "real world."


"This whole business of extrasolar planets has been a real boon for theorists
because so far they had only one planetary system to study-and that was ours,"
Mandushev said in a telephone interview.


For instance, when does an object stop being a planet and become a star, a
threshold that theory places at 10 to 15 Jupiter masses and beyond which an
object can ignite hydrogen fusion to power a stellar glow'


The real goal


The ultimate goal, say many planet hunters, is to find Earth-like planets, or
those with similar masses, orbits and rocky compositions to Earth. And beyond
finding the physical Earth-like attributes would be to find life. So far no
"Earths" have been identified, though observatories are coming online with the
sensitivity to detect small objects that orbit far from their host stars, as our
planet does.


"The hunt is still on for rocky, Earth-like planets," said Jason Wright, an
astronomer at the University of California, Berkeley, who was part of the team
compiling the exoplanet catalog.


And astronomers have identified the first Earth-like planet that could support
liquid water and harbor life. The "super Earth," Gliese 581 C, weighs about five
Earth masses and is either a rocky planet or one covered entirely by oceans,
astronomers speculate.


Multi-planet systems are also a goal. So far about 25 multi-planet systems have
been identified with two such systems supporting four planets.


"We haven't found a clone of the solar system yet," Boss said. "But that's only
ruling out maybe 10 percent of the stars. The other 90 percent could have exact
solar system analogs and we wouldn't know it because we haven't been able to
take data for long enough to actually find their planetary systems."
Received on Mon 11 Jun 2007 03:52:49 PM PDT