[meteorite-list] Major Breakthrough: First Photos of Planets Around Other Stars

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Thu, 13 Nov 2008 16:24:01 -0600
Message-ID: <000c01c945de$8875d650$274ae146_at_ATARIENGINE>

http://www.space.com/scienceastronomy/081113-hubble-exoplanet.html

Major Breakthrough: First Photos of Planets Around Other Stars
By Jeanna Bryner -- 13 November 2008


Astronomers have taken what they say are the first-ever
images of planets outside of our solar system, including
a visible-light snapshot of a single-planet system and an
infrared picture of a multiple-planet system.

Earth-like worlds might also exist in the three-planet system,
but if so they are too dim to photograph. The other newfound
planet orbits a star called Fomalhaut, which is visible without
the aid of a telescope. It is the 18th brightest star in the sky.

The massive worlds, each much heftier than Jupiter (at least
for the three-planet system), could change how astronomers
define the term "planet," one planet-hunter said.

Breakthrough technology
Until now, scientists have inferred the presence of planets
mainly by detecting an unseen world's gravitational tug on
its host star or waiting for the planet to transit in front of its
star and then detecting a dip in the star's light. While these
methods have helped to identify more than 300 extrasolar
planets to date, astronomers have struggled to actually
directly image and see such inferred planets.

The four photographed exoplanets are discussed in two
research papers published online today by the journal
Science.

"Every extrasolar planet detected so far has been a wobble
on a graph. These are the first pictures of an entire system,"
said Bruce Macintosh, an astrophysicist from Lawrence
Livermore National Laboratory in California, and part of
the team that photographed the multi-planet system in
infrared light. "We've been trying to image planets for
eight years with no luck and now we have pictures of
three planets at once."

Astronomers have claimed previously to have directly
imaged a planet, with at least two such objects, though
not everybody agreed the objects were planets. Instead,
they may be dim, failed stars known as brown dwarfs.

Multi-planet snapshots
Macintosh, lead researcher Christian Marois of the NRC
Herzberg Institute of Astrophysics in Canada, and colleagues
used the Gemini North telescope and W.M. Keck
Observatory on Hawaii's Mauna Kea to obtain infrared
images. Infrared radiation represents heat and, along with
everything from radio waves to visible light and X-rays,
is part of the electromagnetic spectrum.

The trio of worlds orbits a star named HR 8799, which is
about 130 light-years away in the constellation Pegasus and
about 1.5 times as massive as the sun. The planets are located
at distances from their star of 24, 38 and 68 astronomical
units (AU). (An astronomical unit equals the average Earth-sun
distance of 93 million miles, or about 150 million km.) Other
planet-finding techniques work out to only about 5 AU from a star.

The planet closest to the star weighs in at 10 times the mass of
Jupiter, followed by another 10 Jupiter-mass planet and then,
farther out, a world seven times the heft of Jupiter.

By astronomical standards, the planets are fresh out of the oven,
forming about 60 million years ago. That means the orbs are still
glowing from heat leftover from their formation. Earth, by
comparison, is about 4.5 billion years old.

The most distant planet orbits just inside a disk of dusty debris,
similar to that produced by the icy objects of the solar system's
Kuiper belt, which lies just beyond the orbit of Neptune.

The setup of this planetary system, along with its dusty belt,
suggests it is a scaled-up version of our solar system,
Macintosh said. That means other planets closer in to the
host star could be waiting for discovery.

"I think there's a very high probability that there are more
planets in the system that we can't detect yet," Macintosh
said. "One of the things that distinguishes this system from
most of the extrasolar planets that are already known is that
HR 8799 has its giant planets in the outer parts - like our
solar system does - and so has 'room' for smaller terrestrial
planets, far beyond our current ability to see, in the inner parts."

Hubble's discovery
University of California, Berkeley, astronomer Paul Kalas
led the team of astronomers who took the visible-light
snapshot of the single-planet system. The exoplanet has
been named Fomalhaut b, and is estimated to weigh no
more than three Jupiter masses.

The Hubble Space Telescope's Advanced Camera for
Surveys was used to make the image. The camera is
equipped with a coronagraph that blocks out the light
of the host star, allowing astronomers to view a much
fainter planet.

"It's kind of like if driving into the sun and suddenly
you flip down your visor, you can see the road easier,"
Kalas said during a telephone interview. In fact,
Fomalhaut b is 1 billion times fainter than its star. "
It's not easy to see. That kind of sensitivity has never
been seen before," he added.

Fomalhaut b is about 25 light-years from Earth. Photos
taken in 2004 and 2006 show the planet's movement over
a 21-month period and suggest the planet likely orbits its
star Fomalhaut every 872 years at a distance of 119 a
stronomical units (AU), or 11 billion miles (nearly 18 billion
km). That's about four times the distance between Neptune
and the sun.

Kalas suspected the planet's existence in 2004 (published in
2005) after Hubble images he had taken revealed a dusty belt
that had a sharp inner edge around Fomalhaut. The sculpted
nature of the ring suggested a planet in an elliptical orbit was
shaping the belt's inner edge. And it was.

"The gravity of Fomalhaut b is the key reason that the vast
dust belt surrounding Fomalhaut is cleanly sculpted into a
ring and offset from the star," Kalas said. "We predicted this
in 2005, and now we have the direct proof."

Kalas' team also suspects that the planet could be surrounded
by a ring system with the dimensions of Jupiter's early rings,
before the dust and debris coalesced into the four Galilean moons.

What's a planet?
The successful image results could change how planets are
defined, said Sara Seager, an astrophysicist at MIT who was
not involved in the discoveries.

Until now, mass has been one of the critical pieces of
information that could place an object into or out of the
planet club. Objects that are too massive, above about 13
Jupiter masses, are considered brown dwarfs. But now
formation could also be part of the formula. Both of the
new planetary systems revealed dusty disks and suggest
the planets must have formed similar to how planets in
our solar system and elsewhere are thought to have formed.

So, most astronomers would call the four objects planets,
although their masses are only inferred from the luminosities
seen in the images.

"Taken together, these discoveries are going to change
what we call a planet," Seager told SPACE.com. "Until
now people have been arguing about how big can an
object be and still be a planet."
Seager added, referring to the multi-planet system,
"People want to call the upper mass 12 Jupiter masses.
I think it's going to force us to reconsider what a planet is,
because even if they are more massive than what we
want to call a planet, they're in a disk." In addition,
she said, nobody has ever spotted three stars orbiting
a host star, as would have to be the case if you were
to call the three planets something other than planets.

Aiming for Earth-like planets
These recent direct images reveal giant, gaseous exoplanets
in a new light for the first time, revealing not the effects of
the planets but the planets themselves. The next goal would
be direct images of an Earth-like planet, the astronomers say.

"The discovery of the HR 8799 system is a crucial step on
the road to the ultimate detection of another Earth," Macintosh
said.

The problem is that terrestrial (Earth-like) planets are orders
of magnitude fainter than the giant Jupiter-like worlds, and
they are much closer in to their host stars. That means the
glare from the star would be overwhelming with today's
technology.

The pay-off could be big, though, as such rocky planets
could orbit within their habitable zones (where temperatures
would allow the existence of liquid water).

"There is plenty of empty space between Fomalhaut b and
the star for other planets to happily reside in stable orbits,"
Kalas said. "We'll probably have to wait for the James Webb
Space Telescope to give us a clear view of the region closer
to the star where a planet could host liquid water on the surface."
Received on Thu 13 Nov 2008 05:24:01 PM PST