Exoplanet Measured with Remarkable Precision
 
August 18, 2014: Barely 30 years ago, the only planets astronomers had
found were located right here in our own solar system.  The Milky Way is
chock-full of stars, millions of them similar to our own sun.  Yet the
tally of known worlds in other star systems was exactly zero.
 
What a difference a few decades can make.
 
As 2014 unfolds, astronomers have not only found more than a thousand
"exoplanets" circling distant suns, but also they're beginning to
make precise measurements of them.  The old void of ignorance about
exoplanets is now being filled with data precise to the second decimal
place.
 
http://www.youtube.com/watch?v=lA6MJkHJXVk&feature=youtu.be
 
A new ScienceCast video examines the extraordinary precision which with
researchers are beginning to measure exoplanets.  Play it
 
A team led by Sarah Ballard, a NASA Carl Sagan Fellow at the University of
Washington in Seattle, recently measured the diameter of a "super
Earth" to within an accuracy of 148 miles total or about 1 percent -
remarkable accuracy for an exoplanet located about 300 light years from
Earth.
 
"It does indeed seem amazing," says Ballard. "The landscape
of exoplanet research has changed to an almost unrecognizable degree since
I started graduate school in 2007."
 
To size up the planet, named "Kepler 93 b," Ballard used data
from NASA's Kepler and Spitzer Space Telescopes.
 
First, Kepler discovered the planet. As seen from Earth, Kepler 93 b passes
directly in front of its parent star, causing the starlight to dim during
the transit. That dimming, which occurs once per orbit, is what allowed
Kepler mission scientists to find the planet in the first place.
 
Next, both Spitzer and Kepler recorded multiple transits at visible and
infrared wavelengths. Data from the observatories agreed: Kepler 93 b was
really a planet and not some artefact of stellar variability. Ballard then
knew that by looking carefully at the light curve she could calculate the
size of the planet relative to the star.
 
At that point, the only missing piece was the diameter of the star itself.
 
http://kepler.nasa.gov/
 
Click to visit the Kepler home page"The precision with which we
measured the size of the planet is linked directly to our measurement of
the star," says Ballard.  "And we measured the star using a
technique called asteroseismology."
 
Most people have heard of "seismology," the study of seismic
waves moving through the Earth.  "We can learn a lot about the
structure of our planet by studying seismic waves," she says.
 
Asteroseismology is the same thing, except for stars: The outer layers of
stars boil like water on top of a hot stove.  Those convective motions
create seismic waves that bounce around inside the core, causing the star
to ring like an enormous bell.  Kepler can detect that "ringing,"
which reveals itself as fluctuations in a star's brightness.
 
Ballard's colleague, University of Birmingham professor Bill Chaplin led
the asteroseismic analysis for Kepler-93 b. "By analyzing the seismic
modes of the star, he was able to deduce its radius and mass to an accuracy
of a percent," she says.
 
The new measurements confirm that Kepler-93 b is a "super-Earth"
sized exoplanet, with a diameter about one-and-a-half times the size of our
planet. Previous measurements by the Keck Observatory in Hawaii had put
Kepler-93 b's mass at about 3.8 times that of Earth. The density of
Kepler-93 b, derived from its mass and newly obtained radius, suggests the
planet is very likely made of iron and rock, like Earth itself.
 
Although super-Earths are common in the galaxy, none exist in our solar
system. That makes them tricky to study.  Ballard's team has shown,
however, that it is possible to learn a lot about an exoplanet even when it
is very far away.
 
Credits:
Author: Dr. Tony Phillips | Production editor: Dr. Tony Phillips | Credit:
Science{at}NASA
 
 
Regards,
 
Roger

--- D'Bridge 3.99