Andrew Yee[_1_]
January 10th 07, 11:54 PM
Office of News and Information
University of Washington
Seattle, Washington
CONTACT:
Vince Stricherz, 206-543-2580
Jan. 9, 2007
Earth's strongest winds wouldn't even be a breeze on these planets
Earth's inhabitants are used to temperatures that vary, sometimes greatly,
between day and night. New measurements for three planets outside our solar
system indicate their temperatures remain fairly constant -- and blazing hot
-- from day to night, even though it is likely one side of each planet
always faces its sun and the other is in permanent darkness.
The reason apparently is supersonic winds, perhaps as strong as 9,000 miles
an hour, that constantly churn the planets' atmospheres and keep
temperatures on the dark side from plunging.
The planets, gas giants similar in size to Jupiter, were discovered in the
last decade orbiting stars about the same size as our sun and less than 150
light years from Earth. All of them orbit within about 5 million miles of
their stars, far less than Mercury's distance from our sun.
Astronomers have wondered whether planets orbiting so close to their stars
but with one side in constant daylight and the other permanently dark would
exhibit sharp temperature differences between the day side and the night
side. For the three planets in this study, the temperatures appear to be
constant, likely because of the strong winds that mix the atmosphere
planetwide, said Eric Agol, a University of Washington assistant professor
of astronomy and co-author of a poster presenting the findings today at the
American Astronomical Society national meeting in Seattle.
"We can't say for sure that we've ruled out significant day-night
temperature differences, but it seems unlikely there is a very big contrast
based on our measurements and what we know about these systems," said Agol,
who is lead scientist for a project using the Spitzer Space Telescope to
measure the temperature properties of extrasolar planets.
Agol and colleagues Nicolas Cowan, a UW astronomy doctoral student and lead
author of the poster, and David Charbonneau of the Harvard-Smithsonian
Center for Astrophysics measured infrared light from each of the planetary
systems at eight different positions in their orbits in late 2005. They
measured the thermal brightness of the systems when the planets' day sides
faced the Earth, when the night sides faced the Earth and at various phases
in between. They detected no infrared brightness variations in any of the
systems, suggesting there are not big differences in temperatures on the day
and night sides.
Instead the planets appear to have a fairly uniform temperature of about 925
degrees Celsius, or about 1700 degrees Fahrenheit.
"If heat from the parent star is carried to the dark side, then the overall
temperature would be lowered somewhat because the heat is being distributed
across the planet," Agol said. "Some theorists believe that supersonic winds
are responsible for recirculating the heat."
Measuring the planets' temperatures is a painstaking process because a
planet's radiation is drowned out by the light from its host star. Even when
a planet goes behind the parent star and disappears completely from view,
the decline in light from the entire system is almost imperceptible, on the
order of 0.25 percent, Agol said. Making the observations requires precise
calibration and light measurements.
The three planets are 51 Pegasi, about 50 light years from our sun,
HD179949b about 100 light years distant, and HD209458b about 147 light years
away. A light year is about 5.88 trillion miles. In 1995, 51 Pegasi became
the first planet orbiting another star to be discovered. Since then numerous
planets -- gas giants the mass of Jupiter or larger -- have been observed
from Earth. Most orbit very close to their stars. A common theory is that
they formed far away from their stars, perhaps in about the same position as
Jupiter is to our sun, and then migrated close to their stars. Their
distance makes it difficult to gather much direct data about the planets.
To date no Earth-sized planets have been reported orbiting other stars like
our sun.
Agol noted that the planets probably have the same side always facing the
star because they are so close to their parent stars. The effect is the same
as the Earth has on the moon, which has had its rotation slowed so much by
Earth's gravity that the same side always faces Earth.
"These planets are so close to their host stars that the tidal forces are
enormous, a few thousand times as strong as on Earth," he said. "The tides
are so strong and form a bulge that distorts the planet so much that the
orbit is slowed by the star's tug on the tidal bulge."
The Spitzer telescope is managed by NASA's Jet Propulsion Laboratory in
Pasadena, Calif., and its science operations are conducted at the California
Institute of Technology.
###
For more information, contact Agol at (206) 543-7106; or Cowan at (206)
251-0093.
See an animation at
http://sscws1.ipac.caltech.edu/Imagegallery/image.php?image_name=svg07-01
IMAGE CAPTION:
[http://uwnews.washington.edu/ni/photos.asp?articleID=29397&spid=29398]
An artist's conception shows a gas-giant planet orbiting very close to its
parent star, creating searingly hot conditions on the planet's surface. New
research suggests that for three such planets lying from 50 to 150
light-years from Earth, strong winds thousands of miles per hour mix the
atmosphere so that the temperature is relatively uniform from the
permanently light side to the permanently dark side. This illustration
represents an infrared view of a planetary system, in which brightness
indicates warmer temperatures. For example, the bright band around the
equator of the planet denotes warmer temperatures on both the dark and
sunlit sides. The planet's poles, shown in darker colors, would be cooler.
NASA/JPL-Caltech/R. Hurt
University of Washington
Seattle, Washington
CONTACT:
Vince Stricherz, 206-543-2580
Jan. 9, 2007
Earth's strongest winds wouldn't even be a breeze on these planets
Earth's inhabitants are used to temperatures that vary, sometimes greatly,
between day and night. New measurements for three planets outside our solar
system indicate their temperatures remain fairly constant -- and blazing hot
-- from day to night, even though it is likely one side of each planet
always faces its sun and the other is in permanent darkness.
The reason apparently is supersonic winds, perhaps as strong as 9,000 miles
an hour, that constantly churn the planets' atmospheres and keep
temperatures on the dark side from plunging.
The planets, gas giants similar in size to Jupiter, were discovered in the
last decade orbiting stars about the same size as our sun and less than 150
light years from Earth. All of them orbit within about 5 million miles of
their stars, far less than Mercury's distance from our sun.
Astronomers have wondered whether planets orbiting so close to their stars
but with one side in constant daylight and the other permanently dark would
exhibit sharp temperature differences between the day side and the night
side. For the three planets in this study, the temperatures appear to be
constant, likely because of the strong winds that mix the atmosphere
planetwide, said Eric Agol, a University of Washington assistant professor
of astronomy and co-author of a poster presenting the findings today at the
American Astronomical Society national meeting in Seattle.
"We can't say for sure that we've ruled out significant day-night
temperature differences, but it seems unlikely there is a very big contrast
based on our measurements and what we know about these systems," said Agol,
who is lead scientist for a project using the Spitzer Space Telescope to
measure the temperature properties of extrasolar planets.
Agol and colleagues Nicolas Cowan, a UW astronomy doctoral student and lead
author of the poster, and David Charbonneau of the Harvard-Smithsonian
Center for Astrophysics measured infrared light from each of the planetary
systems at eight different positions in their orbits in late 2005. They
measured the thermal brightness of the systems when the planets' day sides
faced the Earth, when the night sides faced the Earth and at various phases
in between. They detected no infrared brightness variations in any of the
systems, suggesting there are not big differences in temperatures on the day
and night sides.
Instead the planets appear to have a fairly uniform temperature of about 925
degrees Celsius, or about 1700 degrees Fahrenheit.
"If heat from the parent star is carried to the dark side, then the overall
temperature would be lowered somewhat because the heat is being distributed
across the planet," Agol said. "Some theorists believe that supersonic winds
are responsible for recirculating the heat."
Measuring the planets' temperatures is a painstaking process because a
planet's radiation is drowned out by the light from its host star. Even when
a planet goes behind the parent star and disappears completely from view,
the decline in light from the entire system is almost imperceptible, on the
order of 0.25 percent, Agol said. Making the observations requires precise
calibration and light measurements.
The three planets are 51 Pegasi, about 50 light years from our sun,
HD179949b about 100 light years distant, and HD209458b about 147 light years
away. A light year is about 5.88 trillion miles. In 1995, 51 Pegasi became
the first planet orbiting another star to be discovered. Since then numerous
planets -- gas giants the mass of Jupiter or larger -- have been observed
from Earth. Most orbit very close to their stars. A common theory is that
they formed far away from their stars, perhaps in about the same position as
Jupiter is to our sun, and then migrated close to their stars. Their
distance makes it difficult to gather much direct data about the planets.
To date no Earth-sized planets have been reported orbiting other stars like
our sun.
Agol noted that the planets probably have the same side always facing the
star because they are so close to their parent stars. The effect is the same
as the Earth has on the moon, which has had its rotation slowed so much by
Earth's gravity that the same side always faces Earth.
"These planets are so close to their host stars that the tidal forces are
enormous, a few thousand times as strong as on Earth," he said. "The tides
are so strong and form a bulge that distorts the planet so much that the
orbit is slowed by the star's tug on the tidal bulge."
The Spitzer telescope is managed by NASA's Jet Propulsion Laboratory in
Pasadena, Calif., and its science operations are conducted at the California
Institute of Technology.
###
For more information, contact Agol at (206) 543-7106; or Cowan at (206)
251-0093.
See an animation at
http://sscws1.ipac.caltech.edu/Imagegallery/image.php?image_name=svg07-01
IMAGE CAPTION:
[http://uwnews.washington.edu/ni/photos.asp?articleID=29397&spid=29398]
An artist's conception shows a gas-giant planet orbiting very close to its
parent star, creating searingly hot conditions on the planet's surface. New
research suggests that for three such planets lying from 50 to 150
light-years from Earth, strong winds thousands of miles per hour mix the
atmosphere so that the temperature is relatively uniform from the
permanently light side to the permanently dark side. This illustration
represents an infrared view of a planetary system, in which brightness
indicates warmer temperatures. For example, the bright band around the
equator of the planet denotes warmer temperatures on both the dark and
sunlit sides. The planet's poles, shown in darker colors, would be cooler.
NASA/JPL-Caltech/R. Hurt