Global Temperature Map of WASP-43b
This is a temperature map of exoplanet WASP-43b. The gas giant planet
orbits very close to its parent star with a period of 19.5 hours.
Because the planet keeps one side facing its star, there are huge
temperature extremes between the day and night sides. The white-colored
region on the daytime side is 2,800 degrees Fahrenheit. The
nighttime-side temperatures drop below 1,000 degrees Fahrenheit. This
steep gradient is in stark contrast to the predominantly uniform
temperatures of the solar system's giant planets. Infrared observations
with the Hubble Space Telescope measured how temperatures change with
both altitude and longitude on the planet. Credit: NASA, ESA, and K. Stevenson, L. Kreidberg, and J. Bean (University of Chicago)
Artist's Illustration of WASP-43b (Annotated)
Credit: NASA, ESA, K. Stevenson, L. Kreidberg, and J. Bean (University of Chicago), and Z. Levay (STScI)
A team of scientists using NASA's Hubble Space Telescope have made
the most detailed global map yet of the glow from a planet orbiting
another star, revealing secrets of air temperatures and water.
The map provides information about temperatures at different layers
of the world's atmosphere and traces the amount and distribution of
water vapor on the planet. The findings have ramifications for the
understanding of atmospheric dynamics and the formation of giant
planets like Jupiter.
"These measurements have opened the door for a new kind of
comparative planetology," said team leader Jacob Bean of the University
of Chicago.
"Our observations are the first of their kind in terms of providing a
two-dimensional map of the planet's thermal structure that can be used
to constrain atmospheric circulation and dynamical models for hot
exoplanets," said team member Kevin Stevenson of the University of
Chicago.
The Hubble observations show that the planet, called WASP-43b, is no
place to call home. It's a world of extremes, where seething winds howl
at the speed of sound from a 3,000-degree-Fahrenheit day side that is
hot enough to melt steel to a pitch-black night side that sees
temperatures plunge below a relatively cool 1,000 degrees Fahrenheit.
As a hot ball of predominantly hydrogen gas, there are no surface
features on the planet, such as oceans or continents that can be used
to track its rotation. Only the severe temperature difference between
the day and night sides can be used by a remote observer to mark the
passage of a day on this world.
WASP-43b is located 260 light-years away and was first discovered in
2011. WASP-43b is too distant to be photographed, but because its orbit
is observed edge-on to Earth, astronomers detected it by observing
regular dips in the light of its parent star as the planet passes in
front of it.
The planet is about the same size as Jupiter, but is nearly twice as
massive. The planet is so close to its orange dwarf host star that it
completes an orbit in just 19 hours. The planet is also gravitationally
locked so that it keeps one hemisphere facing the star, just as our
moon keeps one face toward Earth.
The scientists combined two previous methods of analyzing exoplanets
and put them together in one for the first time to study the atmosphere
of WASP-43b. Spectroscopy allowed them to determine the water
abundance and temperature structure of the atmosphere. By observing the
planet's rotation, the astronomers were also able to measure the water
abundances and temperatures at different longitudes.
Because there's no planet with these tortured conditions in our solar
system, characterizing the atmosphere of such a bizarre world provides
a unique laboratory for better understanding planet formation and
planetary physics. "The planet is so hot that all the water in its
atmosphere is vaporized, rather than condensed into icy clouds like on
Jupiter," said team member Laura Kreidberg of the University of Chicago.
"Water is thought to play an important role in the formation of giant
planets, since comet-like bodies bombard young planets, delivering
most of the water and other molecules that we can observe," said
Jonathan Fortney, a member of the team from the University of
California, Santa Cruz.
However, the water abundances in the giant planets of our solar
system are poorly known because water is locked away as ice that has
precipitated out of their upper atmospheres. But on "hot Jupiters" —
that is, large planets like Jupiter that have high surface temperatures
because they orbit very close to their stars — water is in a vapor
that can be readily traced. Kreidberg also emphasized that the team
didn't simply detect water in the atmosphere of WASP-43b, but also
precisely measured how much of it there is and how it is distributed
with longitude.
In order to understand how giant planets form, astronomers want to
know how enriched they are in different elements. The team found that
WASP-43b has about the same amount of water as we would expect for an
object with the same chemical composition as the Sun. Kreidberg said
that this tells something fundamental about how the planet formed.
For the first time astronomers were able to observe three complete
rotations of a planet, which occurred during a span of four days. This
was essential to making such a precise measurement according to
Jean-Michel Désert of the University of Colorado, Boulder.
The team next aims to make water-abundance measurements for different
planets to explore their chemical abundances. Hubble's planned
successor, the James Webb Space Telescope, will be able to not only
measure water abundances, but also the abundances of carbon monoxide,
carbon dioxide, ammonia, and methane, depending on the planet's
temperature.
The results are presented in two new papers, one published online in
Science Express on Oct. 9, and the other published in The Astrophysical
Journal Letters on Sept. 12.
Contact:
Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4514
villard@stsci.edu
Source: HubbleSite
