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Observations from NASA's Spitzer Space
Telescope have led to the first temperature map of a super-Earth planet -- a
rocky planet nearly two times as big as ours. The map reveals extreme
temperature swings from one side of the planet to the other, and hints that a
possible reason for this is the presence of lava flows.
"Our view of this planet keeps
evolving," said Brice Olivier Demory of the University of Cambridge,
England, lead author of a new report appearing in the March 30 issue of the
journal Nature. "The latest findings tell us the planet has hot nights
and significantly hotter days. This indicates the planet inefficiently
transports heat around the planet. We propose this could be explained by an
atmosphere that would exist only on the day side of the planet, or by lava
flows at the planet surface."
The toasty super-Earth 55 Cancri e is
relatively close to Earth at 40 light-years away. It orbits very close to its
star, whipping around it every 18 hours. Because of the planet's proximity to
the star, it is tidally locked by gravity just as our moon is to Earth. That
means one side of 55 Cancri, referred to as the day side, is always cooking
under the intense heat of its star, while the night side remains in the dark
and is much cooler.
"Spitzer observed the phases of 55
Cancri e, similar to the phases of the moon as seen from the Earth. We were
able to observe the first, last quarters, new and full phases of this small
exoplanet," said Demory. "In return, these observations helped us
build a map of the planet. This map informs us which regions are hot on the
planet."
Spitzer stared at the planet with its
infrared vision for a total of 80 hours, watching it orbit all the way around
its star multiple times. These data allowed scientists to map temperature
changes across the entire planet. To their surprise, they found a dramatic
temperature difference of 2,340 degrees Fahrenheit (1,300 Kelvin) from one
side of the planet to the other. The hottest side is nearly 4,400 degrees
Fahrenheit (2,700 Kelvin), and the coolest is 2,060 degrees Fahrenheit (1,400
Kelvin).
The fact Spitzer found the night side to be
significantly colder than the day side means heat is not being distributed
around the planet very well. The data argues against the notion that a thick
atmosphere and winds are moving heat around the planet as previously thought.
Instead, the findings suggest a planet devoid of a massive atmosphere, and
possibly hint at a lava world where the lava would become hardened on the
night side and unable to transport heat.
"The day side could possibly have
rivers of lava and big pools of extremely hot magma, but we think the night
side would have solidified lava flows like those found in Hawaii," said
Michael Gillon, University of Liège, Belgium.
The Spitzer data also revealed the hottest
spot on the planet has shifted over a bit from where it was expected to be:
directly under the blazing star. This shift either indicates some degree of
heat recirculation confined to the day side, or points to surface features
with extremely high temperatures, such as lava flows.
Additional observations, including from
NASA's upcoming James Webb Space Telescope,
will help to confirm the true nature of 55 Cancri e.
The new Spitzer observations of 55 Cancri
are more detailed thanks to the telescope’s increased
sensitivity to exoplanets. Over the past several years, scientists and
engineers have figured out new ways to enhance
Spitzer’s ability to measure changes in the brightness of exoplanet
systems. One method involves precisely characterizing Spitzer’s detectors,
specifically measuring “the sweet spot” -- a single pixel on the detector --
which was determined to be optimal for exoplanet studies.
“By understanding the characteristics of
the instrument -- and using novel calibration techniques of a small region of
a single pixel -- we are attempting to eke out every bit of science possible
from a detector that was not designed for this type of high-precision
observation,” said Jessica Krick of NASA’s Spitzer Space Science Center, at
the California Institute of Technology in Pasadena.
NASA's Jet Propulsion Laboratory (JPL) in
Pasadena, California, manages the Spitzer Space Telescope mission for NASA's
Science Mission Directorate, Washington. Science operations are conducted at
the Spitzer Science Center. Spacecraft operations are based at Lockheed
Martin Space Systems Company, Littleton, Colorado. Data are archived at
the Infrared Science Archive housed at the Infrared Processing and Analysis
Center at Caltech. Caltech manages JPL for NASA.
For more information about Spitzer, visit:
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