Using the powerful eye of NASA's Hubble Space Telescope, two teams of scientists have found faint signatures of water in the atmospheres of five distant planets.
The presence of atmospheric water was reported previously on a few exoplanets orbiting stars beyond our solar system, but this is the first study to conclusively measure and compare the profiles and intensities of these signatures on multiple worlds.
The presence of atmospheric water was reported previously on a few exoplanets orbiting stars beyond our solar system, but this is the first study to conclusively measure and compare the profiles and intensities of these signatures on multiple worlds.
Although
exoplanets are too far away to be imaged, detailed studies of their
size, composition and atmospheric makeup are possible. This video
explains how researchers investigate those characteristics.Image Credit: NASA Goddard/ESA/Hubble. Download this video in HD formats from NASA Goddard's Scientific Visualization Studio
NASA
scientists found faint signatures of water in the atmospheres of five
distant planets orbiting three different stars. All five planets appear
to be hazy. This illustration shows a star's light illuminating the
atmosphere of a planet.Image Credit: NASA's Goddard Space Flight Center. Large image
The five planets -- WASP-17b, HD209458b, WASP-12b, WASP-19b and XO-1b --
orbit nearby stars. The strengths of their water signatures varied.
WASP-17b, a planet with an especially puffed-up atmosphere, and
HD209458b had the strongest signals. The signatures for the other three
planets, WASP-12b, WASP-19b and XO-1b, also are consistent with water.
"We're very confident that we see a water signature for multiple
planets," said Avi Mandell, a planetary scientist at NASA's Goddard
Space Flight Center in Greenbelt, Md., and lead author of an
Astrophysical Journal paper, published today, describing the findings
for WASP-12b, WASP-17b and WASP-19b. "This work really opens the door
for comparing how much water is present in atmospheres on different
kinds of exoplanets, for example hotter versus cooler ones."
The
studies were part of a census of exoplanet atmospheres led by L. Drake
Deming of the University of Maryland in College Park. Both teams used
Hubble's Wide Field Camera 3 to explore the details of absorption of
light through the planets' atmospheres. The observations were made in a
range of infrared wavelengths where the water signature, if present,
would appear. The teams compared the shapes and intensities of the
absorption profiles, and the consistency of the signatures gave them
confidence they saw water. The observations demonstrate Hubble's
continuing exemplary performance in exoplanet research.
"To actually detect the atmosphere of an exoplanet is extraordinarily
difficult. But we were able to pull out a very clear signal, and it is
water," said Deming, whose team reported results for HD209458b and XO-1b
in a Sept. 10 paper in the same journal. Deming's team employed a new
technique with longer exposure times, which increased the sensitivity of
their measurements.
To
determine what’s in the atmosphere of an exoplanet, astronomers watch
the planet pass in front of its host star and look at which wavelengths
of light are transmitted and which are partially absorbed.Image Credit: NASA's Goddard Space Flight Center. Large image
The water signals were all less pronounced than expected, and the
scientists suspect this is because a layer of haze or dust blankets each
of the five planets. This haze can reduce the intensity of all signals
from the atmosphere in the same way fog can make colors in a photograph
appear muted. At the same time, haze alters the profiles of water
signals and other important molecules in a distinctive way.
The five planets are hot Jupiters, massive worlds that orbit close to
their host stars. The researchers were initially surprised that all
five appeared to be hazy. But Deming and Mandell noted that other
researchers are finding evidence of haze around exoplanets.
"These studies, combined with other Hubble observations, are showing
us that there are a surprisingly large number of systems for which the
signal of water is either attenuated or completely absent," said Heather
Knutson of the California Institute of Technology, a co-author on
Deming's paper. "This suggests that cloudy or hazy atmospheres may in
fact be rather common for hot Jupiters."
Hubble's high-performance Wide Field Camera 3 is one of few capable
of peering into the atmospheres of exoplanets many trillions of miles
away. These exceptionally challenging studies can be done only if the
planets are spotted while they are passing in front of their stars.
Researchers can identify the gases in a planet's atmosphere by
determining which wavelengths of the star's light are transmitted and
which are partially absorbed.
Source: Hubble Space Telescope
