- Webb’s enormous mirror, precise instruments
joined forces to capture most detailed measurements of starlight filtering
through atmosphere of a planet outside our solar system to date
- The spectrum of light – which contains
information about the makeup of a planetary atmosphere 1,150 light-years
away – reveals distinct signature of water
- The strength of the signal that Webb detected
hints at the significant role the telescope will play in the search for
potentially habitable planets in coming years
- Webb’s powerful new view also shows evidence of
haze and clouds that previous studies of this planet did not detect
NASA’s James Webb Space Telescope has captured the distinct signature of
water, along with evidence for clouds and haze, in the atmosphere surrounding a
hot, puffy gas giant planet orbiting a distant Sun-like star.
The observation, which reveals the presence of specific gas molecules based
on tiny decreases in the brightness of precise colors of light, is the most
detailed of its kind to date, demonstrating Webb’s unprecedented ability to
analyze atmospheres hundreds of light-years away.
While the Hubble Space Telescope has analyzed numerous exoplanet
atmospheres over the past two decades, capturing the first clear detection of
water in 2013, Webb’s immediate and more detailed observation marks a giant
leap forward in the quest to characterize potentially habitable planets beyond
Earth.
WASP-96 b is one of more than 5,000 confirmed exoplanets in the Milky Way.
Located roughly 1,150 light-years away in the southern-sky constellation
Phoenix, it represents a type of gas giant that has no direct analog in our
solar system. With a mass less than half that of Jupiter and a diameter 1.2
times greater, WASP-96 b is much puffier than any planet orbiting our Sun. And
with a temperature greater than 1000°F, it is significantly hotter. WASP-96 b
orbits extremely close to its Sun-like star, just one-ninth of the distance
between Mercury and the Sun, completing one circuit every 3½ Earth-days.
The combination of large size, short orbital period, puffy atmosphere, and
lack of contaminating light from objects nearby in the sky makes WASP-96 b an
ideal target for atmospheric observations.
On June 21, Webb’s Near-Infrared Imager
and Slitless Spectrograph (NIRISS) measured light from the
WASP-96 system for 6.4 hours as the planet moved across the star. The result is
a light curve showing the overall dimming of starlight during the transit, and
a transmission spectrum revealing the brightness change of individual wavelengths of infrared
light between 0.6 and 2.8 microns.
While the light curve confirms properties of the planet that had already
been determined from other observations – the existence, size, and orbit of the
planet – the transmission spectrum reveals previously hidden details of the
atmosphere: the unambiguous signature of water, indications of haze, and
evidence of clouds that were thought not to exist based on prior observations.
A transmission spectrum is made by comparing starlight filtered through a
planet’s atmosphere as it moves across the star to the unfiltered starlight
detected when the planet is beside the star. Researchers are able to detect and
measure the abundances of key gases in a planet’s atmosphere based on the
absorption pattern – the locations and heights of peaks on the graph. In the
same way that people have distinctive fingerprints and DNA sequences, atoms and
molecules have characteristic patterns of wavelengths that they absorb.
The spectrum of WASP-96 b captured by NIRISS is not only the most detailed
near-infrared transmission spectrum of an exoplanet atmosphere captured to
date, but it also covers a remarkably wide range of wavelengths, including
visible red light and a portion of the spectrum that has not previously been
accessible from other telescopes (wavelengths longer than 1.6 microns). This
part of the spectrum is particularly sensitive to water as well as other key
molecules like oxygen, methane, and carbon dioxide, which are not immediately
obvious in the WASP-96 b spectrum but which should be detectable in other
exoplanets planned for observation by Webb.
Researchers will be able to use the spectrum to measure the amount of water
vapor in the atmosphere, constrain the abundance of various elements like
carbon and oxygen, and estimate the temperature of the atmosphere with depth.
They can then use this information to make inferences about the overall make-up
of the planet, as well as how, when, and where it formed. The blue line on the
graph is a best-fit model that takes into account the data, the known
properties of WASP-96 b and its star (e.g., size, mass, temperature), and
assumed characteristics of the atmosphere.
The exceptional detail and clarity of these measurements is possible
because of Webb’s state-of-the-art design. Its 270-square-foot gold-coated
mirror collects infrared light efficiently. Its precision spectrographs spread
light out into rainbows of thousands of infrared colors. And its sensitive
infrared detectors measure extremely subtle differences in brightness. NIRISS
is able to detect color differences of only about one thousandth of a micron
(the difference between green and yellow is about 50 microns), and differences
in the brightness between those colors of a few hundred parts per million.
In addition, Webb’s extreme stability and its orbital location around
Lagrange Point 2 roughly a million miles away from the contaminating effects of
Earth’s atmosphere makes for an uninterrupted view and clean data that can be
analyzed relatively quickly.
The extraordinarily detailed spectrum – made by simultaneously analyzing
280 individual spectra captured over the observation – provides just a hint of
what Webb has in store for exoplanet research. Over the coming year,
researchers will use spectroscopy to analyze the surfaces and atmospheres of several dozen exoplanets,
from small rocky planets to gas- and ice-rich
giants. Nearly one-quarter of Webb’s Cycle 1 observation time is allocated to studying exoplanets and the
materials that form them.
This NIRISS observation demonstrates that Webb has the power to
characterize the atmospheres of exoplanets—including those of potentially
habitable planets—in exquisite detail.
Image credit: NASA, ESA, CSA, and STScI
Source: NASA’s
Webb Reveals Steamy Atmosphere of Distant Planet in Detail | NASA
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