Science canada

NASA Instrument to Probe Planet Clouds on European Mission

NASA will contribute
an instrument to a European space mission that will explore the atmospheres of
hundreds of planets orbiting stars beyond our Sun, or exoplanets, for the first time.

The instrument,
called the Contribution to ARIEL Spectroscopy of Exoplanets, or CASE, adds
scientific capabilities to ESA’s (the European Space Agency’s) Atmospheric
Remote-sensing Infrared Exoplanet Large-survey, or ARIEL, mission.

The ARIEL spacecraft
with CASE on board is expected to launch in 2028. CASE will be managed by
NASA’s Jet Propulsion Laboratory in Pasadena, California, with JPL
astrophysicist Mark Swain as the principal investigator.

“I am
thrilled that NASA will partner with ESA in this historic mission to push the
envelope in our understanding of what the atmospheres of exoplanets are made
of, and how these planets form and evolve,” said Thomas Zurbuchen,
associate administrator for NASA’s Science Mission Directorate in Washington.
“The more information we have about exoplanets, the closer we get to
understanding the origins of our solar system, and advancing our search for
Earth-like planets elsewhere.”

So far,
scientists have found more than 4,000 confirmed exoplanets in the Milky Way.
NASA’s retired Kepler space telescope and active Transiting Exoplanet Survey Satellite (TESS) are two observatories that have
contributed to this count. These telescopes have discovered planets by
observing brightness of a star’s light dimming as a planet crosses its face, an event called a “transit.”
ARIEL, carrying CASE, will take planet-hunting through transits one step
further, by delving deeper into planets already known to exist.

ARIEL will be
able to see the chemical fingerprints, or “spectra,” of a planet’s
atmosphere in the light of its star. To do this, the
spacecraft will observe starlight streaming through the atmospheres of planets
as they pass in front their stars, as well as light emitted by the planets’
atmospheres just before and after they disappear behind their stars.
These fingerprints will allow
scientists to study the compositions, temperatures, and chemical processes in
the atmospheres of the planets ARIEL observes.

These chemical
fingerprints of exoplanet atmospheres are extremely faint. Identifying them is
a huge challenge for astronomers, and requires a telescope to stare at individual
stars for a long time. But many space observatories are multi-purpose, and must
split up their time among different kinds of scientific investigations. ARIEL
will be the first spacecraft fully devoted to observing hundreds of exoplanet
atmospheres, looking to identify their contents, temperatures and chemical
processes. The addition of CASE, which will observe clouds and hazes, will
provide a more comprehensive picture of the exoplanet atmospheres ARIEL
observes.

So far,
telescopes have only been able to carefully probe the atmospheres of a handful
of exoplanets to determine their chemistries. ARIEL’s much larger, more diverse
sample will enable scientists to look at these worlds not just as individual
exotic objects, but as a population, and discover new trends in their
commonalities and differences.

The CASE
instrument will be sensitive to light at near-infrared wavelengths, which is
invisible to human eyes, as well as visible light. This complements ARIEL’s
other instrument, called an infrared spectrometer, which operates at longer
wavelengths. CASE will specifically look at exoplanets’ clouds and hazes -
determining how common they are, as well how they influence the compositions
and other properties of planetary atmospheres. CASE will also allow
measurements of each planet’s albedo, the amount of light the planet reflects.

The spacecraft
will focus on exceptionally hot planets in our galaxy, with temperatures
greater than 600 degrees Fahrenheit (320 degrees Celsius). Such planets are
more likely to transit their star than planets orbiting farther out, and their
short orbital periods provide more opportunities to observe transits in a given
period of time. More transits give astronomers more data, allowing them to
reveal the weak chemical fingerprint of a planet’s atmosphere.

ARIEL’s hot
planet population will include gas giants like Jupiter, as well as smaller
gaseous planets called mini-Neptunes and rocky worlds bigger than our planet
called super-Earths. While these planets are too hot to host life as we know
it, they will tell us a lot about how planets and planetary systems form and
evolve. Additionally the techniques and insights learned in studying exoplanets
with ARIEL and CASE will be useful when scientists use future telescopes to look
toward smaller, colder, rockier worlds with conditions that more closely
resemble Earth’s.

The CASE instrument
consists of two detectors and associated electronics that contribute to ARIEL’s
guidance system. CASE takes advantage of the same detectors and electronics
that NASA is contributing to ESA’s Euclid mission, which will probe deep
questions about the structure of the universe and its two biggest mystery
components: dark matter and dark energy.

The ARIEL
spacecraft with CASE on board will be in the same orbit as NASA’s James Webb
Space Telescope, which is expected to launch in 2021. Both will travel some 1
million miles (1.5 million kilometers) from Earth to a special point of
gravitational stability called Lagrange Point 2. This location allows the spacecraft to circle the Sun along with the Earth, while
using little fuel to maintain its orbit.

While Webb will
also be capable of studying exoplanet atmospheres, and its instruments cover a
similar range of light as ARIEL, Webb will target a smaller sample of
exoplanets to study in greater detail. Because Webb’s time will be divided,
shared with investigations into other aspects of the universe, it will deliver
detailed knowledge about particular exoplanets rather than surveying hundreds.
ARIEL will launch several years after Webb, so it will be able to capitalize on
lessons learned from Webb in terms of planning observations and selecting which
planets to study.

“This is
an exciting time for exoplanet science as we look toward the next generation of
space telescopes and instruments,” said Paul Hertz, director of the
astrophysics division at NASA Headquarters, Washington. “CASE adds to an
exceptional set of technologies that will help us better understand our place
in the galaxy.”

CASE is an
Astrophysics Explorers Mission of Opportunity, managed by JPL. The Astrophysics
Explorers Program is managed by NASA’s Goddard Space Flight Center in
Greenbelt, Maryland, for the Science Mission Directorate at NASA Headquarters
in Washington, DC.

News Media Contact

Calla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
626-808-2469
calla.e.cofield@jpl.nasa.gov

Felicia Chou

NASA Headquarters, Washington

202-358-0257

felicia.chou@nasa.gov

Written by Elizabeth Landau

NASA Headquarters, Washington

2019-225


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