Illustration Credit: NASA, ESA, and G. Bacon (STScI)
Using NASA's Hubble Space Telescope, astronomers have conducted the
first search for atmospheres around temperate, Earth-sized planets
beyond our solar system and found indications that increase the chances
of habitability on two exoplanets.
Specifically, they discovered that the exoplanets TRAPPIST-1b and
TRAPPIST-1c, approximately 40 light-years away, are unlikely to have
puffy, hydrogen-dominated atmospheres usually found on gaseous worlds.
"The lack of a smothering hydrogen-helium envelope increases the
chances for habitability on these planets," said team member Nikole
Lewis of the Space Telescope Science Institute (STScI) in Baltimore,
Maryland. "If they had a significant hydrogen-helium envelope, there is
no chance that either one of them could potentially support life
because the dense atmosphere would act like a greenhouse."
Julien de Wit of the Massachusetts Institute of Technology in
Cambridge, Massachusetts, led a team of scientists to observe the
planets in near-infrared light using Hubble's Wide Field Camera 3. They
used spectroscopy to decode the light and reveal clues to the chemical
makeup of an atmosphere. While the content of the atmospheres is
unknown and will have to await further observations, the low
concentration of hydrogen and helium has scientists excited about the
implications.
"These initial Hubble observations are a promising first step in
learning more about these nearby worlds, whether they could be rocky
like Earth, and whether they could sustain life," said Geoff Yoder,
acting associate administrator for NASA's Science Mission Directorate
in Washington, D.C. "This is an exciting time for NASA and exoplanet
research."
The planets orbit a red dwarf star at least 500 million years old, in
the constellation of Aquarius. They were discovered in late 2015
through a series of observations by the TRAnsiting Planets and
PlanetesImals Small Telescope (TRAPPIST), a Belgian robotic telescope
located at the European Southern Observatory’s (ESO’s) La Silla
Observatory in Chile.
TRAPPIST-1b completes a circuit around its red dwarf star in 1.5 days
and TRAPPIST-1c in 2.4 days. The planets are between 20 and 100 times
closer to their star than Earth is to the sun. Because their star is so
much fainter than our sun, researchers think that at least one of the
planets, or possibly both, may be within the star's habitable zone,
where moderate temperatures could allow for liquid water to pool.
On May 4, astronomers took advantage of a rare simultaneous transit,
when both planets crossed the face of their star within minutes of each
other, to measure starlight as it filtered through any existing
atmosphere. This double-transit, which occurs only every two years,
provided a combined signal that offered simultaneous indicators of the
atmospheric characteristics of the planets.
The researchers hope to use Hubble to conduct follow-up observations
to search for thinner atmospheres, composed of elements heavier than
hydrogen, like those of Earth and Venus.
"With more data, we could perhaps detect methane or see water
features in the atmospheres, which would give us estimates of the depth
of the atmospheres," said Hannah Wakeford, the paper's second author,
at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
Observations from future telescopes, including NASA's James Webb
Space Telescope, will help determine the full composition of these
atmospheres and hunt for potential biosignatures, such as carbon
dioxide and ozone, in addition to water vapor and methane. Webb also
will analyze a planet's temperature and surface pressure — key factors
in assessing its habitability.
These planets are the first Earth-sized worlds found in the Search
for habitable Planets EClipsing ULtra-cOOl Stars (SPECULOOS) survey,
which will search more than 1,000 nearby red dwarf stars for
Earth-sized worlds. So far, the survey has analyzed only 15 of those
stars.
"These Earth-sized planets are the first worlds that astronomers can
study in detail with current and planned telescopes to determine
whether they are suitable for life," said de Wit. "Hubble has the
ability to play the central atmospheric pre-screening role to tell
astronomers which of these Earth-sized planets are prime candidates for
more detailed study with the Webb telescope."
The results of the study appear in the July 20 issue of the journal Nature.
Contact
Felicia Chou
NASA Headquarters, Washington, D.C
202-358-0257
felicia.chou@nasa.gov
Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu
Julien de Wit
Massachusetts Institute of Technology, Cambridge, Massachusetts
jdewitt@mit.edu
Hannah Wakeford
NASA Goddard Spaceflight Center, Greenbelt, Maryland
301-286-7975
hannah.wakeford@nasa.gov
Nikole Lewis
Space Telescope Science Institute, Baltimore, Maryland
410-338-4820
nlewis@stsci.edu
Source: HubbleSite
