This
illustration shows the possible surface of TRAPPIST-1f, one of the
newly discovered planets in the TRAPPIST-1 system. Scientists using the
Spitzer Space Telescope and ground-based telescopes have discovered that
there are seven Earth-size planets in the system.
Credits: NASA/JPL-Caltech
NASA's Spitzer Space Telescope has revealed the first known system of seven Earth-size planets around a single star.
Three of these planets are firmly located in the habitable zone, the
area around the parent star where a rocky planet is most likely to have
liquid water.
The
discovery sets a new record for greatest number of habitable-zone
planets found around a single star outside our solar system. All of
these seven planets could have liquid water – key to life as we know it –
under the right atmospheric conditions, but the chances are highest
with the three in the habitable zone.
“This
discovery could be a significant piece in the puzzle of finding
habitable environments, places that are conducive to life,” said Thomas
Zurbuchen, associate administrator of the agency’s Science Mission
Directorate in Washington. “Answering the question ‘are we alone’ is a
top science priority and finding so many planets like these for the
first time in the habitable zone is a remarkable step forward toward
that goal.”
Seven
Earth-sized planets have been observed by NASA's Spitzer Space
Telescope around a tiny, nearby, ultra-cool dwarf star called
TRAPPIST-1. Three of these planets are firmly in the habitable zone.
Credits: NASA
The
TRAPPIST-1 star, an ultra-cool dwarf, has seven Earth-size planets
orbiting it. This artist's concept appeared on the cover of the journal
Nature on Feb. 23, 2017.
Credits: NASA/JPL-Caltech
At
about 40 light-years (235 trillion miles) from Earth, the system of
planets is relatively close to us, in the constellation Aquarius.
Because they are located outside of our solar system, these planets are
scientifically known as exoplanets.
This
exoplanet system is called TRAPPIST-1, named for The Transiting Planets
and Planetesimals Small Telescope (TRAPPIST) in Chile. In May 2016,
researchers using TRAPPIST announced they had discovered three planets
in the system. Assisted by several ground-based telescopes, including
the European Southern Observatory's Very Large Telescope, Spitzer
confirmed the existence of two of these planets and discovered five
additional ones, increasing the number of known planets in the system to
seven.
The
new results were published Wednesday in the journal Nature, and
announced at a news briefing at NASA Headquarters in Washington.
Using
Spitzer data, the team precisely measured the sizes of the seven
planets and developed first estimates of the masses of six of them,
allowing their density to be estimated.
Based
on their densities, all of the TRAPPIST-1 planets are likely to be
rocky. Further observations will not only help determine whether they
are rich in water, but also possibly reveal whether any could have
liquid water on their surfaces. The mass of the seventh and farthest
exoplanet has not yet been estimated – scientists believe it could be an
icy, "snowball-like" world, but further observations are needed.
"The
seven wonders of TRAPPIST-1 are the first Earth-size planets that have
been found orbiting this kind of star," said Michael Gillon, lead author
of the paper and the principal investigator of the TRAPPIST exoplanet
survey at the University of Liege, Belgium. "It is also the best target
yet for studying the atmospheres of potentially habitable, Earth-size
worlds."
This
artist's concept shows what each of the TRAPPIST-1 planets may look
like, based on available data about their sizes, masses and orbital
distances.
Credits: NASA/JPL-Caltech
In
contrast to our sun, the TRAPPIST-1 star – classified as an ultra-cool
dwarf – is so cool that liquid water could survive on planets orbiting
very close to it, closer than is possible on planets in our solar
system. All seven of the TRAPPIST-1 planetary orbits are closer to their
host star than Mercury is to our sun. The planets also are very close
to each other. If a person was standing on one of the planet’s surface,
they could gaze up and potentially see geological features or clouds of
neighboring worlds, which would sometimes appear larger than the moon in
Earth's sky.
The
planets may also be tidally locked to their star, which means the same
side of the planet is always facing the star, therefore each side is
either perpetual day or night. This could mean they have weather
patterns totally unlike those on Earth, such as strong winds blowing
from the day side to the night side, and extreme temperature changes.
Spitzer,
an infrared telescope that trails Earth as it orbits the sun, was
well-suited for studying TRAPPIST-1 because the star glows brightest in
infrared light, whose wavelengths are longer than the eye can see. In
the fall of 2016, Spitzer observed TRAPPIST-1 nearly continuously for
500 hours. Spitzer is uniquely positioned in its orbit to observe enough
crossing – transits – of the planets in front of the host star to
reveal the complex architecture of the system. Engineers optimized
Spitzer’s ability to observe transiting planets during Spitzer’s “warm
mission,” which began after the spacecraft’s coolant ran out as planned
after the first five years of operations.
"This
is the most exciting result I have seen in the 14 years of Spitzer
operations," said Sean Carey, manager of NASA's Spitzer Science Center
at Caltech/IPAC in Pasadena, California. "Spitzer will follow up in the
fall to further refine our understanding of these planets so that the
James Webb Space Telescope can follow up. More observations of the
system are sure to reveal more secrets.”
Following
up on the Spitzer discovery, NASA's Hubble Space Telescope has
initiated the screening of four of the planets, including the three
inside the habitable zone. These observations aim at assessing the
presence of puffy, hydrogen-dominated atmospheres, typical for gaseous
worlds like Neptune, around these planets.
This
360-degree panorama depicts the surface of a newly detected planet,
TRAPPIST 1-d, part of a seven planet system some 40 light years away.
Explore this artist’s rendering of an alien world by moving the view
using your mouse or your mobile device.
Credits: NASA
In May 2016, the Hubble team observed the two innermost planets,
and found no evidence for such puffy atmospheres. This strengthened the
case that the planets closest to the star are rocky in nature.
"The
TRAPPIST-1 system provides one of the best opportunities in the next
decade to study the atmospheres around Earth-size planets," said Nikole
Lewis, co-leader of the Hubble study and astronomer at the Space
Telescope Science Institute in Baltimore, Maryland. NASA's
planet-hunting Kepler space telescope also is studying the TRAPPIST-1
system, making measurements of the star's minuscule changes in
brightness due to transiting planets. Operating as the K2 mission, the
spacecraft's observations will allow astronomers to refine the
properties of the known planets, as well as search for additional
planets in the system. The K2 observations conclude in early March and
will be made available on the public archive.
This poster imagines what a trip to TRAPPIST-1e might be like.
Credits: NASA/JPL-Caltech
Spitzer,
Hubble, and Kepler will help astronomers plan for follow-up studies
using NASA's upcoming James Webb Space Telescope, launching in 2018.
With much greater sensitivity, Webb will be able to detect the chemical
fingerprints of water, methane, oxygen, ozone, and other components of a
planet's atmosphere. Webb also will analyze planets' temperatures and
surface pressures – key factors in assessing their habitability.
NASA’s
Jet Propulsion Laboratory (JPL) in Pasadena, California, manages the
Spitzer Space Telescope mission for NASA's Science Mission Directorate.
Science operations are conducted at the Spitzer Science Center, at
Caltech, in Pasadena, California. Spacecraft operations are based at
Lockheed Martin Space Systems Company, Littleton, Colorado. Data are
archived at the Infrared Science Archive housed at Caltech/IPAC. Caltech
manages JPL for NASA.
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