Location of the faint red star LHS 1140 in the constellation of Cetus (The Sea Monster)
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Artist’s impression of a trip to the super-Earth exoplanet LHS 1140b
Transiting rocky super-Earth found in habitable zone of quiet red dwarf star
An exoplanet orbiting a red dwarf star 40
light-years from Earth may be the new holder of the title “best place
to look for signs of life beyond the Solar System”. Using ESO’s HARPS
instrument at La Silla, and other telescopes around the world, an
international team of astronomers discovered a “super-Earth” orbiting in
the habitable zone around the faint star LHS 1140. This world is a
little larger and much more massive than the Earth and has likely
retained most of its atmosphere. This, along with the fact that it
passes in front of its parent star as it orbits, makes it one of the
most exciting future targets for atmospheric studies. The results will
appear in the 20 April 2017 issue of the journal Nature.
The newly discovered super-Earth LHS 1140b orbits in the habitable zone around a faint red dwarf star, named LHS 1140, in the constellation of Cetus (The Sea Monster) [1].
Red dwarfs are much smaller and cooler than the Sun and, although LHS
1140b is ten times closer to its star than the Earth is to the Sun, it
only receives about half as much sunlight from its star as the Earth and
lies in the middle of the habitable zone. The orbit is seen almost
edge-on from Earth and as the exoplanet passes in front of the star once
per orbit it blocks a little of its light every 25 days.
“This is the most exciting exoplanet I’ve seen in the past decade,” said lead author Jason Dittmann of the Harvard-Smithsonian Center for Astrophysics (Cambridge, USA). “We
could hardly hope for a better target to perform one of the biggest
quests in science — searching for evidence of life beyond Earth.”
"The present conditions of the red
dwarf are particularly favourable — LHS 1140 spins more slowly and
emits less high-energy radiation than other similar low-mass stars," explains team member Nicola Astudillo-Defru from Geneva Observatory, Switzerland [2].
For life as we know it to exist, a planet must have liquid
surface water and retain an atmosphere. When red dwarf stars are
young, they are known to emit radiation that can be damaging for
the atmospheres of the planets that orbit them. In this case, the
planet's large size means that a magma ocean could have existed on
its surface for millions of years. This seething ocean of lava
could feed steam into the atmosphere long after the star has
calmed to its current, steady glow, replenishing the planet with
water.
The discovery was initially made with the MEarth facility, which detected the first telltale, characteristic dips in light as the exoplanet passed in front of the star. ESO’s HARPS
instrument, the High Accuracy Radial velocity Planet Searcher, then
made crucial follow-up observations which confirmed the presence of the
super-Earth. HARPS also helped pin down the orbital period and allowed
the exoplanet’s mass and density to be deduced [3].
The astronomers estimate the age of the planet to be at
least five billion years. They also deduced that it has a diameter 1.4
times larger than the Earth — almost 18 000 kilometres. But with a mass
around seven times greater than the Earth, and hence a much higher
density, it implies that the exoplanet is probably made of rock with a
dense iron core.
This super-Earth may be the best candidate yet for future
observations to study and characterise its atmosphere, if one exists.
Two of the European members of the team, Xavier Delfosse and Xavier
Bonfils both at the CNRS and IPAG in Grenoble, France, conclude: “The
LHS 1140 system might prove to be an even more important target for the
future characterisation of planets in the habitable zone than Proxima b
or TRAPPIST-1. This has been a remarkable year for exoplanet
discoveries!” [4,5].
In particular, observations coming up soon with the NASA/ESA Hubble Space Telescope
will be able to assess exactly how much high-energy radiation is
showered upon LHS 1140b, so that its capacity to support life can be
further constrained.
Further into the future — when new telescopes like ESO’s Extremely Large Telescope are operating — it is likely that we will be able to make detailed observations of the atmospheres of exoplanets, and LHS 1140b is an exceptional candidate for such studies.
Notes
[1] The habitable zone is defined by the range of orbits around a
star, for which a planet possesses the appropriate temperature needed
for liquid water to exist on the planet’s surface.
[2] Although the planet is located in the zone in which life as we know it could potentially exist, it probably did not enter this region until approximately forty million years after the formation of the red dwarf star. During this phase, the exoplanet would have been subjected to the active and volatile past of its host star. A young red dwarf can easily strip away the water from the atmosphere of a planet forming within its vicinity, leading to a runaway greenhouse effect similar to that on Venus.
[3] This effort enabled other transit events to be detected by MEarth so that the astronomers could nail down the detection of the exoplanet once and for all.
[4] The planet around Proxima Centauri (eso1629) is much closer to Earth, but it probably does not transit its star, making it very difficult to determine whether it holds an atmosphere.
[5] Unlike the TRAPPIST-1 system (eso1706), no other exoplanets around LHS 1140 have been found. Multi-planet systems are thought to be common around red dwarfs, so it is possible that additional exoplanets have gone undetected so far because they are too small.
More Information
This research was presented in a paper entitled “A
temperate rocky super-Earth transiting a nearby cool star”, by J. A.
Dittmann et al. to appear in the journal Nature on 20 April 2017.
The team is composed of Jason A. Dittmann (Harvard Smithsonian Center for Astrophysics, USA), Jonathan M. Irwin (Harvard Smithsonian Center for Astrophysics, USA), David Charbonneau (Harvard Smithsonian Center for Astrophysics, USA), Xavier Bonfils (Institut de Planétologie et d'Astrophysique de Grenoble – Université Grenoble-Alpes/CNRS, France), Nicola Astudillo-Defru (Observatoire de Genève, Switzerland), Raphaëlle D. Haywood (Harvard Smithsonian Center for Astrophysics, USA), Zachory K. Berta-Thompson (University of Colorado, USA), Elisabeth R. Newton (MIT, USA), Joseph E. Rodriguez (Harvard Smithsonian Center for Astrophysics, USA), Jennifer G. Winters (Harvard Smithsonian Center for Astrophysics, USA), Thiam-Guan Tan (Perth Exoplanet Survey Telescope, Australia), José-Manuel Almenara (Institut de Planétologie et d'Astrophysique de Grenoble - Université Grenoble-Alpes/CNRS, France; Observatoire de Genève, Switzerland), François Bouchy (Aix Marseille Université, France), Xavier Delfosse (Institut de Planétologie et d'Astrophysique de Grenoble – Université Grenoble-Alpes / CNRS, France), Thierry Forveille (Institut de Planétologie et d'Astrophysique de Grenoble – Université Grenoble-Alpes/CNRS, France), Christophe Lovis (Observatoire de Genève, Switzerland), Felipe Murgas (Institut de Planétologie et d'Astrophysique de Grenoble – Université Grenoble-Alpes / CNRS, France; IAC, Spain), Francesco Pepe (Observatoire de Genève, Switzerland), Nuno C. Santos (Instituto de Astrofísica e Ciências do Espaço and Universidade do Porto, Portugal), Stephane Udry (Observatoire de Genève, Switzerland), Anaël Wünsche (CNRS/IPAG, France), Gilbert A. Esquerdo (Harvard Smithsonian Center for Astrophysics, USA), David W. Latham (Harvard Smithsonian Center for Astrophysics, USA) and Courtney D. Dressing (Caltech, USA).
ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.
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Contacts
Harvard-Smithsonian Center for Astrophysics
Cambridge, USA
Email: jdittmann@cfa.harvard.edu
Nicola Astudillo-Defru
Geneva Observatory - Université of Geneva
Geneva, Switzerland
Email: nicola.astudillo@unige.ch
Xavier Bonfils
Institut de Planétologie et d'Astrophysique de Grenoble – Université Grenoble-Alpes/CNRS
Grenoble, France
Email: xavier.bonfils@univ-grenoble-alpes.fr
Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Megan Watzke
Harvard-Smithsonian Center for Astrophysics
Cambridge, USA
Tel: +1 617-496-7998
Email: mwatzke@cfa.harvard.edu
