The sky around the red dwarf star Ross 128
The red dwarf star Ross 128 in the constellation of Virgo
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ESO’s HARPS instrument finds Earth-mass exoplanet around Ross 128
A team working with ESO’s High Accuracy Radial velocity Planet Searcher (HARPS) at the La Silla Observatory in Chile has found that the red dwarf star Ross 128 is orbited by a low-mass exoplanet every 9.9 days. This Earth-sized world is expected to be temperate, with a surface temperature that may also be close to that of the Earth. Ross 128 is the “quietest” nearby star to host such a temperate exoplanet.
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Xavier Bonfils
ESOcast 137 Light: Temperate Planet Orbiting Quiet Red Dwarf (4K UHD)
Flying through the Ross 128 planetary system
ESO’s HARPS instrument finds Earth-mass exoplanet around Ross 128
A temperate Earth-sized planet has been
discovered only 11 light-years from the Solar System by a team using
ESO’s unique planet-hunting HARPS instrument. The new world has the
designation Ross 128 b and is now the second-closest temperate planet to
be detected after Proxima b. It is also the closest planet to be
discovered orbiting an inactive red dwarf star, which may increase the
likelihood that this planet could potentially sustain life. Ross 128 b
will be a prime target for ESO’s Extremely Large Telescope, which will
be able to search for biomarkers in the planet's atmosphere.
A team working with ESO’s High Accuracy Radial velocity Planet Searcher (HARPS) at the La Silla Observatory in Chile has found that the red dwarf star Ross 128 is orbited by a low-mass exoplanet every 9.9 days. This Earth-sized world is expected to be temperate, with a surface temperature that may also be close to that of the Earth. Ross 128 is the “quietest” nearby star to host such a temperate exoplanet.
“This discovery is based on more than a decade of HARPS
intensive monitoring together with state-of-the-art data reduction and
analysis techniques. Only HARPS has demonstrated such a precision and it
remains the best planet hunter of its kind, 15 years after it began
operations,” explains Nicola Astudillo-Defru (Geneva Observatory –
University of Geneva, Switzerland), who co-authored the discovery paper.
Red dwarfs are some of the coolest, faintest — and most
common — stars in the Universe. This makes them very good targets in the
search for exoplanets and so they are increasingly being studied. In
fact, lead author Xavier Bonfils (Institut de Planétologie et
d'Astrophysique de Grenoble – Université Grenoble-Alpes/CNRS, Grenoble,
France), named their HARPS programme The shortcut to happiness, as it is
easier to detect small cool siblings of Earth around these stars, than
around stars more similar to the Sun [1].
Many red dwarf stars, including Proxima Centauri,
are subject to flares that occasionally bathe their orbiting planets in
deadly ultraviolet and X-ray radiation. However, it seems that Ross 128
is a much quieter star, and so its planets may be the closest known
comfortable abode for possible life.
Although it is currently 11 light-years from Earth, Ross
128 is moving towards us and is expected to become our nearest stellar
neighbour in just 79 000 years
— a blink of the eye in cosmic terms. Ross 128 b will by then take the
crown from Proxima b and become the closest exoplanet to Earth!
With the data from HARPS, the team found that Ross 128 b
orbits 20 times closer than the Earth orbits the Sun. Despite this
proximity, Ross 128 b receives only 1.38 times more irradiation than the
Earth. As a result, Ross 128 b’s equilibrium temperature is estimated
to lie between -60 and 20°C, thanks to the cool and faint nature of its
small red dwarf host star, which has just over half the surface
temperature of the Sun. While the scientists involved in this discovery
consider Ross 128b to be a temperate planet, uncertainty remains as to
whether the planet lies inside, outside, or on the cusp of the habitable zone, where liquid water may exist on a planet’s surface [2].
Astronomers are now detecting more and more temperate
exoplanets, and the next stage will be to study their atmospheres,
composition and chemistry in more detail. Vitally, the detection of
biomarkers such as oxygen in the very closest exoplanet atmospheres will
be a huge next step, which ESO’s Extremely Large Telescope (ELT) is in prime position to take [3].
“New facilities at ESO will first play a critical role in
building the census of Earth-mass planets amenable to characterisation.
In particular, NIRPS,
the infrared arm of HARPS, will boost our efficiency in observing red
dwarfs, which emit most of their radiation in the infrared. And then,
the ELT will provide the opportunity to observe and characterise a large
fraction of these planets,” concludes Xavier Bonfils.
Notes
[1] A planet
orbiting close to a low-mass red dwarf star has a larger gravitational
effect on the star than a similar planet orbiting further out from a
more massive star like the Sun. As a result, this “reflex motion”
velocity is much easier to spot. However, the fact that red dwarfs are
fainter makes it harder to collect enough signal for the very precise
measurements that are needed.
[2] The habitable zone is
defined by the range of orbits around a star in which a planet can
possess the appropriate temperature for liquid water to exist on the
planet’s surface.
[3] This is only possible
for the very few exoplanets that are close enough to the Earth to be
angularly resolved from their stars.
More Information
This research was presented in a
paper entitled “A temperate exo-Earth around a quiet M dwarf at 3.4
parsecs”, by X. Bonfils et al., to appear in the journal Astronomy & Astrophysics.
The team is composed of X. Bonfils (Univ. Grenoble Alpes,
CNRS, IPAG, Grenoble, France [IPAG]), N. Astudillo-Defru (Observatoire
de Genève, Université de Genève, Sauverny, Switzerland), R. Díaz (CONICET – Universidad de Buenos Aires, Instituto de Astronomía y Física del Espacio (IAFE), Buenos Aires, Argentina),
J.-M. Almenara (Observatoire de Genève, Université de Genève, Sauverny,
Switzerland), T. Forveille (IPAG), F. Bouchy (Observatoire de Genève,
Université de Genève, Sauverny, Switzerland), X. Delfosse (IPAG), C.
Lovis (Observatoire de Genève, Université de Genève, Sauverny,
Switzerland), M. Mayor (Observatoire de Genève, Université de Genève,
Sauverny, Switzerland), F. Murgas (Instituto de Astrofísica de Canarias,
La Laguna, Tenerife, Spain), F. Pepe (Observatoire de Genève,
Université de Genève, Sauverny, Switzerland), N. C. Santos (Instituto de
Astrofísica e Ciências do Espaço and Universidade do Porto, Portugal),
D. Ségransan (Observatoire de Genève, Université de Genève, Sauverny,
Switzerland), S. Udry (Observatoire de Genève, Université de Genève,
Sauverny, Switzerland) and A. Wü̈nsche (IPAG).
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
and by Australia as a strategic partner. 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 and its
world-leading Very Large Telescope Interferometer as well as two survey
telescopes, VISTA working in the infrared and the visible-light VLT
Survey Telescope. ESO is also a major partner in two facilities on
Chajnantor, APEX and 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”.
Links
Links
- Research paper in Astronomy & Astrophysics
- Photos of the ESO 3.6-metre telescope
- More information about HARPS
Contacts
Xavier Bonfils
Institut de Planétologie et d'Astrophysique de Grenoble – Université Grenoble-Alpes/CNRS
Grenoble, France
Nicola Astudillo-Defru
Geneva Observatory – University of Geneva
Geneva, Switzerland
Email: nicola.astudillo@unige.ch
Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Source: ESO
