A fly-through of the Proxima Centauri system
Numerical simulation of possible surface temperatures on Proxima b (synchronous rotation)
Numerical simulation of possible surface temperatures on Proxima b (3:2 resonance)
Interviews with Pale Red Dot scientists
Press Conference at ESO HQ
Pale Red Dot campaign reveals Earth-mass world in orbit around Proxima Centauri
Astronomers using ESO telescopes and
other facilities have found clear evidence of a planet orbiting the
closest star to Earth, Proxima Centauri. The long-sought world,
designated Proxima b, orbits its cool red parent star every 11 days and
has a temperature suitable for liquid water to exist on its surface.
This rocky world is a little more massive than the Earth and is the
closest exoplanet to us — and it may also be the closest possible abode
for life outside the Solar System. A paper describing this milestone
finding will be published in the journal Nature on 25 August 2016.
Just over four light-years from the Solar System lies a red dwarf star that has been named
Proxima Centauri
as it is the closest star to Earth apart from the Sun. This cool star
in the constellation of Centaurus is too faint to be seen with the
unaided eye and lies near to the much brighter pair of stars known as
Alpha Centauri AB.
During the first half of 2016 Proxima Centauri was regularly observed with the
HARPS spectrograph on the
ESO 3.6-metre telescope at La Silla in Chile and simultaneously monitored by other telescopes around the world
[1]. This was the
Pale Red Dot
campaign, in which a team of astronomers led by Guillem Anglada-Escudé,
from Queen Mary University of London, was looking for the tiny back and
forth wobble of the star that would be caused by the gravitational pull
of a possible orbiting planet
[2].
As this was a topic with very wide public interest, the progress of
the campaign between mid-January and April 2016 was shared publicly as
it happened on the
Pale Red Dot
website and via social media.
The reports were accompanied by numerous
outreach articles written by specialists around the world.
Guillem Anglada-Escudé explains the background to this unique search: “The
first hints of a possible planet were spotted back in 2013, but the
detection was not convincing. Since then we have worked hard to get
further observations off the ground with help from ESO and others. The
recent Pale Red Dot campaign has been about two years in the planning.”
The
Pale Red Dot data, when combined with earlier
observations made at ESO observatories and elsewhere, revealed the clear
signal of a truly exciting result. At times Proxima Centauri is
approaching Earth at about 5 kilometres per hour — normal human walking
pace — and at times receding at the same speed. This regular pattern of
changing radial velocities repeats with a period of 11.2 days. Careful
analysis of the resulting tiny
Doppler shifts
showed that they indicated the presence of a planet with a mass at
least 1.3 times that of the Earth, orbiting about 7 million kilometres
from Proxima Centauri — only 5% of the Earth-Sun distance
[3].
Guillem Anglada-Escudé comments on the excitement of the last few months: "I
kept checking the consistency of the signal every single day during the
60 nights of the Pale Red Dot campaign. The first 10 were promising,
the first 20 were consistent with expectations, and at 30 days the
result was pretty much definitive, so we started drafting the paper!"
Red dwarfs like Proxima Centauri are active stars and can vary in
ways that would mimic the presence of a planet. To exclude this
possibility the team also monitored the changing brightness of the star
very carefully during the campaign using the ASH2 telescope at the
San Pedro de Atacama Celestial Explorations Observatory in Chile and the
Las Cumbres Observatory telescope network. Radial velocity data taken when the star was flaring were excluded from the final analysis.
Although Proxima b orbits much closer to its star than Mercury does
to the Sun in the Solar System, the star itself is far fainter than the
Sun. As a result Proxima b lies well within the
habitable zone
around the star and has an estimated surface temperature that would
allow the presence of liquid water. Despite the temperate orbit of
Proxima b, the conditions on the surface may be strongly affected by the
ultraviolet and X-ray flares from the star — far more intense than the
Earth experiences from the Sun
[4].
Two separate
papers discuss
the habitability of Proxima b and its climate. They find that the
existence of liquid water on the planet today cannot be ruled out and,
in such case, it may be present over the surface of the planet only in
the sunniest regions, either in an area in the hemisphere of the planet
facing the star (
synchronous rotation) or in a tropical belt (
3:2 resonance rotation).
Proxima b's rotation, the strong radiation from its star and the
formation history of the planet makes its climate quite different from
that of the Earth, and it is unlikely that Proxima b has seasons.
This discovery will be the beginning of extensive further observations, both with current instruments
[5] and with the next generation of giant telescopes such as the European Extremely Large Telescope (
E-ELT).
Proxima b will be a prime target for the hunt for evidence of life
elsewhere in the Universe. Indeed, the Alpha Centauri system is also the
target of humankind’s first attempt to travel to another star system,
the
StarShot project.
Guillem Anglada-Escudé concludes: "Many exoplanets have been
found and many more will be found, but searching for the closest
potential Earth-analogue and succeeding has been the experience of a
lifetime for all of us. Many people’s stories and efforts have converged
on this discovery. The result is also a tribute to all of them. The
search for life on Proxima b comes next..."
Notes
[1] Besides data from the recent Pale Red Dot campaign, the
paper incorporates contributions from scientists who have been observing
Proxima Centauri for many years. These include members of the original
UVES/ESO M-dwarf programme (Martin Kürster and Michael Endl), and
exoplanet search pioneers such as R. Paul Butler. Public observations
from the HARPS/Geneva team obtained over many years were also included.
[2] The name Pale Red Dot reflects Carl Sagan’s famous reference to the Earth as a pale blue dot. As Proxima Centauri is a red dwarf star it will bathe its orbiting planet in a pale red glow.
[3] The detection reported today has
been technically possible for the last 10 years. In fact, signals with
smaller amplitudes have been detected previously. However, stars are not
smooth balls of gas and Proxima Centauri is an active star. The robust
detection of Proxima b has only been possible after reaching a detailed
understanding of how the star changes on timescales from minutes to a
decade, and monitoring its brightness with photometric telescopes.
[4] The actual suitability of this
kind of planet to support water and Earth-like life is a matter of
intense but mostly theoretical debate. Major concerns that count against
the presence of life are related to the closeness of the star. For
example gravitational forces probably lock the same side of the planet
in perpetual daylight, while the other side is in perpetual night. The
planet's atmosphere might also slowly be evaporating or have more
complex chemistry than Earth’s due to stronger ultraviolet and X-ray
radiation, especially during the first billion years of the star’s life.
However, none of the arguments has been proven conclusively and they
are unlikely to be settled without direct observational evidence and
characterisation of the planet’s atmosphere. Similar factors apply to
the planets recently found around TRAPPIST-1.
[5] Some methods to study a planet’s
atmosphere depend on it passing in front of its star and the starlight
passing through the atmosphere on its way to Earth. Currently there is
no evidence that Proxima b transits across the disc of its parent star,
and the chances of this happening seem small, but further observations
to check this possibility are in progress.
More Information
This research is presented in a paper entitled “A terrestrial planet
candidate in a temperate orbit around Proxima Centauri”, by G.
Anglada-Escudé et al., to appear in the journal Nature on 25 August 2016.
The team is composed of Guillem Anglada-Escudé (Queen Mary University
of London, London, UK), Pedro J. Amado (Instituto de Astrofísica de
Andalucía - CSIC, Granada, Spain), John Barnes (Open University, Milton
Keynes, UK), Zaira M. Berdiñas (Instituto de Astrofísica de Andalucia -
CSIC, Granada, Spain), R. Paul Butler (Carnegie Institution of
Washington, Department of Terrestrial Magnetism, Washington, USA), Gavin
A. L. Coleman (Queen Mary University of London, London, UK), Ignacio de
la Cueva (Astroimagen, Ibiza, Spain), Stefan Dreizler (Institut für
Astrophysik, Georg-August-Universität Göttingen, Göttingen, Germany),
Michael Endl (The University of Texas at Austin and McDonald
Observatory, Austin, Texas, USA), Benjamin Giesers (Institut für
Astrophysik, Georg-August-Universität Göttingen, Göttingen, Germany),
Sandra V. Jeffers (Institut für Astrophysik, Georg-August-Universität
Göttingen, Göttingen, Germany), James S. Jenkins (Universidad de Chile,
Santiago, Chile), Hugh R. A. Jones (University of Hertfordshire,
Hatfield, UK), Marcin Kiraga (Warsaw University Observatory, Warsaw,
Poland), Martin Kürster (Max-Planck-Institut für Astronomie, Heidelberg,
Germany), María J. López-González (Instituto de Astrofísica de
Andalucía - CSIC, Granada, Spain), Christopher J. Marvin (Institut für
Astrophysik, Georg-August-Universität Göttingen, Göttingen, Germany),
Nicolás Morales (Instituto de Astrofísica de Andalucía - CSIC, Granada,
Spain), Julien Morin (Laboratoire Univers et Particules de Montpellier,
Université de Montpellier & CNRS, Montpellier, France), Richard P.
Nelson (Queen Mary University of London, London, UK), José L. Ortiz
(Instituto de Astrofísica de Andalucía - CSIC, Granada, Spain), Aviv
Ofir (Weizmann Institute of Science, Rehovot, Israel), Sijme-Jan
Paardekooper (Queen Mary University of London, London, UK), Ansgar
Reiners (Institut für Astrophysik, Georg-August-Universität Göttingen,
Göttingen, Germany), Eloy Rodriguez (Instituto de Astrofísica de
Andalucía - CSIC, Granada, Spain), Cristina Rodriguez-Lopez (Instituto
de Astrofísica de Andalucía - CSIC, Granada, Spain), Luis F. Sarmiento
(Institut für Astrophysik, Georg-August-Universität Göttingen,
Göttingen, Germany), John P. Strachan (Queen Mary University of London,
London, UK), Yiannis Tsapras (Astronomisches Rechen-Institut,
Heidelberg, Germany), Mikko Tuomi (University of Hertfordshire,
Hatfield, UK) and Mathias Zechmeister (Institut für Astrophysik,
Georg-August-Universität Göttingen, Göttingen, Germany).
ESO is the foremost intergovernmental astronomy organisation in
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Links
Contacts:
Guillem Anglada-Escudé (Lead Scientist)
Queen Mary University of London
London, United Kingdom
Tel: +44 (0)20 7882 3002
Pedro J. Amado (Scientist)
Instituto de Astrofísica de Andalucía - Consejo Superior de Investigaciones Cientificas (IAA/CSIC)
Granada, Spain
Tel: +34 958 23 06 39
Ansgar Reiners (Scientist)
Institut für Astrophysik, Universität Göttingen
Göttingen, Germany
Tel: +49 551 3913825
James S. Jenkins (Scientist)
Departamento de Astronomia, Universidad de Chile
Santiago, Chile
Tel: +56 (2) 2 977 1125
Michael Endl (Scientist)
McDonald Observatory, The University of Texas at Austin
Austin, Texas, USA
Tel: +1 512 471 8312
Richard Hook (Coordinating Public Information Officer)
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Martin Archer (Public Information Officer)
Queen Mary University of London
London, United Kingdom
Tel: +44 (0) 20 7882 6963
Silbia López de Lacalle (Public Information Officer)
Instituto de Astrofísica de Andalucía
Granada, Spain
Tel: +34 958 23 05 32
Romas Bielke (Public Information Officer)
Georg August Universität Göttingen
Göttingen, Germany
Tel: +49 551 39-12172
Natasha Metzler (Public Information Officer)
Carnegie Institution for Science
Washington DC, USA
Tel: +1 (202) 939 1142
David Azocar (Public Information Officer)
Departamento de Astronomia, Universidad de Chile
Santiago, Chile
Rebecca Johnson (Public Information Officer)
McDonald Observatory, The University of Texas at Austin
Austin, Texas, USA
Tel: +1 512 475 6763
Hugh Jones (Scientist)
University of Hertfordshire
Hatfield, United Kingdom
Tel: +44 (0)1707 284426
Jordan Kenny (Public Information Officer)
University of Hertfordshire
Hatfield, United Kingdom
Tel: +44 1707 286476
Cell: +44 7730318371
Yiannis Tsapras (Scientist)
Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg
Heidelberg, Germany
Tel: +49 6221 54-181
Source: ESO
