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14 November 2018
Red Dots campaign uncovers compelling evidence of exoplanet around closest single star to Sun
Artist’s impression of the surface of a super-Earth orbiting Barnard’s Star
The nearest single star to the Sun hosts an exoplanet at least 3.2 times as massive as Earth — a so-called super-Earth. One of the largest observing campaigns to date using data from a world-wide array of telescopes, including ESO’s planet-hunting HARPS instrument, have revealed this frozen, dimly lit world. The newly discovered planet is the second-closest known exoplanet to the Earth. Barnard’s star is the fastest moving star in the night sky.
Artist’s impression of super-Earth orbiting Barnard’s Star
A planet has been detected orbiting Barnard’s Star, a mere 6 light-years away. This breakthrough — announced in a paper published today in the journal Nature — is a result of the Red Dots and CARMENES projects, whose search for local rocky planets has already uncovered a new world orbiting our nearest neighbour, Proxima Centauri.
Barnard’s Star in the constellation Ophiuchus
The planet, designated Barnard's Star b, now steps in as the second-closest known exoplanet to Earth [1]. The gathered data indicate that the planet could be a super-Earth, having a mass at least 3.2 times that of the Earth, which orbits its host star in roughly 233 days. Barnard’s Star, the planet’s host star, is a red dwarf, a cool, low-mass star, which only dimly illuminates this newly-discovered world. Light from Barnard’s Star provides its planet with only 2% of the energy the Earth receives from the Sun.
Widefield image of the sky around Barnard’s Star showing its motion
Despite being relatively close to its parent star — at a distance only 0.4 times that between Earth and the Sun — the exoplanet lies close to the snow line, the region where volatile compounds such as water can condense into solid ice. This freezing, shadowy world could have a temperature of –170 ℃, making it inhospitable for life as we know it.
Named for astronomer E. E. Barnard, Barnard’s Star is the closest single star to the Sun. While the star itself is ancient — probably twice the age of our Sun — and relatively inactive, it also has the fastest apparent motion of any star in the night sky [2]. Super-Earths are the most common type of planet to form around low-mass stars such as Barnard’s Star, lending credibility to this newly discovered planetary candidate. Furthermore, current theories of planetary formation predict that the snow line is the ideal location for such planets to form.
Artist’s impression of Barnard’s Star and its super-Earth
Previous searches for a planet around Barnard’s Star have had disappointing results — this recent breakthrough was possible only by combining measurements from several high-precision instruments mounted on telescopes all over the world [3].
“After a very careful analysis, we are 99% confident that the planet is there,” stated the team’s lead scientist, Ignasi Ribas (Institute of Space Studies of Catalonia and the Institute of Space Sciences, CSIC in Spain). “However, we’ll continue to observe this fast-moving star to exclude possible, but improbable, natural variations of the stellar brightness which could masquerade as a planet.”
Exploring the surface of a super-Earth orbiting Barnard’s Star (Artist’s impression)
Among the instruments used were ESO’s famous planet-hunting HARPS and UVES spectrographs. “HARPS played a vital part in this project. We combined archival data from other teams with new, overlapping, measurements of Barnard’s star from different facilities,” commented Guillem Anglada Escudé (Queen Mary University of London), co-lead scientist of the team behind this result [4]. “The combination of instruments was key to allowing us to cross-check our result.”
The astronomers used the Doppler effect to find the exoplanet candidate. While the planet orbits the star, its gravitational pull causes the star to wobble. When the star moves away from the Earth, its spectrum redshifts; that is, it moves towards longer wavelengths. Similarly, starlight is shifted towards shorter, bluer, wavelengths when the star moves towards Earth.
Barnard’s Star in the Solar neighborhood
Astronomers take advantage of this effect to measure the changes in a star’s velocity due to an orbiting exoplanet — with astounding accuracy. HARPS can detect changes in the star’s velocity as small as 3.5 km/h — about walking pace. This approach to exoplanet hunting is known as the radial velocity method, and has never before been used to detect a similar super-Earth type exoplanet in such a large orbit around its star.
“We used observations from seven different instruments, spanning 20 years of measurements, making this one of the largest and most extensive datasets ever used for precise radial velocity studies.” explained Ribas. ”The combination of all data led to a total of 771 measurements — a huge amount of information!”
“We have all worked very hard on this breakthrough,” concluded Anglada-Escudé. “This discovery is the result of a large collaboration organised in the context of the Red Dots project, that included contributions from teams all over the world. Follow-up observations are already underway at different observatories worldwide.”
Notes:
[1] The only stars closer to the Sun make up the triple star system Alpha Centauri. In 2016, astronomers using ESO telescopes and other facilities found clear evidence of a planet orbiting the closest star to Earth in this system, Proxima Centauri. That planet lies just over 4 light-years from Earth, and was discovered by a team led by Guillem Anglada Escudé.
[2] The total velocity of Barnard’s Star with respect to the Sun is about 500 000 km/h. Despite this blistering pace, it is not the fastest known star. What makes the star’s motion noteworthy is how fast it appears to move across the night sky as seen from the Earth, known as its apparent motion. Barnard’s Star travels a distance equivalent to the Moon's diameter across the sky every 180 years — while this may not seem like much, it is by far the fastest apparent motion of any star.
[3] The facilities used in this research were: HARPS at the ESO 3.6-metre telescope; UVES at the ESO VLT; HARPS-N at the Telescopio Nazionale Galileo; HIRES at the Keck 10-metre telescope; PFS at the Carnegie’s Magellan 6.5-m telescope; APF at the 2.4-m telescope at Lick Observatory; and CARMENES at the Calar Alto Observatory. Additionally, observations were made with the 90-cm telescope at the Sierra Nevada Observatory, the 40-cm robotic telescope at the SPACEOBS observatory, and the 80-cm Joan Oró Telescope of the Montsec Astronomical Observatory (OAdM).
[4] The story behind this discovery will be explored in more detail in this week’s ESOBlog: https://www.eso.org/public/blog/
More information:
This research was presented in the paper A super-Earth planet candidate orbiting at the snow-line of Barnard’s star published in the journal Nature on 15 November.
The team was composed of I. Ribas (Institut de Ciències de l’Espai, Spain & Institut d’Estudis Espacials de Catalunya, Spain), M. Tuomi (Centre for Astrophysics Research, University of Hertfordshire, United Kingdom), A. Reiners (Institut für Astrophysik Göttingen, Germany), R. P. Butler (Department of Terrestrial Magnetism, Carnegie Institution for Science, USA), J. C. Morales (Institut de Ciències de l’Espai, Spain & Institut d’Estudis Espacials de Catalunya, Spain), M. Perger (Institut de Ciències de l’Espai, Spain & Institut d’Estudis Espacials de Catalunya, Spain), S. Dreizler (Institut für Astrophysik Göttingen, Germany), C. Rodríguez-López (Instituto de Astrofísica de Andalucía, Spain), J. I. González Hernández (Instituto de Astrofísica de Canarias Spain & Universidad de La Laguna, Spain), A. Rosich (Institut de Ciències de l’Espai, Spain & Institut d’Estudis Espacials de Catalunya, Spain), F. Feng (Centre for Astrophysics Research, University of Hertfordshire, United Kingdom), T. Trifonov (Max-Planck-Institut für Astronomie, Germany), S. S. Vogt (Lick Observatory, University of California, USA), J. A. Caballero (Centro de Astrobiología, CSIC-INTA, Spain), A. Hatzes (Thüringer Landessternwarte, Germany), E. Herrero (Institut de Ciències de l’Espai, Spain & Institut d’Estudis Espacials de Catalunya, Spain), S. V. Jeffers (Institut für Astrophysik Göttingen, Germany), M. Lafarga (Institut de Ciències de l’Espai, Spain & Institut d’Estudis Espacials de Catalunya, Spain), F. Murgas (Instituto de Astrofísica de Canarias, Spain & Universidad de La Laguna, Spain), R. P. Nelson (School of Physics and Astronomy, Queen Mary University of London, United Kingdom), E. Rodríguez (Instituto de Astrofísica de Andalucía, Spain), J. B. P. Strachan (School of Physics and Astronomy, Queen Mary University of London, United Kingdom), L. Tal-Or (Institut für Astrophysik Göttingen, Germany & School of Geosciences, Tel-Aviv University, Israel), J. Teske (Department of Terrestrial Magnetism, Carnegie Institution for Science, USA & Hubble Fellow), B. Toledo-Padrón (Instituto de Astrofísica de Canarias, Spain & Universidad de La Laguna, Spain), M. Zechmeister (Institut für Astrophysik Göttingen, Germany), A. Quirrenbach (Landessternwarte, Universität Heidelberg, Germany), P. J. Amado (Instituto de Astrofísica de Andalucía, Spain), M. Azzaro (Centro Astronómico Hispano-Alemán, Spain), V. J. S. Béjar (Instituto de Astrofísica de Canarias, Spain & Universidad de La Laguna, Spain), J. R. Barnes (School of Physical Sciences, The Open University, United Kingdom), Z. M. Berdiñas (Departamento de Astronomía, Universidad de Chile), J. Burt (Kavli Institute, Massachusetts Institute of Technology, USA), G. Coleman (Physikalisches Institut, Universität Bern, Switzerland), M. Cortés-Contreras (Centro de Astrobiología, CSIC-INTA, Spain), J. Crane (The Observatories, Carnegie Institution for Science, USA), S. G. Engle (Department of Astrophysics & Planetary Science, Villanova University, USA), E. F. Guinan (Department of Astrophysics & Planetary Science, Villanova University, USA), C. A. Haswell (School of Physical Sciences, The Open University, United Kingdom), Th. Henning (Max-Planck-Institut für Astronomie, Germany), B. Holden (Lick Observatory, University of California, USA), J. Jenkins (Departamento de Astronomía, Universidad de Chile), H. R. A. Jones (Centre for Astrophysics Research, University of Hertfordshire, United Kingdom), A. Kaminski (Landessternwarte, Universität Heidelberg, Germany), M. Kiraga (Warsaw University Observatory, Poland), M. Kürster (Max-Planck-Institut für Astronomie, Germany), M. H. Lee (Department of Earth Sciences and Department of Physics, The University of Hong Kong), M. J. López-González (Instituto de Astrofísica de Andalucía, Spain), D. Montes (Dep. de Física de la Tierra Astronomía y Astrofísica & Unidad de Física de Partículas y del Cosmos de la Universidad Complutense de Madrid, Spain), J. Morin (Laboratoire Univers et Particules de Montpellier, Université de Montpellier, France), A. Ofir (Department of Earth and Planetary Sciences, Weizmann Institute of Science. Israel), E. Pallé (Instituto de Astrofísica de Canarias, Spain & Universidad de La Laguna, Spain), R. Rebolo (Instituto de Astrofísica de Canarias, Spain, & Consejo Superior de Investigaciones Científicas & Universidad de La Laguna, Spain), S. Reffert (Landessternwarte, Universität Heidelberg, Germany), A. Schweitzer (Hamburger Sternwarte, Universität Hamburg, Germany), W. Seifert (Landessternwarte, Universität Heidelberg, Germany), S. A. Shectman (The Observatories, Carnegie Institution for Science, USA), D. Staab (School of Physical Sciences, The Open University, United Kingdom), R. A. Street (Las Cumbres Observatory Global Telescope Network, USA), A. Suárez Mascareño (Observatoire Astronomique de l'Université de Genève, Switzerland & Instituto de Astrofísica de Canarias Spain), Y. Tsapras (Zentrum für Astronomie der Universität Heidelberg, Germany), S. X. Wang (Department of Terrestrial Magnetism, Carnegie Institution for Science, USA), and G. Anglada-Escudé (School of Physics and Astronomy, Queen Mary University of London, United Kingdom & Instituto de Astrofísica de Andalucía, Spain).
ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It has 16 Member States: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and with 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:
ESOcast 184 Light: Super-Earth Orbiting Barnard’s Star: https://www.eso.org/public/videos/eso1837a/
Research paper: https://www.eso.org/public/archives/releases/sciencepapers/eso1837/eso1837a.pdf
Red Dots project: https://reddots.space/
Pale Red Dot campaign discovers Proxima Centauri b: https://www.eso.org/public/news/eso1629/
Red Dots: https://reddots.space/
CARMENES: https://carmenes.caha.es/
HARPS: https://www.eso.org/public/teles-instr/lasilla/36/harps/
ESO 3.6-metre telescope: https://www.eso.org/public/teles-instr/lasilla/36/
ESO VLT: https://en.wikipedia.org/wiki/Very_Large_Telescope
UVES: https://www.eso.org/public/teles-instr/paranal-observatory/vlt/vlt-instr/uves/
Telescopio Nazionale Galileo: https://en.wikipedia.org/wiki/Galileo_National_Telescope
2.4-m telescope at Lick Observatory: https://en.wikipedia.org/wiki/Lick_Observatory
Calar Alto Observatory: https://en.wikipedia.org/wiki/Calar_Alto_Observatory
Sierra Nevada Observatory: https://en.wikipedia.org/wiki/Sierra_Nevada_Observatory
Joan Oró Telescope of the Montsec Astronomical Observatory (OAdM): http://oadm.ieec.cat/en/inici.htm
Images, Text, Credits: ESO/Calum Turner/Queen Mary University of London/Guillem Anglada-Escudé/Institut d’Estudis Espacials de Catalunya and the Institute of Space Sciences (CSIC)/Ignasi Ribas/M. Kornmesser/IAU and Sky & Telescope/Digitized Sky Survey 2 Acknowledgement: Davide De Martin/E — Red Dots/Videos: ESO/M. Kornmesser/L. Calçada/Vladimir Romanyuk (spaceengine.org). Music: Astral Electronics.
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