The existence of a second exoplanet around the star Proxima centauri, only about 4.2 light years from the Sun, has been announced. The discovery of Proxima Centauri c will undoubtedly need to be consolidated, but it would be a superterre, unfortunately not in the habitable zone as is the case for Proxima Centauri b.
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Interview: what is an exoplanet? The question of exoplanets is very old in astronomy. Their existence was indirectly attested for the first time in the 1990s. Futura-Sciences met Jean-Pierre Luminet, renowned astrophysicist, so that he could tell us more about this fascinating subject.
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In 2012, astrophysicists announced the discovery ofexoplanet Alpha Centauri Bb in orbit around one of the components of the Alpha Centauri triple system. It consists of two stars close to each other to the point of forming a star binary, Centaur Alpha A and B (at 4.36 light years of the Earth), and a third star, Alpha Centauri C, 4.22 light years from Solar system. The latter is also called Centaur Proxima. The existence of the exoplanet Alpha Centauri Bb, which was to orbit around of Alpha Centauri B, as it is also called, has since been questioned. But, in 2016, it is the still admitted existence of another exoplanet, around Proxima Centauri this time, which was announced: Proxima Centauri b.
Today, the existence of a second exoplanet, Proxima Centauri c (already suspected a few years ago), is seriously suggested by the analysis of data collected at the La Silla observatory, in Chile, using famous spectrograph Harps (High Accuracy Radial Velocity Planet Searcher) which can detect exoplanets using the radial velocity method and who equips the telescope 3.6 meters on this siteESO. It’s a large international team ofastronomers who makes it known via an article published in the newspaper Nature and free access. It would be a Super-Earth in orbit at 1.5 astronomical unit of its star whose mass would be about half that of Neptune, which is about 17 times that of Earth – there should be a transit to remove ambiguity in estimating the mass of Proxima Centauri c.
The principle of detecting an exoplanet by measuring a spectral shift by Doppler-Fizeau effect. A planet orbiting a star attracts it so that the star itself revolves around the center of mass of the star-planet system. The closer the planet is to its star and mass, the faster this movement will be. Observed with a spectrometer, the elements in the atmosphere of the star will appear in the form of a kind of bar code which shifts periodically towards blue and red when the star approaches and moves away from us, as this video shows it. The greater this offset, the greater the radial speed of the star in our direction. This is how we can determine the minimum mass of the planet and its period of revolution. © ESO, L. Calçada, YouTube
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Alpha and Proxima du Centaure make dream exobiologists and authors of SF
Let us recall that the triple system of Alpha of the Centaur made dream the exobiologists and in particular the authors of science fiction for a long time, because they are the stars closest to the Sun, and especially because of the characteristics of the stars of its double system. Alpha Centauri A is indeed a star of spectral type G2, that is to say a yellow dwarf very similar to the Sun, and Alpha Centauri B, a little less luminous, is of spectral type K1 therefore of a type close to the Sun. It is therefore not surprising that many SF narratives mention habitable planets with extraterrestrial life forms around one of the Alpha Centauri stars.
In the previous article below, via an animation, Futura also mentioned the existence of the mythical work Space ships from the year 2000 to the year 2100 by Stewart Cowley. With illustrations by painters, this book, the first in a series, tells the story of the discovery in 2036 of the civilizations of Alpha, then of Centaur Proxima, and the ensuing war with the latter. Combining these illustrations in the manner of a history book presenting planes from the Second World War (the book dates from 1978), it leaves you wondering when you think of the latest discoveries on exoplanets.
Proxima Centauri c, a target for direct imaging of exoplanets
However, Proxima Centauri being a red dwarf type M and Proxima Centauri c orbiting about 5 years around its sun, we can show that its surface equilibrium temperature, in the absence of a atmosphere, is only 40 Kelvin (Thenitrogen East liquid with a boiling point at 77.36 Kelvin on Earth). Difficult to envisage a form of life in these conditions, except to imagine a scenario similar to that proposed by exobiologists for Europe, the frozen moon of Jupiter.
Finally, as one of the authors of this discovery explains, Hugh jones, teacherastrophysics at the University of Hertfordshire (UK), it is not entirely excluded that the periodic signal extracted from Harps data is in fact only a product of the periodic activity of the star Proxima Centauri, just like the Sun has a cycle of sunspot 11 years old brightness.
The researchers explain, however, that the astrometric data from Gaia regarding the speed of Proxima Centauri should allow, combined with those of Harps, to make much more solid the discovery of Proxima Centauri c. Above all, because of its relative great distance to its star, the superterre should be able to be imaged directly with the next generation of large telescopes on the ground (like theExtremely Large Telescope), or even in space. It is indeed not possible at the moment to obtain a result comparable to that concerning Beta Pictoris b.
The discovery of the exoplanet Proxima Centauri b, located around Proxima Centauri, is similar to that of Proxima Centauri c. To obtain a fairly faithful translation into French, click on the white rectangle at the bottom right. English subtitles should then appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Choose “French”. © European Southern Observatory (ESO)
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What you must remember
- The existence of a second exoplanet around the star Proxima centauri, only about 4.2 light years from the Sun, has been announced.
- The discovery of Proxima Centauri c will undoubtedly need to be consolidated, but it would be a superterre, unfortunately not in the habitable zone as is the case for Proxima Centauri b.
- Detected by the radial velocity method, it could be imaged with the next generation of large telescopes.
- Estimated to be about 8 times that of Earth, its mass is still uncertain. On the other hand, it would be 1.5 AU from its sun, a type M star.
Alpha centauri Bb: is there a 4.3-light-year land?
Article by Laurent Sacco published on 14/03/2015
Alpha Centauri Bb is an exoplanet in orbit around the Alpha star of Centaur B, located about 4.3 light years from the Sun. Its exact mass, at least equal to that of Earth, is still unknown. However, astronomers believe it is not a gas giant but rather of a super-earth … Enough to make all science fiction lovers dream.
Alpha Centauri is a triple system, with two close stars, Alpha Centauri A and B, 4.36 light years from Earth and a third, Alpha Centauri C – or Proxima Centaur – at 4.22 light years. This system has been the dream of exobiologists and science fiction authors for a long time because of the special characteristics of the stars of its dual system. Alpha Centauri A, as it is also called, is a star of spectral type G2, that is to say very similar to the Sun, although a little larger and brighter. Alpha Centauri B is a little less bright and spectral type K1. It too is therefore of a type close to the Sun. Both orbit around each other over an 80-year period, their distance varying from 11.2 to 35.6 AU (astronomical units).
These dreams came closer to reality when astronomers announced in 2012 that they had discovered a exoplanet by the method of radial velocities around Alpha of Centaur B. Unfortunately, as every time with the discovery of an exoplanet in this way, in the absence of planetary transits, the mass of thestar detected remains partly undetermined, because it is not known from which angle the orbit of the exoplanet is viewed.
The mythical book Space ships from the year 2000 to the year 2100 by Stewart Cowley tells the story of the discovery in 2036 of the civilizations of Alpha then Proxima of the Centaur, and of the war which followed with this last. Gathering illustrations like a History book presenting planes from the Second World War (the book dates from 1978), the latest discoveries on exoplanets give it surprising topicality. Indeed, there are good reasons to think that the nearest exoterre could be less than 22 light years away. In addition, we now know that there is at least one planet in orbit around Alpha of Centaur B. Unfortunately, it is far too hot to be habitable. Computer generated images bring the Alpha Centaur warships to life today. © Adrian Mann, Vimeo
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A mass between 1.1 and 2.7 land masses
The mass ofAlpha Centauri Bb (abbreviated : α Cen Bb) could thus be between 1.1 times that of Earth to that of Jupiter. To try to see more clearly, a team of astronomers modeled on computer the triple system of Alpha Centauri to study it using all the arsenal of modern celestial mechanics. The researchers went so far as to take into account the post-Newtonian corrections that the equations of the general relativity to the movements of the stars as well as the effects, among others, of the famous mechanism of Kozai. In this way, their goal was to try to put constraints on the authorized values of the inclination of the plane of the orbit of α Cen Bb and therefore reduce the indeterminacy of the value of its mass.
The results of this research were presented in an open access article on arxiv. It now seems likely that the mass of α Cen Bb is less than 2.7 land masses which would make it, in the worst case, Super-Earth and not a hot Jupiter or Neptune. Indeed, the exoplanet located about 0.042 AU from its star, its orbit is complete in 3.24 days, would be a hellish world where the temperatures are sufficient to melt the lead. However, this does not exclude that others terrestrial planets which would be habitable could exist around Alpha Centauri B.
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