A European team, led by Xavier Dumusque, an astronomer at the Center for Astrophysics at the University of Porto (CAUP), detected a planet with a mass similar to Earth's in Alpha of Centaur B, in the star system closest to the Sun.
This result1, published in this Thursday, October 18th edition of the magazine Nature, was done using the radial speed method2, with the high resolution spectrograph HARP3, installed on the 3,6 meter telescope of the Observatory of La Silla (ESO).
The team4, which also includes the participation of Nuno Cardoso Santos (Astrophysics Center5 e Faculty of Science from the University of Porto), determined that the now discovered planet (called Alpha Centaur B b) is only 0,04 astronomical units from its star (or 25 times closer than the Earth is to the Sun), and completes one orbit every 3,236 days (about 77 hours and 40 minutes).
To this end, the team used data collected by HARPS between February 2008 and July 2011. Dumusque (Geneva Observatory/CAUP), the first author of the article comments: “Our observations with HARPS spanned over four years and revealed a small but real sign of a planet orbiting Alpha Centaur B every 3,2 days".
During this campaign, the star was observed repeatedly, whenever possible every two hours, three times a night and with an integration time of 10 minutes. Only in this way was it possible to eliminate the numerous sources of contamination, in order to achieve the necessary precision to detect the planet. Some examples of contamination include instrument noise, rotation and activity of the star itself (such as wobbles and grain), orbital motion of the binary, or contamination of companion star light.
For Nuno Santos, this was a great challenge: “It was a lot of work! It's almost like trying to hear a person several meters away while celebrating a goal in a football game. We are using the instrument beyond hitherto known limits. This is very encouraging because it gives us confidence to continue the work to build ESPRESSO in the near future.6, an even more precise and stable instrument”.
Stéphane Udry, team member and researcher at the Geneva Observatory commented: “This is the first planet discovered that has an Earth-like mass and orbits a sun-like star. It is too close to its star and will therefore be too hot to support life, but it may well be one of several orbiting this star system. Recent results seem to clearly indicate that most low-mass planets will be in this type of system.”
Dumusque added that this "was an important step towards one day finding a planet with the characteristics of Earth, orbiting a star like the Sun at a safe distance, where it will be possible to have liquid water on its surface."
Alpha Centaur is one of the brightest stars in the sky, visible to the naked eye in the southern hemisphere. At a distance of just 4,3 light-years away, it is often designated as the closest star to our Sun. eyes appears to be just one star, it is actually a triple system, composed of two Sun-like stars (Alpha Centaur A and B) that rotate around each other and, in a further outer orbit, the Near Centaur star, smaller and less shiny, which rotates around the other two.
Author Ricardo Cardoso Reis (Astrophysics Center of the University of Porto CAUP)
Science in the Regional Press – Ciência Viva
Video: A trip to Alpha Centaur:
More information:
1. The article “An Earth-mass planet orbiting a Centauri B” will be published in the October 18 issue of the magazine Nature.
2. The Radial Velocity Method detects exoplanets by measuring small variations in the (radial) speed of the star, due to the movement that the orbits of these planets impart on the star. Through this method it is only possible to estimate the minimum mass of the planet, as the calculation depends on the inclination of the orbit. However, statistically the minimum mass is often very close to the planet's actual mass. By comparison, the variation in speed that the Earth's motion imparts to the Sun is only 10 cm/s (about 0,36 km/h).
3. The team is composed of Xavier Dumusque (Observatory of Geneva/CAUP), Francesco Pepe (Geneva Observatory), Christophe Lovis (Geneva Observatory), Damien Ségransan (Geneva Observatory), Johannes Sahlmann (Geneva Observatory), Willy Benz (U. Bern), François Bouchy (Geneva Observatory/Institute of Paris Astrophysics), Michel Mayor (Geneva Observatory), Didier Queloz (Geneva Observatory), Nuno Cardoso Santos (CAUP) and Stéphane Udry (Geneva Observatory).
4. The University of Porto Astrophysics Center (CAUP) was created in May 1989 and started its activities in October 1990. It is a non-profit private scientific and technical association of the University of Porto, recognized as being of public utility. Its objectives include supporting and promoting Astronomy through scientific research, training at postgraduate and university levels, teaching Astronomy at non-university level (basic and secondary) and disseminating science and promoting scientific culture.
5. It is the largest research institute in Astronomy in Portugal, with more than 60 people. Since 2000, it has been evaluated as “Excellent” by international panels, organized by the Foundation for Science and Technology (FCT).
6. The EXPRESS (Echelle SPectrogaph for Rocky Exoplanet and Stable Spectroscopic Observations) will be a high resolution spectrograph, to be installed at the VLT observatory (ESO). Its purpose is to search for and detect Earth-like planets capable of supporting life. It will be able to detect speed variations of around 0,3 km/h (or the maximum speed of a walking Galapagos tortoise). This spectrograph is being developed by a consortium involving Portugal, Italy, Switzerland and Spain. In Portugal, the project is led by CAUP and also includes the participation of researchers from the Faculty of Sciences of the University of Lisbon.
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