A solar sibling identical to the Sun

2018 November 16

Open star cluster Trumpler 14, a cluster with more than two thousand stars, similar to the one where the Sun was born. Credit: ESO/H. Sana Image of the Sun. Credit: SDO/NASA

The team is Vardan Adibekyan, Sérgio Sousa, Elisa Delgado-Mena, Andressa Ferreira, Maria Tsantaki (Instituto de Astrofísica e Ciências do Espaço), Nuno Cardoso Santos (Instituto de Astrofísica e Ciências do Espaço and Faculdade de Ciências da Universidade do Porto), Patrick de Laverny, Alejandra Recio–Blanco, Georges Kordopatis (Observatoire de la Côte d’Azur), Arthur Hakobyan (Byurakan Astrophysical Observatory). The Instituto de Astrofísica e Ciências do Espaço (Institute of Astrophysics and Space Sciences – IA) is the largest Portuguese research unit of space sciences, which integrates researchers from University of Porto and University of Lisbon, and encompasses most of the field’s national scientific output. It was evaluated as Excellent in the last evaluation from the European Science Foundation (ESF). IA’s activity is funded by national and international funds, including Fundação para a Ciência e a Tecnologia (UID/FIS/04434/2013), POPH/FSE and FEDER through COMPETE 2020. The article “The AMBRE project: searching for the closest solar siblings” was published in the journal Astronomy & Astrophysics, Vol. 619, November 2018 (DOI: 10.1051/0004-6361/201834285). HARPS (High Accuracy Radial velocity Planet Searcher) is a high resolution spectrograph, installed at ESO’s 3.6 meter telescope in La Silla Observatory (Chile). It can detect variations in velocity smaller than 4 km/h (or roughly the speed of a person walking). ESPRESSO (Echelle SPectrogaph for Rocky Exoplanet and Stable Spectroscopic Observations) is a high resolution spectrograph, installed at ESO’s Very Large Telescope (VLT). It has been designed with the goal of searching and detecting Earth-like planets, capable of supporting life. To do so, it can measure variations in velocity as low as 0.3 km/h. It also aims to test the stability of the fundamental constants of the Universe. The consortium that developed and built ESPRESSO gathers academic and scientific institutions from Portugal, Italy, Switzerland and Spain, as well as the European Southern Observatory (ESO). In Portugal, the effort was led by IA (University of Porto and University of Lisbon) and Faculdade de Ciências da Universidade de Lisboa (FCUL).

An international team, led by Instituto de Astrofísica e Ciências do Espaço (IA) researcher Vardan Adibekyan , used a novel method to detect solar siblings. The articlewas published in the journal Astronomy & Astrophysics Solar siblings are the thousands of stars which formed in the same massive cluster as the Sun, about 4.6 billion years ago. As time went by, the stars in the cluster disbanded and scattered throughout our galaxy, making it very difficult to find them.Vardan Adibekyan (IA & University of Porto ) explains the importance of finding these stars: “Since there isn’t much information about the Sun’s past, studying these stars can help us understand where in the Galaxy and under which conditions the Sun was formed.”He adds: “With the collaboration of Patrick de Laverny and Alejandra Recio-Blanco, from the Côte d'Azur observatory , we got a sample of 230 000 spectra from the AMBRE project.” AMBRE is a galactic archaeology project set up by ESO and the Observatoire de la Côte d’Azur, in order to determine the stellar atmospheric parameters for the archived spectra from ESO’s FEROS, HARPS , UVES and GIRAFFE spectrographs.Next, the team used these very high quality spectral data from the AMBRE project together with very precise astrometric data retrieved from the second release of ESA ’s GAIA mission, in order to: “make a selection of stars with chemical compositions which best match the Sun’s composition, followed by an estimate of these stars age and kinematic properties”, said Vardan Adibekyan.Although only a single solar sibling was found in this work - HD186302, it was a special one. This G3 type main sequence star is not only a solar sibling by both age and chemical composition, but it is also a solar twin.Solar siblings might also be good candidates to search for life since there is a possibility that life could have been transported between planets around stars of the solar cluster. The transfer of life between exoplanetary systems is called interstellar lithopanspermia.Adibekyan is cautiously excited about this possibility: “Some theoretical calculations show that there is non-negligible probability that life spread from Earth to other planets or exoplanetary systems, during the period of the late heavy bombardment. If we are lucky, and our sibling candidate has a planet, and the planet is a rocky type, in the habitable zone, and finally if this planet was 'contaminated' by the life seeds from Earth, then we have what one could dream – an Earth 2.0, orbiting a Sun 2.0.”The team at IA plans to start a campaign to search for planets around this star using both HARPS and ESPRESSO spectrographs. Finding and characterizing planetary systems around solar siblings could return very important information about the outcome of planet formation in a common environment. Daniel Folha

Sérgio Pereira

Ricardo Cardoso Reis (Coordination, Porto)

João Retrê (Coordination, Lisboa)