D. Briot’s research while affiliated with Paris Observatory and other places

Nowadays the more powerful method to detect extrasolar planets is the transit method. We review the planet transits which were anticipated, searched, and the first ones which were observed all through history. Indeed transits of planets in front of their star were first investigated and studied in the solar system. The first observations of sunspots were sometimes mistaken for transits of unknown planets. The first scientific observation and study of a transit in the solar system was the observation of Mercury transit by Pierre Gassendi in 1631. Because observations of Venus transits could give a way to determine the distance Sun-Earth, transits of Venus were overwhelmingly observed. Some objects which actually do not exist were searched by their hypothetical transits on the Sun, as some examples a Venus satellite and an infra-mercurial planet. We evoke the possibly first use of the hypothesis of an exoplanet transit to explain some periodic variations of the luminosity of a star, namely the star Algol, during the eighteen century. Then we review the predictions of detection of exoplanets by their transits, those predictions being sometimes ancient, and made by astronomers as well as popular science writers. However, these very interesting predictions were never published in peer-reviewed journals specialized in astronomical discoveries and results. A possible transit of the planet beta Pic b was observed in 1981. Shall we see another transit expected for the same planet during 2018? Today, some studies of transits which are connected to hypothetical extraterrestrial civilisations are published in astronomical refereed journals. Some studies which would be classified not long ago as science fiction are now considered as scientific ones.

Reliable determination of the basic physical properties of hot emission-line binaries with Roche-lobe filling secondaries is important for developing the theory of mass exchange in binaries. It is a very hard task, however, which is complicated by the presence of circumstellar matter in these systems. So far, only a small number of systems with accurate values of component masses, radii, and other properties are known. Here, we report the first detailed study of a new representative of this class of binaries, BR CMi, based on the analysis of radial velocities and multichannel photometry from several observatories, and compare its physical properties with those for other well-studied systems. BR CMi is an ellipsoidal variable seen under an intermediate orbital inclination of ~51 degrees, and it has an orbital period of 12.919059(15) d and a circular orbit. We used the disentangled component spectra to estimate the effective temperatures 9500(200) K and 4655(50) K by comparing them with model spectra. They correspond to spectral types B9.5e and G8III. We also used the disentangled spectra of both binary components as templates for the 2-D cross-correlation to obtain accurate RVs and a reliable orbital solution. Some evidence of a secular period increase at a rate of 1.1+/-0.5 s per year was found. This, together with a very low mass ratio of 0.06 and a normal mass and radius of the mass gaining component, indicates that BR CMi is in a slow phase of the mass exchange after the mass-ratio reversal. It thus belongs to a still poorly populated subgroup of Be stars for which the origin of Balmer emission lines is safely explained as a consequence of mass transfer between the binary components.

In the context of life detection on terrestrial exoplanets, new methods of search for spectral signatures of chlorophyll and other biomarkers in the Earthshine have been developed in the last few decades. Astronomical observations made at OHP and ESO (NTT) showed a significant signal when continents are facing the Moon. This signal, called the Vegetation Red Edge (VRE), is undoubtedly due to chlorophyll absorption properties. In order to strengthen these results, the LUCAS (LUmière Cendrée en Antarctique par Spectroscopie) project dedicated to the measurement of the Earthshine from the Concordia Research Station (C Dome, Antarctica) has been set up. One of the objectives of LUCAS was to observe prolonged variations of the VRE corresponding to various parts of the Earth facing the Moon. An extension of this project, called LUCAS II, would allow long-term observations to detect seasonal variations of the vegetation signal. These data, together with accurate measurements of the Earth's albedo, will help validate a model of global and spectral albedo of our planet.

It is likely that images of Earth-like planets will be obtained in the next years. The first images will actually come down to single dots, in which biomarkers can be searched. Taking the Earth as a example of planet providing life, Earthshine observations showed that the spectral signature of photosynthetic pigments and atmospheric biogenic molecules was detectable, suggesting that, in principle, life on other planets could be detected on a global scale, if it is widely spread and distinguishable from known abiotic spectral signatures. As for the Earth, we already showed that the Vegetation Red Edge which is related to chlorophyll absorption features was larger when continents, versus oceans, were facing the Moon. It proved that an elementary mapping of a planet was even possible. In the frame of the LUCAS (LUmière Cendrée en Antarctique par Spectroscopie) project, the Earthshine has been measured in the Concordia Research Station (Dome C, Antarctica) long enough to observe variations corresponding to different parts of the Earth facing the Moon. An extension of this project, called LUCAS II, would allow long-term observations to detect seasonal variations in the vegetation signal. These data, together with precise measurements of the Earth's albedo, will help to validate a model of global and spectral albedo of our planet.

On the occasion of the 50th anniversary of the Drake formula, it appears timely to briefly review the history of Astrobiology from the origins up to the epoch of the Drake formula. After reminding the main steps of this history during Antiquity, the Middle Ages, and the Renaissance, we point out some little known or unknown studies published during the Modern and Contemporary epochs. Then we review the importance of Astrobiology and the search for life in the Universe in scientific publications during the 20th century.

The Russian astronomer, Gavriil Adrianovich Tikhov (1875-1960), was one of the main pioneers of astrobiology and was the creator of astrobotany. From 1906 to 1941, he began his career as an astronomer in the Pulkovo Observatory, near Saint Petersburg, and then moved to Alma-Ata (Kazakhstan) until the end of his life. He specialized in many different fields of astronomy: besides astrobotany and astrobiology, he studied the Sun, the planets, the comets, the blue color and polarization of the sky, the Earthshine, variable stars, as well as interstellar absorption. He designed new instruments and wrote more than 230 scientific papers. As early as 1914, on the basis of observations of Earthshine, he concluded that Earth seen from space has to be seen with a pale blue color. Tikhov's main research was focused on the search for extraterrestrial life, particularly the presence of vegetation on Mars. At this time, many astronomers believed in the existence of canals on the Martian surface. Seasonal variations of color on the surface of Mars were often interpreted as changes of vegetation, as on Earth. From 1909, he observed Mars during favorable configurations, that is to say Mars oppositions, first using filters and then with a spectrograph. However, he failed to detect chlorophyll in Mars' spectra. So he decided to go looking for plants with no chlorophyll, especially plants growing in extreme environments like on Mars and to study and measure their reflectance spectrum. Tikhov, who was one of the first scientists to use the word "astrobiology," coined the word "astrobotany" in 1945. In 1947 he founded a Department of Astrobotany at Alma-Ata Observatory, where students, biologists, botanists, and physicists joined to study the reflectance spectra of plants growing in conditions similar to those found on Mars. Expeditions were organized in very cold or very dry places with this aim in view. After he died, the Department of Astrobotany was dismantled. After nearly half a century of lack of interest, the work of G.A. Tikhov appears really modern. Nowadays, in order to prepare for the detection of life in remote extrasolar planets, astronomers observe Earthshine to detect the spectrum of terrestrial chlorophyll, and specifically the Vegetation Red Edge (VRE) in the near infrared. Although the VRE is only a few percent, it is higher when continents covered by vegetation are facing the Moon, and lower in the case of oceans. In order to study the daily variation of chlorophyll spectra in the Earthshine according the part of Earth facing the Moon, we developed an observational program from the scientific station Concordia in Antarctica.

Abstract The word astrobiology was possibly first used in 1935, in an article published in a French popular science magazine. The author was Ary J. Sternfeld (1905-1980), a pioneer of astronautics who wrote numerous scientific books and papers. The article is remarkable because his portrayal of the concept is very similar to the way it is used today. Here I review the 1935 article and provide a brief history of Sternfeld's life, which was heavily influenced by the tragic events of 20(th) century history. Key Words: History-Pioneers. Astrobiology 12, xxx-xxx.

On the occasion of the 50th anniversary of the Drake formula, it appears interesting to briefly review the history of Astrobiology from the origins up to the epoch of the Drake formula. After recalling the main steps of this history during Antiquity, the Middle Ages, and the Renaissance, we point out some little known or unknown studies during the Modern and Contemporary epochs. Then we review the importance of astrobiology and the search for life in the Universe in the scientific publications during the 20th century.

The research of life in Universe is a ancient quest that has taken different forms over the centuries. It has given rise to a new science, which is normally referred as Astrobiology. It is interesting to research when this word was used for the first time and when this science developed to represent the search for life in Universe as is done today. There are records of the usage of the word "Astrobiology" as early as 1935, in an article published in a French popular science magazine. Moreover this article is quite remarkable because its portrayal of the concept of the subject is very similar to that considered today. The author of this paper was Ary J. Sternfeld (1905 - 1980), who was ortherwise known as a poorly respected great pioneer of astronautics. We provide a brief description of his life, which was heavily influenced by the tragic events of the 20th century history, from Poland and France to Russia. He was a prolific scientific writer who wrote a number of very successful scientific books and papers.