8. The Creator of Astrobotany, Gavriil Adrianovich Tikhov

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.