2019-07-24 12:31:17
Our view of the Universe is changing day by day as new instruments reveal the existence of new objects never seen before. Barely 24 years ago I worked at Radio Exterior in Spain and broke the news of the discovery of a planet revolving around a star similar to the Sun. That news made front pages, not only in scientific magazines but also in the world press. But that first extrasolar planet was not only the demonstration that there are other worlds orbiting stars other than our Sun, but also showed how diverse they could be. The planet that revolves around 51 Pegasi, as the star is known, is half the size of Jupiter and is located so close to the star that it takes just over 4 days to complete one orbit around it.
That first detection was the starting signal for a whole series of discoveries that is forging a wiser and less anthropocentric vision of the Universe. At this moment thousands of planets have been discovered, many of them forming planetary systems that have nothing to envy ours and some, still few due to the difficulties involved in finding them, show intriguing similarities with Earth.
Techniques for detecting extrasolar planets have been perfected over the last 25 years. Planets are now being searched for from the earth’s surface and from space, with increasingly specialized instruments paving the way for new discoveries. One of the instruments that have demonstrated their good work has a very Spanish name: CARMEN IS. The name is an acronym for “Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Échelle Spectrographs”. Said in Spanish, it is a spectrograph capable of analyzing visible and infrared light from M-type dwarf stars to detect exoplanets using the radial velocity technique from the Calar Alto Observatory, located in Almería, southern Spain.
The radial velocity technique makes it possible to detect the movement of a star due to the attraction of a planet revolving around it. Logically, this movement is much more evident when the star is small and that is the reason why CARMEN IS places special emphasis on the study of M-type dwarf stars. Our guest today in Talking to Scientists, Pedro José Amado González, astrophysicist and researcher at the Institute of Astrophysics of Andalusia and co-principal investigator of CARMEN IS, tells what these stars are like and why they are good candidates for detecting planets similar to Earth. To begin with, they are very small, their mass oscillates between 7.5% and 50% of the mass of the Sun. Their temperature is much lower and their brightness is so dim that they are invisible to the naked eye, although we can observe them with telescopes. However, they are the most abundant in the universe, it is estimated that 70% of the stars that exist are of this type. Can you imagine what the night sky would look like if we could see them? To get an idea of its abundance, of the 30 closest stars to Earth, 20 are red dwarfs.
When CARMEN IS came into operation in 2014, it began to study the light from the red dwarf stars captured by the 3.5-meter telescope at Calar Alto, focused on those closest to us. The search was bearing fruit in the form of a series of findings that have culminated in the discovery of two Earth-sized planets around the star Teegarden, a small red dwarf located 12.5 light-years from Earth. Proof of how small Teegarden is is that it wasn’t discovered until 2003, despite being the 24th closest star to us.
For three years, scientists have been observing Teegarden and accurately measuring its movements forced by the attraction of the planets that surround it. Little by little, the measurements revealed a pattern of movements that was repeated following a temporal sequence that agrees with the attraction of two planets. The discovery could be verified by different means and they were assigned the name of Teegarden by c.
The data sequence has allowed to obtain some of its characteristics. Teegerden b is very similar in mass to Earth and rotates so close to the star that it takes less than 5 days to complete one orbit around it. The second planet is also similar in size to Earth but is located a little further away, it takes 11.4 days to make a full rotation. But the most interesting thing for us is that, given the low radiation emitted by the star, both planets are located in what is known as the “temperate” or “habitable” zone, that is, an area in which the radiation received allows have temperatures compatible with the existence of liquid water, something that, as we know, is essential for life.
Logically, the fact that a planet is in a temperate zone does not mean that it can contain liquid water and life, as proof of what I am saying, Mars is within the temperate zone of the Sun and we know that there, at the moment, does not exist. liquid water, at least on the surface. However, the existence of two terrestrial planets in the temperate zone around a star of the type that is most abundant in the Universe is a discovery that opens up a whole world of possibilities.
I invite you to listen to Pedro José Amado González, astrophysicist, researcher at the Institute of Astrophysics of Andalusia, member of the Group of Low Mass Stars and Exoplanets of the IAA and co-principal investigator of CARMEN IS.
References:
M. Zechmeister et al. “The CARMEN IS search for exoplanets around M dwarfs. Two temperate Earth-mass planet candidates around Teegarden’s Star”. Astronomy & Astrophysics, June 2019.
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