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The planets beyond our solar system are called exoplanets and two of the most fascinating questions in science are first, what is the frequency of telluric exoplanets? And, secondly, has life appeared elsewhere in the universe outside the Earth?
Promising approaches to answer this last question are underway and it seems that a qualified response to the first is "not too rare". The new telescopes, a NASA project and the other a project of the European Space Agency (ESA), will answer these questions. NASA's mission, called the Exoplanets in Transit Survey Satellite (TESS), was launched last April and the ESA mission, called the Characteristic Exoplanet Satellite (CHEOPS) , will be launched later this year. The search for exoplanets is described by Joshua Winn in the edition of Scientific American of March 2018.
The transit method is the most common way to detect exoplanets in orbit around distant stars of the Earth. Basically, the astronomer watches a star looking for small periodic drops of luminosity signaling an exoplanet in orbit pbading through the field of view and blocking a small fraction of the star's light. A less common way is to observe the Doppler effect on the light emitted by a star under the gravitational pull of its exoplanet into orbit.
Doppler Effect
As the planet in orbit darkens the light of the Star pbading between the star and the telescope, he pulls the star toward the telescope. When he turns behind the star, he now pulls the star away from the telescope. The wavelength of the star light detected by the telescope varies depending on how the star is drawn. We all know the Doppler effect regarding the sound – the height of an ambulance siren approaching rapidly changes suddenly as it pbades in front of you and backs into the distance.
The first transit of exoplanets was detected in 1999 and in the space of 10 years, more than 100 exoplanets were detected. But most of what we know about exoplanets comes from NASA's Kepler mission launched in 2009. This mission will end soon and the search for exoplanets will be taken over by TESS and CHEOPS. Only space telescopes can measure the tiny dimming effect of an exoplanet in transit. The earth's atmosphere would blur this little signal for a terrestrial telescope. Astronomers have now detected nearly 4,000 exoplanets
Most of the stars discovered by Kepler with orbiting planets only have one known planet, but a few hundred stars have several planets. Most exoplanets fall into two categories, planets the size of an Earth and those slightly smaller than the planet Neptune.
What is the frequency of telluric exoplanets? Earth means a rocky planet of similar size to the Earth orbiting its star at a distance where the temperature is sufficient to melt the ice but not to vaporize the liquid water, so one can reasonably expect that the planet is home to large quantities of liquid water. "Living area". It is believed that liquid water was essential to start life on Earth. Kepler found about 12 potentially rocky exoplanets orbiting their stars in the habitable zone
Sunlight
In some cases, space telescopes can also collect information on the composition of exoplanet atmospheres. When the exoplanet transits between its star and a telescope, the starlight must traverse the atmosphere of the planet before reaching the telescope. Depending on the chemical composition of the atmosphere of the exoplanet, some of the sunlight will be absorbed preferentially at certain wavelengths and the badysis of this effect highlights the composition of the Atmosphere of the planet
port life. One approach to answer this question is to examine the atmospheres of exoplanets for telltale signs that the planet carries life. For example, if the planet houses a life built on the same principles as earthly life, its atmosphere will contain oxygen. The atmosphere of the Earth is rich in oxygen, but if all life on Earth dies, this atmospheric oxygen would be quickly recovered from the atmosphere, converted to oxides and buried in rocks.
There is already a well-established program of terrestrial intelligence research (SETI) scanning the sky with terrestrial radio telescopes hoping to detect radiofrequency emissions from extraterrestrial civilizations
The discovery of extraterrestrial life would be a monumental landmark in the history of civilization. The detection of extraterrestrial intelligence would be truly transcendent
William Reville is Professor Emeritus of Biochemistry at the UCC
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