The Search for Extra-Terrestrial Life - by Dr. Chris Marker

Since the dawn of mankind we have looked up at the stars and asked - are we alone? A number of recent discoveries may pave the way to finally answering that question.

Recent findings released by NASA from the Cassini probe, which currently orbits Saturn, have shown that one of Saturn's moons, Enceladus, has a promising environment which may be able to host life. Enceladus is mostly covered by fresh, clean ice with an ocean of liquid water underneath. Some of this water is vented into space in plumes which Cassini has flown through and chemically analyzed. Cassini has found strong evidence that the seafloor of Enceladus has hydrothermal vents similar to those found on Earth around which microbes and more complex organisms live. Cassini determined this through confirming a process called 'serpentinization,' which is when seawater reacts with hot upwelling rocks that are rich in iron and magnesium, thus releasing hydrogen.

The latest announcement from NASA was based on a definitive signal from Cassini indicating molecular hydrogen in the water jets. Cassini itself does not have the necessary instruments to directly detect life, but NASA has already planned a mission to Europa (one of the four major moons of Jupiter) which also has a subsurface sea. Unlike Enceladus, however, its ice shell is very much thicker and thus harder to get to, and it has yet to be confirmed that it has hydrothermal vents.

And that was not the only exciting, extra-terrestrial themed discovery made this year. In February of this year, NASA announced a record seven Earth-sized planets orbiting a single star. The system of planets orbits a star called Trappist-1, and includes three planets within the conventional "habitable" zone where scientists believe life could exist. The planets are close to each other and the star itself, but since the star is small and cold, the planets are likely to be temperate, which means they could have liquid water on the surface.

The observation of these planets was done by NASA's Spitzer Space Telescope and some ground based telescopes using the transit method. This method relies upon the planet passing in front of the star, which slightly reduces the amount of light we see on Earth from the star. The size of the planet can then be determined from the exact way the light dims as the planet passes the star. In addition, if you can find the radius of the planet, you can also determine the density of the planet and infer something of its structure.

The transit method can also be used to study the atmosphere of a planet. As light from the star passes through the upper atmosphere of the planet, its spectrum will be affected. Then, by analyzing the light spectrum carefully, you can thus detect elements present in the planet's atmosphere, such as hydrogen and carbon.

These are just two of the more recent discoveries surrounding mankind’s never-ending search for extra-terrestrial life, a search that becomes more fascinating as our probes and telescopes increase in power and we seemingly find the potential for extra-terrestrial life all around us.

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