EXOPLANETS

 

What is an Exoplanet? It is a planet that orbits a star other than the Sun.

Till the 1990’s all the planets we knew were in orbit around the Sun. Since the year 1992, astronomers have discovered many Exoplanets. Based on the data at our disposal there could be hundreds of billions of Exoplanets in the Milkyway alone.

The first discovered Exo planets were much bigger than Jupiter and were detected by their gravity tugging the star they orbit. Some were found by light difference in the star when the Exo planet passes between earth and the star they orbit. Most Exo planets we know of are rocky planets much larger than the earth known as super earths or mini Neptunes which are made up of compressed gases. These type of planets do not occur in our solar system, so researchers do not know how different they are from the worlds we know. As of today there are 6022 confirmed Exoplanets in 4490 planetary systems.

About 1 in 5 stars have an earth like planet in the habitable zone. The Milkyway has about 200 billion stars. Based on that there would potentially be 11 billion such planets in our Galaxy.

The nearest Exoplanets discovered are orbiting Proxima Centauri, the nearest star to our Sun at a distance on 4.2 light years.

Many Exo planet systems are tightly packed with their innermost planet orbiting the star much closer than Mercury does. As of now we do not know why such solar systems are more common in our galaxy and why they are not like ours.

Astronomers have found many Exoplanets in their stars habitable zones; ie those zones where liquid water is likely to exist coupled with proper kind of atmosphere. So far the planets discovered are much larger than earth or the star is much smaller and redder than our Sun which would emanate much less heat. With the methods we are adopting to find Exoplanets, it is much more difficult to find Exoplanets of Earth’s size. Upcoming observations are designed to find Exoplanets with greater sensitivity which would let us see more earth sized worlds allowing us to compare them with our Solar system.

However, more than their size, far more essential is the chemical composition of their atmosphere before we can know if it can support life. So far we could not study the surfaces of Exoplanets. Whatever information we got is when the time the Exoplanet transits its star. Then, the gases of the planet absorbed or emitted by its atmospheric gases astronomers can identify some molecules like water, Oxygen or Methane. But it is a very difficult process because the planets are too small and too far away for allowing us to make any precise observations.

The Giant Magellan Telescope (GMT), is an Extremely Large Telescope (ELT) and is a ground based telescope currently under construction at Chile’s Las Campanas Observatory in the Atacama desert. It has an altitude of 2516 Meters. The construction of this telescope would be completed by the year 2030. It is a reflecting telescope and the diameter of the mirror of the telescope would be 1000 inches (25.4 Mtrs) whereas the largest optical telescope ever built till now only has a mirror with a diameter of 406 inches.  This is for observation in optical and mid infrared wavelengths. The GMT would contain 7 of the world’s largest mirrors and its resolving power is 10 times that of the Hubble Space Telescope and 4 times that of the James Webb Space Telescope. However, it would not have the observing power of the Space Telescopes in the infrared region. The GMT would be used to observe a wide range of phenomena including the search for signs of life on Exoplanets and study of the cosmic origin of chemical elements.

Las Campanas has exceptional astronomic seeing conditions and clear weather through much of the year. The area is also very sparsely populated combined with favourable geographical conditions ensures minimal atmospheric and light pollution.

We still have a long way to go in discovering Exoplanets and those among them that are habitable, and it may yet take a long time, but we are on the job.