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Ancy K Sunny
Ancy K Sunny

SPACE

How does NASA actually find exoplanets?

nasa-exoplanet An artist's depiction of the possible surface of one of seven newly discovered planets | Reuters

Considered one of the most spectacular discoveries in recent times, NASA on Wednesday announced it had found seven earth-like exoplanets orbiting a dwarf star, Trappist-1, about 40 light years from earth. These planets could potentially harbour life; a shot in the arm for the search of alien life outside the solar system. These exoplanets were observed by the Spitzer space telescope of NASA.

NASA has been discovering exoplanets for a long time now. Which brings us to the imminent question: what exactly is an exoplanet? Simple. An exoplanet is just a planet outside our solar system.According to the space agency, there are 3,449 confirmed exoplanets. The first exoplanet was discovered in 1995 by NASA's Kepler team. It is believed that, on an average, every star has a planet orbiting around it, which amounts to about a trillion planets in the Milky Way alone.

The hunt for potentially habitable planets rely on a handful of criteria. Ideally, astronomers want to find planets just like earth— about the size of earth that orbit at just the right distance from their star, in a region termed the habitable zone. The habitable zone is the belt around a star where temperatures are ideal for liquid water, an essential ingredient for life. For instance, earth lies within the habitable zone of our star, the sun. Beyond this zone, a planet would either be too cold or too steamy to support life.

Here are four major methods NASA uses to detect exoplanets:

 1. Watching for wobble: This involves observing the changes in the colour of light emitted by stars due to the gravitational pull of possible invisible planets orbiting them. As planets orbit around stars, the planet causes the stars to 'wobble around' a little bit. Bigger the planet, bigger the effect it has on the star.  As the planet moves to and fro, the light waves compress and stretch, changing the colour of the light we see. This method, also known as radial velocity method, has been one of the first successful methods to detect exoplanets. According to NASA, 621 of the exoplanets have been discovered using this technique.

 2. Searching for shadows: When a planet passes directly between its star and and an observer, it dims the star's light by a tiny amount. By an observer, we refer to an astronomer looking through a telescope or a satellite keeping an eye on the star. Though the the stars go dimmer for a small period of time, it's enough for astronomers to figure there is an exoplanet lurking somewhere between. This method is referred to as the transit method. The duration of the transit gives us information about the size and position of the planet. For instance, bigger the planet, more light gets blocked, which in turn reflects on a chart which astronomers call a light curve. Farther the planet, the more time it takes to orbit the star and pass in front of it. This technique has been the most successful in NASA's exoplanet hunt, having found 2,703 of the total, including the seven recently found.

 3. Taking images: Trying to photograph an exoplanet is like attempting to spot a flea on a glowing light bulb. This pretty much describes the greatest challenge astronomers face while trying to photograph an exoplanet. The photograph gets drowned in the overwhelming light radiated by the planet's host star which is a million times brighter. Scientists have found a way around by devising methods to block the light.  They use devices like coronographs and starshades, which essentially blocks the light from a star before it enters a telescope. Direct imaging is still in its nascent stages of being an exoplanet-finding technique, and has detected only 44 planets so far.

 4. Microlensing: While the other techniques seem quite easy to grasp, this one requires a deeper understanding of physics and the interesting properties of gravity. The gravitational field of a massive object (like a planet or star) will extend far into space, and cause light rays passing close to that object to be bent and refocused somewhere else. The more massive the object, the stronger its gravitational field and hence the greater the bending of light rays. This is what astronomers call lensing. In this technique, when a planet passes between the star and the earth, gravity of the planet causes the star's light to get bent and focused on to an observer. According to NASA, 44 exoplanets have been discovered using this technique.

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Topics : #NASA

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