What is an Exoplanet? Space missions to detect Exoplanets | Methods to detect Exoplanets | About Habitable zone

All planets in the solar system orbits around the Sun. In the same way many planets orbit their host stars outside the solar system called as Exoplanets. Our own Milky way galaxy contains billions of stars in which billions of planets orbiting around them. We will find these Exoplanets through

1. Ground based observatories

2. Space observatories

From ground based observatories, it's hard to find an Exoplanet because of

• In day time, Sun blocks most of the light reaching us.

• In night time, it's hard due to the Earth rotation, atmosphere and climatic conditions.

Through ground based observatories, we have traced out nearly 600 Exoplanets until now. So therefore the other way to find Exoplanets is through space observatories, but it will costs huge amount of money. So until now only 9 spacecrafts were launched to detect Exoplanets. Here is a small brief about each of them.

1. EPOXI - It is organised by NASA. It didn't detected any Exoplanet. (2005 - 2013)

2. Gaia - It is organised by ESA. It didn't detected any Exoplanet until now. (2013 - ongoing)

3. ASTERIA - It is organised by NASA's JPL in collaboration with MIT. It didn't detected any Exoplanet until now. (2017 - ongoing)

4. CHEOPS - It is organised by ESA. It didn't detected any Exoplanet until now. (2019 - ongoing)

5. MOST - It is organised by CSA. It confirmed 1 Exoplanet until now. (2003 - ongoing)

6. SWEEPS - It is organised by NASA, ESA and Space telescope science institute. It confirmed nearly 16 Exoplanets. It started in the year 2006 and ended in the same year.

7. COROT - It is organised by CNES in collaboration with ESA. It confirmed nearly 29 Exoplanets. (2006 - 2012)

8. TESS - It is organised by NASA. It confirmed nearly 38 Exoplanets until now. (2018 - ongoing)

9. Kepler/K2 - It is one of the major space telescopes, which is dedicated to detect Exoplanets. It is organised by NASA. It confirmed nearly 2774 Exoplanets. It explored for a total of nine years from 2009 to 2018.

Kepler_space_telescope_Into_the_dark_space
Image credit: NASA

So if we want to know about the Exoplanets and their existence, we have to mainly depend on the NASA.

There are many ways to find an Exoplanet, but mainly 6 methods were used. They are:

1. Transit Photometry method

2. Radial Velocity method

3. Direct Imaging

4. Gravitational Microlensing

5. Astrometry

6. Timing variations

Other methods used are Phase curves, Polarimetry, Interferometry, Ellipsoidal variations etc.,

The first Exoplanet was discovered in the year 1995, named as ‘51 Pegasi b’ also called as ‘Dimidium’ orbiting around Sun like star called ‘51 Pegasi’.

Does finding an Exoplanet benefit mankind?

Yes, but in very less amount of profit. Using this information we can estimate the possibility of carbon based life beyond our solar system.

For example, in our own solar system life exists only on earth because

• Earth contains planetary surface which supports liquid water to stay on the surface creating atmospheric pressure.

• Earth position is also well balanced to encounter the Sun's radiations.

The planets which are nearer to the Sun, will face higher radiation leading to increase in temperatures. So there is very less chances of liquid water to exist.

The planets which are in long distances from the Sun, will have lower temperatures because of very less amount of Sunlight reaches surface. So in these planets water will exist in the form of ice.

So Earth is in the right position where liquid water can exists. This zone is called Goldilocks zone or habitable zone.

Habitable_Zone_Into_the dark_space
Image credit: NASA

Similar to Earth many Exoplanets are in habitable zone orbiting their host stars where liquid water and life can exists. The position of habitable zone will depend upon the star properties.

• In hotter star, the position of habitable zone is in long distances.

• In cooler star, the position of habitable zone is in near to the star.

• In stars like Sun, the position of habitable zone is in right at the place of earth.

Habitable_Zone_for_different_stars_Into_the dark_space
Image credit: NASA/Kepler mission/Ames Research Center

Like that of the Earth scientists discovered 17 exoplanets which are in habitable zone orbiting their host stars and other 30 exoplanets have chances to be in habitable zone.

In the journey of finding of Exoplanets, Kepler space telescope helped us the most. It can observe light from distant stars and planets. To find Exoplanets, it uses a technique called transit photometry which is simply called transit method. This process will go on for a total of 2 to 16 hours continuously and scientists will made some calculations to confirm an Exoplanet.

Kepler_research_in_milky_way_Into_the_dark_space
Imagr credit: Painting by Jon Lomberg, Kepler mission diagram added by NASA

How names will be given to Exoplanets?

If a telescope detects any new celestial object, then the country which organised that telescope can give any name to that new celestial object under the International Astronomical Union (IAU). Astronomers belonging to all countries are in the part of IAU.

Let us understand the procedure with an example.

Assume we found a Exoplanet using Kepler telescope,

If it detected a new star system then, star will be given name after Kepler as: Kepler + Number.

Planets around that star: Star name + lowercase letter (starting with b).

In case of multiple star system,

for star: Kepler + Number + uppercase letter and for planets around them: Star name + lowercase letter (starting with b).

Trappist-1_system_Into_the_dark_space
Image credit: NASA/JPL-Caltech

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