The Earth is not alone in the solar system. There are planets or say terrestrial bodies which have any one of the parameters of supporting life. And the solar system is not isolated, there are millions alike it. Scientists have discovered exoplanets resembling Earth and also the ones smaller or bigger than that in the habitable zones. Struggling to comprehend exoplanets? Read further in the post to know about the history of exoplanets from a scientifical perspective.
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The planets orbiting a sun-like star in a system like ours sighted in our galaxy or other galaxies are known as Exoplanets. Exoplanets can be bigger or smaller than the size of the Earth. They are found in the habitual zones around their respective stars which they orbit. Stars can be larger / smaller compared to the sun. Some systems may have multiple stars too.
What history gossip about Exoplanets?
On the 9th of January 1992, radio astronomers Aleksander Wolszczan and Dale Frail announced the discovery of two planets orbiting the pulsar PSR 1257+12. This was an awaited eureka moment in the history of planetary science.
After a three-year-long period of anticipation, on October 6th - 1995 the star 51 PEGASI - B was sighted with a planet orbiting it. The planet was giant, completing its one year in four days. These two to two strikes have foundationed present discoveries.
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Kind of exoplanets found till date
Scientists say that there are a trillion exoplanets in our galaxy. Nearly 300 million of them are habitable. 5 to 20% of exoplanets that are earth-like are not habitable.
An exoplanet which is revolving around two stars at a time is a circum-binary exoplanet system. For example, planet – Kepler-6B.
A planetary system with only one planet revolving around a star.
Similarly, there are systems that have a many number of stars.
Systems with a giant/ dwarf star
TESS (launched in 2018) discovered a planetary system in which heliocentric stars revolve around TOI 709 DWARF.
Planets in habitable/inhabitable zone
While not all the treasure is silver and gold, all the exoplanets discovered so far may not support life. Scientists claim that in our solar system alone there are trillions of exoplanets. 5- 20% of which have the resemblance of Earth, 'resemblance' doesn't include habitability. It is estimated that only 300 million of exoplanets exist in the habitable zones.
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Exoplanets within the solar family
Assumptions are being made that life may exist on some remote bodies of our solar system. Scientists study the components of the body which is assumed to support life is made of. If the body consists of the three ingredients of life i.e., 1. Organic compound 2. Liquid 3. Energy source; then the body is believed to be suitable to resurrect life. Till date, four planets in our solar system are been assessed to be able to harbor life .
We all are quite familiar with the statements given by Elon Musk who claims to build a city on Mars. Now, why Mars? Mars has a surface to live on. The atmosphere there is composed of carbon, nitrogen, and hydrogen gases. Moreover, water - the essential component of life is found on Mars.
Jupiter's moon, Europa has a sea crust on its surface which was estimated to be 100 kilometers deep measured by the Galilean and Voyager spacecraft. This indicates that water is present abundantly on Europa denoting the existence of life.
The voyager spacecraft proclaims the presence of water on Titan. Titan is the second biggest moon of Saturn. The seas sighted on Titan are composed of methane and ethane solutions. Scientists say that this mixture when boiled to 180⁰ transforms into water i.e. when burnt, methane gives CO2 (carbon dioxide) and H20(water). The atmosphere of Titan has Nitrogen abundantly as earth's atmosphere.
One of the moons of Saturn, Enceladus happens to show one of the parameters of life's existence on it. Enceladus is often called by the name – 'icy moon'. Undoubtedly, water may be present beneath the icy surface of Enceladus. In addition to that, the vast jets of water ice erupting from it several miles into space affirms the presence of water underneath its icy surface.
"The second genesis within the same solar system implies that the origin of life is a likely event. If it happens in the same solar system it's likely happening everywhere in the universe".
– Alfonso Davila (Research scientist, Carl Sagan Centre)
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First Exoplanets were not discovered till 1992
In 1992, two super-earth exoplanets were found around 'pulsar psr1257+12' at a remote distance of 2300 light years away. This was a eureka moment in the realm of Planetary Science as it was the first multiplanet solar system ever sighted.
Pulsar – The Dead Star
A step away from being a blackhole - Pulsar is a dead star. Pulsar was formed after the explosion of a massive star ending up as a supernova. Pulsar stars are not really habitable zones i.e., life expectancy is next to impossible.
Supernovae – The Planet-phobic Clouds
Supernovae is a cloud of dust that processes stars out of it. Here too, the expectation of life on exoplanets is null. A Supernovae is usually bathed in a cocktail of X-rays and charged particles emitted by a star. So, the chances of life in such a weird and hostile environment will be remote.
October-6-1995 – A D-Day
Fifty one lights years away from our galaxy a giant exoplanet was announced to be revolving around a sun-like star, '51 Pegasi - B' on this day.
"Unless something very unusual happened here and nowhere else, there is going to be biology all over the place."
– Seth shostak (Director of centre for SETI research
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Kepler — The exoplanet-friendly spacecraft
On 7th of march 2009 at 3:49 am – Kepler, the planet hunter spaceflight was launched from the Canaveral Air Force Station, Florida. To date, Kepler has hunted around 5000 exoplanets and the line is increasing day by day with new exoplanets being discovered every day. It was named after the scientist 'Johannes Kepler'.
"We filled it up with fuel to let it go as long as it could".
– Charlie Sobek (project system engineer for the Kepler spacecraft)
Kepler was the potential of capturing images receding 3000 light years from our galaxy. In 2018 Kepler stopped functioning. In that very year Hubble launched its second planet-hunter TESS telescope. Kepler is now revolving the sun along the earth and its return to the earth is estimated to be in 2060.
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