THE SEARCH OF LIFE ON EXOPLANETS
Ever wondered how would be the life outside our Earth exists? No wonder we’ve grown up enjoying science fiction stories or movies about alien life. But do you think it might be possible for us to study or prove its existence? That’s the toughest question to answer for the entire homo sapiens. But think about life on the Earth. It is the only planet in the whole Solar System having a developed intelligent life. But what if I told you that there are Earth-like planets that revolve around other stars in our Milky Way galaxy that probably capable to sustain life? We call them Exoplanets.
Started from the visionary cosmological theory of multiple worlds by Giordano Bruno in around 16th century to the current study, it allows to discover multiple worlds with an estimation that there must be at least one planet revolving around every star in the Universe. The study of this interstellar world would help scientists to improve and revolutionize the planet formation theory.
Exoplanets are those planets revolving around other stars except our Sun. Up to now, there are more than 4000 confirmed exoplanets in the catalogue, and the number of discoveries is increasing day by day with the advancement in computational astrophysics. According to the hypothesis, there are 11 billion potentially habitable exoplanets in the Milky Way galaxy. The history of the first discovery is not too old for us. It started in the 90s’ with the discovery of Jupiter-like exoplanets. Now, we’re able to discover small rocky planets like Earth also.
Searching for a planet orbiting the host star is a very difficult task because of the difficulty to separate or resolve star and its companion planet and second one, huge glare of the star. How so? Because the planet doesn’t generate light of its own like the star using nuclear fusion. Instead, they reflect very little starlight and because of their very small size compared to the star, it requires very precise and high-spatial resolution telescopes to capture the image of that planet-star system in visible spectrum. It’s like looking at a roaming firefly in front of a bright floodlight. Although it seems a tremendous job to capture it, it is not impossible to direct imaging in infrared spectrum as planet emits intense thermal radiation in comparable to star’s radiation in infrared, it only needs to cover the star’s glare using coronagraph.
Astrophysicists use indirect methods to detect it because planet exerts effect on star’s motion and luminosity. By measuring doppler shifts occurs due to wobbling of the star by the planet’s gravitational tug. This method is called Doppler Spectroscopy. Transit photometry is the most used indirect method for finding a planet by observing transit phenomena like a Venus transit observed from Earth.
Thanks to Einstein’s General Relativity, planet(s) from a distant star or star clusters can be found using the Gravitational Microlensing effect, lensing of background star by planet companion foreground star at exact line of view of observer which gradually varies the brightness of a star. It’s a rare event used to detect rogue planets and planet around distant stars.
This new topic of research opens a new chapter to refurnish the theory of life with a most astonishing question:
What is Life? Because life is not always relatable to evolution of humans; it may be plants, animals and microorganisms. Even we are ahead in the scientific field, we don’t have any well-defined theory which explains the origin of the very first lifeform according to the geology of different planets. We can understand this situation by considering the analogous fact that for a habitable life on a planet, it is not necessary to locate in Goldilocks zone (a zone at a particular distance from the sun where the temperature is not too hot and not too cold for the water to exist in a liquid state on the planet), it can nourish under the icy surface and in hydrocarbon sea where the sunlight reaches typically low.
Such places are the Gas Giants’ moon of our solar system where scientists detected the presence of water and ammonia in the plumes of water geyser exposed in space from the south pole of Enceladus, a moon of Saturn, responsible for ejecting icy materials in the E- ring of Saturn’s ring structure. Also, the presence of methane sea on the surface of Saturn’s moon Titan and underground ocean beneath the icy surface of Jupiter’s moon Europa which hints a signature of microbes’ lifeform, and therefore, NASA put these places in Planetary Protection Policy’s restricted 5th category to prevent the contamination of these valuable biospheres of our solar system by any spacecraft materials. But for a search of an ideal place like our planet, we prefer to explore exoplanet revolves in a habitable zone. This provides the advantage of having favourable geology with a minimum average temperature throughout the day and night, thick atmosphere, and most important, liquid water on the surface which is a habitable solvent for cyanobacterial microbes who produce oxygen and helps to have an oxygenated atmosphere with an ozone layer which act as a shield from hazardous UV rays ejected from star’s chromosphere.
If we want to search for life on exoplanets, we have to study Physics, Chemistry, Biology, and Geology of a planetary bodies. These combinedly come into the new field: Astrobiology. Astrophysicists study the atmospheric composition of the exoplanets using spectroscopy, auroral radio emissions, and next-generation telescopes like the James Webb Space Telescope which will decode the key elements or in other words, Biosignature gases, a gas that reflects the evidence of past and present life. For example, if an alien civilization is looking at the Earth and observing our atmosphere, they would get oxygen as a biosignature gas because what we breathe and due to plant’s photosynthesis, that will sign towards oxygen as a fundamental gas in the Earth’s atmosphere.
Because of serpentinization, rocks and minerals like olivine act as a powerhouse for microbes in their early stages. So, the motto of ‘Follow the Water’ to search life must be ‘Follow the Rocks’ too. Therefore, we carry on experiments with the Martian soils and rocks for the significant organic molecules of carbon-based life on Mars using rovers. Even we haven’t got any clue of liquid water on the surface, it might be there under the Martian crust for survival from the extreme temperature variation and low air pressure due to the thin atmosphere. We’re still in progress and recent missions like Perseverance rover will be used to dig out the surface and investigate it further using very sophisticated laboratory present on it.
Exoplanets always surprise us with their features beyond the human imagination which includes the short period of revolution, location of Jupiter-like planets very close to host star even closer than mercury’s location from Sun, planetary rings extend up to the astronomical unit, planets orbiting binary stars and neutron stars and many more.
You could imagine the scenario of such extraordinary interstellar worlds by taking the reference of ‘Star Wars’ world having two Suns and now, think about another scenario of the night sky filled with infinite stars if you were standing on an exoplanet from a Globular star cluster or surrounded by the bizarre Gargantua as shown in ‘Interstellar’ movie if you were at Edmunds’ planet type exoplanet, isn’t it wonderful?
In the excitement of the discovery of habitable exoplanet destiny in the future and technical engineering progress, we must understand the practical limitations. The nearest exoplanet from Earth is at a distance of 4.2 light-years around Proxima Centauri. With the consideration of present space technology, it will take around 20,000 years to reach there. Suppose a situation where we finally discovered alien life on an exoplanet, there will arise a question on how to communicate with them? Are they using advanced technology like us? Are they underdeveloped species or ultra-intelligent species? Do they have a similar law of science like us? And many more.
The interesting storyline shown in ‘Arrival’ movie predicts that they might be using universal symbolic language which controls the space-time, the same thought Einstein had to derive a universal equation which will prove both quantum and classical mechanics simultaneously. Also, He had a vision of a unified theory which explains the dynamics of the Universe.
Other possibilities about extra-terrestrials are: they are not so intelligent like us to speak or maybe they are affected by the Fermi paradox which contradicts the lack of evidence for alien civilization and the probability of devasted alien life by any intelligent extra-terrestrial civilization. Although its look like entering into the thinking of numerous possibilities, but that’s the beauty of science which guide us to voyage into deep space and dig out the secret of the Universe. As upcoming development in astrophysics is concerned, we will accurately study the exoplanets deeply in the next 2-20 years and regular discoveries of these planets will never let the astrophysicist and scholars like us rest until we get the answer to the question:
Are we alone in this Universe?
Article by-
-Kartik Gokhe
Nice article
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