The universe we live in, is pretty big and there are a lot of stars and massive bodies floating around. Our very own Solar System is just one of the uncountable clusters of planets and asteroids orbiting the massive bodies such as stars, black holes and pulsars. A question that has grasped our imagination ever since the inception of astronomy was “Will we ever find other planets resembling the Earth?”. That question has been answered partially by the discovery of Exoplanets within this near-infinite array of objects in the universe.
Breaking the word Exo-planet, we get “exo” meaning on the outside and “planet” meaning a sufficiently rounded object that orbits a larger and massive object over time. This does give a rough idea about the origin of the word itself, but, lets find out more!
Alright, so the term “exo” in the term actually means outside the Solar System. Yes,not surprisingly, planets do exist outside of the solar system as well. Also, the variety of planets that have been found over the years is definitely similar to the ones of our Solar System, if not greater.
The science behind discovering an exoplanet has evolved over the years. The methods that were followed in the early stages involved direct image capturing and analysis of the objects observed. However, this method has too many disadvantages as it involves a large amount of guesswork and as most exoplanets are very small compared to the body they are orbiting, they are inherently faint enough to avoid detection .
The earliest exoplanets were discovered back in 1992, a pair orbiting the pulsar PSR B1257+12, followed by the discovery of one more planet orbiting the same pulsar.
The Indirect methods of discovery are used today are much more efficient and reliable than direct observation.
- The Transit method: This method uses the eclipse-like phenomenon observed when the planet travels across the line of sight between the star and Earth. The planet blocks out a portion of the star, reducing its intensity for a small amount of time. This process has the benefit of being automated and is used on the Kepler Telescope. The photographic data from a portion of the sky is analysed and possible exoplanets are consequently confirmed by other accurate methods.
- Astrometry: The tug of an exoplanet causes the relative movement of the star itself in respect to multiple stars surrounding this star. These can be measured by observation over a period of time.
- The Doppler method: Consider a planet orbiting a larger body such as our Sun. As the body orbits around the Sun due to the pulling effect of the Sun’s gravity, the planet itself also “tugs” on the Sun. This little tug is effectively very minute, but can be spotted by careful and constant observation over a period of time. The Doppler effect is the variation in the amplitude of a light source with variation in distance. This effect can be used to measure the variation in the Spectral lines of the star as the exoplanet in question orbits circularly or elliptically in front of the star.from the star. This is the most frequently used method and has yielded the maximum number of exoplanets detected.
- Gravitational Microlensing: When a star’s gravity is massive enough, it acts as a lens producing a magnifying effect on the light of distant objects. A planet orbiting this star causes an observable shift in this magnifying effect due to light interference. This shift can be observed over a period of time and is used to confirm the existence of the exoplanet.
- Pulsar timing: Every pulsar produces a strong burst of energy in the form of radiowaves as it revolves. The presence of a planet in the near vicinity causes a minor variation in the timing of these pulses. This was the way in which the first exoplanet was observed. This method is not widely used today as the number of exoplanets orbiting stars is much greater than the number of planets orbiting pulsars.
As of today, a total of 3285 exoplanets have been confirmed in about 2445 solar systems and 2416 planets are awaiting confirmation by further analysis.
Discovery of Exoplanets over the past few years
The colours represent the method of detection for the above graph : Radial velocity method=dark blue, The Doppler method =green, Direct Imaging =red, Gravitational microlensing = orange.
A lot of weird exoplanets have been found to date, here are a few:
- Kepler 186-F: This was discovered by the Kepler telescope and is one of the planets with the closest resemblance to our Planet Earth within the habitable zone of its star and which can also support liquid water formation.
- Methuselah: At an age of 12.7 Billion years, this is the oldest planet ever found. In comparison, our Earth is just about 4.5 Billion years old.
- 91 Aquarii b : A planet orbiting not one, not two but three Suns!
- 55 Cancri e : A planet made entirely of carbon with about a third of it made of diamonds.
- WASP-17b : The largest exoplanet ever found. It is four times the size of Jupiter
- Kepler-37b: The smallest exoplanet discovered, almost the size of the Earth’s moon.
Well, I’ll end this post on a positive note. There are thousands of planets yet to be discovered in star systems and galaxies that we don’t even know yet. The future is bright and we can always hope that we find a planet much similiar to Earth. The James Webb Telescope is about to be launched quite soon(2018) and will offer even further insights into exoplanets.
Until Next time!
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