Looking for Exoplanets

Artist's depiction of Kepler 452b
Source: Wikipedia

"That is a big question we all have: are we alone in the Universe? And exoplanets confirm the suspicion that planets are not rare."

- Niel deGrasse Tyson 

We often talk about the length scale of the universe and its beauty. We never miss a chance to appreciate God's (?) creation and how finely everything is tuned. However, one thing we never forget to mention, directly or indirectly, is that we are not unique. There are thousands and thousands of solar systems in our galaxy and thousands and thousands of galaxies in our supercluster; this also means there are a lot of planets revolving around other stars, much like our planets in our solar system revolve around the sun. These planets, which revolve around a star not belonging to our solar system, are called Exoplanets. Yes, these do exist and yes, there is a way to detect them. In this post, we are going to talk about a few ways in which we humans have found exoplanets. 

Radial Velocity Method

Whenever we are talking about the revolution of one body about another, we often carry a misconception that the heavier body remains still and just the lighter body performs orbital motion. The truth is, both heavier and lighter bodies revolve around, what we call as the point of the center of mass of the system. For instance, because of the immense gravitational field of Jupiter by the virtue of its mass, our sun also wobbles around the center of mass of the system (here system refers to just the sun and Jupiter). The speed of this wobbling is, however, merely 13 m/s. This means that if anyone watches our sun along the line of sight parallel to the plane of the orbit of Jupiter, he/she will see it moving back and forth with a velocity of 13 m/s. In the case of the Earth-Sun system, this velocity is just 9 centimeters/s. 

We make use of similar phenomena to detect exoplanets far far away from us. We point highly collimated spectrometers to the stars and measure the shift in the wavelength of light emitted from them with great precision to detect exoplanets, as shown below. 

Transit Method

We have all seen a solar eclipse (or at least know about it). It happens when the moon comes in between the sun and earth and the luminosity of the sun is greatly reduced. This is nothing but the best example of a transit method; the only difference is that here an exoplanet crosses the path between us and the distant star. We see a dip in the luminosity versus time plot whenever an exoplanet goes through the line of sight. With this technique, scientists have discovered 3,187 exoplanets; highest in number than in any other way. Following is the animation for this method.

Direct Imaging

As the name suggests, probably the simplest way of finding an exoplanet. The supersensitive telescope is aimed at a potential star-system and the exoplanets, if any, are captured using infra-red cameras. This method is the least prone to false negatives and usually also used in studies of the atmosphere on the other planets.

Source: Universe Today

Gravitational Microlensing

Our space-time is like a fabric that gets curved by the presence of any mass. When a large exoplanet is in orbit of a star, the light from the star gets lensed (like a lensing effect). We on earth, observe some unusual spikes in intensities whenever the star performs a transit and this is how an exoplanet is detected.  This method comes handy especially when the density of the exoplanet is too high as compared to its volume. 

Almost 96 planets have been so far discovered by this technique. 

You must have noticed that some of the methods tend to overlap, for instance, why would someone perform a gravitational lensing observation when there is something as simple as transit method data? Scientists have to be sure of the detected body to be an exoplanet and thus they rely on more than one technique to verify the presence of an exoplanet. Of course, there are many more methods of exoplanet detection but the ones mentioned above are the most widely used. We have found more than 4,000 exoplanets to date and there are even more potential objects under constant observation. 

Well, we are back at the same point which had originally motivated us to look up to the sky. How likely is it for anyone of them to be a habitable second home for us? What's the probability of finding life on those planets? Should we expect someone waiting for us there? Thousands of years later, a time will definitely come, when we will have to leave behind our home, our planet Earth, in order to survive. We will be like a refugee looking for a new place we would call home. 

Perhaps the tiny pixels we humans are looking at now on our computer screens in the form of 'observation data' is where we would be traveling to. 

Until then try preserving this planet.

All the animations in this post are taken from the official website of Nasa.