Captivating Cosmos - Transit Photometry/Exoplanets
Stars & Planets

How Exoplanets Are Discovered and How We Learn So Much About Them

As modern advancements in space technology continues to improve, we hear of more and more discoveries of planets orbiting ‘Stars’ beyond our solar system. These planets are what’s known as ‘Exoplanets’.

We investigate how Exoplanets are discovered and how we learn so much about them.

First, we look back to the earliest discoveries.

The Radial Velocity Method

In 1995, two scientists made a major breakthrough when they discovered a planet beyond our solar system. This planet was orbiting a Star within close proximity. Later, scientists would reveal that this new planet displayed similar characteristics to Jupiter, at around half its size.

The scientists had been studying the Star using a method called ‘Radial Velocity’, in simple terms, this method studies the changes in wavelength of light from a Star.

A change in readings was noticed over period of time. The changes were consistent and repetitive, exactly what scientists had been hoping for.

Stars ‘wobble’ as planets orbit them, even the smallest planets have this effect on its Star, this ‘wobble’ occurs due to the planets gravitational pull on the Star.

But What Effect Do ‘Wobbles’ Have On The Spectrum Of Light?

The scientists had been studying this distant Star from Earth using a highly technical telescope. A change in the spectrum of light from the Star was noticed over a period of time, later they would discover that a planet was causing the Star to wobble as it orbited.

As a planet orbits its star, the gravitational pull causes it to move either closer or further away from Earth, depending on its position. When the star moves away from Earth the spectrum of light is ‘redshifted’ and when it moves towards Earth, the spectrum of light is ‘blueshifted’.

The radial velocity method had proved successful, it began an era of searching for distant planets, with the hope of discovering another Earth-like planet capable of supporting life. Although, this method favoured the discovery of large planets, as larger planets equal larger gravitational pull.

If scientists were going to discover Earth like planets, they would need to improve on their strategy. And that’s exactly what they did.

Introducing The Kepler Space Telescope – Exoplanet Hunter

The Kepler space telescope was launched in March 2009. It was a major moment for space exploration, designed specifically to search for Exoplanets.

Unlike the radial velocity method which measures the changes in wavelength of light due to the movement of a Star, the Kepler uses a different technique, it has the ability to detect the most minuscule changes in the brightness of light from a star, otherwise known as Transit Photometry.

Basically, Kepler can detect when a planet passes a Star, it notices a dip or ‘dimming’ of the Star’s brightness.

Captivating Cosmos - Transit Photometry

How Does Kepler Provide So Much Information About Exoplanets

Its hard to believe that a dip in the brightness of a Star can provide scientists with so much information about a planet.

For example, scientists can estimate a planet’s diameter, they can also calculate how long it takes the planet to orbit its Star. This information uncovers how long the planets ‘year’ is.

Transit photometry combined with information about the characteristics of the Star, also allow scientists to discover the temperature on the surface of a planet. This is particularly important when hunting for Exoplanets capable of supporting complex life.  

It really is amazing how much detail can be gathered by the most miniscule dip in brightness of a distant Star.

We have gathered so much data on Exoplanets, with many Earth-like planets discovered.

But, the hunt for intelligent life still continues.