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Locating Our Long Distance Neighbors

For years, we believed that the Earth was the only thing in the universe. Then we started finding planets, and the bright, sparkling lights in the night sky earned names like Venus and Jupiter, etc. Before long, we knew that there was a set of 8 planets orbiting our sun. For a while, that was all we knew about the universe, as exoplanets, nebulas, and black holes were purely speculation – ideas that were born out of theories. 

But in 1995, the first exoplanet was found. An exoplanet is a planet that lies outside of our solar system. The outermost bounds of our system are defined by the Oort cloud. Any planet that lies beyond that point is classified as an exoplanet.  The first one to ever be found was named 51 Pegasi b (or Dimidium) and was the first big sign that proved that there were worlds beyond the 8 that we knew. 

After that, scientists raced to find more of these strange planets, and to help, they build huge telescopes located both in orbit around the Earth and on the surface. These telescopes carried large mirrors and sophisticated technology that let them find nearly 4,000 different exoplanets all across the galaxy. 

Finding an exoplanet at those distances, however, proved to be a large problem, and over time, multiple solutions have been presented. I would like to discuss a few details about the various solutions here:

Transit:

The most common way of detecting exoplanets is the transit method. Each of the 3,155 planets discovered this way were found as they passed in front of their star. When a solid object passes infant of a source of light, it blocks the light. This is how a shadow is created and the same principle is used to detect exoplanets hundreds of light years away.

 As a planet passes in front of its host star, a bit of the light is blocked. This dip in the star’s brightness can be recorded and tell us the size and atmospheric composition of the planet. The larger the planet is, the larger the dip in the star’s brightness will be. Similarly, the closer it is to its star, the more frequently the light will be affected.

 When the light from the host star interacts with the molecules in the atmosphere of the planet, certain colors of light are reflected back. This is the same reason why our sky looks blue during the day time. The sun’s rays are interacting with the molecules in our atmosphere and reflect back the color that we perceive as blue. It’s the same concept that happens on other planets, and scientist can use this data to determine the planet’s atmosphere. 

Telescopes like Hubble and TESS use this method and found hundreds of different planets each.

Radial Velocity:

Radial velocity is a unique method that has found around 796 different exoplanets. This method relies on the gravitational attraction between the star and it’s planets. 

The bigger an object is, the more gravity it will have. Since planets are significantly smaller than stars, they are automatically trapped within the star’s gravity. However, planets do have some gravity themselves and can still affect their star. 

As the planet orbits its star, it causes the star to wobble a little. This wobble is extremely small and hard to detect, but not impossible. With the right technology that is sensitive enough to detect these small wobbles, scientists can determine if a star has planets, the number of planets, and the size of the planets. 

The more planets a star has, the more wobbles it will experience because it will be interacting with the gravity of multiple objects all in different places as they orbit. The larger a planet is, the more gravity it will have, and therefore the more it will cause the star to wobble. 

But seeing a star hundreds of light years away wobble an incredibly small amount is extremely difficult. But the Doppler effect makes this significantly easier. 

The Doppler effect explains the correlation between sound waves and the distance from which the sound originated. The closer the sound is, the more bunched up the waves will be and the farther away the sound originates from, the wider the waves will be. Using this method, scientists can see where the light waves coming from a star bunch up and where they are spread apart. Spread apart waves show when the star is tilting away from us and the bunched waves show when its tilting towards our position. 

Many observatories use this method, most notably the Keck telescopes in Hawaii and La Silla observatory in Chile.

Direct Imaging:

Direct imaging is another way to detect exoplanets, yet it’s far less effective that other methods. The 50 exponents thus found were directly photographed. 

The problem with this method, is that a star emits a lot of light which can easily overpower the planet. But new techniques have offered a solution. 

A telescope using direct imaging would be equipped with special technology that would block out and reduce the glare from the star, the same way we would as if we put on sunglasses on a bright day. With the reduced glare, it’s much easier to see what’s orbiting the star. 

There are a few ways to block out the light. 

The first would be to have a “star shade.” For space based operations, this would require another spacecraft that could position itself a certain distance away from the main spacecraft and at the perfect angle which would successfully block out the light from the star before it even reached the telescope. For example, if you were looking up at the sky on a bright, clear day, you might put your hand up to shade yourself from the intense light of the sun. The same process is occurring with this method, but the source of light is hundreds of light years away. 

Another method is to install a device inside the telescope which would block out the light before it reaches the detecters. So the telescope would never record the light and would be free to observe without the obstruction of the light from the star. 

Direct imaging is a less developed method of finding exoplanets as we don’t have the necessary technology yet to look directly at a star and successfully block off a large portion of its light. Scientists, however, are hopeful that future improvements could lead to easier identification of oceans, atmospheric patters, and detecting the presence of landmasses on the surface of exoplanets.