How Many Exoplanets Are There?

Exoplanets is the phrase given to describe planets that orbit a star outside of our solar system, and there’s far more than you may think.

In fact, NASA has discovered thousands of exoplanets in the last decade alone- and the number keeps rising.

These exoplanets were often discovered using data gathered from the Kepler Space Telescope, which retired back in 2018. Nevertheless, scientists at NASA are still finding evidence of new exoplanets every single year by analyzing Kepler’s data.

So, Exactly How Many Exoplanets Are Out There?

According to astronomers, there is approximately 1 exoplanet for every star in the sky. And yet, some stars have several planets — our sun, for example, has 8, whereas other stars have no planets at all. 

However, if a star survives long enough, planet formation appears to be the normal course of action, rather than a rare occurrence. This knowledge implies that the Milky Way should have roughly a hundred thousand million exoplanets.

That still doesn’t mean scientists will be able to pinpoint all of them though. The number of exoplanets that have been detected or recorded in some way is substantially smaller.

As of writing, the number of confirmed exoplanets stands at 4,512. On top of this, NASA has listed 7,721 additional planets to their list of “potential exoplanets,” but these are still yet to be confirmed. 

The very first exoplanets were found back in the 1990s, and since then, the number of confirmed exoplanets has doubled roughly every 27 months. The number of confirmed exoplanets is expected to continue to rise indefinitely as technology and space exploration improves.

How Are Exoplanets Found?

As mentioned above, most of the confirmed exoplanets were found using NASA’s Kepler Space Telescope. However, astronomers use certain techniques and unique technology to spot them. They often try to detect an exoplanet by examining how potential exoplanets affect the stars that they orbit. 

The Wobbly Star Method

The first course of action for astronomers trying to find new exoplanets is to look for “wobbly” stars. A wobbly star isn’t always obvious to spot, and the wobble is usually very slight. They spot them by comparing their movements to that of other stars surrounding them.

When a wobble is spotted, it is almost always the case that the star in question is being orbited by an undetected planet. This means that astronomers are capable of detecting exoplanets without ever actually seeing them, which is undeniably impressive. 

Thousands of exoplanets have been discovered by using the wobbly star method, but there’s a catch. It’s often only very large planets, such as Jupiter, that can influence a star enough to make it wobble.

Smaller planets, like those that are a similar size to Earth, are much harder to spot as they’re unlikely to have such a visible effect on a star. This is where the transit method comes into play. 

The Transit Method

To get a better understanding of just how many exoplanets are out there, NASA launched their Kepler Telescope back in 2009. This telescope was made specifically to detect planets, regardless of their size, which was something that had never been done before.

The data obtained from the Kepler telescope allowed astronomers to detect planets that orbited stars of all sizes and temperatures, giving us a whole new perspective of just how many planets exist in the universe. 

NASA’s Kepler Telescope discovered all sorts of new planets that we weren’t aware of before. The most interesting discoveries, however, were certain rocky planetary bodies located at a particular distance away from their star.

These planets are positioned in what’s known as the habitable zone, which is the sweet spot that scientists believe can sustain life. 

Exoplanets located in the habitable zone found by the Kepler Telescope were discovered using what’s known as the transit method. While this may sound complicated, it’s pretty easy to understand. NASA explains that when a planet orbits right in front of its star, this is called a transit.

During this transit, the planet will block out a tiny percentage of the star’s light. When this occurs, the star will appear a little less bright than it was before. By observing this slight change in brightness, astronomers can calculate the size of the exoplanet in question. 

And if that blows your mind, sit tight— there’s more. When scientists measure the time that passes between transits, they can use this information to calculate just how far away the exoplanet sits from its star.

While this information may seem fruitless and unnecessary, it can lead to further interesting discoveries. For example, by knowing the distance between an exoplanet and a star, they can figure out the estimated temperature of said planet. This is where things get crazy. 

When astronomers figure out the temperature of an exoplanet, they can determine whether or not the planet has the capacity to contain liquid water. And of course, where there’s water, there is often life. As of writing, NASA has discovered 55 confirmed potentially habitable exoplanets.

These vary in size: some are a similar size to Earth, and others are much bigger. This monumental discovery confirmed that it’s very likely that there are other habitable planets out there, just like ours, that are home to living organisms. 

What Is The Closest Exoplanet To Earth?

In terms of distance, the nearest exoplanet to Earth is named Proxima Centauri b, which sits a modest four light-years away from us. While this may sound close, it’s still pretty far away.

To put it into perspective, if you were to hop in your car and drive there at 60mph, you wouldn’t arrive on Proxima’s surface until 47 million years later. To bypass this long journey time, NASA has sent probes in the direction of the planet to help us understand more about it. 

These probes are known as the Voyager probes and are soaring out of our solar system at an impressive speed of 35,000mph.

Nevertheless, even at this incredible speed, they’re not expected to reach the exoplanet for another 75 thousand years, so don’t expect any new information anytime soon. When it comes to space exploration and tackling the vastness of the universe, it’s all about playing the long game. 

Which Exoplanets Are Likely To Sustain Life?

While NASA has pinpointed multiple planets that are likely to sustain life (an impressive 55 as of writing), there is one exoplanet in particular that piques their interest. This exoplanet has been named K2-18b and was first discovered in 2015. But in 2019, astronomers made an intriguing discovery.

It was revealed that K2-18b was found to have the ideal conditions to sustain life. NASA concluded that not only did the planet have a hydrogen-rich atmosphere, but that it also showed signs of water vapor.

While this doesn’t necessarily prove the existence of life, it indicates that the planet is likely to be home to a large ocean on its surface, similar to ours here on Earth. 

What’s even more mind-blowing is that K2-18b is approximately 2.6 times larger than Earth and has a mass of more than 8 times that of ours.

However, it is possible that the temperature and water pressure are too high for life (or at least life as we know it) to thrive. Regardless of this fact, K2-18b has the most promising chances of exoplanet life that we have found so far. 

Gordon Watts