Introduction to Exoplanets — Planets Beyond our Solar System

Exoplanets are planets that are outside the Solar System, so they are the same thing after all. However, they are much crazier and more extraordinary, and therefore, they’re more worth researching. There is a List of the Most Amazing Planets. So, here’s the introduction to exoplanets and what you need to know on the basics.

The History of Exoplanets

Long ago, many astronomers have already guessed the existence of planets beyond our Solar System. Anyone knows it’s hard to believe the Sun is the only star that can form planets. However, exoplanets could not be verified as the telescopes were not that advanced yet. You know, these worlds are light-years away and are very tiny relative to the star, so they are arduous to find. Therefore, the speculation of “Are we alone” still hung in moderation. (CrashCourse, 2015).

In 1992, astronomers found the first two exoplanets around a weird world called a pulsar. This object type’s birth is from supernova remnants, and no one knows whether the pair is from the dust, not the original shining star. Therefore, the question was still there: “Are there genuine planets that live with main-sequence stars?”

In 1995, the first exoplanet from a Sun-like star was finally found, but it is a world absent in our system — a hot Jupiter. They are gas giant planets that are very close to their star, and thus, they are high in temperature. Soon after, different methods came across divergent planets. To date (as of December 10, 2020), there are more than 4,300 exoplanets on NASA’s list, and more than 5,600 are candidates. (Exoplanet Exploration — Exoplanets beyond our Solar System – NASA, 2020).

The Categories of Exoplanets

Before talking about anything else, let’s discuss the categories of exoplanets. There are three primary groups: terrestrial, neptune-like planets, and gas giants. The rocky worlds are the tiniest while the gas giants are the largest. Because of the detection methods, most exoplanets discovered are made of gas, in the neptune-like and gas giants’ classes since they’re more massive. According to NASA, there are also a term of super-Earths, which are terrestrial planets but are larger than Earth, and is a complete category.

The Discovery Methods

To search for exoplanets like a pin in a haystack, we require state-of-the-art technological appliances and many skills.

The Transit Method

The most common one is the transit method, having discovered about 76% of all found exoplanets. The well-known Kepler space telescope utilizes that skill. When the observer, the planet, and the star lines up in a straight line, the planet causes a dip in the star’s seen luminosity, perceptible by the most sensitive stuff such as Kepler. That way, the spacecraft will determine the dimensions and orbital period of the planet, judging it between the broad categories. What’s more, the light from nearby zones can reveal the planet’s atmospheric composition due to the different spectrum of elements and compounds.

Radial Velocity

Then, another method of that is radial velocity. That is because the star is actually orbiting the center of mass, formed by the planet and the star. In that case, even though the planet might not shade the stellar object, the massive world is still measurable. That is because of the Doppler Effect, in which an object further turns “redder”, and the object closer turns “bluer”, having wavelength modifications according to the observer. Even the little changes by a tiny planet can cause it to be an item on NASA’s array if that happens.

Direct Imaging

As technology enhances throughout the years, the myth of “Exoplanets can’t be photographed” has become false. Nowadays, astronomers can process photos of stars by extracting their powerful glare, just like when you shade the sunlight with your hands, and exoplanets might be captured in the image. Although there aren’t many, their discovery is a great milestone in modern technological progress.

Section Credit: (NASA Exoplanets, n.d.)⁶

Other ways?

Despite how common the ways above are, there are some newer methods of finding exoplanets successfully. For example, astronomers can use pulsar timing, which uses the identical algorithm as the radial velocity, but calculates the time very accurately to find out the difference. Or, we can use gravitational microlensing, which measures bends coming from the starlight. Remember that the planet’s gravitational tug on the star is discoverable by various techniques!

Conclusion

So, here’s an introduction to exoplanets, their categories, and discovery methods. We hope you can learn more from the references below and the NASA Exoplanets‘ site for each planet’s information.

References and Credits

1. Angeli Gabriel, Marielina Planas, Dan Steinmetz, Mark Levenstein, Nicholas Karlin, Jay Olszewski. (2019, February 27). Exoplanets 101 – National Geographic Video. Retrieved December 10, 2020, from https://video.nationalgeographic.com/video/science/101-videos/00000169-30f6-dc18-a17b-35ffb92f0000
2. (2020, December 3). What is an Exoplanet? – NASA Exoplanets. Retrieved December 10, 2020, from https://exoplanets.nasa.gov/what-is-an-exoplanet/overview/
3. (n.d.). Historic Timeline | Explore – Exoplanet Exploration: Planets Beyond our Solar System. Retrieved December 10, 2020, from https://exoplanets.nasa.gov/alien-worlds/historic-timeline/
4. (n.d.). Exoplanet Exploration: Planets Beyond our Solar System. Retrieved December 10, 2020, from https://exoplanets.nasa.gov/
5. Phil Plait, CrashCourse. (2015, August 6). Exoplanets: Crash Course Astronomy #27 – YouTube. Retrieved December 10, 2020, from https://www.youtube.com/watch/7ATtD8x7vV0
6. (n.d.). 5 Ways to Find a Planet – NASA Exoplanets. Retrieved December 10, 2020, from https://exoplanets.nasa.gov/alien-worlds/ways-to-find-a-planet/