Exoplanets

A planet that lies beyond our Solar System is an exoplanet. However, objects must be labeled as exoplanet candidates before it can be called an exoplanet. Once labeled as an exoplanet candidate, two other telescopes must make additional observations and collect data to verify that the object is indeed an exoplanet.

Evidence of exoplanets was first discovered by Van Maanen in 1917. However, it wasn’t until the 1990s when the first exoplanet was discovered. The nearest exoplanet to Earth is Proxima Centauri b, located about four light-years away from the Earth.

How are exoplanets detected?

There are many ways to detect exoplanets, but two methods used to do so are called the Transit Method and the Radial Velocity Method. As an exoplanet passes between the observer and the star, it blocks some of that star's light from reaching the observer. This is similar to solar eclipses, where as the Moon passes between the Sun and the Earth, it blocks off the Sun’s light for the duration of its transit. Thus, when the light of a star becomes dimmer, astronomers can detect exoplanets when they are transiting. Another way to detect exoplanets is through a technique called the radial velocity method. Essentially, “orbiting planets cause stars to wobble in space”, which changes the color of the light from the star- in terms of redshift or blueshift (NASA, 2022). Blueshift is when an object moves towards the observer, while redshift is when an object moves away from the observer.

What telescopes are used to detect exoplanets?

A specific telescope that detects exoplanets is the Kepler Space Telescope. Kepler was explicitly designed “to survey our region of [our galaxy][...] to discover” exoplanets. Unfortunately, Kepler retired in 2018, but its data is “still being used to kind exoplanets” (NASA, 2022). Another telescope that assists with discovering is the Spitzer Space Telescope. While it was not designed to search for exoplanets, its infrared instruments were the perfect tools for exoplanet exploration. In addition, the newly launched James Webb Telescope helps to further expand our knowledge of exoplanets through a technique called spectroscopy, in which light signatures of exoplanets are recorded to aid astronomers in learning more about the exoplanets and their atmospheres.

Types of Exoplanets

Exoplanets come in many different sizes and temperatures, similar to the different types of planets in our Solar System. Planets are classified into four types: gas giants, super-Earth, Neptune-like, or Terrestrial. Gas giants are planets that are large in size and are composed of gasses, such as helium and hydrogen. Gas giants located near their stars can sometimes be called "hot Jupiters". Some examples of gas giants beyond our Solar System are Kelt-9b and Kepler-7b. Super-Earth planets are larger than the Earth and lighter than ice giants (an example of an ice giant would be Neptune or Uranus). They can be composed of a combination of gas and rock. It is important to note that while their classification may suggest that they are similar to Earth, they aren't necessarily due to the fact that the "true nature of these planets" remains unknown (NASA, 2022). Some examples of Super-Earths are GJ 15 A b and 55 Cancri e. Neptune-like planets, on the other hand, are planets that "are similar in size to Neptune or Uranus" (NASA, 2022). They are typically composed of hydrogen and helium, "with cores of rock or heavier metals (NASA, 2022). Some examples of Neptune-like planets are HAT-P-26b and GJ 436 b. Lastly, terrestrial planets are planets that have rocky surfaces. Terrestrial planets that are larger than Earth are instead classified as super-Earths. Two examples of terrestrial planets are TRAPPIST-1 e and TRAPPIST-1 d.

---

Thank you for reaching the end of this blog. Be sure to check out other blogs as well to continue to learn more about astronomy! Don't forget to like and share and stay tuned for our next blog post. And as always, keep gazing skywards!

---

Bibliography

Information@eso.org. (n.d.). 32 new exoplanets found. www.eso.org. Retrieved November 12, 2022, from

https://www.eso.org/public/news/eso0939/

NASA. (2022, April 13). In depth. NASA. Retrieved November 12, 2022, from

https://exoplanets.nasa.gov/what-is-an-exoplanet/in-depth/

NASA. (2022, April 13). Overview. NASA. Retrieved November 12, 2022, from

https://exoplanets.nasa.gov/what-is-an-exoplanet/planet-types/overview/