What Are Exoplanets?

Various Types of Exoplanets

Exo is a prefix meaning external, something that comes from "outside".

If you combine that with planet then the meaning of the word "exoplanet" should become quite apparent.

Indeed, you may have guessed that exoplanets are worlds that exist outside of our solar system. These oddities orbit alien stars and have shown us, thus far, that the structure of solar systems are more diverse than we could have imagined.

In fact, let's make a list of both factual and fictitious classifications for exoplanets and see which one's you can identify.

While there are certainly many more different types of exoplanets, we will be focusing on the ones mentioned above in the next few paragraphs.

Hot Jupiters

Imagine Jupiter barreling through the inner solar system throwing itself past Mars, Earth, Venus and Even Mercury and ending up a mere .015 au from our star. For many solar systems in other parts of our galaxy, this is a reality. Hot Jupiters are know for their extremely unusual position relative to their stars. Large gaseous planets don't form naturally near their host stars and therefore, upon the discovery of the first Hot Jupiter, astronomers were baffled. Therefore, it is theorized that these planets form normally and migrate in toward their stars. Upon doing so their surface temperature skyrockets, hitting 700C. Their gaseous atmosphere begins to evaporate away and they slowly lose mass. This is the beginning of their metamorphosis.

Chthonian Planets

These are the remnants of Hot Jupiters. Their atmosphere has been burned away and in its place there is only a rocky core. Some think that this surface may even be molten due to the planet's proximity to its star. However, realize that these planets are largely undocumented to us and live mostly in theory. Realize that a fully degraded Hot Jupiter atmosphere isn't something astronomers have observed. The first exoplanets orbiting sun-like stars were found in the mid 90's and observing these planets up close is currently impossible (due to their distance from us, our telescope capabilities, and the fact that a star's luminosity blocks our view of these planets). Still, there is reason to believe these oddities do exist, in fact COROT-7b may be the first Chthonian planet discovered.

Super Earths

Super Earths are just what one might expect. They're Earth-like planets with radii of .8 of Earth's to about 1.25. However, the use of Super Earth is fairly use in both the media and astronomy, sometimes the upper limit is closer to 5 Earth masses. The truly defining characteristic the terrestrial nature of the planet. The term "Super-Earth" can be attributed to the Kepler Missions- responsible for the discover of hundreds of exoplanets, and counting. In the pursuit of another home for mankind there have been many amazing innovations in the study of exoplanets. One important marker is the determintation of the planet's position relative to its star. Astronomers look for planets that exist inside the habitable zone, or the area around the star that isn't too hot or too cold for water to exist in a liquid to exist. Beyond that scientists can take the spectra of a planets atmosphere to determine if it has a chemical composition conducive to life. This certainly isn't possible with all planets but this study is becoming more commonplace as we discover more planets.