An exoplanet is an extra-solar planet located out of the familiar solar system that humans on planet Earth occupy. The existence of such planets outside of this solar system has been speculated on for decades, if not centuries, but wasn’t confirmed until the 1990s. There was a simple reason for this: Astronomers didn’t have the technology to detect worlds so distant until fairly recently.
With that said, it clearly stood to reason that there had to be planets all over the universe. A 2010 article printed in the Huffington Post suggests that there could be as many as 300 sextillion stars in just the visible portion. On paper, this is a rather staggering number: 300,000,000,000,000,000,000,000! To say the least, it would be quite naïve and pretentious for mankind to believe that just one rather ordinary, average-sized star located in one of billions of galaxies would sustain orbiting planets. It would likewise be quite narrow-minded to assume that Earth is the only planet that supports living organisms and intelligent beings.
Thanks to radial velocity measurements of stars that are considered to be relatively “nearby,” over 700 such planets have been confirmed at this writing. Odd as it may seem to the lay person, less than 5% of these newly-discovered exoplanets have been a result of direct observation. This initially comes as a surprise because massive telescopes placed in Earth orbit have been able to detect galaxies and stars billions of light-years away.
The problem with actually seeing planets lies in the fact that the brilliant glare from the parent star itself typically makes any orbiting planet invisible. However, one must keep in mind that if not for developments such as the Hubble and Kepler Space Telescopes, as well as the employment of several different methods in observing distant stars, those that support these exoplanets wouldn’t have been able to be viewed with as much scrutiny in the first place.
So what are the characteristics of these known exoplanets? Are any similar to Earth, or are they gigantic gas balls like Jupiter and Saturn? The answer is that both of these types of planets as well as other classifications have been found.
Certain gas giants have been described as a “Hot Jupiter” because they are very close to their sun, like Mercury is in this solar system. There are also Pulsar planets that orbit what are essentially remnants of a supernova. A “Super-Earth” is a solid, rocky planet with a mass up to 10 times that of Earth. Eccentric planets have a highly elliptical orbit around their sun, which results in distances ranging from very close to vary far away, depending the time of its “year.” Similar to “Hot Jupiters,” “Hot Neptunes” are planets 10 to 20 times more massive than Earth, but again as close or closer to their suns as Mercury. Other planets are virtual water worlds covered entirely by oceans. A Chthonian planet is essentially a “Hot Jupiter or Neptune” that has had its gas evaporated by the heat of its sun. What is left is a rocky core, possibly covered with lava. Free-floating planets, which could roughly be compared to asteroids, have either escaped their respective sun’s orbit or never had a parent sun to begin with. Finally, Exo-Earths are terrestrial planets with Earth-like qualities including size.
Finding Earth-like planets in a star’s habitable zone isn’t easy, but a few have been located. As time progresses, the number of such newly-discovered “earths” will increase. However, with budget cuts to the space program and the sheer distances to potential human-friendly worlds, astronomers and physicists are still left mostly with a large-scale guessing game. At the very least, the existence of other worlds outside of this solar system is finally no longer in question.