One of the best-kept secrets of our times is the fact that planets exist outside of our Solar System. Exoplanets are the new cool kids when it comes to astronomical discovery. As our ability to search through the vastness of space increases, we continue to find ourselves faced with an ever-expanding potential of discovering planets that could look and behave a lot like Earth. That’s all fine and dandy, but wouldn’t you instead impress your friends with your exoplanetary knowledge? Look no further!
The History of Exoplanetary Exploration
Humans began their interest in exoplanets around the 16th century. The Italian philosopher Giordano Bruno was the first to publicly support the idea based off of his belief in the Copernican theory that Earth and the other known planets of the time were indeed orbiting around the sun. He speculated that this should also be the case for other stars in the universe as well. In the 18th Century, Isaac Newton revisited this idea in several of his writings on the subject. By the 1950’s scientists were beginning to consider using Doppler spectroscopy and the transit method as a means of confirming the existence of massive, gaseous exoplanets surrounding far-away stars.
Our interest in exoplanets hit the mainstream after the launch of the Hubble telescope in 1990. We were able to appreciate the complexity of our universe visually for the first time in history. The first two exoplanets to be officially recognized were discovered in 1992 in orbit around the pulsar 51 Pegasi. Before that time, several other potential planets had been found but were controversial. Eventually, the two bodies in question (Gamma Sephi Ab, discovered in 1989 using radial-velocity data and HD 114762 b from the Coma Berenices constellation) were confirmed to be in fact, planets.
After the first initial discoveries in the late 80’s and early 90’s, the number of exoplanets recognized by science exploded in the following two decades. As of March 1, 2017, over 2,691 different planetary systems and 603 multiple planetary systems have been discovered and cataloged by astronomers. The search for exoplanets is an ongoing endeavor. The Kepler Space Telescope has played a significant role in the discovery of these new worlds. Since 2014 alone, at least 2,900 planetary candidates have been discovered by the Kepler mission alone.
How Do We Find Exoplanets?
There are four primary methods used by astronomers to discover new planetary bodies.
Direct Imaging is most well-known, but least effective way of finding exoplanets. This method involves direct visual observation via telescope with the aid of chronographs and thermal imaging. Direct imaging works better for locating exoplanets that exhibit a face-on orbit. A face-on orbit is an orbit parallel to the sky. A satellite that orbits the Earth directly above the equator has a face-on orbit.
The Transit Method measures a star’s overall light output for variation. A star’s brightness is decreased temporarily when a planet passes in front of it. We can monitor the dips in brightness. If the star displays is a consistent, patterned dimming, then there may be a planet in orbit around the star. This method is meticulous and requires lots of patience, but even you can do it! Visit Planet Hunters if you don’t believe me. This approach is only useful for planets that cross directly in between the star and the observer’s line of sight. It also tends to deliver many false positive results. However, when the data is accurate, the transit method can be used for determining the overall size of the planet and its atmospheric makeup.
The Radial Velocity Method, also known as Doppler spectroscopy or the “wobble method” is used to discover new exoplanets by observing the shift in a star’s orbit due to the gravitational pull of its surrounding celestial bodies. Gravity from a small planet can affect the speed of a star and changes its spectral lines due to the Doppler effect. Modern spectrographs can measure a change in a star’s velocity to less than one mile per second.
The Gravitational Microlensing Method depends on alignment between two stars were the closest of the two’s gravity acts as a lens to magnify the light of the farther star. When the closer star has an associated planet, the gravity of that planet enhances the effect. This technique is most useful when looking toward the center of the galaxy since there is a higher density of background stars.
Popular Stars With Exoplanets
Below is a list of a few stars with associated exoplanets. The next time you’re stargazing with that nice date, impress them with your exoplanetary knowledge!
Pegasi 51– As earlier mentioned this star hosts the first confirmed exoplanet. Look to the constellation Pegasus to view this beauty.
Gliese 581 – This red dwarf resides in the constellation of Libra. This star hosts at least three known planets with a fourth under observation.
Fomalhaut – You will find this star in the constellation Piscis Austrinus. It is one of the brightest stars in the sky and is famous for its exoplanet Dagon. Dagon is one of the first exoplanets to receive an official name.
47 Ursa Major – also known as Chalawan, resides below the Big Dipper, within the Ursa Major constellation. Three planets surround this star, Taphao Thong, Taphao Kaew and 47 Ursae Majoris b.
Upsilon Andromedae – This is a binary star system (two stars orbiting each other) and was the first multi-planetary system to be discovered. Four planets orbit υ Andromedae A also named Titawin. The planet’s names are Saffar, Samh, Majriti and Upsilon Andromedae e.
Trappist-1 – We refuse to use all caps for “Trappist,” it’s just uncivilized! Unfortunately, we are unable to see Trappist-1 in the nighttime sky because it’s too dim. It has a magnitude of +18.8, more than 100,000 times fainter than what can be seen with the naked eye. Saturn, the 8th brightest object in the sky has a magnitude of “1” for reference. The Trappist-1 system is popular because it made the news in February 2017 for containing seven temperate terrestrial planets, three of which inhabit the habitable zone. The Trappist system contains the largest number of Earth-like worlds discovered in one system. The Trappist System discovery is well documented. For more information see the below videos. Very inspirational.
Visual Exoplanet Model
Below is a digital orrery of our intergalactic neighborhood illustrating the just how many planets we have discovered. The video was put together by from Ethan Kruse, an astronomy graduate at the University of Washington. The visuals and music are exceptionally done. It illustrates just far we have come since humanity pointed curved glass towards the sky. The video is a visualization of 1,705 planets in 685 systems as of November 24, 2015, found by Kepler. As of today, (Mar 2, 2017) we have found 3,572 exoplanets in 2,682 planetary systems. That’s a shit ton of planets! We have come a long way from the first discovery of the exoplanet in 1988.
The Kepler Orrery IV video, an update from the Kepler Orrery III version, is the latest installment in findings from the Kepler Telescope and its search for planets outside our Solar System.
The planetary systems are shown orbiting at the same scale as our Solar System for reference. The size of planetary orbits is to scale while the planetary sizes aren’t exactly to scale but are relative. Planetary sizes are much smaller or larger than illustrated. Therefore, compare the planetary sizes to other planets. The planet colors are based on their approximate equilibrium temperatures, as shown in the legend with Earth temperatures represented by the blue color.
As you know by now, we love music! The track to this video is from Csillagköd – The Birth of the Solar System. You can also find the track on Csillagköd’ Spotify page. And for the truly adventurous, I found this page.
For more information on the history of exoplanets check out NASA’s Historic Timeline of Exoplanetary Exploration.