A Whole New Universe: 20 Years of Exoplanets
Artist impression of the exoplanet 51 Pegasi b 

ESO/M. Kornmesser/Nick Risinger (skysurvey.org) - ESO website.
Licensed under CC BY 4.0 via Wikimedia Commons - source

The discovery of "Bellerophon," the nickname astronomers gave to exoplanet Pegasi 51 b, rocked the astronomical world. Announced in 1995 by astronomers Michel Mayor and Didier Queloz, and quickly confirmed by Geoffrey Marcy and Paul Butler, this gas giant planet orbits closer to its star than previously thought possible for a planet of its type-just 7 million kilometers away from its star, or eight times less than the distance of Mercury from our own Sun!

51Pegasi b was detected using the radial velocity method, which involves very carefully measuring the changes in the spectra of the host star caused by the tug of the planet as it orbits around the star. As this planet is very large and orbits very quickly around its star, it was possible to take repeated measurement very quickly and for other astronomers to confirm this discovery using their own telescopes and sensitive spectrometers. Inspired by the new realization that giant planets could orbit very close to their stars and so be detected using their own equipment, astronomers rushed to discover "hot Jupiters" of their own and began to find many dozens, then hundreds, then thousands of extrasolar planets in our galaxy.

It has been a mere twenty years since this paradigm-shifting discovery, and now there is an entire generation of people who have grown up with the knowledge that there are indeed planets outside of our solar system. We have not found an exact match for our own solar system, but what we have found are other solar systems that defied what we thought was possible, from "hot Jupiters" to "Super Earths," to multiple planets orbtiting very tightly around their host stars, to planets that just may be in the habitable zone for liquid water to exisit on their surface. Planets are around all kinds of stars, even exotic stars such as pulsars (and in fact, the very first extrasolar planets were detected around a pulsar in 1992!). We have even found "rogue planets," planets that seem to have been ejected from their home systems and now roam between the stars. With improved techniques and equipment we have now even begun to identify the makeup of the atmospheres of these stars, including Pegasi 51 b, and have even clocked massive winds at thousands of miles an hour and the darkening and lightening of atmospheric features on these distant worlds. All this is just two decades-what will we discover in the next twenty years? Will we find earthlike worlds, perhaps worlds with life?

There are many resources and activities about exoplanets available on the Night Sky Network and NASA's PlanetQuest site. The "Where are the Distant Worlds?" monthly star charts have been updated with the latest discoveries, so you can find and point out some of the brightest stars with planets. There are also audio and transcripts from telecons with scientists looking for exoplanets, such as this telecon with Dr. Nick Gautier from the Kepler mission. The NSN Universe Discovery Guides also feature information on exoplanets and how they relate to each topic, such as June's guide on globular clusters and the types of planets we could expect to find around these older, metal-poor stars.
an image of 51 Pegasi b as visualized by NASA's Eyes on Exoplanets software
51 Pegasi b as visualized in the Eyes on Exoplanets software
PlanetQuest's 20 years of Exoplanets site has many additional and excellent resources too. You can "visit" these worlds by using the free NASA's Eyes on Exoplanets software-just don't get lost! You can also find more fun facts and cool travel posters for some exoplanets on the Exoplanet Travel Bureau. You can even to find exoplanets from your own computer by helping to sort through the Kepler Mission's data on Planethunters.org. These are just a few of the many resourses available from NASA and other agencies and organizations about the new science of exoplanets, with more to come! 
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