In CELESTIA you can even visit exoplanets orbiting pulsars! Like PSR 1257+12 (1.6.x)!
Note: after running each link above in CELESTIA, Right Drag its window with your mouse to get a sense of the 3-D aspects of the stars and their orbits.
Are you unfamiliar with our 1.6.x and 1.4.1 links? For an explanation click here.
The following will help you enjoy this page's 1.6.x and 1.4.1 links that run events directly in CELESTIA. If you're new to the program, these tips will also help you learn to use it.
You'll find more information about many of CELESTIA's controls on our Learning Center page.
PLANETS BEYOND OUR SOLAR SYSTEM
Exoplanets, also called extrasolar planets, are planets that are beyond our own Solar System. Representing one of today's most exciting areas of astronomy, their study is important because it may one day answer the pivotal question: is life abundant in the universe?
For centuries exoplanets have been theorized to orbit stars other than our Sun. However the first exoplamet was not confirmed to exist until 1992. Since then more have been discovered with increasing regularity due to improving detection techniques. By mid-2013 the total number of confirmed exoplanets was approaching one thousand, these in orbit around approximately seven hundred stars! Meanwhile over 3,500 more "candidate exoplanets" were awaiting confirmation.
In addition, at least one exoplanet has been detected which is not in orbit around any star system! Just 80 light years from Earth, this "free-floating" exoplanet seems to confirm theories that planet-sized bodies can form well away from stars, as well as in protoplanetary disks. Here is a short ESO video of how this exoplanet may look: Free-Floating Planet.
NASA's and JPL's mind-blowing Exoplanet Exploration and NASA Exoplanet Archive pages give their latest Exoplanet Count and much more. For an impressive table of related information, here's NASA's Current List of Confirmed Exoplanets. And here's a Q & A page that explains why this count differs from others published.
Want to visit the known exoplanets? You can streak across the cosmos to tour them in 3-D with NASA's excellent Eyes on Exoplanets, an awesome interactive feature. Here are the links to its tutorial video pages: Tutorial 1 Tutorial 2 Tutorial 3.
Astronomers have devised clever methods of detecting exoplanets. Most involve measuring subtle, exoplanet-induced variations in the electromagnetic radiation that reaches us from the stars they orbit. These variations are generally quite small and may manifest themselves in the radiation's direction, intensity, spectrum, timing, consistency and more.
One of the easiest-to-understand ways of detecting exoplanets is the "transit method", which measures the tiny decrease in light reaching us from a star when one or more of its planets pass in front of it. Kepler Transit Graph Also from the Kepler site, here's a superb interactive that lets you gather light from stars and find their exoplanets: KEPLER's Exoplanet Transit Hunt! But be forewarned, this will test your ability to observe and do a bit of math!
Another of the easiest-to-understand ways of detecting exoplanets is the "astrometry method", also often called the "wiggle method". This accurately measures the position of a star as it moves through space. If the star has one or more planets, their mutual gravity may cause the star's path to "wiggle" or oscillate like the star in the animation directly above.
You'll find information on the ways astronomers find planets in orbit around other stars in NASA's Five Ways to Find a Planet, in HubbleSite's Hunting for Planets and on Wikipedia's Methods of Detecting Exoplanets pages.
PROPERTIES OF EXOPLANETS
As the diagram above suggests, exoplants are proving quite varied. In fact, they are proving to be more varied than the planets in our own Solar System! Given the variety of stars they orbit, and the diverse conditions possible around any star and in collapsing interstellar molecular clouds, this is not surprising. Scientists speculate that the range of possible types of exoplanets is vast indeed.
Many of the earliest confirmed exoplanets were found using methods that favor detecting sizeable planets in modest-sized, short-period orbits (some as short as a few days!) This is why so many have been dubbed "hot Jupiters"! Even so, considerable numbers of smaller, Earth-sized exoplanets have now been detected, and over a billion are now estimated to exist in our galaxy alone. Considering all types, exoplanets in our galaxy may total in the hundreds of billions, perhaps trillions! And that estimate seems to continue to rise!
Of particular interest in the quest to learn more about exoplanets is the treasure trove of secrets that their atmospheres may one day reveal. Its atmosphere can give hints as to whether an exoplanet is likely to harbor conditions that may support life. (To this end, Hubble spied the first atmosphere of an exoplanet in the year 2000!) Of course, scientists have long recognized that life found on exoplanets may exist under conditions radically different from those found here on Earth. In HubbleSite's flash animation Alien Atmospheres you will get an introduction into just how weird life beyond our Solar system may be!
Here are links to some short but cool NASA videos that show some of the types of exoplanets we are already discovering or are one day likely to encounter. Viewed in full-screen they look awesome!
An Exoplanet Most Like Earth
Kuiper Belt World
Weird Warm Spot on Exoplanet
Kepler-20, An Unusual Planetary System
Hot Lava World
Kepler: Diversity of life possible on other planets
As mentioned above, many of the earliest confirmed exoplanets were found using methods that favor detecting sizeable planets in modest-sized, short-period orbits (some as short as a few days!) However, other techniques have identified exoplanets that orbit considerably further from their host stars. You can study the characteristics of many exoplanets detected by the Kepler mission by starting on the site's Kepler and K2 page.
Here's a link to another interactive that can help you get a feel for the orbital properties of exoplanets, a NY Times 2-D animated diagram, Kepler's Tally of Planets that shows the relative numbers and sizes of the exoplanetary systems discovered by Kepler.
One of the most important aspects of a stellar system which possesses exoplanets is its "habitable zone". Because our quest to understand exoplanets is largely a quest to find extraterrestrial life, and because life as we know it requires liquid water to exist, a star system's habitable zone is the region around its star (or stars) where a planet-sized body could be expected to maintain liquid water on its surface. This has also been popularly called the "Goldilocks zone", as it is where it is neither too hot nor too cold for liquid water, but rather is "just right".
As this short NASA video shows, the temperature and size of a star determine the size of its habitable zone: Comparative Life Zones. Excitement in the astronomical community is growing as more and more Earth-sized and Earth-like planets are being found in their host stars' habitable zones.
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SCALE OF THE COSMOS
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FUN FACTS ABOUT
The first exoplanet ever discovered orbits a pulsar!
Some exoplanets orbit two stars, not just one! That is, they orbit both stars in a binary systems!
Evidence suggests that, in the Milky Way alone, there are hundreds of billions of exoplanets! Of these, billions may be Earth-like!
One exoplanet has been nicknamed "Methuselah" because evidence suggests that it is 13 billion years old! If that is correct, it became a planet at the same time that the earliest galaxies were forming, less than a billion years after the Big Bang!
Exoplanet Kepler-22b may be an "ocean planet", that is, covered completely by water!
Exoplanets discovered thus far come in a range of sizes! The smallest is roughly the size the Moon! The largest has a diameter that is twice as great as Jupiter's!
QUICK ACCESS LIST
Note: some links are echoed elsewhere on this page and may include descriptive text. Note too that there are a few links to interactives in the center column immediately next to this list, so they are not duplicated here.
Link to the NY Times feature Kepler's Tally of Planets
Link to NewScientist's cool How Many Earths?
Test your knowledge of planets & exoplanets with NASA's Our World/Other Worlds