Illustration of planet very close to star.

Artist's concept of 51 Pegasi b, which was discovered in October 1995. The giant planet is about half the size of Jupiter and orbits its star in about four days. Credit: NASA/JPL-Caltech

10 Things: Exoplanets 101

By Celeste Hoang

Feature | March 19, 2018

Let the planet-hunting begin.

NASA’s Transiting Exoplanet Survey Satellite (TESS), which will scan the skies to look for planets beyond our solar system—known as exoplanets—is now in Florida to begin preparations for launch in April. Below, 10 Things to know about the many, many unknown planets out there awaiting our discovery.


We call planets in our solar system, well, planets, but the many planets we’re starting to discover outside of our solar system are called exoplanets. Basically, they’re planets that orbit another star.

Exoplanet GIF
Just 1.6 times larger than Earth and orbiting in the habitable zone of a sun-like star, Kepler-452b could be one of the best place in our galaxy so far to look for extraterrestrial life. Further investigation will require advanced, space-based telescopes such as those currently in development at NASA. (Artist's concept.)

2All eyes on TRAPPIST-1.

Remember the major 2016 announcement that NASA had discovered seven planets 40 light-years away, orbiting a star called TRAPPIST-1? Those are all exoplanets. (Here’s a refresher.)

3Add 95 new ones to that.

Just last month, NASA’s Kepler telescope discovered 95 new exoplanets beyond our solar system (on top of the thousands of exoplanets Kepler has discovered so far). The total known planet count beyond our solar system is now more than 3,700. The planets range in size from mostly rocky super-Earths and fluffy mini-Neptunes, to Jupiter-like giants. They include a new planet orbiting a very bright star—the brightest star ever discovered by Kepler to have a transiting planet.

4Here comes TESS.

How many more exoplanets are out there waiting to be discovered? TESS will monitor more than 200,000 of the nearest and brightest stars in search of transit events—periodic dips in a star’s brightness caused by planets passing in front—and is expected to find thousands of exoplanets.

TESS Spacecraft
The fully integrated Transiting Exoplanet Survey Satellite (TESS) will launch in 2018 to find thousands of new planets orbiting other stars. Credit: Orbital ATK

5With a sidekick, too.

NASA’s upcoming James Webb Space Telescope will provide important follow-up observations of some of the most promising TESS-discovered exoplanets. It will also allow scientists to study their atmospheres and, in some special cases, search for signs that these planets could support life.

6Prepped for launch.

TESS is scheduled to launch on a SpaceX Falcon 9 rocket from Cape Canaveral Air Force Station nearby NASA’s Kennedy Space Center in Florida, no earlier than April 16, pending range approval.

7A groundbreaking find.

In 1995, 51 Pegasi b (also called "Dimidium") was the first exoplanet discovered orbiting a star like our Sun. This find confirmed that planets like the ones in our solar system could exist elsewhere in the universe.

8Trillions await.

A recent statistical estimate places, on average, at least one planet around every star in the galaxy. That means there could be a trillion planets in our galaxy alone, many of them in the range of Earth’s size.

9Signs of life.

Of course, the NASA's ultimate science goal is to find unmistakable signs of current life. How soon can that happen? It depends on two unknowns: the prevalence of life in the galaxy and a bit of luck. Read more about the search for life.

10Want to explore the galaxy?

No need to be an astronaut. Take a trip outside our solar system with help from NASA’s Exoplanet Travel Bureau.