NASA's Spitzer Space Telescope has revealed a new exoplanet discovery: the first known system of seven Earth-size planets around a single star. Three of these planets are firmly located in the habitable zone, the area around the parent star where a rocky planet is most likely to have liquid water.

7 New Exoplanets Discovered by NASA

7 New Exoplanets Discovered  by NASA Credit: NASA-JPL/Caltech

This artist's concept shows what the TRAPPIST-1 planetary system may look like, based on available data about the planets’ diameters, masses and distances from the host star. 

What is an exoplanet?

What is an Exoplanet?

An exoplanet is any planet that is outside of our solar system - ie anything that is not orbiting our star. The first exoplanet was discovered in 1988, but over 3,500 have been discovered since then.

Only a tiny fraction of these have been deemed capable of supporting life in any way. Oceans and closeness to a star are two factors that scientists take into account.

The discovery sets a new record for greatest number of habitable-zone planets found around a single star outside our solar system. All of these seven planets could have liquid water–key to life as we know it–under the right atmospheric conditions, but the chances are highest with the three in the habitable zone.

“This discovery could be a significant piece in the puzzle of finding habitable environments, places that are conducive to life,” said Thomas Zurbuchen, associate administrator of the agency’s Science Mission Directorate in Washington. “Answering the question ‘are we alone’ is a top science priority and finding so many planets like these for the first time in the habitable zone is a remarkable step forward toward that goal.”

Why all the excitement?

Three of TRAPPIST-1's "exoplanets" are smack dab in the so-called habitable zone, also known as the Goldilocks zone, where conditions are just right for watery oceans - not too much and not too little stellar energy - greatly increasing the likelihood of life.

No other star system known contains such a large number of Earth-sized and probably rocky planets.

All are about the same size as Earth or Venus, or slightly smaller. Because the parent star is so dim, the planets are warmed gently despite having orbits much smaller than that of Mercury, the planet closest to the sun.

Based on their densities, all of the TRAPPIST-1 planets are likely to be rocky. Further observations will not only help determine whether they are rich in water, but also possibly reveal whether any could have liquid water on their surfaces. The mass of the seventh and farthest exoplanet has not yet been estimated–scientists believe it could be an icy, "snowball-like" world, but further observations are needed.

What is TRAPPIST-1?

TRAPPIST-1 stands for Transiting Planets and Planetesimals Small Telescope. The discovery is a small, dim star in the constellation Aquarius, less than 40 light-years from Earth, or 235 trillion miles away, according to Nasa and the Belgian-led research team who announced its discovery on Wednesday. 

Seven planets circle Trappist-1, with orbits ranging from one and a half to 20 days. If Trappist-1 were our sun, all these planets would fit inside the orbit of Mercury. That's how close they are to their star and why their orbits are so short. The planets have no real names. They're only known by letters, "b" through "h." The letter "A" refers to the star itself.

Exoplanet Glossary

  • Exoplanet: a planet that orbits a star other than our Sun
  • Habitable zone: a band of potential habitability, the right distance and temperature for liquid water to exist on the surface of a planet
  • Light year: a measure of distance, not time. It is the total distance that a beam of light, moving in a straight line, travels in one year
  • Orbital period: the time it takes a satellite to make one full orbit is called its period. For example, Earth has an orbital period of one year
  • TRAPPIST-1: a dim and ultra-cool dwarf star, much cooler and redder than the Sun and barely larger than Jupiter

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