Exoplanets Facts

Extrasolar planets are called exoplanets and these are worlds that orbit other stars.

Both ground and space-based telescopes and observatories have found thousands of possible exoplanets.

Almost 2,000 of the exoplanets have been confirmed and the rest await study from astronomers to make sure that they are planets. Given the billions of galaxies, astronomers estimate that there is a good possibility that there are trillions of planets orbiting other stars.

If you look at our solar system you will see that planets exist in all sizes, orbital positions and masses.

The same ruling is used when you talk about any exoplanet. They can be as small as the Earth or as gigantic as the super worlds like Jupiter.

Their orbits can be close to the sun like Venus very far away from their parent sun.

Finding and Measuring

Astronomers are finding and measuring atmospheres around far away exoplanets. Knowing information about the atmosphere can help them understand more about the planet itself.

Some of the characteristics that astronomers use to determine if a celestial body is an exoplanet include: temperature of the surface, the magnetic field, orbit, and even an exoplanet’s color.

Astronomers group types of exoplanets as: Earth-size, Earth-like, Super-Jupiters, gas giants, rocky worlds the size of Earth, rocky giants, Super-Earths, mini-Neptunes, and gas dwarfs.

What did Scientists find

Scientists have found at least one exoplanet to contain an exomoon. In another case, the exoplanet is too close to its star and is leaving behind a trail of vapor.

The goal of researching exoplanets is to also find out which are the most Earth-like.

The area around a star that allows an exoplanet to have liquid water on the surface of a solid planet is called “the habitable zone.”

Some explain this as the “Goldilocks Zone.” Not to hot and not too cold.

Those worlds that are positioned in the habitable zone are the ones that are the best candidates for supporting life.

Earth-Like Planets

Where once we thought that there weren’t that many potential exoplanets that could support life, we are now finding that over 22% of the Sun-like stars being researched have Earth-sized exoplanets in their habitable zones.

The Kepler Mission was designed to seek out distant worlds and is continuing its mission today. There are many missions around the globe that are assisting in finding exoplanets.

Some of these include: the Hubble Space Telescope, the CoROT mission from the European Space Agency, the WISE mission, and the Herschel spacecraft.

Facts about Exoplanets

  • Exoplanets that are Earth-like and Earth-size are the ones that are similar in size to our planet. They have a lot in common with earth including similar atmosphere, the potential for liquid water, and are made of rocky substances.
  • Super-Earth Earth-type planets are bigger than earth and have a greater mass than our planet. They are less massive than the ice giants or gas giants that are in the same orbiting system. The first super-Earth exoplanet was found in 1992 and it was orbiting a pulsar.
  • Gas giant exoplanets and super-Jupiters are the biggest and larger than Jupiter. Gas dwarf exoplanets are often call mini-Neptunes and are typically smaller than Neptune or Uranus but can have thick atmospheres and up to ten times Earth’s mass.

Examples of exoplanets that have been found so far:

  • Gamma Cephei Ab: The very first exoplanet found; in 1998 it was detected around the Gamma Cephei star but not confirmed until 2003 when improved technology became available.
  • PSR 1267+12 B and C: Found in 1992, this was the first pulsar planets. They are orbiting fast, spinning the remains of the star that went supernova. Later, astronomers found a third planet in the system and a trying to figure out how they all survived a supernova explosion as well as how they formed. One of the planets found in this group is a Super-Earth.
  • 51 Pegasi b: Using the ground-based facility Observatoire de Haute-Provence in France, this is the first planet found to be around a star similar to our sun. It appears to be an extremely warm gas-giant and is known as a “hot Jupiter.”
  • Kepler 186f: Found by the Kepler Mission in 2014, this is the first Earth-size planet circling in the habitable zone of its star.
  • Kepler 11-f: This exoplanet is 2.3 times the mass of the Earth and is orbiting a Sun-like star. Scientists are unsure if it is a gas dwarf as it has low density and possibly an atmosphere of hydrogen-helium.
  • Mu Arae c: This is the first hot Neptune that ha ever been discovered and it is orbiting very close to its parent star.


  • What is an exoplanet?
    worlds that orbit other stars
  • What is the percentage of Earth-like planets that scientists think exist?
  • How many exoplanets have been found?
    around 2,000
  • What is another name for the habitable zone of a solar system?
    Goldilocks Zone
  • What is the moon of an exoplanet called?
  • When was the first Super-Earth exoplanet found?