Our ancient ancestors made every effort to try to understand and organize the Earth and how it played in our solar system and the sun. All of the planets in our solar system orbit around the sun, and any planet that orbits around other stars are called exoplanets.

Due to the bright light of the stars that they orbit, they are very difficult to see, even with telescopes. Astronomers had to get very creative in figuring out ways to detect and study the exoplanets that were so far away. One of the main ways that they can study them is to look for the effects that exoplanets have on the stars that they orbit around.

An exoplanet that doesn’t orbit perfectly around the center will cause the star to “wobble.” Astronomers are looking for wobbly stars to identify if they have an exoplanet.

ExoplanetComparison Introduction

Thanks to NASA’s Kepler Space Telescope, thousands of exoplanets have been found in the last few decades. These worlds are in a variety of orbits and sizes. Some of the exoplanets are huge and located very close to their parent star, while others are icy or rocky.

NASA as well as other space research agencies from all over the world are looking for a specific type of planet that is fairly close to the same size as our Earth and orbiting a sun-like star in what is known as the “Goldilocks Zone.” This is the area that scientists believe that would be habitable for life.

The habitable zone is the distance range where the temperature is just right for liquid water, one of the requirements of life on Earth. Each exoplanet’s habitable zone will be dependent upon the greenhouse effect of the planet’s atmosphere as well as a few other factors.


An exoplanet or “extrasolar planet” is any planet that is not within our solar system.


As of 2019, scientists have discovered 4,071 confirmed planets outside our solar system in 3,043 systems. 659 of these have more than one planet.

Types of exoplanets:

Astronomers have created a group of exopolanet types that include: Earth-size, Earth-like, Super-Jupiters, as giants, rocky worlds that are the size of Earth, rocky giants, Super-Earths, mini-Neptunes, and gas dwarfs.

Earth-size exoplanets are those that have the similar size to Earth. Earth-like planets are those exoplanets that share some of the characteristics that we have with Earth including atmosphere and surface liquid water. These can include the rocky Earth-size worlds as well as the rocky giant exoplanets.

Super-Earth and Earth-type are those exoplanets that are larger than our Earth, and have a greater mass than Earth. They are typically smaller than the ice giants or gas giants that may be within the same system. The first super-Earth was found in 1992 orbiting around the pulsar 1275+12.

Exoplanets that are gas giants, super-Jupiters are those giants that are even bigger than Jupiter. There are others that are called gas dwarfs or mini-Neptunes, and they are typically smaller than Neptune or Uranus. They can be as large as ten times Earth’s mass and have atmospheres that are very thick.


The first time astronomers located an exoplanet was in 1917, however, they didn’t recognize it as anything but a possible anomaly. The first scientific detection occurred many years later in 1988, and yet it wasn’t confirmed as an exoplanet until 2012.

For many years in the past, astronomers were convinced that there were other worlds out there beyond our solar system, they just couldn’t prove it.  Once astronomers had figured out how our solar system happened, they knew that the universe probably had other solar systems and planets. Our own solar system had its origins with a cloud of spinning dust and gas that collapsed under its own gravity and formed the planets and the sun.

Studying our solar system, astronomers learned that when our sun was young it had an extremely strong magnetic field with a force that reached out and dragged in the disk of swirling gas. The field lines from the magnetic field connected with the gas’ charged particles and acted like a kind of anchor, slowly down the spin and creating the sun. Astronomers assumed that the same kind of “magnetic braking” must occur with other suns so that planets could form around them.

Using this logic, the original astronomers that sought out exoplanets limited their search to those stars that were the most like our sun. However, the first two discoveries of exoplanets were found around a pulsar, which is a fast spinning star that died and turned into a supernova in 1992.

The first exoplanet found orbiting a sun-like star was in 1995. This one was a Jupiter-mass planet that was twenty times closer to its sun than Earth is to our sun. This surprised astronomers and they thought it just might be an unusual find until they began to find more.

In 1988, A Canadian team discovered a Jupiter-sized exoplanet around Gamma Cephei. However, due to the fact that its orbit was much smaller than our Jupiter, the scientists didn’t make the claim of planetary detection. They weren’t expecting to find planets that were so different from our own solar system.

The unusual exoplanet history

Most of the initial discoveries of exoplanets turned out to be the huge Jupiter-size or even bigger, gas giants that orbited really close to their parent stars. The reason for this was in the method that the scientists were using, which was to locate those suns that had a “wobble” to indicate that something was orbiting around it. The easiest wobble to detect are those stars with big planets close to their orbit.

Prior to the discovery of exoplanets, the technology instruments being used could only measure stellar motions down to a km/second. This wasn’t efficient enough to be able to detect a wobble when a planet was present. The instruments that we are using today can measure velocities that are as low as a centimeter per second.

Between better equipment and astronomers that now know what to look for, we are seeing the discovery of a lot more exoplanets.

NASA’s 2009 Kepler spacecraft was sent out into space in search of exoplanets in a variety of orbits and sizes as well as around stars that varied in temperature and size. Kepler used the transit method, which is measuring the amount of light that dips when a planet orbits in front of the star.

By studying the time in between the dips in light or transits, astronomers have been able to figure out the distance of the planet from its parent star as well as possible temperature. The temperature is important because it will give the data as to if liquid water could be on the surface.

Thus far, the Kepler mission has detected thousands of exoplanets and we now that they are very common in the universe.

The 2016 discovery of an exoplanet in the habitable zone is Proxima b, orbiting around Proxima Centari. The world is around 1.3 more massive that our Earth and its thought that it is a rocky world. It completes its orbit one time every 11.2 Earth days and is believed that the exoplanet is tidally locked so that it only shows one side to its star.

Kepler is expected to complete its mission when it runs out of fuel in 2018. It has discovered over 2,300 confirmed exoplanets and revealed the possibility of around 2,200 others. Observatories that have been searching have found a total of 3,706 exoplanets.

The Kepler space probe has revealed an incredible number of exoplanets. It accomplished its original mission and was then sent on a secondary mission to use the solar wind to keep its position in space. Kepler has found both terrestrial planets and gas giants and helped to define a whole new class that astronomers call “super-Earths.”

These are the planets most like Earth but are at a size between Neptune and Earth. Kepler found some of the super-Earths in habitable zones around the stars that they orbit and this has caused scientists to rethink how life might develop on these worlds.

The discoveries have shown that there is an abundance of super-Earths in our universe. Scientists have been puzzled that our solar system seems to one of the few that doesn’t contain a planet of that size.

Just as the Kepler mission was wrapping up – there is a new observatory called TESS (Transiting Exoplanet Survey Satellite) that is doing an all-sky survey that covers both hemispheres and is expected to locate at least fifty exoplanets that are Earth-sized.

Most Notable:

51 Pegasi b: This was the first exoplanet that was confirmed to be orbiting around a sun-like star. It’s half of Jupiter’s mass and orbits about the same distance as Mercury from our sun. Scientists see that it is so close to its sun that it is more than likely tidally locked showing only one side to the sun.

HD 209458 b: This exoplanet was discovered in 1999 to transit its star. It was noted that it was actually discovered using the Doppler wobble method. It was the first planet outside of our solar system where scientists detected an atmosphere as well as lack of clouds and a profile for temperature.

55 Cancri e: This is a super-Earth that orbits a star that is incredibly bright. It has a 17 hour and 41 minute “year,” and scientists think that it might have a diamond core and be carbon-rich.

Artist impression stars Effect

HD 80606 b: Discovered in 2001, it had the record for being the most eccentric exoplanet ever found. It has an odd orbit similar to the one that Halley’s Comet has, and this might be due to being influenced by another star.

WASP-33b: Discovered in 2011, this exoplanet has a layer that is a kind of “sunscreen” for a stratosphere. It absorbs some of the visible as well as ultraviolet light from its parent star. This exoplanet not only orbits backwards but it triggers the most vibrations seen by any satellite.

Effects on Human Life:

Locating exoplanets that are of interest is a priority, but the largest priority is in finding those that are within the habitable zone of their parent planet. Our sun has a limited life span, and while it will still be billions of years before it makes its change, the time to look for places that we can move to is now.

Interesting Information:

  • Exoplanets that are known cover a wide range of masses, sizes, and positions in orbit around their parent star. Sizes and masses can be smaller and less massive that our Earth, all the way to super-Jupiter types of worlds. Positions in orbit can be very close to the star or extremely distance.
  • The more that astronomers study exoplanets the more that they are finding and measuring atmospheres around them. The research gives needed data to understand what gases exist in the gaseous envelopes around many types of planets.
  • Astronomers have become so adept at learning about exoplanets that they can now measure surface temperatures, magnetic fields, orbits, and even their colors. As technology and detection methods improve and become more sophisticated, they will be able to get even more data from these far off worlds.
  • Astronomers have found one exoplanet that has an exomoon.
  • Astronomers have found another exoplanet that is leaving a material trail as it vaporizes during its orbit that is too close to its parent star.
  • The area around a star where an exoplanet can have liquid water is called the habitable zone and nicknamed the “Goldilocks Zone.” The nickname is because the zone isn’t too hot and isn’t too cold; it’s just right.
  • The exoplanets with habitable zones are the ones that scientists are most interested in for possible human habitation.
  • Over 22% of the sun-like stars have Earth-sized exoplanets in their habitable zones.
  • The Kepler Mission was launched to seek out distant worlds, but other research is also being done with the Hubble Space Telescope, the CoROT mission from the European Space Agency, the WISE mission, and the Herschel spacecraft. Additional ground-based observatories are continuing the search for exoplanets.