Extrasolar Planets


Exoplanets or Extrasolar Planets are planets that orbit distant stars. At least 100 Extrasolar Planets (exoplanets) have been found in other Star Systems, but they cannot be seen visually.

Painting of a Saturn-sized planet around the white star Fomalhaut

These planets vary from Jupiter-like planets that orbit much closer to their star than our Planet Mercury to giant planets that have orbits beyond our Planet Pluto in distance from their star.

Planet Hunters

Planet Hunters refers to astronomers looking for planets beyond our Solar System. Planet Hunting involves studying the movement of the stars and their light. The aim of many astronomers is to find Earth-sized planets that might harbour life.

How to find a Planet?

The reason astronomers cannot see the planets around stars is because there is too much light and glare as the planets are too close to their star.

In the future, space telescopes such as the Terrestrial Planet Finder may use masking techniques to mask out the light.

At present the most powerful telescopes cannot see planets around stars, however, astronomers have developed techniques to detect them. The techniques include:

  1. Wobble – Light from a star can reveal hints that the gravity of an unseen planet is tugging it back and forth.
  2. Shadow– A planet crossing the face of  a star causes the starlight to dim. The dimming can reveal the planets size and even hint at its composition.
  3. Glow– A newly formed planet will still be hot from its formation and will emit infra red light perhaps enough for a telescope to pick up.

Type of Exoplanets

Brown Dwarf is smaller that a star and too low in mass to sustain hydrogen fusiion. Example: Gliese 229B

Chthonian Planet is a Hot Jupiter that has lost all of its thick atmosphere, leaving the rocky core. An Example is COROT-7b.

Gas Giant is a huge planet with a thick atmosphere of mostly hydrogen and helium surrounding a tiny rocky core. Example: Jupiter.

Hot Neptune is a Giant planet with a mass similar to Neptune (or Uranus) in an orbit close to its star. Example: Gliese 436 b (33 light years away).

Hot Jupiter is a massive gas giant planet orbiting close to its star. Example: 5r1 Pegasi b.

Hot Neptune is a giant gas planet orbiting close to its star. Example: Gliese 436 b.

Mega-Earth has a mass similar to Neptune, but is a rocky planet. Example: Kepler-10c.

Neptune is a gas giant with a thick atmosphere of hydrogen, helium, ammonia and methane surrounding a tiny, rocky core. Example. Neptune.

Rogue Planet is a planet ejected from their solar ystem and now wander between the stars. Eg. Cha 110913-773444

Super Earth is larger than Earth, but smaller than a gas giant like Neptune. Example: Kepler-22b.

Terrestrial Planet – finding an analog of Earth. Example: Earth.

Water World (Ocean World) is a super Earth that may have vast oceans of liquid water. Example: Gliese 1214 b (42 light years away)

How Many Exoplanets?

2003 – 100?
October 2016 – 3500


In 1995, Astronomers, Michel Mayor and Didier Queloz from Switzerland discovered the first planet orbiting another star like the Sun. The star is called 51 Pegasi. The extra solar planet was detected by observing the star wobble.

Kepler 186f is the first Earth-size planet orbiting in the habitable zone of its star. It was announced by Kepler Mission in April 2014.

In August 2016 astronomers announced the closest exoplanet to Earth is Proxima-B orbiting Proxima Centauri.


1. New Worlds in the Cosmos : The Discovery of Exoplanets
by Michel Mayor (Author), Pierre-Yves Frei (Author), Boud Roukema (Translator)

From Amazon.comAmazon.co.ukAmazon.ca,

2. Planet Quest: The Epic Discovery of Alien Solar Systems
by Ken Croswell

From Amazon.comAmazon.co.ukAmazon.ca,

3. Distant Wanderers: The Search for Planets Beyond the Solar System by Bruce Dorminey
From Amazon.comAmazon.co.ukAmazon.caBN.com

– 4. Rare Earth: Why Complex Life is Uncommon in the Universe 
by Peter Douglas Ward, Donald Brownlee
From Amazon.comAmazon.co.ukAmazon.caBN.com

Painting of a Saturn-sized planet around the white star Fomalhaut.
Copyright (c) 2000-2003 David A Hardy. All rights reserved.
This photo  may not be copied for any purpose without David A Hardy’s Permission.


Extrasolar Planets Links