Universe Guide

What is a Rogue Planet?

A Rogue Planet is a planet that doesn't orbit a star. Instead of a star, a Rogue Planet orbits the Galactic Centre of a galaxy or is free floating between galaxies in Intergalactic Space. Like normal planets, they can be Gas Giants such as Jupiter, Saturn. They can also be rocky planets such as Earth or Mars and even a dwarf planet like Pluto. There could be thousands, millions or billions of them but there hard to spot so we won't be finding as many as we do with exoplanets.

There are no photos of rogue planets, only artists impressions of these types of planets. They are too far away and will not be viewable by any telescope or binoculars from Earth.

A similar type of phenomena are rogue stars, these are stars that do not orbit round the Galactic Centre of a galaxy. They have been expelled from the galaxy through an event. An event could be that it got too close to the Supermassive black hole that is found at the centre of the galaxy and instead of being consumed, it is ejected as out as a Hypervelocity Star. A Hypervelocity Star is a star that is moving faster than what would otherwise be referred to as normal.

Rogue Planets are hard to spot because they are small and don't give off heat or radiation as much as stars. One way to spot them is if they moved in front of something and made that object blink. This method of discovery is the transit method. It is a method that scientists used to discover exoplanets that orbit round stars.

Rogue Planets should be assumed to be only found in the milky way but could potentially exist in every galaxy in the Universe. If you take the number of potential rogue planets in our galaxy and multiple by the number of galaxies, the total number in the universe is massive.

Rogue Planet Discoveries


OTS-44 is one of the first Rogue Planets to be identified as a candidate in 1998. The planet is located in the southern hemispheric constellation of Chameleon in 1998. Its status as a rogue planet is in question as it could quite possibly be a low mass Brown Star, these are amongst the coolest stars in the universe and are often failed stars. The planet is estimated at being at a distance of 554 Light Years from our solar system.


In January 2019, a paper was published that detailed two rogue planets discovered by microlensing. The two planets are known as OGLE-2017-BLG-0560 (Ophiuchus) and OGLE-2012-BLG-1323 (Sagittarius).

Micro-lensing is where light from a distant object is enhanced and magnified by a closer object. It is a technique that is not just limited to planet spotting but has also been linked to looking at galaxies far away. It was an idea that began at the beginning of the twentieth century during the First World War but it was not until after the war that Arthur Eddington, a British scientist was able to put the theory to the test with the 1919 Solar Eclipse. Arthur Eddington showed that during the Eclipse, the light from a distant object could be moved by the gravity of a closer object, in this case, the Sun. Headstuff.

Life on a Rogue Planet

Rogue Planets will be cold as there will be nothing nearby to heat up the atmosphere. There could be an underground heat source but nothing to provide sufficient heat to live on the surface. The planets will be dark as there will be nothing to give it light. There will be no natural life forms on the planet as life needs heat to survive.

Enclosed settlements could be positioned on the planet as a means to break up a journey between locations. All light would be artificial and supplies would have to be brought to the planet or grown in an artificial environment.

Europa, a way for Life to Exist

Although life might not be able to exist on the surface of the planet, life could exist under a frozen icy surface. It is widely speculated that life could exist under the icy crust of Europa, a moon orbiting Jupiter. The core of the planet would be able to heat the lower levels of the lake. It has been proven that life does not need light to survive. Extremophiles are life forms, no more complex that a beetle or a scorpion have been known to exist in the harshest of environments.

According to scientists, a planet that was about 3.5 times the mass of the Earth could produce enough heat from its core to maintain a liquid ocean under an icy crust. The ocean could last for 5 billion years. Whilst Europa is not 3.5 times the mass of the Earth, it does have Jupiter's gravity affecting it therefore causing the core to heat up. Wired

Movile Cave

In 1986, Romanian technicians looking to test the local area to find out its suitability for a power plant came across Movile Cave. The cave is near Mangalia in eastern Romania. When the technicians went down into the cave, they found an ecosystem cut off from the above world. The life forms used Chemosynthesis rather than Photosyntheseis to survive. The environment in the cave is poisonous to us but the life down there was able to survive. B.B.C.

The whole cave had no access to light and life adapted to ensure its survival. If life could exist down there, there's no reason why it can't exist on Europa or any rogue planet under the surface.

Formation of a Rogue Planet

Failed Star

How the planet got to be a rogue planet is speculatively. If we assume that gas giants such as Jupiter is a failed star, one that was not massive enough to start nuclear fusion then it is one way a rogue planet can be created. The smallest star so far discovered, EBLM J055557ab, is smaller than Jupiter . We can therefore assume rogue gas giants are possibly failed stars.

Unnova Implosion

There is a theory that instead of a star going supernova and exploding, a star might just go in the opposite direction. These events are known as Failed Supernova and Unnova A star will collapse and disappear quietly. Any orbiting planets will be left orphaned and become rogue planets as they'll have nothing to orbit.

Ejected from a Solar System

A rogue planet could have been orbiting a star in the same way as the Earth orbits the Sun. Something could have happened that cause the planet to be forcibly ejected from . There is a theory that our Solar System had nine planets (excluding Pluto) and that the ninth planet was ejected from the Solar System. Where that planet is, is currently the subject of debate and investigation, that is if it ever existed.

The theory is that the fifth planet was ejected from the solar system during the early years of the solar system. The planet is out there somewhere and to use cliché, its like looking for a needle in a haystack. The planet won't be giving off heat or radiation so its going to be hard to pick up. Arxiv

The scientists behind the Eris discovery made a bold prediction that our solar system has a ninth planet with the ninth planet orbiting at a distance further out than Eris. One of the reason they predict is that a lot of of the found kuiper belt objects so far discovered are all in one part of the solar system, why are there more in the other part. There are some objects found in the barren part of the solar system but there should be more. The ninth planet if it is found is likely to be found in the Taurus constellation. If the ninth planet is found and found to be in orbit then it won't therefore be a Rogue Planet. N.A.S.A.

The star HD 106906 in the constellation of Crux has a planet that is 16 times away from its star than Pluto is from the Sun. It is a star that has been ejected from its solar system destined to become a Rogue Planet eventually. If the planet continues to move away, the gravitational effect of the star will no longer keep it in orbit. National Geographic

Rogue Planets in Entertainment

Founders Homeworld

Rogue Planets featured quite a few times in Star Trek. The Changeling or Founders who were from the Gamma Quadrant in the Star Trek - Deep Space Nine franchise was discovered on a Rogue Planet in the Omarion nebula. The Changelings hid themselves away from the rest of the galaxy from where they controlled the Dominion. The planet featured in The Search when the crew of the Deep Space 9 Station go in search of the Dominion leaders.

Rogue Planet

A Rogue Planet also featured in the Star Trek - Enterprise episode aptly called Rogue Planet. In the episode, Captain Jonathon Archer is tasked with investigating the newly discovered planet.

Space 1999

The British television series, Space 1999 featured scientists living on the moon in the year 1999. At the time of developing the series, it had been envisaged that we might have a moonbase, that prediction didn't quite work out. The premise was that an explosion caused the moon to move out of orbit and travel through space. The series followed the survivors as the moon travelled through space. The moon could therefore be reclassified as a Rogue Moon or Rogue Planet. It no longer satisfies the conditions of a moon, that is an object orbiting a planet.

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