Word of the Day



1. a planet which is outside the Earth’s solar system

Origin and usage

Exoplanet is derived from two Ancient Greek words, ‘exo’, meaning external and ‘planetes’, meaning wanderer.


The word exoplanet refers to the numerous worlds which orbit stars other than the Earth’s sun. These can vary in size and shape, ranging from small rocky exoplanets, about the same size as Mars, to gas giants which are even larger than Jupiter. They may be fiercely hot or cool enough to remain deeply frozen; some have a very short orbit of their star and some orbit two stars. An exoplanet may also be alone without a sun and permanently dark. In 2016 NASA announced the discovery of seven planets which were located 40 light years away; each of these is an exoplanet.

In August 2018, a team of astronomers from the European Space Agency and NASA, alongside John Livingston from the University of Tokyo, revealed they had found 44 previously unconfirmed exoplanets. Their findings were impressive considering that surveys usually only reveal 12 or more exoplanet discoveries. This data is used to create a more accurate model of the universe. It also enables investigators to learn more about the atmosphere on each exoplanet and learn whether or not they would be inhabitable.


“The first exoplanet orbiting another star like our sun was discovered in 1995. Exoplanets, especially small Earth-size worlds, belonged within the realm of science fiction just 21 years ago. Today, and thousands of discoveries later, astronomers are on the cusp of finding something people have dreamt about for thousands of years – another Earth.”


“The ability to observe a spectrum of light passing through the atmosphere of an exoplanet. It would be able to tell us if there are biomarkers indicating that life thrives on the surface.”

(Neil deGrasse Tyson)


exosolar planet, extrasolar planet

View the full definition in the Macmillan Dictionary.

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Macmillan Dictionary

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