Astronomical bodies: Exoplanets - What are they and what are they like?
Proxima b and HD189733 are both exoplanets that you visit in the Lander game, but there are so many more that have been discovered. This page explains what an exoplanet is, the most commonly used classification system, and a little about the habitable zone.
What is an exoplanet?
An exoplanet is simply a planet which orbits a star outside of our solar system. The first confirmed detection of an exoplanet was announced in 1992, where two planets were found orbiting a pulsar. The planets were originally named according to the classification system being used at the time (which has since changed slightly), but were renamed to Draugr and Poltergeist after a public voting process.
Classifying exoplanets
There are many different types of exoplanet, and there is no real “gold standard” classification system in order to categorise them.
However, the classification system used by the Planetary Habitability Laboratory separates exoplanets into 18 categories based on size and temperature.
There are 6 size categories which can be divided into two broader groups: Terran and Gas Giants.
Terran planets are rocky planets, such as Mars (Warm subterran), Venus (Hot terran), Mercury (Hot subterran) and of course Earth (Warm terran). You could also include our moon in this list as a warm miniterran, and basically all other moons in our solar system as cold miniterrans.
The remaining six categories are the gas giants, and again, using our solar system as a guide, Saturn and Jupiter would be classified as cold Jovians, and Neptune a cold Neptunian. However, terms such as “Hot Jupiter” and “terrestrial planet” are commonly used in the scientific community.
Could exoplanets host life?
If a 'super-Earth' lies within the habitable zone of its star system then there may be potential for it to host life, however this also depends on other factors such as the composition of its atmosphere. The habitable zone is the range of orbits around a star at which planets may contain surface liquid water. This is a popular area of current research, internationally as well as at the University of Exeter.
One of the most famous Earth-like exoplanets is Kepler-62f, which lies within the Lyra constellation, 368 lightyears away from Earth. Its fame arises from the fact that a modelling study, performed by researchers at the Harvard-Smithsonian Center for Astrophysics and led by Lisa Kaltenegger, has revealed that the planet has the potential to have large oceans on its surface, which could provide the ability to host life. However it is expected that its atmosphere is thin, due to its position as the outermost planet in the system, which could mean its surface is covered in ice. Despite the uncertainty it is still considered a promising candidate for potentially habitable planets.