- Related Topics:
- Extrasolar planet
- Planet
- snowball planet
- mini-Neptune
Super-Earth
-
What is a super-Earth?
A super-Earth is an extrasolar planet with a mass between two and ten times that of Earth. They can also be defined by size, having a radius slightly larger than Earth's but smaller than Neptune's (about four Earth radii).
Super-Earths are common, making up about 30% of all known extrasolar planets. These planets exhibit a wide range of characteristics; some orbit very close to their stars, creating lava worlds, while others orbit far away, becoming snowball worlds. Because of their size, super-Earths may be more likely to support liquid water, which could make them habitable.
5 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How is a super-Earth different from Earth or other planets in our solar system?
A super-Earth is an extrasolar planet with a mass between two and ten times that of Earth. They can also be defined by size, having a radius slightly larger than Earth but smaller than Neptune.
Super-Earths are common in the galaxy, but the solar system lacks them. The solar system contains the smaller, rocky terrestrial planets (Mercury, Venus, Earth, and Mars) and the larger gas and ice giants (Jupiter, Saturn, Uranus, and Neptune).
Super-Earths exhibit a wide variety of properties. Some are similar to smaller versions of Neptune, called mini-Neptunes, while others are rocky. Some orbit so close to their stars that they are covered in magma oceans, while others are so far that their oceans are frozen. The question of whether super-Earths could support life is a key area of study, with the possibility of liquid water on their surfaces being a major factor. It has been theorized that Jupiter migrating closer to the sun may be the reason why the solar system lacks super-Earths.
2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What makes a planet an 'extrasolar planet'?
An extrasolar planet, or exoplanet, is any planetary body that exists outside of our solar system and typically orbits a star other than our Sun.
Since planets are much fainter than the stars they orbit, exoplanets are extremely difficult to detect directly. The first exoplanets were discovered in 1992. As of today, more than 6,000 exoplanets are known, with over 8,000 awaiting further confirmation.
Super-Earths, a type of exoplanet, are between two and ten times the mass of Earth.
3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How are super-Earths discovered by astronomers?
Astronomers use several techniques to discover super-Earths.
- Transit photometry measures drops in starlight as planets pass between their star and the telescope, revealing the planet's size and orbital period.
- The radial velocity method detects the motion of host stars caused by the gravitational pull of planets.
- Microlensing measures the gravitational bending of light from a distant source by an intervening star and its planets.
- Pulsation timing measures changes in distance between a signal source and the telescope using the arrival times of periodic signals. This method has been used to detect planets as small as Earth's Moon around pulsars.
- Direct imaging captures starlight reflected off the planet or thermal infrared radiation emitted by the planet. This works best for planets orbiting stars nearest to the Sun.
4 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What are some features scientists look for to see if a super-Earth could support life?
When determining whether a super-Earth could support life, scientists look for several key features. The presence of liquid water is crucial, leading them to identify the habitable zone around a star where a planet's surface temperature allows water to exist in liquid form.
Also, the existence of an atmosphere with thermodynamic disequilibrium, such as high levels of molecular oxygen and methane, may imply biological activity. Detecting complex organic molecules such as terpenes could also serve as a sign of life.
5 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
Why are super-Earths important for our understanding of planets and the search for life beyond Earth?
Super-Earths, planets with masses 2 to 10 times greater than Earth's, are vital in understanding planets and the search for life beyond Earth because they represent a type of planet absent from our solar system but common elsewhere.
The discovery of super-Earths has expanded the range of known planetary types and challenged previous assumptions based solely on our solar system. Super-Earths may have advantages in supporting liquid water due to their larger size. For example, heavier snowball planets could have high pressures at the bottom of their frozen oceans, leading to layers of liquid water. Hycean worlds, a type of super-Earth with watery oceans and hydrogen-helium atmospheres, could also support liquid water on their surfaces over a larger habitable zone than Earth.
1 Britannica SourceCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Super-Earth, type of planet that is between about 2 to 10 times the mass of Earth. Some astronomers use a size criterion to define super-Earths as being planets with a radius slightly larger than that of Earth but less than that of Neptune (about 4 Earth radii).
Prior to the discovery of extrasolar planets in the 1990s, the only known planetary system, the solar system, had two basic types of planets: the four smaller inner terrestrial planets (Mercury, Venus, Earth, and Mars) made of rock, and the four larger outer giant planets (Jupiter, Saturn, Uranus, and Neptune). The giant planets are further divided into the gas giants (Jupiter and Saturn), made mostly of hydrogen and helium, and the ice giants (Uranus and Neptune), each made up of a hydrogen and helium atmosphere surrounding a large outer core of methane, ammonia, and water ices, which contains much of each planet’s mass, and a small rocky inner core. Earth is the largest of the terrestrial planets, and Uranus is the smaller of the ice giants, at about 15 Earth masses. Thus, the solar system has no super-Earths.
The first extrasolar planets to be discovered were two super-Earths of about 4 Earth masses orbiting the pulsar PSR 1257+12. As the number of known extrasolar planets increased, super-Earths, a previously unknown type of planet, were found to be surprisingly common. Of the more than 5,000 known extrasolar planets, about 30 percent are super-Earths.
" height="20" alt="HEW Logo">
A wide variety of worlds are super-Earths. The heaviest are worlds like Neptune but smaller; these are therefore called mini-Neptunes, or sub-Neptunes. The smallest are likely rocky planets. It is not known at what mass rocky super-Earths give way to mini-Neptunes. (Some astronomers even prefer to define the mini-Neptunes as forming a type distinct from the super-Earths.) Those super-Earths that are very young or orbit very close to their stars are lava worlds, covered in magma oceans. Some super-Earths that orbit far from their stars are likely snowball worlds, whose oceans have frozen over.
The key question in studying extrasolar planets is: Could such worlds host life? Are they habitable? Astronomers have defined an orbital region around a star as the habitable zone, in which a planet could support liquid water on its surface and thus could possibly also support life. Earth orbits comfortably in the middle of the Sun’s habitable zone. Because of their larger size, super-Earths may have advantages in supporting liquid water. For example, on snowball planets heavier than Earth that are completely frozen, the higher gravity would lead to high pressures at the bottom of the frozen oceans that would melt the ice and thus lead to layers of liquid water. One type of super-Earth, the Hycean world, is a mini-Neptune with most of its mass as a watery ocean surrounded by a hydrogen-helium atmosphere. (The word Hycean is a portmanteau of hydrogen and ocean.) If their atmospheres were thin enough, such worlds could have liquid water at the surface over a much larger habitable zone than that for Earth-like planets.