2023-08-17 04:00:14
Since astronomers began scanning space for exoplanets three decades ago, we’ve discovered that planets in the Milky Way — and likely the Universe — vary wildly in size and mass.
Kappa Andromedae b has a mass about 12.8 times that of Jupiter.
CrĂ©dit d’image: NASA’s Goddard Space Flight Center/S. Wiessinger
But what is the largest possible size for a planet? Prior to 1992, Jupiter, 11 times larger than Earth, was the largest known planet. However, some monsters we’ve discovered since far outclass it.
Two measurements define the size of a planet: its width (double its radius) and its mass. Solène Ulmer-Moll, postdoctoral researcher at the University of Geneva (The University of Geneva (UNIGE) is the public university of the canton of Geneva in…), affirms that “the largest exoplanets have a radius of approximately twice that of Jupiter”. These extreme objects orbit very close to their star (A star is a celestial object emitting light autonomously, similar to a…).
A planet’s width and mass are related, but density also plays a role. The gas giant (The gas giants are the largest of the planets. They are called gaseous, by…) HAT-P-67 b, although twice as large as Jupiter, is only a third of its mass , emphasizes Ulmer-Moll. Rocky planets never reach the size of “super-Jupiters”. The largest, called “super-Earths”, are twice as wide as our planet.
The most massive planets are about 13 times the mass of Jupiter, such as HD 39091 b, located 60 light years from Earth.
What is the maximum possible size for a planet?
We do not expect to find planets much larger than super-Jupiters. Beyond a certain size, a planet becomes a “brown dwarf (A brown dwarf is an object massive enough to be considered a…)”.
Illustration of a “super-Jupiter” orbiting a brown dwarf.
Image Credit: NASA/STScI
Nolan Grieves, another researcher from the University of Geneva, explains that the major difference between brown dwarfs and planets is their mass and combustion ( Combustion is an exothermic redox chemical reaction. When the…) of deuterium (Deuterium (symbol 2H or D) is a natural isotope of hydrogen. Its atomic nucleus…). Beyond 14 times the mass of Jupiter, an object is considered a brown dwarf.
The most massive brown dwarf discovered to date is SDSS J0104+1535, 750 light-years from Earth. Although it is 90 times more massive than Jupiter, it could be smaller in volume than the largest planet in our solar system (The solar system is a planetary system composed of a star, the…).
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