Eris is one of the largest known dwarf planets, orbiting the Sun far beyond Neptune in the distant scattered disk of the Solar System. Its discovery in 2005 spurred the reclassification of Pluto, highlighting the existence of a population of large, icy worlds in the outer reaches. This distant location defines Eris’s environment, characterized by extreme cold, which dictates its surface geology and atmospheric behavior.
Eris’s Average Temperature Range
The surface temperature of Eris fluctuates dramatically as it travels along its vast, elongated orbit, but it remains profoundly cold at all times. Scientists estimate that Eris experiences a temperature range between a low of about 30 Kelvin (K) and a high of approximately 56 K. This translates to a chilling range of roughly -243 degrees Celsius (-405 degrees Fahrenheit) to -217 degrees Celsius (-359 degrees Fahrenheit).
The planet’s lowest temperatures occur when it is farthest from the Sun. Even the warmest temperature Eris experiences is far colder than any natural environment found on Earth. This maximum temperature is only achieved when the dwarf planet swings closest to the Sun during its centuries-long journey.
The Role of Extreme Solar Distance
The primary reason Eris is so intensely cold is its enormous distance from the Sun, which significantly limits the amount of solar energy it receives. Eris follows a highly elliptical orbit that takes approximately 560 years to complete. This orbital path carries it far beyond the main concentration of objects in the Kuiper Belt, placing it in the scattered disk.
The dwarf planet’s orbit has an aphelion, or farthest point, of nearly 97.7 astronomical units (AU) from the Sun. Its perihelion, or closest point, is still a distant 38.3 AU. The inverse square law of light dictates that the intensity of sunlight drops rapidly with distance, meaning that at nearly 100 times the distance of Earth, the energy Eris receives is minuscule.
Eris is currently near its aphelion, meaning it experiences temperatures near the absolute minimum of its range. This profound lack of stellar heat is the single most important factor determining the dwarf planet’s frigid environment.
Surface Ices and Atmospheric Collapse
The extreme cold on Eris has a physical manifestation on its surface, which is covered in a layer of exotic ices. Spectroscopic analysis indicates the surface is dominated by frozen methane and nitrogen. These compounds exist in a solid state because the surface temperatures are far below their freezing points.
The nitrogen and methane ices create a highly reflective surface, giving Eris an exceptionally high albedo. When Eris is at its greatest distance from the Sun, its atmosphere, which is composed of trace amounts of nitrogen and methane gas, is believed to collapse entirely.
This phenomenon, known as atmospheric collapse, causes the faint gases to freeze solid and fall onto the surface as a fresh layer of ice. As Eris slowly approaches its perihelion over centuries, the slight increase in solar energy causes the surface ices to sublimate, or turn directly back into gas, temporarily forming a thin, tenuous atmosphere. This cyclical freezing and thawing is a direct consequence of the dwarf planet’s long, cold orbit.
How Cold is Eris Compared to Other Objects?
Eris is significantly colder than many other known icy worlds in the outer Solar System. For instance, the coldest temperatures recorded on Earth, such as those in Antarctica, are still over 100 degrees Celsius warmer than the warmest point on Eris.
Eris is often compared to Pluto, the dwarf planet whose reclassification it prompted, as they are similar in size and surface composition. Pluto’s surface temperature ranges from about 33 K to 55 K, making Eris’s minimum temperature of 30 K slightly colder. Eris is generally colder than Pluto because its orbit takes it much farther away from the Sun. The planet’s temperatures are similar to other distant objects, such as Neptune’s moon Triton, which also features a surface composition of frozen nitrogen and methane.