Theros (also designated TRAPPIST-1b) is a rocky exoplanet orbiting the ultracool M8.2V red dwarf star TRAPPIST-1. It is the first planet of the system and one of just three worlds around that star with no oceans. Theros is a volcanic desert world being strangled by the gravitational influences of its star and 6 sibling planets.

Theros was first added in version 1.0 of Interstellar Adventure Revived as a way to celebrate the real life discovery of the TRAPPIST-1 system. Following the new data released on February 23rd, 2017, it was completely re-done to be as realistic as possible and to be very similar to NASA's official rendition of the planet.

This world is covered in global deserts a few kilometers above sea level. It has a dangerous atmosphere, albiet slightly less dense and cooler than that of Eve.

In-Game Description

"Theros, aka TRAPPIST-1b, was the first planet found in the TRAPPIST-1 system and was found to have an atmosphere two days after its discovery. While this atmosphere is similar to that of Kerbin, Theros is no place for life."
Kerbal Astronomical Union


Mass, Radius, and Density

Theros is a roughly Kerbin-sized planet. With a radius of about 694 kilometers (compared to Kerbin's at 600 km), Theros is similar in size to Eve. This is about 1.156 times the size of the Kerbal's home planet. While such a rather large object, Theros has an unusually low mass. It is only around 80% the mass of Kerbin with a [real-scale] density of 3.659 g/cm^3. Such a low density points towards an unusual internal composition, one made of lighter solids and no iron/nickle core.


The surface of Theros is primarily volcanic. The planet's terrain is a pallet of different shades of red, orange, and yellow. Such an appearance is shared with volcanic worlds like the moon Kevari in the Cercani system. These are flows of magma made of both molten rock and sulfur compounds, which react with TRAPPIST-1's strong X-Ray flares, producing the vivid colors. Specific shades of orange depend on the ratio of basalt to sulfur-based materials, with the darker colors being more rich the the former and lighter colors richer in the latter.

Another volcanic feature of Theros are its enormous volcanoes. These are shield volcanoes that have built up over millions and billions of years. Due to the strong tidal friction from TRAPPIST-1 and the lack of plate tectonics, Theros's shield volcanoes have grown to enormous scales unseen in the Kerbol system. Most of them are around 10 to 20 kilometers high and close to twice as wide. Many have clear calderas, or volcanic craters, visible from space. However, a good amount appear as large lumps because they became extinct and prone to atmospheric weathering.

A large amount of the planet is covered in dunes. Due to a lower gravitational pull (~0.72 gees) and a thicker atmosphere, sand on Theros is able to be carried much higher and farther than even on Duna. Unlike Duna, the dunes here are not all caused by sand. Strong winds have etched the rocky crust of the planet into a series of many large, wide "spikes" that can even be found on the volcanoes. This suggests that the atmospheric forces of the past are still working on this planet.

Atmosphere and Climate

The atmosphere of Theros is similar to that of Eve - thick, toxic, and hot. By composition, the atmosphere already looks quite inhospitable. About 70% is a mix of carbon dioxide and hydrogen, with smaller amounts of sulfur compounds (15%), argon (3%), methane (1.6%) and others (0.4%). There are incredibly tiny amounts of oxygen, making breathing and jet engines impossible. Carbon dioxide levels are far above the lethal limit for Kerbals, so taking of your helmet here is not recommended.

The toxic air of Theros is also quite thick. At sea level, the atmospheric pressure is over 3 times that of Kerbin, not too different than that of Eve. It has a rather linear pressure increase as altitude drops. This is mainly caused by the planet's low gravity and the large quantity of light gases, which causes the atmosphere to "poof" up. The atmosphere of Kerbin, by comparison, has a non-linear trend and tends to multiply in pressure when getting closer to the surface. That unique feature of Theros's atmosphere makes it better for parachute and space plane landings, as there is more air higher up to slow down a spacecraft.

Theros's thick atmosphere has about 3.2 times the surface pressure of Kerbin's atmosphere. This, combined with the tidal locking of the planet, creates large winds that whip around the planet. These high winds can reach speeds of 150-300 mph, similar to that of Category 5 hurricanes and EF3 to EF5 tornadoes on Earth.


  • The low density of Theros in real life implies that it could have a supercritical ocean of liquid water. However, the author of Interstellar Adventure Revived finds this unlikely.
  • Theros used to have the texture of a classical tidally locked desert planet prior to the February 23rd, 2017 announcement regarding the system. It has now been textured like NASA's official art for the planet.

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