Exoplanet Diversity: Atmosphere
Starlight filtered through distant atmospheres
An Earth-sized planet like TRAPPIST-1e could have an atmosphere similar to Earth’s.
Some warm Neptune-sized planets like GJ 436b are thought to be rich in methane.
Water can even exist on hot gas giants like WASP-62b, which are inhospitable to life as we know it.
Thicker and denser atmospheres block more light.
A Story Of Exoplanet Diversity: Atmosphere
Every planet has a unique atmosphere.
Researchers have detected thousands of planets orbiting stars other than the Sun. The data show that these planets are even more varied than the planets and moons in our solar system. They range from small rocky planets a fraction of the size of Earth to large gas giants several times the size of Jupiter. Some orbit cool dwarf stars while others circle stars much hotter and more massive than the Sun. And like the objects in our solar system, they have a wide variety of compositions and structures.
Although no exoplanet is close enough to visit with a space probe, we can—under the right conditions—study an exoplanet’s atmosphere. When a planet passes in front of its star, some of the starlight is filtered through the planet’s atmosphere. We can analyze the pattern of the filtered light (a transmission spectrum) to figure out what the atmosphere is made of. The peaks in the graph above represent the amount of light blocked by the exoplanet’s atmosphere – the largest peaks represent more light being filtered out.
The transmission spectra shown here are models based on assumptions about the composition, temperature, and structure of the exoplanet’s atmosphere. As observatories like the James Webb Space Telescope continue to operate, scientists will compare their data to the models to figure out which assumptions are correct and which are not.
Quick Facts: Atmosphere
Temperate Earth-sized exoplanet:
TRAPPIST-1 system, 40 light-years from Earth (inside the Milky Way)
0.9 times the size of Earth's diameter
TRAPPIST-1, a very cool red dwarf
Warm Neptune-sized exoplanet:
GJ 436 b
Gliese 436 system, 30 light-years from Earth (inside the Milky Way)
4 times the size of Earth's diameter
Gliese 436, a cool red dwarf
Hot Jupiter exoplanet:
WASP-62 system, 520 light-years away (inside the Milky Way)
15 times the size of Earth's diameter
WASP-62, a hot blue-white star
Explore More About Exoplanet Diversity
Find out more with these additional resources from NASA’s Universe of Learning
Illustration of exoplanet Trappist-1e: NASA, JPL-Caltech
Illustration of exoplanet GJ 436b: NASA, ESA, A. Feild, G. Bacon (STScI)
Illustration of exoplanet WASP-62b: Kyoto UniversityModel transmission spectra of Hot Jupiter and Warm Neptune exoplanet from ExoCTK and the generic grid based on the ATMO grid published in Goyal, J., et al., 2018b, MNRAS
Model transmission spectrum of Temperate Earth-sized exoplanet: Tyler Robinson
Subject-matter expertise provided by Dr. Hannah Wakeford, Dr. Kevin Stevenson
Produced by the Space Telescope Science Institute’s Office of Public Outreach