NASA’s James Webb Space Telescope (JWST) has detected a hydrogen-rich atmosphere on 55 Cancri e, a “super Earth” located 41 light years away. According to research submitted to Nature Astronomy, the presence of hydrogen and carbon monoxide suggests the planet possesses a reduced magma ocean that releases gases through volcanic outgassing.
JWST Observations Reveal Hydrogen-Rich Atmosphere on 55 Cancri e
Researchers used the James Webb Space Telescope to observe five separate eclipses of 55 Cancri e. The goal was to test the planet’s atmospheric composition against long-standing rocky exoplanet evolution models. While those models typically predict atmospheres dominated by carbon dioxide (CO2) and carbon monoxide (CO), the JWST data showed a different reality.
The findings indicate an atmosphere with abundant carbon monoxide and surprisingly high levels of hydrogen, while carbon dioxide remains relatively scarce. This chemical signature provides a direct link to the planet’s interior redox state—the balance between oxygen and hydrogen or iron.
Did you know? 55 Cancri e is so close to its host star that it completes a full orbit in just 0.7 days. For comparison, Mercury takes 88 days to orbit our Sun.
Magma Oceans and Volcanic Outgassing
The research suggests that the atmosphere of 55 Cancri e is not static. The team noted differences among the five eclipse observations, which they attribute to volcanic outgassing or the formation of clouds made from material released from the planet’s interior.
These clouds may temporarily cool the surface before continued outgassing disperses them. Because the atmosphere reflects the interior’s composition, the preference for hydrogen-rich models suggests an interior with low oxygen fugacity. In simpler terms, the planet likely has a reduced magma ocean that fuels its atmospheric chemistry.
Measuring roughly 1.88 Earth radii and about 8 Earth masses, 55 Cancri e is a massive rocky world. Due to its proximity to its star, scientists believe the surface is hot enough to remain molten, creating a landscape of liquid rock.
Comparing Lava Exoplanets to Jupiter’s Moon Io
While both 55 Cancri e and Jupiter’s moon Io feature intense volcanism, the heat sources are fundamentally different. According to the study, the mechanisms driving these geological extremes are as follows:
| Feature | 55 Cancri e (Lava Exoplanet) | Io (Volcanic Moon) |
|---|---|---|
| Primary Heat Source | Stellar heating (proximity to star) | Tidal heating (Jupiter’s gravity) |
| Surface State | Molten rock on sunlit side | Widespread volcanic eruptions |
| Orbital Lock | Tidally locked to star | Tidally locked to Jupiter |
The Growing Catalog of Extreme Rocky Worlds
First identified in 2004, 55 Cancri e is part of a growing class of “lava exoplanets.” These worlds are characterized by extreme temperatures and tidally locked rotations, meaning one side permanently faces the star.
Other known lava exoplanets include:
- K2-141 b: Orbital period of approximately 6.7 hours.
- L 98-59 d: Orbital period of 7.5 days; potentially covered by a global magma ocean.
- TOI-561 b: Orbital period of 10.5 hours.
- HD 63433 d: Orbital period of 4.2 days.
- CoRoT-7 b: Orbital period of 20.4 hours.
Astronomers are now using the James Webb Space Telescope to determine if these planets share similar interior chemistries or if their atmospheres vary based on their specific host stars.
Frequently Asked Questions
What is a “super Earth”?
A super Earth is an exoplanet with a mass higher than Earth’s but substantially below those of ice giants like Uranus or Neptune. 55 Cancri e, for example, is about 8 Earth masses.
Can humans visit 55 Cancri e?
What is a redox state in planetary science?
The redox state describes the chemical balance between oxygen and elements like hydrogen or iron within a planet’s interior, which influences what gases are released into the atmosphere.
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