Researchers Detect Dense Carbon-Rich Atmosphere Around Nearby Super-Earth

Scientists have confirmed the presence of a dense atmosphere enveloping a rocky planet twice Earth’s size within a neighboring star system.

This super-Earth, designated 55 Cancri e, stands out as one of the rare rocky exoplanets with a substantial atmosphere, dominated by carbon dioxide and carbon monoxide, though the exact proportions remain uncertain. Unlike Earth’s atmosphere, which contains nitrogen and oxygen, this planet’s gaseous envelope is fundamentally different.

What Makes 55 Cancri e a Fascinating Super-Earth

Orbiting the sun-like star 55 Cancri A, this exoplanet weighs roughly eight times as much as Earth and has nearly double the diameter. It was first identified on August 30, 2004, marking it as the earliest known super-Earth orbiting a main sequence star, preceding Gliese 876 d by one year.

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The planet lies closest to its star in the system, completing an orbit in under 18 hours—a faster revolution than what was initially estimated before 2010, when its orbital period was thought to be 2.8 days.

Due to its close proximity, 55 Cancri e experiences extreme surface temperatures exceeding 3,000 Kelvin, accompanied by brightness variations that may be linked to intense volcanic eruptions. Some hypotheses suggest it could be a carbon-based world.

Previous atmosphere studies have delivered mixed results. Early evidence pointed to a hydrogen-helium atmosphere, but follow-up observations contradicted this, favoring heavier molecular compositions or a thin layer of vaporized rock.

Recent observations made by the James Webb Space Telescope in 2024 ruled out a rock vapor atmosphere, instead unveiling a thick, carbon-rich atmospheric layer containing carbon dioxide and carbon monoxide.

Revealing Atmospheric Characteristics and Planetary Evolution

The planet’s scorching heat, with temperatures soaring to nearly 4,200 degrees Fahrenheit, makes it inhospitable for life as we know it.

Nonetheless, this discovery highlights the possibility that other rocky planets with dense atmospheres might exist, some potentially offering more suitable conditions for life.

Located approximately 41 light-years away, 55 Cancri e's mass is eight times that of Earth, and it is tidally locked to its host star, Copernicus, resulting in continuous day and night hemispheres. Its surface is dominated by vast magma oceans.

To analyze the atmosphere’s composition, researchers studied data from the Webb Space Telescope collected before and after the planet passed behind its star.

This method allowed them to separate the planet’s emitted light from the star’s and calculate surface temperatures, revealing evidence that heat distribution across the planet is more uniform than expected—an indication of an atmosphere moderating temperature extremes.

Outgassing from the planet’s molten surface may support atmospheric retention, offering insights into the early conditions of rocky planets like Earth and Mars, which once had lava lakes.

The team identified absorption of specific light wavelengths by molecules in the atmosphere, suggesting the presence of carbon dioxide and carbon monoxide, as these gases block light in those spectral regions.

Scientists believe that 55 Cancri e’s atmosphere has evolved significantly over time. Its original atmosphere was likely stripped away by intense radiation and heat from its host star long ago. Renyu Hu, a co-author and planetary scientist at NASA’s Jet Propulsion Laboratory (JPL), explained to Space.com’s Robert Lea that the current detected atmosphere is a secondary one, generated by gases released from the planet’s lava oceans.