Possible atmosphere on rocky exoplanet found for 1st time

View larger. | Is there an atmosphere on rocky exoplanet 55 Cancri e? This is an artist’s concept of 55 Cancri e, 41 light-years from Earth. Analysis by the Webb Space Telescope shows that it likely has a substantial atmosphere of carbon dioxide or carbon monoxide. Image via NASA/ ESA/ CSA/ Ralf Crawford (STScI).
  • An international team of astronomers studied rocky exoplanet 55 Cancri e for evidence of an atmosphere. Scientists have long debated whether an atmosphere of any kind existed.
  • They found that the planet likely does have a substantial atmosphere of either carbon dioxide or carbon monoxide.
  • 55 Cancri e is a super-Earth about twice the size of Earth. It is only 41 light-years away, and extremely hot. In fact, its entire surface is probably covered by molten lava.

Potential atmosphere on rocky exoplanet

For the first time, astronomers say that they have detected a possible atmosphere on a rocky exoplanet. The researchers said on May 8, 2024, that they used the James Webb Space Telescope to make the discovery. Atmospheres have been found and analyzed on a large and growing number of gas giant planets, but those are much easier to detect. This smaller rocky world, 55 Cancri e, is nearby in galactic terms, only 41 light-years from Earth. It is a super-Earth, almost twice the size of Earth. But unlike our planet, it is extremely hot and likely has a molten surface. So while it may be rocky with an atmosphere, it is not like the Earth.

The international research team published its peer-reviewed findings in the journal Nature on May 8, 2024. Read here.

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This potential discovery is a new milestone for Webb. Finding rocky exoplanets with atmospheres is a major goal for astronomers. Lead author Renyu Hu at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, said:

Webb is pushing the frontiers of exoplanet characterization to rocky planets. It is truly enabling a new type of science.

Atmosphere or no atmosphere?

Astronomers discovered 55 Cancri e in 2011. Since then, scientists have continued to debate if the planet had an atmosphere or not. And if it did, how dense was it? It was possible that 55 Cancri e didn’t have any atmosphere at all. That’s because it orbits only 1.4 million miles (2.3 million km) from its sun-like star. That’s only 1/25 the distance that Mercury is from our sun. Radiation from the star would likely strip the atmosphere away. Also, the planet is probably tidally locked to its star, so that the same side always faces the star. And, it’s extremely hot, about 2,800 degrees Fahrenheit, or 1,540 degrees Celsius. Therefore, its entire surface is likely molten lava.

2 possibilities

If it did have an atmosphere, then scientists said there were two likely possibilities. One was a substantial atmosphere of oxygen, nitrogen and carbon dioxide. The other was a more tenuous atmosphere of vaporized rock, rich in silicon, iron, aluminum and calcium. Now, Webb might finally help answer these questions. As co-author Diana Dragomir, an exoplanet researcher at the University of New Mexico, noted:

I’ve worked on this planet for more than a decade. It’s been really frustrating that none of the observations we’ve been getting have robustly solved these mysteries. I am thrilled that we’re finally getting some answers!

Co-author Yamila Miguel at the Leiden Observatory and the Netherlands Institute for Space Research (SRON) added:

We’ve spent the last 10 years modeling different scenarios, trying to imagine what this world might look like. Finally getting some confirmation of our work is priceless!

Graph: varied height horizontal lines beneath different configurations of star and planet.
View larger. | Secondary eclipse light curve of 55 Cancri e from the MIRI instrument on Webb. The decrease in brightness occurred when the planet moved behind its star, as seen from Earth. Image via NASA/ ESA/ CSA/ Joseph Olmsted (STScI)/ Aaron Bello-Arufe (JPL).

A substantial atmosphere (probably) on rocky exoplanet 55 Cancri e

Webb observed 55 Cancri e with its Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI), using the secondary eclipse spectroscopy method. It looked for subtle changes in the mid-infrared and near-infrared light coming from the planet. The researchers subtracted the brightness of the star itself during the secondary eclipse – when the planet was behind the star – from when the planet was beside the star (light from both the star and planet), as seen from Earth.

Cooler than expected, but still hot

Interestingly, Webb found that the planet is a bit cooler than had been expected. If it had no atmosphere, or only a thin one from vaporized rock, then the temperature on the dayside of the planet would be about 4,000 degrees Fahrenheit (2,200 degrees Celsius). However, with its MIRI instrument, Webb measured a temperature of 2,800 degrees F (1,540 degrees C). That indicated a thicker atmosphere, probably composed of carbon dioxide or carbon monoxide and other volatiles. As Hu said:

Instead, the MIRI data showed a relatively low temperature of about 2,800 degrees Fahrenheit [~1540 degrees Celsius]. This is a very strong indication that energy is being distributed from the dayside to the nightside, most likely by a volatile-rich atmosphere.

The NIRCam instrument provided similar results. Co-author Aaron Bello-Arufe at NASA JPL said:

We see evidence of a dip in the spectrum between 4 and 5 microns; less of this light is reaching the telescope. This suggests the presence of an atmosphere containing carbon monoxide or carbon dioxide, which absorb these wavelengths of light.

Graph with jagged blue and red lines with labels for different elements along them.
View larger. | Emission spectrum of 55 Cancri e, from the MIRI and NIRCam instruments on Webb. The results indicate that the planet likely has a substantial atmosphere of carbon dioxide or carbon monoxide and other volatiles, not just vaporized rock. Image via NASA/ ESA/ CSA/ Joseph Olmsted (STScI)/ Renyu Hu (JPL)/ Aaron Bello-Arufe (JPL)/ Michael Zhang (University of Chicago)/ Mantas Zilinskas (SRON Netherlands Institute for Space Research).

A magma ocean world

Unfortunately for the prospects of life, 55 Cancri e is quite inhospitable. It is so hot that scientists think its surface is a vast magma ocean instead of being solid. Consequently, the atmosphere is likely coming from the interior of the planet, instead of being the original primordial atmosphere from when it first formed. The magma ocean would help to replenish the atmosphere. Bello-Arufe said:

The primary atmosphere would be long gone because of the high temperature and intense radiation from the star. This would be a secondary atmosphere that is continuously replenished by the magma ocean. Magma is not just crystals and liquid rock; there’s a lot of dissolved gas in it, too.

However, the finding shows that rocky planets outside our solar system can indeed maintain atmospheres. If it can happen on 55 Cancri e, then it should also occur on other rocky worlds, including ones more potentially habitable, as Hu noted:

Ultimately, we want to understand what conditions make it possible for a rocky planet to sustain a gas-rich atmosphere: a key ingredient for a habitable planet.

Bottom line: NASA’s Webb telescope has tentatively detected an atmosphere on rocky exoplanet 55 Cancri e, a hot super-Earth world only 41 light-years away.

Source: A secondary atmosphere on the rocky Exoplanet 55 Cancri e


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