Webb finds atmosphere on a rocky exoplanet for the first time

Gas rising from a lava-covered surface on 55 Cancri e may feed an atmosphere rich in carbon dioxide or carbon monoxide.

These days, detecting a planet’s atmosphere tens or even hundreds of light-years from Earth may not seem like a big deal. Scientists have found evidence of atmospheres surrounding dozens of exoplanets over the past two decades. The problem is that all of these planets have thick, hydrogen-dominated atmospheres that are relatively easy to study. The thin blankets of gas surrounding some small, rocky exoplanets have remained elusive.

Researchers think they may have finally caught a glimpse of the rich, volatile atmosphere surrounding a rocky planet. Light emitted from hot areas is highly radiant Exoplanet 55 Cancri e shows compelling evidence of an atmosphere, possibly rich in carbon dioxide or carbon monoxide, that would flow from a vast ocean of lava covering the planet’s surface.

The result is the best evidence yet of the existence of an atmosphere for a rocky planet outside our solar system.

This artist’s concept shows what exoplanet 55 Cancri e could look like. Also called Janssen, 55 Cancri e is a so-called super-Earth, a rocky planet much larger than Earth but smaller than Neptune, which orbits its star at a distance of just 1.4 million miles (0.015 AU), completing a complete orbit. In less than 18 hours. (Mercury is 25 times farther from the Sun than its star, 55 Cancri e). This system, which also includes four large gas giant planets, is located about 41 light-years from Earth, in the constellation Cancer. Image credit: NASA, ESA, CSA, Ralph Crawford (STScI)

The Webb Space Telescope hints at a possible atmosphere surrounding a rocky exoplanet

Researchers use NASA‘s James Webb Space Telescope They may have detected atmospheric gases surrounding 55 Cancri e, a hot, rocky exoplanet located 41 light-years from Earth. This is the best evidence yet that any rocky planet outside our solar system has any atmosphere.

Renew is from NASA’s Jet Propulsion Laboratory (Jet Propulsion Laboratory) in Pasadena, California, is the lead author of a paper published May 8 nature. “Webb pushes the boundaries of characterizing exoplanets to rocky planets,” Hu said. “It really enables a new kind of science.”

Super-Hot Earth 55 Cancri E

55 Cancri e, also known as Janssen, is one of five known planets orbiting the Sun-like star 55 Cancri, in the constellation Cancer. With a diameter nearly twice that of Earth and a slightly larger density, the planet is classified as a super-Earth: larger than Earth and smaller than Earth. NeptuneThey are likely similar in composition to the rocky planets in our solar system.

However, describing the 55 Cancri e as “rocky” might leave the wrong impression. The planet orbits close to its star (about 1.4 million miles, or 20/25 the distance between Mercury and the Sun), and its surface is likely molten — a bubbling ocean of magma. With such a tight orbit, the planet is also likely tidally locked, with its day side facing the star at all times and its night side in perpetual darkness.

Despite numerous observations since its transit was discovered in 2011, the question of whether or not 55 Cancri e has an atmosphere — or even could One of them has remained unanswered due to its high temperature and the constant attack of stellar radiation and winds from its star.

“I’ve been working on this planet for more than a decade,” said Diana Dragomir, an exoplanet researcher at the University of New Mexico and co-author of the study. “It was really frustrating that none of the feedback we received made a solid solution to these mysteries. I’m glad we finally have some answers!”

Unlike the atmospheres of gas giant planets, which are relatively easy to detect ( It was revealed for the first time By NASA Hubble Space Telescope For more than two decades), the thinner, denser atmospheres surrounding rocky planets have remained elusive.

Previous studies on 55 Cancri e using data from NASA’s now-retired Spitzer Space Telescope have suggested the presence of a large atmosphere rich in volatiles (molecules found in gas form on Earth) such as oxygen, nitrogen and carbon dioxide. But researchers were unable to rule out another possibility: that the planet is empty, except for a fragile blanket of evaporated rock, rich in elements such as silicon, iron, aluminum and calcium. “The planet is so hot that some of the molten rock must have evaporated,” Ho explained.

This light curve shows the change in brightness of the 55 Cancri system, as the rocky planet 55 Cancri e, the closest of the five known planets in the system, moves behind the star. This phenomenon is known as a secondary eclipse.
When the planet is near the star, mid-infrared light from both the star and the planet’s day side reaches the telescope, making the system appear brighter. When the planet is behind the star, the light from the planet is blocked and only the star’s light reaches the telescope, resulting in a decrease in apparent brightness.
Astronomers can subtract a star’s brightness from the combined brightness of the star and planet to calculate how much infrared light is coming from the planet’s dayside. This is then used to calculate the daytime temperature and deduce whether or not the planet has an atmosphere.
Image credit: NASA, ESA, CSA, Joseph Olmsted (STScI), Aaron Belo-Aroff (NASA-JPL)

Measure subtle differences in infrared colors

To distinguish between the two possibilities, the team used Webb’s NIRCam (near-infrared camera) and MIRI (mid-infrared instrument) to measure 4- to 12-micron infrared light coming from the planet.

Although Webb cannot take a direct image of 55 Cancri e, it can measure subtle changes in the light from the system as the planet orbits the star.

By subtracting the brightness during a secondary eclipse (see image above), when the planet is behind the star (starlight only), from the brightness when the planet is right next to the star (light from the star and planet combined), the team was able to calculate the amount of different wavelengths of rays Infrared light coming from the day side of the planet.

This method, known as secondary eclipse spectroscopy, is similar to that used by other research teams to search for atmospheres on other rocky exoplanets, such as TRAPPIST-1 b.

The thermal emission spectrum captured by Webb NIRCam (Near Infrared Camera) in November 2022, and MIRI (Mid-Infrared Instrument) in March 2023, shows the brightness (y-axis) of different wavelengths of infrared light (x-axis ) emitted. By the giant exoplanet 55 Cancri e. The spectrum shows that the planet may be surrounded by an atmosphere rich in carbon dioxide or carbon monoxide and other volatiles, not just vaporized rock.
The graph compares data collected by NIRCam (orange dots) and MIRI (purple dots) with two different models. Model A, in red, shows what the emission spectrum of 55 Cancri e should look like if it had an atmosphere made of evaporating rock. Model B, in blue, shows what the emission spectrum should look like if the planet had a volatile-rich atmosphere emitted from a magma ocean that has a volatile content similar to Earth’s mantle. MIRI and NIRCam data are consistent with the volatile-rich model.
The amount of mid-infrared light emitted by the planet (MIRI) shows that the daytime temperature is much lower than it would be if it did not have an atmosphere to distribute heat from the day side to the night side. The dip in the spectrum between 4 and 5 microns (NIRCam data) can be explained by the absorption of those wavelengths by carbon monoxide or carbon dioxide molecules in the atmosphere.
Image credits: NASA, ESA, CSA, Joseph Olmstead (STScI), Renew Ho (NASA-JPL), Aaron Bello-Aroff (NASA-JPL), Michael Chang (University of Chicago), Mantas Zilinskas (SRON)

Colder than expected

The first indication that 55 Cancri e could have a significant atmosphere came from temperature measurements based on its thermal emission (see image above), or thermal energy emitted in the form of infrared light. If the planet were covered in dark, molten rock with a thin veil of vaporized rock or no atmosphere at all, the dayside should be about 4,000 degrees F (~2200 degrees Celsius).

“Instead, the MIRI data showed a relatively low temperature of about 2,800 degrees Fahrenheit [~1540 degrees Celsius]He said. “This is a very strong indication that energy is distributed from the day side to the night side, most likely through a volatile, rich atmosphere.” While lava flows can carry some heat to the nightside, they cannot move it efficiently enough to account for the cooling effect.

When the team looked at the NIRCam data, they saw patterns consistent with a rich, volatile atmosphere.

“We see evidence of a dip in the spectrum between 4 and 5 microns, and less of this light reaches the telescope,” explained co-author Aaron Bello-Aroff, also of NASA JPL. “This indicates the presence of an atmosphere containing carbon monoxide or carbon dioxide, which absorbs these wavelengths of light.” A planet that has no atmosphere or an atmosphere consisting only of vaporized rock would not have this specific spectral feature.

“We have spent the last 10 years modeling different scenarios, trying to imagine what this world might look like,” said co-author Yamila Miguel from Leiden Observatory and the Netherlands Institute for Space Research (SRON). “Finally, getting some validation for our invaluable work!”

Bubbling magma ocean

The team believes that the gases covering 55 Cancri e will emerge from within, rather than being present since the planet formed. “The core atmosphere will have disappeared long ago due to the high temperature and intense radiation from the star,” Bello-Arov said. “This will be a secondary atmosphere that is constantly being replenished by the magma ocean. Magma is not just liquid crystals and rock; there is a lot of gas dissolved in it as well.

While 55 Cancri e is too hot to be habitable, researchers believe it could provide a unique window to study interactions between the atmosphere, surfaces and interiors of rocky planets, and perhaps offer insight into early Earth conditions. VenusAnd MarsWhich is believed to have been covered by magma oceans in the distant past. “Ultimately, we want to understand what conditions make it possible for a rocky planet to maintain a gas-rich atmosphere: an essential ingredient for a habitable planet,” Hu said.

This research was conducted as part of the General Observers (GO) Webb Program for 1952. Additional secondary eclipse observations of 55 Cancri e are currently being analyzed.

Reference: “A secondary atmosphere on the rocky exoplanet 55 Cancri e” by Renyu Hu, Aaron Belo-Aroff, Michael Zhang, Kimberly Paragas, Mantas Zilinskas, Christian van Botchem, Michael Pace, Jaishel Patel, Yuichi Ito, Mario Damiano, Markus Shusher, Apoorva V. Oza, Heather A. Knutson, Yamila Miguel, Diana Dragomir, Alexis Brandecker and Bryce Olivier Demauri, May 8, 2024, nature.
doi: 10.1038/s41586-024-07432-x

The James Webb Space Telescope is the world’s leading space science observatory. Webb solves the mysteries of our solar system, looks beyond the distant worlds around other stars, and explores the mysterious structures and origins of our universe and our place in it. WEB is an international program led by NASA with its partners the European Space Agency (ESA).European Space Agency) and the Canadian Space Agency.