May 10, 2023
NASA’s James Webb Space Telescope has made a significant discovery, providing insight into the atmosphere of a “mini-Neptune,” a type of planet that is common in the galaxy but is not well-understood. The telescope observed GJ 1214 b, a distant planet outside our solar system, and found that it is likely a highly reflective world with a steamy atmosphere. This is the closest look yet at this type of planet, which was largely impenetrable to previous observations. The planet is too hot to harbor liquid-water oceans, but water in vaporized form could still be a significant part of its atmosphere. According to Eliza Kempton, a researcher at the University of Maryland and lead author of a new paper on the planet published in Nature, “The planet is totally blanketed by some sort of haze or cloud layer. The atmosphere just remained totally hidden from us until this observation.” If the planet is water-rich, it could have been a “water world” with large amounts of watery and icy material at the time of its formation.
The research team took a novel approach to penetrate the thick barrier by tracking GJ 1214 b through nearly its entire orbit around the star, in addition to making the standard observation of capturing the host star’s light that has filtered through the planet’s atmosphere. The team used Webb’s Mid-Infrared Instrument (MIRI), which views wavelengths of light outside the part of the electromagnetic spectrum that human eyes can see. Using MIRI, the team created a kind of “heat map” of the planet as it orbited the star. The heat map revealed both its day and night sides, unveiling details of the atmosphere’s composition just before the planet’s orbit carried it behind the star and as it emerged on the other side.
According to Kempton, “The ability to get a full orbit was really critical to understand how the planet distributes heat from the day side to the night side. There’s a lot of contrast between day and night. The night side is colder than the day side.” The temperatures shifted from 535 to 326 degrees Fahrenheit (from 279 to 165 degrees Celsius), which is only possible in an atmosphere made up of heavier molecules, such as water or methane. This means that the atmosphere of GJ 1214 b is not composed mainly of lighter hydrogen molecules, which is a potentially important clue to the planet’s history and formation – and perhaps its watery start.
Kempton also noted that the planet is much cooler than expected because its unusually shiny atmosphere reflects a large fraction of the light from its parent star rather than absorbing it and growing hotter. This discovery could open the door to deeper knowledge of a planet type shrouded in uncertainty. Mini-Neptunes – or sub-Neptunes as they’re called in the paper – are the most common type of planet in the galaxy, but we know little about them because they don’t occur in our solar system. Measurements so far show they are broadly similar to a downsized version of our own Neptune.
Rob Zellem, an exoplanet researcher who works with co-author and fellow exoplanet researcher Tiffany Kataria at NASA’s Jet Propulsion Laboratory in Southern California, said, “For the last almost decade, the only thing we really knew about this planet was that the atmosphere was cloudy or hazy. This paper has really cool implications for additional detailed climate interpretations – to look at the detailed physics happening inside this planet’s atmosphere.”
The new work suggests that the planet might have formed farther from its star, a type known as a red dwarf, then spiraled gradually inward to its present, close orbit. The planet’s year – one orbit around the star – takes only 1.6 Earth days. This discovery of GJ 1214 b and the unique observations made possible by the James Webb Space Telescope (JWST) could pave the way for future discoveries about other mini-Neptunes. Understanding how these planets formed and evolved can give us clues about the formation of our own solar system and the possibility of other habitable worlds in our galaxy.
The JWST is a next-generation space telescope that was launched in December 2021, and it promises to revolutionize our understanding of the universe. Its advanced technology and sensitivity allow it to study exoplanets and other celestial objects in unprecedented detail, and its unique position in space enables it to observe wavelengths of light that are not visible from Earth.
As one of the most ambitious space missions ever undertaken, the JWST is expected to make many more groundbreaking discoveries in the coming years. Its observations of GJ 1214 b have already provided valuable insights into the composition and behavior of mini-Neptunes, and its continued study of these planets could unlock even more secrets of the universe.
The study of exoplanets and the search for extraterrestrial life is one of the most exciting and rapidly evolving fields in astronomy, and the JWST is poised to make major contributions to this area of research. As more exoplanets are discovered and studied, scientists will continue to refine their understanding of the formation and evolution of planetary systems, and perhaps one day we will find evidence of life beyond our own planet.
The recent discovery of the "mini-Neptune" GJ 1214 b by the James Webb Space Telescope marks an important milestone in the study of exoplanets. With its unique observations of the planet's atmosphere and composition, the JWST has provided valuable insights into the behavior and formation of mini-Neptunes, a type of planet that is common in the galaxy but largely unknown. This discovery is just the beginning, and the JWST is expected to make many more groundbreaking discoveries in the coming years that will advance our understanding of the universe and the possibility of life beyond Earth.