Astronomers steamed up over possible 'water world.'
By Amanda Jermyn

Planets beyond our solar system are no longer just the stuff of science fiction. Since 1992 3,607 exoplanets have been discovered in 2,701 planetary systems. The search continues, with no shortage of new discoveries in the works.

What might these strange new worlds be like, and could some of them harbor life? One of the key factors in establishing if a planet is habitable is whether it has an atmosphere, and if so, what kind. While atmospheres have previously been detected in some large gaseous exoplanets, now, for the first time, astronomers have detected an atmosphere around an Earth-like planet beyond our solar system.

The planet, known as Gliese 1132b, or GJ 1132b, was first discovered in 2015. It orbits a red dwarf star only 39 light years from Earth, relatively close in astronomical terms. As it orbits its star, the planet transits, or passes between Earth and the star every 1.6 days, blocking a small fraction of the star’s light as it does so. By observing the amount of light lost researchers were able to calculate the size of the planet, which turned out to be about 1.4 times that of Earth.

Using the 2.2-meter ESO/MPG telescope in Chile, the researchers, led by John Southworth of Keele University, observed the planet transiting its star nine times. Their findings were recently published in the Astrophysical Journal. They studied the star’s light in seven wavelengths (or colors) spanning the optical and infrared parts of the spectrum. As the planet transited the star it blocked some of the light in all seven wavelengths. However, in a certain infrared wavelength, the planet appeared larger, meaning that more light was blocked in that particular wavelength. What this means is that certain chemicals in the planet’s atmosphere absorbed that particular wavelength while letting others pass through. By studying which wavelength was absorbed, the researchers were able to infer which chemicals were present in the atmosphere. Their findings suggest that the planet’s atmosphere includes traces of water and methane.

An important feature of the discovery is that Gliese 1132b orbits a very low mass star, a particularly common type of star in the universe. According to John Southworth, “One of the big issues has been that very-low-mass stars typically have strong magnetic fields and thus throw out a lot of X-ray and ultraviolet light.” Such high-energy radiation tends to destroy the molecules in atmospheres, and it was thought that it could evaporate atmospheres completely. However, Southworth notes: “The fact that we have detected an atmosphere around GJ 1132b means this kind of planet is indeed capable of retaining an atmosphere for billions of years, even whilst being bombarded by high-energy photons from their host stars.”

With a surface temperature of about 620 degrees Fahrenheit the planet is too hot to be habitable, and Southworth suggests that it may be a “water world” with an atmosphere of hot steam. It could also have a rocky interior.

Even though this particular planet is too hot for life as we know it, the ability to detect a small planet with an atmosphere increases the chances of finding a habitable planet elsewhere. The fact that it was detected orbiting a low mass star is significant too. Such stars are ubiquitous in the universe and are known to harbor many small planets, and if some of these planets have atmospheres, the prerequisites for life might be quite common in the universe. Perhaps somewhere out there in the vastness of space we might find an alien world hospitable to life.

Join the Springfield Stars Club on Tuesday, May 23rd at 7:00pm at the Springfield Science Museum for a talk by Steve Herzberg, “One Pair of Stars is Like Another?” Since we can’t take a sample of a star and bring it back to the lab to analyze, how can we know whether or not one star is just like another? This talk will shed light on how we can study a universe beyond our physical reach. Steve Herzberg taught astronomy at Keen State College, and has served as vice president of both the Amherst Area Amateur Astronomy Association and the Amateur Telescope Makers of Boston. Refreshments will be served, and the public is welcome. The meeting is free of charge for members, with a suggested donation of $2 per non-member.