In the new film Avatar, humans visit an alien moon called Pandora; now, scientist Lisa Kaltenegger is showing that the James Webb Space Telescope (JWST) can study the atmosphere of alien moons and planets, as well as detect key gases like carbon dioxide, oxygen, and water vapor.
Lisa Kaltenegger is a researcher at the Harvard-Smithsonian Center for Astrophysics (CfA).
“If Pandora existed, we potentially could detect it and study its atmosphere in the next decade,” she said. Up until now, astronomers could detect Jupiter-sized objects – but these are gas giants which are easier to detect but unsuitable to maintain atmosphere. “All of the gas giant planets in our solar system have rocky and icy moons,” said Kaltenegger. “That raises the possibility that alien Jupiters will also have moons. Some of those may be Earth-sized and able to hold onto an atmosphere.” The study offers methods in which a larger variety of stellar objects could be found.
In her study, she describes the Kepler mission, in which it looks for planets that cross in front of their host stars. The result is a mini-eclipse, which dims the star by a small but detectable amount. Since such a transit lasts only hours and requires exact alignment of star and planet, rigorous examination is necessitated. Here Kepler comes in handy.
Once astronomers will find an alien Jupiter, they would probably look for orbiting moons, or exomoons. Implementing this technique will require observing the moon’s ‘tugs’ on the planet: it either speeds or slows its transit; the resulting transit duration variations would indicate the moon’s existence.
If such an exomoon will be found, the next obvious question would be: Does it have an atmosphere? The method in which an atmosphere will be detected relies on the gases’ absorption of a fraction of the star’s light; during the transit, it leaves a tiny, telltale fingerprint to the atmosphere’s composition.
When asked what world has the best conditions to develop atmospheres in alien moons,
Kaltenegger calculates and determines that Alpha Centauri A, the system featured in Avatar, is an excellent target. She explains, “Alpha Centauri A is a bright, nearby star very similar to our Sun, so it gives us a strong signal. You would only need a handful of transits to find water, oxygen, carbon dioxide, and methane on an Earth-like moon such as Pandora.”
While Alpha Centauri A offers tantalizing possibilities, small, dim, red dwarf stars are better targets in the hunt for habitable planets or moons. The habitable zone for a red dwarf is closer to the star, which increases the probability of a transit. However, a possible problem is tidal locking – the star’s gravity might slow until one side always faces the star.
An exomoon in the habitable zone wouldn’t face this problem, since it will be tidally locked to its planet, not to the star; thus, it would have regular day-night cycles just like Earth. Its atmosphere would moderate temperatures, and plant life would have a source of energy moon-wide. “Alien moons orbiting gas giant planets may be more likely to be habitable than tidally locked Earth-sized planets or super-Earths,” said Kaltenegger
When asked about future research in that field, Kaltenegger says: “We should certainly keep exomoons in mind as we work toward the ultimate goal of finding alien life. If the Avatar movie is right in its vision, we could characterize such moons with JWST in the near future.”
TFOT has also covered a New Method for Discovering Extrasolar Planets, developed at the Instituto de Astrofisica de Canarias in Tenerife, and the Biography of Earth’s Atmophere. Other related TFOT stories include a video about NASA’S James Webb Space Telescope, and the discovery of Carbon Dioxide in Space, made by the Hubble Space Telescope.
For more information about Kaltenegger’s research, see the Harvard-Smithsonian website.