A new technique pioneered by a team of scientists from the University of Texas, Arlington, may hold the key to detecting moons orbiting distant exoplanets, a feat which is currently beyond the grasp of modern astronomy. Such a technique would afford scientists a greater opportunity of discovering a planetary body capable of sustaining life.
Current methods of exoplanet detection and observation are unable to pick up the presence of a moon. This is because because they are simply not sensitive enough, especially considering that they already have to compete with the interference of the planet's parent star. For example, one method of detection used by modern telescopes detects exoplanets by looking for a dip in light as an exoplanet passes across the face of a star. However, even though it is theoretically possible to do so, this technique has not yet been able to definitively confirm the presence of a moon orbiting a remote exoplanet.
The new method will attempt to find traces of a tell-tale radio signal, known as an Io-controlled decametric emission that would suggest the presence of an exomoon. The signal was first detected in our own solar system, originating from an interaction between Jupiter and her innermost Galilean moon, Io. Further analysis revealed that the radio signal resulted from friction created by Io's charged ionosphere interacting with Jupiter's magnetosphere, a charged layer of plasma that protects the planet from radiation.
You could be forgiven for thinking that using Io as a model for detecting the radio waves severely limits the type of moon to be detected, as the Galilean moon owes the strength of it's ionosphere (the key to generating the radio waves), to it's extreme volcanic nature. However, Ph.D graduate student Joaquin Noyola, lead author of the team's paper, is keen to state that the technique extends beyond volcanic moons.
"Larger moons – such as Saturn’s largest moon, Titan - can sustain a thick atmosphere, and that could also mean they have an ionosphere," he says. "So volcanic activity isn’t a requirement." Furthermore the paper suggests that the detection of a phenomenon known as Alfvén Waves, could be used in the same way to detect an exomoon.
The team has highlighted two exoplanets that they are optimistic could be harboring exomoons. Gliese 876b sits 15 light years away, with the closer Epsilon Eridani b only 10.5 light years distant from Earth. It is hoped that astrophysicists could use more sensitive telescopes, applying the team's algorithm, to detect large moons in nearby planetary systems.
Arguably, the most exciting aspect of being able to discover exomoons is the increased potential of discovering a celestial body capable of sustaining life. In many cases, a planet's moon is a better candidate in the search for life than the planet itself, as is the case in our own solar system with Europa and Enceladus.
"Most of the detected exoplanets are gas giants, many of which are in the habitable zone," Ph.D graduate student Suman Satyal, a member of the research group and co-author of the paper, explains. "These gas giants cannot support life, but it is believed that the exomoons orbiting these planets could still be habitable."
The paper detailing the team's research has been published in The Astrophysical Journal.
Source: University of Texas, Arlington