Moon Hunting: New Technique Could Detect Exomoons Through Their Planets’ Light

A new method could help astronomers detect exomoons.

Scientists suggested that polarization of the planet's light could help detect exomoons, which are the satellites around exoplanets. Polarized light waves are light waves in which the vibrations occur in a single plane.

"When you use polarized sunglasses, you block one direction of the light waves and not the other," Mark Marley, a research scientist at NASA's Ames Research Center in California and co-author of the study, told Space.com.

"In our case, as the moon passes over the planet, it sort of acts like polarized sunglasses and blocks part of the polarization from the planet."

According to the study, which was published in The Astrophysical Journal, newborn planets typically heat up as a result of the gas and dust. The heat causes the young planet to glow, which may last for millions of years.

Marley and co-researcher Sujan Sengupta, associate professor at the Indian Institute of Astrophysics, used this planetary glow to find their exomoons.

The researchers said that if the planet is cloudy, the clouds can polarize the light from the planet, and this could be the case for most gassy planets. Astronomers who will look at a typical gas exoplanet through a polarized filter will find nothing. But when a moon covers up a part of the planet, it will block some of the light and the polarization changes.

According to Marley, scientists could use the method back on Earth and detect the change in polarization.

"In the right circumstances, it could be easier to detect this change in polarization than the small change in brightness as the moon crosses the planet," Marley said.

Other moon-hunting techniques have also been developed. One technique is the transit method, which was designed by David Kipping of Columbia University in New York. The technique suggests that exomoons could be detected just before or after their planet transits their star, as the moons - just like their planets - are expected to block the star's light as they pass.