Discovered First Compelling Evidence For A Moon Outside Our Solar System

Discovered First Compelling Evidence For A Moon Outside Our Solar System

In flickering light of a distant sun, scientists may have discovered the first moon outside our solar system.

At first, the researchers saw the dip in light caused by the planet passing across the face of the star, but not long afterward, they saw a second, smaller dip, likely caused by the moon transiting across the star.

"We've tried our best to rule out other possibilities such as spacecraft anomalies, other planets in the system or stellar activity, but we're unable to find any other single hypothesis which can explain all of the data we have", said Dr Kipping, from Columbia University in NY.

Exomoons are hard to find because they are smaller than their companion planet and so their transit signal is weak; they also shift position with each transit because the moon is orbiting the planet.

Kipping has spent a decade working on the "exomoon hunt".

Even if it is confirmed as the first ever exomoon discovery, there are still questions to be answered, such as how a gas giant came to have a gas giant moon? Their results were published Wednesday in the journal Science Advances. "Including rocky exomoons in our search for life in space will greatly expand the places we can look".

However, before getting too excited about the prospect of finding Ewoks, it should be noted that the exomoon (formally named as Kepler-1625b-i) has a radius of around four times that of the Earth and a mass of around 16 times that of our planet, so is in fact similar in size and mass to the planet Neptune. In our sky, it would appear two times bigger than Earth's moon, the researchers said.

The researchers found one instance, in Kepler 1625b, that had intriguing anomalies. The exoplanet is a gas giant, several times more massive than Jupiter. The researchers' investigations showed that the HST-recorded transit of Kepler-1625b occurred almost 80 minutes earlier than expected, a pattern suggesting the presence of transit timing variations, or TTVs, which are among the first proposed methods to confirm the presence of exomoons.

An artist's impression shows the Jupiter-sized exoplanet Kepler-1625b transiting its parent star with the Neptune-sized candidate exomoon in tow.

Since the 2009 launch of NASA's Kepler telescope, scientists have identified thousands of planets outside our solar system, which are called exoplanets.

Sadly, Hubble's time is in high demand, which means the time Teachey and Kipping had with the telescope was limited to 40 hours.

Transiting planets are worlds that can be detected by a drop in light as they pass in front of their home stars. The two signals together looked like a moon "trailing the planet like a dog following its owner on a leash," Kipping said in a statement. But the Hubble observations ended before the second dip was complete. This is consistent with the planet and moon orbiting a common center of gravity (barycenter) that would cause the planet to wobble from its predicted location. Our moon does the same to Earth. A second slight drop in the "light curve" indicates the possible presence of a large moon. These enabled astronomers to derive the masses of the planets directly from the transit light curve.

"It was definitely a shocking moment to see that light curve - my heart started beating a little faster and I just kept looking at that signature". "But we knew our job was to keep a level head testing every conceivable way in which the data could be tricking us until we were left with no other explanation".

"That's been a key driver for us for a while, just trying to understand the cosmic habitats out there that we might look for, for life", says Kipping.

"The moon model emerges as the best explanation for the data, and it has the added benefit of being a single explanation for both the timing effects and the dimming of the star that we see in the data", said Alex Teachey. Or perhaps, like Earth's moon, it is a product of its planet, formed in some catastrophic collision.