Astronomers Find What May Be First Exomoon-And It's an Absolute Unit

Michele Stevens
October 7, 2018

The first known moon beyond the Solar System has been discovered by astronomers.

To date more than 3,000 exoplanets - worlds orbiting stars other than the Sun - but no "exomoons".

In a new paper published in Science Advances, Alex Teachey and David Kipping of Columbia University present their case for the first "exomoon", and it's some pretty wild stuff. Despite its size, the mass of Kepler-1625b-i is estimated to be only 1.5 percent of the mass of its companion planet (Kepler-1625b).

If assumptions of scientists confirmed the moon will be the first one discovered outside the Solar system. The new alien moon is roughly the size of Neptune, which has a diameter four times larger than Earth's and is 17 times as massive.

Astronomers used data and observations from both the Kepler and Hubble space telescopes to study the distant star, planet and moon. The mass ratio between the exomoon and Kepler-1625b is similar to the ratio between the moon and Earth.

During a transit period, in which the planet passed in front of its star, Hubble detected a second decrease in the star's brightness after the planet. The celestial body and its planet were also discovered using this method.

"We noticed a certain refractive index, and deviations in the light curve that caught our attention", explained KPMG.

This has helped scientists gain access to 40 hours for a space telescope Hubble.


This is consistent with the planet and moon orbiting a common centre of gravity (barycentre) that would cause the planet to wobble from its predicted location. "It tells a lot about how unique or how common, in fact, that our solar system is-that the setup of having planets with moons may be something quite common", says Andrew Fazekas, an astronomy columnist with National Geographic. Unfortunately, the scheduled Hubble observations ended before the complete transit of the moon could be captured. "The first exomoon is obviously an extraordinary claim and it requires extraordinary evidence", said Teachey.

According to The Guardian, the so-called "aktolun" has a size that is approximately equal to Neptune. But only one of them, Kepler 1625b, demonstrated the kind of properties that they were searching for-a couple of unforeseen variations from the norm. However, the search for moons orbiting these exoplanets was not successful - until today. "But we knew our job was to keep a level head and essentially assume it was bogus, testing every conceivable way in which the data could be tricking us".

This artist's impression depicts the exomoon candidate Kepler-1625b-i, the planet it is orbiting and the star in the centre of the star system.

Although the planet and its possible moon are within the habitable zone of their star, both are considered to be gas giants and "unsuitable for life as we know it", Kipping said.

They followed up with the Hubble Space Telescope. They checked about 300 planets for any weirdness that might mean a moon.

Moons are abundant in our own solar system, with close to 200. The research team hopes to take another look at the star next May, if there is time available on the Hubble.

Exomoons are hard to find because they are very small, so the dip they cause in light is obviously weaker than a planet that is, by comparison, much larger.

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