The first suspicion of exomoon is a big step in our quest for extraterrestrial life

Dan Durda

Astronomers scratch their heads to discover the first potential exomoon. It's the size of Neptune and its planet is about the same size as Jupiter but ten times bigger than its mass. It is also made of gas. In other words: it does not look like any moon we have ever seen before.

Astronomers David Kipping and Alex Teachey have published evidence of the moon in the newspaper Progress of science. Although some have called this the first discovery of an exomoon, it is not so obvious.

This however seems to be the most likely explanation of the data collected so far. And if it turns out to be an exomoon, it's a huge step for astronomy and the hunt for extraterrestrial life.

Finding an exomoon is an incredibly difficult task. We know more than 3,500 exoplanets, but no exonator has been found. If these exoplanets resemble our own solar system, the moons will also be present. It's just that they are hard to find.

Exoplanets are usually found by observing the light of the host star, the sun of the exoplanet, sifted as the planets pass between them and us. This is known as the transit method.

Yet finding an exomoon is another thing. By studying very closely the luminosity, astronomers can look for clues of moons in orbit around exoplanets. For example, if the planet takes longer to pass the star or if the brightness drops more than usual, this could potentially be evidence of a moon orbiting the planet.

That's what Kipping and Teachey discovered by monitoring Kepler 1625b, a gas giant located 8,000 light-years from Earth.

About three and a half hours after the end of the planet's transit, the Hubble telescope recorded another, this time smaller, which attenuated the brightness of the star.

This is consistent with "a moon tracking down the planet like a dog following his owner on a leash," Kipping said. "Unfortunately, Hubble's scheduled sightings ended before the full Moon transit could be measured."

Hubble also discovered that the planet had begun transit 1.25 hours earlier than planned. "An extraterrestrial civilization observing the Earth and the transit of the Moon by the Sun would note similar anomalies in the synchronization of the Earth's transit," Kipping said.

If and when astronomers are able to confirm that it is an exomoon, such discoveries will provide an exciting new venue for the hunt for life beyond the Earth. The moons of our own solar system are among the most exciting places for the potential of life; The Saturn Enceladus has everything you need to live, Titan has methane lakes and Jupiter's Io has ice on the surface.

While the super-Jovian planets – those larger than our largest planet, Jupiter – may not be conducive to life, if each has many moons, it increases our chances of finding a tiny world in good conditions. But first you have to find them.

"We have done our best to exclude other possibilities, such as spacecraft anomalies, other planets in the system or a stellar activity, but we can not find any other unique hypothesis. that can explain all the data we have, "Kipping said. .

"It's exciting, because it shows that we are approaching what would be an incredible" first "in astronomy – the first extrasolar moon detected," says Hugh Osborn, astronomer chasing the exoplanet from the University of Marseille .

Osborn is afraid to call it a discovery for the moment. "For me, whatever the discovery, but especially the first of its kind, the evidence must be convincing," he said. "He has to convincingly eliminate all other possibilities, I do not think we are there with Kepler-1625."

The Kepler Space Telescope first gave hints to an exomoon. That's why Kipping and Teachey wanted to re-examine it with the Hubble Space Telescope. "We found small deviations and oscillations in the light curve that caught our attention," Kipping said.

"But since their first article, the data has improved and the initial signal of an exomoon has been completely erased," says Osborn. "The exomoon hypothesis is almost exclusively based on the new low in Hubble, but it is a very small signal, and there are many other reasons why a star can shrink to a very small size: changes in the telescope, variability in the star itself or a moon. "

Osborn says that there are still other potential explanations; the shift in transit time could point to a moon, but could also point to another planet in the system, for example.

For the time being, astronomers around the world will continue to search in the hope of finding a livable exomoon, and more data on Kepler-1625b will allow us to determine whether the dimming means that there is also a moon.

"We hope that someday we could really find something like a true analogue of the Earth in a moon," Teachey said during a conference call Monday. "It's something that looks more like what people think when they think of a Pandor" Avatar ".

Another chance is that there may be no moons. This is not because our solar system has many moons that they are also common elsewhere.

Our solar system could be an outlier. In some ways, it is already the case. Earth-like planets have been surprisingly rare elsewhere, while the "warm Neptunes" – planets the size of Neptune but close to their star – are very common and we have none.

To find out, we'd better keep searching.

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