The possible discovery of an exomoon announced in a hurry between rumors and prudence

Artist's concept of a gas giant planet with a habitable exomoon (Image courtesy Andy McLatchie)
Artist’s concept of a gas giant planet with a habitable exomoon (Image courtesy Andy McLatchie)

An article sent to arXiv, the famous archive of preprint, describes the discovery of an exomoon candidate. A team of researchers led by David Kipping of Columbia University conducted a search for moons orbiting exoplanets observed by NASA’s Kepler Space Telescope finding the candidate called Kepler-1625b I. Generally, research results are published on a scientific journal at the end of the work but rumors spread convincing the researchers to send an article at least to arXiv.

We’re now used to the announcements of new exoplanets discovered in other solar systems, so much that this makes the news only if they show similarities to the Earth that suggest that they’re potentially habitable by life forms similar to the Earth’s ones. They still remain difficult to find, in fact the thousands that have been found are in the neighborhood from the astronomical point of view. However, it’s clear that it’s normal for stars to have planets, like the Sun, but then it should be normal that at least some of them have moons, where are they?

One of the methods to discover exoplanets is the transit method, detecting the tiny drop in a star’s brightness when a planet passes in front of it. It may also be useful to discover possible moons but they’re smaller than planets so the decline in their starlight caused by their passage is really very tiny.

During the 20 years of history of exoplanet research, it’s already happened that what looked like a planet was instead a brightness variation due to other causes. Such deception has already occurred for possible exomoons due to instrumental problems as Kepler is an extraordinary space telescope but has its limits.

At the end of 2013, what was perhaps the main case of potential discovery of an exomoon gave a negative result but in recent years there were a number of them. Some years ago the astronomer David Kipping founded the Hunt for Exomoons with Kepler (HEK) program, affiliated with the Harvard-Smithsonian Center for Astrophysics, which has precisely the purpose of searching for exomoons using the observations made by NASA’s Kepler space telescope.

Analyzing with his team the details of the Kepler-1625 star system, about 4,000 light years away from Earth, David Kipping discovered what seems to be an anomaly regarding one of its planets, Kepler-1625 b. This planet’s transits in front of its star leave lopsided traces and that suggests the presence of a second object close to the planet that alters its traces.

Data suggests that the Kepler-1625 b planet is similar to Jupiter, the Kepler-1625 b I moon candidate could be really big, even as Neptune. The first exomoon would by far be the largest moon ever discovered, much larger than any moon in the solar system. In February 2017, an article published in the journal “Monthly Notices of the Royal Astronomical Society” described a research on the possible formation of large moons following the collision of two planets but if Kepler-1625 b I was confirmed it would be really huge!

All this for the moment is the result of observations yet to be confirmed. For this reason, David Kipping’s team made a request to observe the Kepler-1625 system with the Hubble Space Telescope but that resulted in rumors on the Internet about that possible discovery and decision to reveal the data collected so far.

Normally, transparency in scientific research is positive but when it leads to publishing articles before a study is completed, problems can arise. The search for exomoons is a hot topic among astronomers but we’ll have to wait for further observations to see whether Kepler-1625 b I really exists or it’s another mistake.

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