Astronomers Spot What Could Be a Neptune-Sized Moon in a Distant Solar System

By scouring archival information from the now-retired Kepler area telescope, astronomers have discovered a promising new exomoon candidate, in what’s an exceptionally uncommon discovery.

To date, astronomers have confirmed the existence of 4,884 planets past our photo voltaic system, with one other 8,414 ready to be confirmed. Despite this, astronomers have but to verify the presence of an exomoon in orbit round any of those exoplanets. That’s stunning when you think about that our photo voltaic system alone hosts over 175 moons.

Yes, potential exomoons have been noticed through the years, together with the very promising Kepler-1625 b-i candidate, which astronomers detected in 2018, together with a batch of supposed exomoons described in 2020 that unbiased analyses have subsequently dominated out (see here and here). But these sightings proceed to be uncommon. Encouragingly, we are able to now add a brand new exomoon to this achingly small candidates checklist, as scientists introduced at this time in a brand new Nature Astronomy paper.

Frustratingly, it’s yet one more candidate exomoon “that will require follow-up” observations, as each the “nature and supporting evidence demand appropriate scepticism at this time,” the scientists write of their research. The paper estimates that there’s a 1% likelihood that the noticed exomoon sign is a false constructive, which, so far as scientists are involved, is an insupportable quantity of uncertainty.

I requested Columbia University’s David Kipping, the primary writer of the brand new research, why astronomers have struggled to verify the presence of pure satellites round distant exoplanets. “Exomoons,” he replied in an e-mail, “are generally expected to be small and have their signals mixed up with their larger planet host, making them challenging to disentangle.”

The transit methodology of detection, it’s honest to say, is partly chargeable for this. Astronomers can spot exoplanets by measuring the periodic dimming of distant stars, a results of an object quickly passing in entrance. Discerning a sign inside this sign—particularly for a tiny moon—is proving to be a problem. At the identical time, the transit methodology has led to a bias by which astronomers favor exoplanets with quick orbital durations (these exoplanets cross in entrance of their host stars extra steadily, permitting for repeated observations over quick timescales). Trouble is, planets in shut proximity to their host stars will not be the very best candidates for internet hosting exomoons.

Our photo voltaic system is a chief instance of this; the fuel and ice giants Jupiter, Saturn, Uranus, and Neptune are situated removed from the Sun, however they’re surrounded by moons. With this in thoughts, Kipping and his colleagues determined to review cool exoplanets with lengthy orbital durations in hopes of recognizing exomoons.

To achieve this, they checked out information gathered by the late, nice Kepler area telescope. A “small sample of long-period planetary candidates was discovered by Kepler—worlds with orbits greater than that of the Earth around the Sun,” the scientists write of their research. “The Jupiter-sized planets amongst these are of particular interest, as satellite formation is thought to be a natural outcome of how such planets form.”

The crew honed in on 70 fuel big exoplanets, all of which characteristic orbital durations longer than one yr. Of these, just one exhibited a sign in step with an exomoon, however it was a sign nonetheless. The obvious exomoon, situated 5,700 mild years from Earth, “causes a transit just like the exoplanet does,” however “that second transit is much shallower and overlaps with the primary dip,” Kipping advised Gizmodo.

The exomoon candidate was discovered with the Jupiter-sized fuel big Kepler-1708 b, which orbits a Sun-like star at a distance of 1.6 AU (by which 1 AU is the typical distance from Earth to the Sun). The candidate has been designated Kepler-1708 b-i, by which the “i” represents the alleged exomoon.

Fascinatingly, at 2.6 instances the scale of Earth, this moon is moderately massive. We clearly don’t have something fairly like this in our photo voltaic system, the most important moon being Jupiter’s Ganymede, which is lower than half the scale of Earth. This statement can also be attention-grabbing as a result of Kepler-1625 b-i, the exomoon candidate noticed in 2018, can also be very large. Thus, “Kepler-1708 b-i joins Kepler-1625 b-i as another example of an unexpectedly large exomoon candidate—echoing the surprise that hot-Jupiter discoveries elicited in the mid-1990s,” the scientists write.

The problem now might be to determine how these massive moons fashioned and the way they got here to settle in orbits round long-period fuel giants. Assuming, after all, these are precise exomoons and never a colossal wild-goose chase. Explanations posited within the new paper embrace planet-on-planet collisions, the formation of moons inside gaseous circumplanetary disks, or direct gravitational seize.

The reply, no matter what it’s, will undoubtedly inform us one thing new about planetary methods and the way they type. But very first thing’s first: Astronomers nonetheless want to verify these objects as being bona fide exomoons. Hopefully, future observations by the not too long ago launched Webb telescope and different observatories will present this much-needed reply.

More: Our galaxy may be teeming with liveable exomoons.