Possible discovery of exomoon excites astronomers, but what is it?

Katie Ramirez
October 6, 2018

And in one instance, they found "deviations and wobbles" in the light curve representing a planet known as Kepler-1625b.

The same is believed to have happened in the Pluto-Charon system - the largest of the five known natural satellites of the dwarf planet. Other moons, such as Neptune's largest moon Triton, may have been captured from the Kuiper belt.

Even if it might be unusual that a Neptune-sized moon could exist out there, at the same time, nothing in physics says that it can't. Exomoons, or moons outside of our solar system, are hard to spot due to their expected smaller size compared to planets.

The celestial object is "big and weird by solar system standards", said Columbia University astronomy professor David Kipping.

Kepler-1625b and its possible moon are both located in the habitable zone of the parent star, Kepler-1625, a Sun-like star about eight percent more massive than the Sun.

The researchers requested time on the Hubble Space Telescope, and their request, which was public, generated a bit of excitement among those who follow new planet discoveries.

They were on the lookout for a second temporary dimming of starlight. When a star's brightness plunges, it means that a planet is passing it.

No such giant moons exist in Earth's solar system.

After it ended the telescope detected a second and much smaller decrease in the star's brightness three-and-a-half hours later. However, the observation period ended before aktolun has completed its turnover. That's why the astronomers need another look with Hubble, hopefully next northern spring. Still, we are urging caution here. The team used the telescope with the aim of finding evidence to either validate or refute the existence of the first exomoon.

But the astronomers are careful to emphasize that this is only a candidate moon.

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"We're not cracking open champagne bottles just yet", Teachey said, according to Nature. And this moon's size defies explanation. They observed the system throughout a predicted transit of the planet Kepler-1625b over the course of 40 hours.

A moon could cause that kind of an uncertain, wobbly path, they noted.

Dr Kipping said this was consistent with "a moon trailing the planet like a dog following its owner on a leash". But Kepler didn't find any other planets around this star.

The researchers note that in principle, this anomaly could be caused by the gravitational pull of a hypothetical second planet in the system, although Kepler found no evidence for additional planets around the star during its four-year mission.

In 2017, Kepler detected hints of an exomoon orbiting the planet Kepler 1625b. Kepler-1625b stood out. The new results are presented in the journal Science Advances.

The journal's deputy editor, Kip Hodges, praised the researchers for their cautious tone, given the hard and complicated process of identifying an exomoon.

Prof Kipping said. "We can expect to see really tiny moons".

"That's something more akin to what people are thinking of when they think of an "Avatar" Pandora", he added. Meanwhile, they encourage other researchers and astronomers to join because the course offers to understand how rare our solar system.

Whether confirmed or not, the subject offers insight into how rare - or how common - our own solar system might be. A faraway observer with a powerful telescope would see our earth-moon system orbiting the sun in a similar fashion. Of the eight planets in our solar system, only Mercury and Venus have none.

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