SciAm: Are Astronomers on the Verge of Finding an Exomoon?

[bystander]

Are Astronomers on the Verge of Finding an Exomoon?
Scientific American | Alex Teachey | 2017 Jul 27

Artist's rendering of what an exomoon (blue) orbiting an exoplanet might look like. Credit: NASA/Wikimedia

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For years I have been fascinated by the search for exomoons—that is, moons orbiting planets in other star systems. These worlds are exciting for a whole host of reasons: they could tell us a great deal about the processes that formed our solar system and others, and whether we share a common formation history with the estimated hundreds of billions of planets in the Milky Way. There's reason to think moons may play an important role in the habitability of their host planets, as some scientists think our Moon has influenced the evolution of life on Earth. And of course, if moons are habitable in their own right, they stand to expand dramatically the amount of real estate in the Universe where life could arise and flourish. The moons in our Solar System are truly remarkable worlds, astonishingly different from one another, and there's every reason to think exomoons could be equally diverse and exotic.


But so far, no one in the scientific community has been able to produce an unambiguous detection of an exomoon. It's not for lack of trying; there are a handful of us around the world actively seeking these objects, and some have dedicated many years of work to the problem. But exomoons are spectacularly tricky to find. They tend to be much smaller than planets, making their transits—small dips in the intensity of the starlight as they pass in front of the star from our point of view—quite shallow, and "lost in the noise." And every time their host planet transits, the moons show up in a different place, making them particularly difficult to detect. Ingenious indirect methods, like looking for the moons' gravitational influence on their host planet, are now routinely employed as part of the search. But this work has been computationally demanding and requires exceptionally careful analysis.
 ...

After carefully analyzing an ensemble of the highest quality planetary transit signals, we have determined that exomoons appear to be quite rare in the inner regions of star systems (regions of space close to the host star). This finding was both remarkable and, frankly, a bit disappointing. ...

In any case, there was another result in our paper that may make a considerably larger splash, which you may have even read about in the news, or soon will: We announced our identification of a single exomoon candidate, indeed the strongest candidate we've seen in the five year history of the Hunt for Exomoons with Kepler (HEK) collaboration. The system, Kepler-1625 b, has withstood a host of preliminary tests aimed at ruling out the presence of a moon, and our proposal to observe this system with the Hubble Space Telescope was recently accepted. We are thrilled to get the chance to observe with Hubble, and hope that the observation will confirm our suspicion unambiguously that this is a genuine exomoon detection, which would be the first of its kind.
 ...

Possible first sighting of an exomoon
Phys.org | 2017 Jul 28

HEK VI: On the Dearth of Galilean Analogs in Kepler
and the Exomoon Candidate Kepler-1625b I - Alex Teachey, David M. Kipping, Allan R. Schmitt

• arXiv.org > astro-ph > arXiv:1707.08563 > 26 Jul 2017

[MargaritaMc]

I was impressed by this paragraph from Alex Teachey's SciAm article
https://blogs.scientificamerican.com/ob ... -exomoon/#

And because a discovery of this sort would be a big deal, we have proceeded so far with an abundance of caution, as we have seen so many times how a sensational scientific discovery announced in the media can evaporate under further scrutiny. Let's be clear: we're not just trying to save ourselves from embarrassment; the announcement and subsequent retraction of potentially ground-breaking results has the effect of eroding public trust in science over time, and we are chiefly concerned with not contributing to that problem.

[MargaritaMc]

http://www.nature.com/news/why-astronom ... ry-1.22377
Why astronomers reluctantly announced a possible exomoon discovery.

After hints leaked out on Twitter, researchers made last-minute decision to reveal what might be the first discovery of a satellite outside our Solar System.
Davide Castelvecchi
28 July 2017

Nature doi:10.1038/nature.2017.22377

[bystander]

That's No Moon? Proposed Exomoon Defies Formation Theories
Scientific American | Nola Taylor Redd | 2018 Feb 21

The mysterious object could be the first moon found beyond our solar system—or something else entirely

Last summer, scientists announced that they had found what could be the first moon to be spotted outside of the solar system. But new research on the supposed moon's evolution calls its existence into question.

If it does exist, the moon is most likely a large, Neptune-size object orbiting an even larger gas-giant planet. But the unwieldy system strains understanding of how it may have formed, researchers have said. ...

René Heller, an astrophysicist at the Max Planck Institute in Germany, took the opportunity to independently analyze the Kepler data. In addition to teasing out a size range for the potential moon, Kepler 1625 b-i, he also explored its possible formation methods.

"It turns out that Kepler 1625 b-i is, in fact, not a good candidate for an exomoon," Heller told Space.com by email, pointing out that the original research team said that the Kepler data alone was ambiguous. (That's why they planned to follow up using the Hubble Space Telescope.) A large part of the problem stems from the fact that the parent star is so far from Earth that it appears dim, resulting in poor data quality, Heller said.

"The bottom line is that Kepler 1625 b-i is one of the best exomoon candidates so far, but it's still not a good candidate," Heller said.

The Nature of the Giant Exomoon Candidate Kepler-1625 b-i - René Heller

• arXiv.org > astro-ph > arXiv:1710.06209 > 17 Oct 2017

[Ann]

Alex Teachey wrote:

After carefully analyzing an ensemble of the highest quality planetary transit signals, we have determined that exomoons appear to be quite rare in the inner regions of star systems (regions of space close to the host star). This finding was both remarkable and, frankly, a bit disappointing.

Why would this finding be surprising?

That is exactly what we see in the Solar system.

Ann

[neufer]

Alex Teachey wrote:

After carefully analyzing an ensemble of the highest quality planetary transit signals, we have determined that exomoons appear to be quite rare in the inner regions of star systems (regions of space close to the host star). This finding was both remarkable and, frankly, a bit disappointing.

Why would this finding be surprising?

That is exactly what we see in the Solar system.

• And...if the large moons of the outer regions of our solar system were
  to wander into the inner regions they would mostly evaporate.
  
  Ergo: this finding was both unremarkable (and, frankly, a bit disappointing).

[Chris Peterson]

Alex Teachey wrote:

After carefully analyzing an ensemble of the highest quality planetary transit signals, we have determined that exomoons appear to be quite rare in the inner regions of star systems (regions of space close to the host star). This finding was both remarkable and, frankly, a bit disappointing.

Why would this finding be surprising?

He didn't say it was surprising. He said it was remarkable. The two words can mean very different things. Scientifically, expected negative results, obtained with difficulty, are reasonably described as remarkable.

[neufer]

Alex Teachey wrote:

After carefully analyzing an ensemble of the highest quality planetary transit signals, we have determined that exomoons appear to be quite rare in the inner regions of star systems (regions of space close to the host star). This finding was both remarkable and, frankly, a bit disappointing.

Why would this finding be surprising?

He didn't say it was surprising. He said it was remarkable. The two words can mean very different things. Scientifically, expected negative results, obtained with difficulty, are reasonably described as remarkable.

It is remarkable that expected negative results, obtained with difficulty,
would be described as remarkable without any sort of clarification.

[Chris Peterson]

It is remarkable that expected negative results, obtained with difficulty,
would be described as remarkable without any sort of clarification.

Do we know that happened? After all, this was a narrow quote mined from a much longer article.

[bystander]

Hubble Finds Compelling Evidence for a Moon Outside the Solar System
ESA Hubble Science Release | 2018 Oct 03

Neptune-sized moon orbits Jupiter-sized planet

Illustration of Kepler-1625 System -- Credit: NASA, ESA, and L. Hustak (STScI)

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Using the NASA/ESA Hubble Space Telescope and older data from the Kepler Space Telescope two astronomers have found the first compelling evidence for a moon outside our own Solar System. The data indicate an exomoon the size of Neptune, in a stellar system 8000 light-years from Earth. The new results are presented in the journal Science Advances.

The hunt for exoplanets — planets outside our own Solar System — provided its first results only 30 years ago. While astronomers now find these planets on a regular basis, the search for moons orbiting exoplanets wasn’t successful — until today.

In 2017 NASA’s Kepler Space Telescope detected hints of an exomoon orbiting the planet Kepler-1625b. Now, two scientists from Columbia University in New York (USA) have used the incomparable capabilities of the NASA/ESA Hubble Space Telescope to study the star Kepler-1625, 8000 light-years away, and its planet in more detail. The new observations made with Hubble show compelling evidence for a large exomoon orbiting the only known planet of Kepler-1625. If confirmed, this would be the first discovery of a moon outside our Solar System.

The candidate moon, with the designation Kepler-1625b-i, is unusual because of its large size; it is comparable in diameter to the planet Neptune. Such gargantuan moons are unknown in our own Solar System. “This may yield new insights into the development of planetary systems and may cause astronomers to revisit theories of how moons form,” Alex Teachey, a graduate student who led the study, explained excitedly [1].

Like its moon, Kepler-1625b is also bigger than its counterparts in the Solar System. The exoplanet is a gas giant, several times more massive than Jupiter [2]. It orbits its parent star at a distance similar to the distance between the Sun and Earth, which puts it — and its candidate moon — at the inner edge of the habitable zone of the star system [3]. ...

Astronomers Find First Evidence of Possible Moon Outside Our Solar System
NASA | STScI | HubbleSite | 2018 Oct 03

Neptune-sized satellite orbits a giant Jupiter around a sunlike star

Click to play embedded YouTube video.

Our solar system has eight major planets, and nearly 200 moons. Though astronomers have to date found nearly 4,000 planets orbiting other stars, no moons have yet been found. That hasn't been for any lack of looking, it’s just that moons are smaller than planets and therefore harder to detect.

The Hubble and Kepler space telescopes found evidence for what could be a giant moon accompanying a gas-giant planet that orbits the star Kepler-1625, located 8,000 light-years away in the constellation Cygnus. The moon may be as big as Neptune and it orbits a planet several times more massive than Jupiter.

If our solar system is a typical example, moons may outnumber planets in our galaxy by at least an order of magnitude or more. This promises a whole new frontier for characterizing the nature of moons and their potential for hosting life as we know it.

The exomoon at Kepler-1625b is too far away to be directly photographed. Its presence is inferred when it passes in front of the star, momentarily dimming its light. Such an event is called a transit. However, the "footprint" of the moon's transit signal is weaker than for the host planet.

The researchers caution that the moon’s presence will need to be conclusively proven by follow-up Hubble observations.

Evidence for a Large Exomoon Orbiting Kepler-1625b ~ Alex Teachey, David M. Kipping

• Science Advances 4(10):eaav1784 (03 Oct 2018) DOI: 10.1126/sciadv.aav1784

Revisiting the exomoon candidate signal around Kepler-1625b ~ Kai Rodenbeck et al

• Astronomy & Astrophysics 617:A49 (Sep 2018) DOI: 10.1051/0004-6361/201833085
  arXiv.org > astro-ph > arXiv:1806.04672 > 12 Jun 2018 (v1), 26 Jun 2018 (v2)

[BDanielMayfield]

A moon as massive as Neptune might well have natural satellites of its own.

I wonder what a moon's moon should be called... A moonite perhaps?

Bruce

[workgazer]

A moons moon has to be a Moomin