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Doubt cast on new “exomoon” Rob Sheldon explains

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Neptune-sized exomoon
artist’s impression of exomoon/Dan Durda

Remember the first known exomoon (moon orbiting an exoplanet)? We wrote about it here. The apparent discovery (which shouldn’t surprise anyone in principle) has come under fire:

Two different groups of researchers took another look at data to search for a telltale dip in starlight that could suggest a moon was passing in front of the star Kepler 1625. Their conflicting results raise questions about whether the exomoon exists.

“When I reanalyzed the data, I don’t see that moonlike dip at all,” says Laura Kreidberg, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. She and colleagues reported the results in a paper posted at arXiv.org on April 25.

In a separate study, astronomer René Heller of the Max Planck Institute for Solar System Research in Göttingen, Germany, and colleagues found inconsistent signs of a moon. The researchers analyzed the same data as Kreidberg, gathered by the Hubble Space Telescope, plus data from Kepler, the now-retired exoplanet-hunting space telescope. Both of those telescopes were used to bolster the initial case for the exomoon. But, Heller’s team writes in a paper published April 17 in Astronomy & Astrophysics, “careful consideration of its statistical evidence leads us to believe that this is not a secure exomoon detection.”Lisa Grossman, “Skepticism grows over whether the first known exomoon exists” at ScienceNews

We asked our physics color commentator Rob Sheldon how to understand this on-again off-again faroff moon. He says,


This brief article captures the essence of “unrepeatability” for physics papers. We all know the problem of repeatability in psychology and biology, but it exists for physics too. The most famous discussion of this was by Irving Langmuir in his 1953 paper “Pathological Science“.

It works like this.
a) You want to be famous.
b) You pick a hard thing to measure.
c) You see something in the data that might could* make you famous.
d) You ignore any criticism and rush to press.
e) When later, the paper is disproved, you blame it on your data.
f) You are no worse off than when you started, and a whole lot more famous. Maybe even funded to improve the data.

Now, why is this paper in that category? Because the noisy data is discovered by looking at “blips” in the light emitted from a distant star as the planet “transits” the disk of the star as seen from Earth. The “size” of the blip tells you its radius. From a double blip, the researchers estimated a “hot Jupiter” about 2 times wider than Jupiter at an orbit of 0.8AU around a 1.08 solar mass star, accompanied by a moon some 0.002 AU away (the distance of our Moon) but with a diameter is something like 2X that of Earth.

Well, what would happen if a super-Earth orbited a super-Jupiter at a distance of 200,000 miles?

Io is a much smaller moon than ours, and it orbits Jupiter at a distance ~16% larger than our moon. Yet the effect of Jupiter’s gravity on Io causes the largest volcanoes in the Solar System. In return, Io causes a beam of electrons that form a hot-spot in Jupiter’s atmosphere as well as aurora. So if we amp up Jupiter’s gravity 10 times, and increase the mass of the moon 1000 times, and put it 20% closer, what could possibly go wrong?

Among other things, the tidal force is proportional to the mass and inversely proportional to the cube of the distance. So the tidal force on this supposed moon is 40,000 bigger than Io’s. The heating rate is force * velocity, and the keplerian velocity is about 6 times faster, so we are up to 240,000 times more heating of this moon than Io. Fortunately, radiative cooling goes as the area times the fourth power of the temperature, and being 4 times larger than Io, corresponds to a temperature only 6 times hotter than Io. Io’s volcanoes are molten sulfur, which melts at a temperature 388K, and so very roughly we suggest that this putative moon should be only 2450 K. For comparison the surface of the sun is 5500 K. So they are suggesting is that they detected a moon with a dip in the light curve, but it should have been a bump in the light curve! (Before evaporating completely, of course, since only a few ceramics stay solid at 2450K.) And we haven’t even addressed the effect of tidal heating and ionospheric bombardment on the super-Jupiter, which should be emitting X-rays like a x-ray binary.

In other words, there are red flags all over this data, but the investigators are standing by their measurement.

This is what irreproducible papers look like in physics, and why the same crisis that afflicts other disciplines also afflicts physics.

*”might could” is a technical term especially used in Alabama.

The Long Ascent: Genesis 1â  11 in Science & Myth, Volume 1 by [Sheldon, Robert]

Rob Sheldon is the author of Genesis: The Long Ascent

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See also: Astronomers: First Possible Exomoon Is The Size Of Neptune, And Orbiting A “Jupiter”

and

Moonmoons

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One Reply to “Doubt cast on new “exomoon” Rob Sheldon explains

  1. 1
    SmartAZ says:

    In other words they are pretending to know something when they don’t. That is a disgrace!

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