Proposed exomoon defies the formation of theories

An artist the image of an Earth-like exomoon orbiting a gas giant planet .


Last summer, scientists announced that they had found what would be the first moon to be spotted outside the solar system. But new research about the alleged moon evolution calls its existence into question.

If it does not exist, the moon is most likely a large, Neptune-size object in orbit around an even larger gas-giant planet. But the cumbersome system the tribes understanding of how the can are formed, researchers have said.

In July 2017, scientists reluctantly announced the possible discovery of an exomoon. A candidate planet, which by the NASA’s Kepler telescope revealed a skewed dips in the light streaming from the planet, star, suggests the possibility of a moon. After exomoon hunter David Kipping, of the Columbia University in New York, the requested time on the Hubble Space Telescope, a follow-up on the unusual activity, in the various media outlets in the extent to which the research. This led Kipping and Columbia Alex Teachey, the scientist about the possible discovery, to announce the possibility of the first sighting of an exomoon.

René Heller, an astrophysicist at the Max Planck Institute in Germany, took the opportunity to independently analyze the Kepler data. In addition to tease out a size for the potential moon, Kepler 1625 b-I, he also explored the possible formation methods. [The Most Intriguing Alien Planet Discoveries of 2017]

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“It turns out that Kepler 1625 b-i is, in fact, not a good candidate for an exomoon,” said Heller by e-mail to indicate that the original investigation team said that the Kepler data alone was ambiguous. (That’s why they plan to do a follow-up with the help of 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 quality of the data, 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.

“A small solar system”

In the Earth, the solar system, the moons are fairly common; only Mercury and Venus have no rocky or icy satellites. While most of our solar system’s moons are inhospitable to life as we know it, the three of them are potentially habitable. Jupiter Europa contains a liquid ocean beneath the moon’s icy crust. Around Saturn, the icy moon Enceladus also hosts an ocean, while the smoggy Titan has lakes of methane and ethane that would have allowed a type of life different from that on Earth. So, the solar system and the only habitable planet (Earth) is exceeded by the system’s potentially habitable moons.

That could mean good news for who is looking for life on moons around other stars. Even if few planets are capable of hosting life as we know it, their moons, could prove to be habitable, Heller said.

“On the challenging side, the moons are expected to be considerably smaller and lighter than their planets,” Heller said. “That’s just what we learn from observations of the solar system moons.”

Because objects with a larger mass and the radius are easier to find from afar, be they planets or moons, natural satellites are more difficult to recognize, Heller said.

When Kepler hunts planets, it does this by looking at the light streaming from a star in what scientists call a light curve. (Kepler not study one star at a time, but instead, examined thousands of stars at once.) When a planet moves between the star and the Earth, the stars, the light dims, allowing researchers to determine the planet’s size. Researchers observe multiple courses to determine how long it takes before the planet is in orbit around the star.

What the original researchers noticed about an object, Kepler 1625 b, was that it was a foreign secondary dip. Heller used the publicly available data set from Kepler to study three transits of Jupiter-size object moving across the star, along with a few wiggles that can be caused by a moon in orbit around the object.

“If, and only if this extra wiggles really come from the moon, then it is possible to derive the mass and radius of the planet and the moon of the dynamics of the planet-moon system that can be derived from the light curve,” Heller said.

Heller determined that the solid object can be anything, from a planet, which is slightly heavier than Saturn, a brown dwarf, an almost-star, not quite hard enough to ignite fusion in the core, or even a very low-mass stars (VLMS) which is a tenth of the mass of the sun. The proposed moon can vary from an Earth-mass gas satellite has a rock-and-water companion with no atmosphere.

Heller concluded that a Neptune-mass exomoon around a giant planet or low-mass brown dwarf would not match the mass-scaling relationship found in our solar system moons. While the Earth and Pluto both have large moons compared to the planets’ sizes, the solar system’s gas giants, and moons closer to 0.01 to 0.03 percent of the planets’ sizes, according to the Planetary Habitability Laboratory of the University of Puerto Rico.

Previous theories predicted that this relationship should extend to higher worlds, seems to exclude that the existence of the potential exomoon. On the other hand, is a mini-Neptune around a high-mass brown dwarf or a VLMS, more in line with that ratio, Heller said. [What Is the Moon Made of?]

“As the primary transit object is a very low-mass stars, and as the Neptune-sized companion is found to exist, then we would see a small solar system in an orbit around a sun-like star to the Earth is the distance to the sun. This would be something on his own!” Heller said.

Even without the potential for a habitable exomoon, the small solar system could help scientists understand how worlds form, ” he said.

“If the primary [object] a [brown dwarf] or a VLMS with a great companion, then this is a fascinating bridge between planet formation around stars and the moon formation around giant planets,” Heller said.

Heller placed his research on the arXiv preprint server.

The birth of moons

With the estimates of the moon and the planet or star in the hand, Heller decided to look at how the moon could have formed.

“The moons in the solar system serve as tracers of their host planets’ formation and evolution,” he said in the new paper. “Hence, it can be expected that the discovery of the moons around exoplanets could give fundamental new insights into the formation and evolution of exoplanets which cannot be obtained by exoplanet observations only.”

With this in mind, Heller, applied to the three different models of the moon formation of the solar system to the new potential exomoon.

The first was the impact model, which describes how scientists think the moon formed. When a large body struck the Earth billions of years ago, the debris cut from the planet made of a new companion. According to Heller, a peculiar feature of this model is the high ratio of the satellites of the planets. While the large size of the proposed moon in comparison with the host would be in accordance with an impact, he expressed concern that the mass of the host planet or star was much higher than that of a planet in Earth solar system.

In the second model of the moon formation, they develop from the gas and dust that remains after the planet is born, and this is how most of the gas giants’ moons are thought to have formed. The mass-scaling relation, which ensures that the moons so much smaller than their planets is the natural result of the moon’s formation in the gas-starved environment around complete planet, Heller wrote in the newspaper. That same relationship makes this formation method is unlikely, he said.

“If the companion around Kepler-1625 b may be confirmed, and both objects can be validated as a gas-giant objects, then it would be difficult to understand how these two gas planets might have formed by a giant impact, or in-situ deposits on their current orbit around the star,” Heller wrote.

The remaining possibility is that the distant world was conquered by a Neptune-size of the object. Neptune moon, Triton, and the two moons of Mars are thought to have formed this way. The exomoon may be originally formed with an Earth-size companion, before he is pulled away by the gravity of the larger object, Heller said. He determined that the capture of a Neptune-mass object by Kepler 1625 b is possible on the planet from the current location.

Still, while such a recording is in principle possible, Heller told he thinks that the scenario is “very unlikely.”

And although scientists are currently three different moon-formation scenarios for planets around the Earth, the sun, that does not mean that natural satellites couldn’t form any other way, Heller said.

“It is possible that this system basically formed by a mechanism that we haven’t seen in the solar system,” Heller said.

He proposed an alternative theory, similar to that of the giant planet formation, in which the two objects started out as a binary system of rocky planets. The couple would have drawn the gas from the disk of leftover material, such as the process by which giant planets form, with the future planet consume more gas than the would-be moon. He cautioned that this is speculation, and that the two objects may not be stable over longer periods.

Still, if the Neptune-size exomoon around Kepler-1625 b is real, the new system can provide a intriguing look at the moon formation outside the solar system, Heller said.

The Kepler data is not the only available research. In October, Teachey and Kipping looked at the system with the help of the Hubble telescope. The results of these observations should be announced soon.

Until that time, however, things don’t look good to the potential exomoon.

“The extraordinary claim of an exomoon is not supported by extraordinary evidence for it,” Heller said.

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