Huge doubts about giant exomoons  Urania

The discovery of giant exomoons around the planets Kepler-1625b and Kepler-1708b has been questioned.

Just as we can assume that about the stars in our country milky way The planets revolve around it, as do the moons around it egzoplanet It shouldn’t be rare. However, detecting them is difficult. So far, only two of the more than 5,300 known exoplanets have been confirmed to have moons. The new data analysis shows that scientific data are rarely clear-cut, that every finding carries a greater or lesser degree of uncertainty, and that the path to a conclusion often resembles a thriller.

In observing planets Kepler-1625b I Kepler-1708b Using space telescopes Keplera I Habla Scientists have discovered traces of such moons for the first time. However, a new study now casts doubt on these previous claims. Scientists from the Max Planck Institute for Solar System Research and the Sonneberg Observatory in their article published In the journal Nature Astronomy it was stated that the interpretation of the “planet only” observations is more conclusive. To analyze them, the scientists used a newly developed computer algorithm called Pandora, which makes the research easier and faster. com. exomoons. In addition, they verified which types of exomoons can actually be found in modern astronomical observations made in space. Their answer is very surprising.

In our Solar System The fact that a planet orbits one or more moons is the rule rather than the exception: with the exception of Mercury and Venus, all the other planets have such companions. In the case of the gas giant planet Saturn, scientists have so far found 140 natural satellites. Therefore, scientists believe that it is likely that planets in distant star systems also have moons. However, so far, evidence of such exomoons has only been found in two cases: Kepler-1625b and Kepler-1708b. This low efficiency is not surprising because distant satellites are naturally much smaller than their home worlds, making them more difficult to find. In addition, combing through observational data from thousands of exoplanets looking for moons takes an extremely long time.

To make the search easier and faster, the authors of the new study developed and improved a search algorithm focused on finding exomoons. Your style They posted Last year, the algorithm was available to all researchers as open source code. When applied to observational data from Kepler-1625b and Kepler-1708b, the results are striking. We wanted to confirm the discovery of exomoons around Kepler-1625b and Kepler-1708b – said the first author of the new study, MPS scientist Dr. Rene Heller. Unfortunately, our analyzes show otherwise – added.

Exomoon hide and seek game
Five years ago, the Jupiter-like planet Kepler-1625b made headlines. Scientists at Columbia University in New York announced strong evidence of the existence of a massive moon orbiting it that would dwarf all the moons of the solar system. Scientists analyzed data from the Kepler space telescope, which observed more than 100,000 stars and discovered more than 2,000 exoplanets during its first mission from 2009 to 2013. However, after discovering the exomoon candidate in 2018, astronomers had to… In the following years they would play a cosmic version of hide-and-seek. First, the filter disappeared after cleaning the Kepler data from systematic noise. However, the clues were found again in further observations using the Hubble Telescope. Last year, this unusual exomoon candidate gained company: according to New York scientists, another giant moon much larger than Earth orbits a Jupiter-sized planet — Kepler-1708b.

Exoplanets are so far away that we can’t see them directly, even with the most powerful modern telescopes – explained Dr. Rene Heller. Instead, telescopes record fluctuations in the brightness of distant stars, which we call Light curve. Scientists then look for signs of the presence of moons in these light curves. If an exoplanet passes in front of its star as seen from Earth, it dims the star by a small fraction. This event is called a transit and is repeated regularly with the planet’s orbital period around the star. An exomoon accompanying the planet will have a similar dimming effect. Not only will its effect on the light curve be dimmer. As the moon and planet move around their mutual center of gravity, this additional darkening of the light curve will follow a complex pattern. Other influences must also be taken into account, such as planetary and lunar eclipses, natural variations in star brightness, and other sources of noise generated during telescopic measurements.

But to detect the moons, both the New York scientists and their German colleagues first calculated many millions of “synthetic” light curves of all possible sizes, mutual distances, and orbital orientations of the planets and moons. The algorithm then compares these simulated light curves with the observed light curve and looks for the best match. Scientists from Göttingen and Sonneberg used the open source Pandora algorithm, optimized for searching for exomoons, which can solve the task several orders of magnitude faster than previous algorithms.

There are no signs of the moons
In the case of Kepler-1708b, German scientists have now found that scenarios without a moon can explain observational data as accurately as those with a moon. Obviously, the probability of a moon orbiting Kepler-1708b is lower than previously assumed – said Michael Hipke of Sonneberg Observatory, co-author of the new study. These data do not indicate the presence of exomoons around Kepler-1708b – Hibiki added.

There are indications that Kepler-1625b also does not have a giant companion. The planet’s transit in front of its star has been previously observed using the Kepler and Hubble telescopes. German scientists now say that the instantaneous change in the star’s brightness, an effect known as star edge dimming, has a major impact on the proposed exomoon signal. For example, the edges of the Sun’s disk appear darker than its center. However, depending on whether you look at Kepler-1625b’s host star through Kepler or Hubble, the dimming effect looks different. This is because the Kepler and Hubble telescopes are sensitive to different wavelengths of the light they receive. Scientists from Göttingen and Sonneberg now say that their model of this effect explains the data more conclusively than the presence of a giant exomoon.

Their comprehensive new analysis shows that algorithms for searching for exomoons often produce false positives. It turns out that they repeatedly “discover” moons, when in reality it is just a planet passing through its host star. For a gentle curve like that of Kepler-1625b, the false positive rate is probably about 11%. Our colleagues in New York’s previous claim of the existence of extrasolar moons was the result of a search for moons around dozens of exoplanets – Heller said. According to our estimates, false positives are not at all surprising, but almost expected – added.

Alien satellites
The researchers used their algorithm to predict the types of actual exomoons that would be clearly detected in the light curves of space missions like Kepler. According to their analysis, only particularly large moons that orbit their planet in a wide orbit can be detected using current technology. Compared with the known moons of our solar system, all the exomoons examined were highly unusual: at least twice the size of Ganymede, the largest moon in the solar system, and thus about the size of Earth. The first exomoons to be discovered in future observations like the PLATO mission are sure to be very unusual and exciting to study – Heller said.

Agnieszka Novak

more information:

Source: mpg

Pictured: An artist’s impression of a gas giant orbiting a sun-like star, as seen from the planet Kepler-1625b. Source: NASA/JPL-Caltech

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