Notre dame scientists develop theory to predict existence of giant planets on fringes of exoplanetary systems

Scientists at Notre Dame has devised a theory that enables the prediction of giant planets located on the outskirts of exoplanetary systems. This theory, proposed by Matthias He and Lauren Weiss and made available on the arXiv pre-print server, combines two distinct datasets that employ different methods to search for planets: transits and radial velocity measurements.

Transits involve measuring the decrease in a star’s brightness when a planet passes in front of it. Telescopes like Kepler excel at detecting fast-moving planets situated in the “inner” region of exoplanetary systems. These planets move swiftly across the star and can be observed multiple times within a given observation window. However, transits are less effective at identifying longer-period planets situated beyond 1 AU—the exoplanetary counterparts of Jupiter, Saturn, and other outer solar system bodies.

Radial velocity (RV) measurements, on the other hand, are better suited for detecting larger exoplanets. Telescopes such as the W.M. Keck Observatory, renowned for its highly accurate RV measurements, can detect the influence of these planets on their host star. By observing the wobbling motion of the star caused by the exoplanet’s orbital movement, astronomers can estimate the planet’s distance from the star and its expected mass. Unlike transit methods, RV measurements do not require the planet to pass directly in front of the star; instead, the planet’s gravitational pull causes the star to move sideways during its elliptical orbit.

By combining data from both transit and RV measurements, the scientists at Notre Dame have developed a comprehensive approach to predict the existence of giant planets in the outer regions of exoplanetary systems. This synthesis of datasets allows for a more comprehensive understanding of planetary dynamics and expands our ability to identify and study these distant celestial objects.

Giant planets have caused plenty of speculation, as Anton Petrov explains in this video. Credit: Anton Petrov YouTube Channel

Previously, the datasets for transiting exoplanet surveys and those utilizing radial velocity (RV) measurements were kept separate, leading to a gap in astronomers’ comprehension of how these methods would converge for the same exoplanetary systems. To address this, the researchers at Notre Dame established the Kepler Giant Planet Survey, which merged data from the Kepler telescope and the Keck Observatory to examine 63 distinct exoplanetary systems. Although most of the planets in these systems were initially detected through transits, approximately 20 out of the 177 planets in the sample were identified using RV measurements.

By combining the datasets, the scientists sought out potential indicators that could suggest the presence of giant planets in the outer regions of exoplanetary systems. Traditional factors such as the number and size of inner planets did not yield significant results in terms of predicting the existence of outer planets within the systems.

However, they discovered a notable correlation with a lesser-known metric of exoplanets—their gap complexity. Gap complexity refers to the variability in the spacing between planetary orbits within a system. Systems with low gap complexity exhibit evenly spaced planets, while those with high gap complexity feature planets with more randomly distributed orbits. The researchers found a significant increase in the likelihood of an exoplanetary system harboring a giant planet in its outer region when the gap complexity was higher. These outer planets could be detected using RV measurements but would not be evident through transits.

One limitation of this approach was the requirement for systems with at least three inner planets to accurately calculate the gap complexity of the inner system. Consequently, only four systems within the sample of 63 exhibited this feature. However, the researchers also observed that the same correlation with gap complexity held true when including the gas giant in the complexity calculation, particularly for systems with only two planets in the inner region.

While statistical significance is crucial in validating scientific theories, a sample size of four can certainly be expanded upon. Data synthesis, exemplified by the work of Drs. He and Weiss, serves as an excellent starting point for accumulating more data. As the number of discovered exoplanetary systems continues to rise, further opportunities will arise to substantiate this theory and deepen our understanding of the influence of giant planet formation on the overall structure of exoplanetary systems.

Source: Universe Today

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