Massive Gas Giant Planets Locked in a Gravitational Struggle

A team of astronomers have discovered a rather curious exoplanetary system that has two gas giant planets that are messing up each other’s orbit! On of them is 3.8 times the mass of Jupiter and completes an orbit every 82 days, the other is just 1.4 Jupiter masses. Hiding in the wings is another mini-Neptunian world. The two gas giants are locked into a 2:1 orbital resonance and, as a result of their gravitational interactions, the orbit of the more massive can vary by up to 4 days!

Exoplanets are alien worlds that orbit around stars beyond our Solar System. They vary by size, mass, composition and environment and studying them provides insight into not only planetary formation but also the liklihood for the presence of alien life! Like all bodies that orbit a common host; moons around a planet or planets around a star, their orbits can become linked in what has become known as a resonance.

This artist’s illustration shows the Neptune-like exoplanet GJ 3470b, which has an atmosphere rich in sulphur. The planet’s atmosphere holds clues to how it and other similar planets formed. Image Credit: Department of Astronomy, UW–Madison

Orbital resonance occurs when two or more orbiting bodies exert regular, periodic gravitational influence on each other, creating a stable orbital relationship. It often results in simple integer ratios between their orbital periods, such as 2:1 or 3:2. Neptune and Pluto for example are in a 2:3 resonance, meaning Pluto completes two orbits around the Sun for every three of Neptune’s. In our solar system, Jupiter’s moons Ganymede, Europa, and Io follow a 4:2:1 resonance, affecting their geological activity. Resonances help maintain orbital stability over long timescales but can also lead to instability in some cases, influencing planetary formation, migration, and even asteroid belt structures.

Kirkwood Gaps, histogram of asteroids as a function of their average distance from the Sun. Regions deplete of asteroids are called Kirkwood Gaps, and those bodies may have been escavated from the main belt owing to orbital resonances (image credit: Alan Chamberlain, JPL/Caltech).

The planetary system just discovered, TOI-4504 was detected by the Transiting Exoplanet Survey Satellite (TESS.) As TOI-4504 c orbits the star, they pass directly in front of the host star causing its light to dim in a transit event. It was this dimming that was spotted by TESS. The orbit of exoplanet TOI-4504 c is affected by the non-transiting planet TOI-4504 d. The gravitational interaction of this planet causes the transit times of TOI-4504 c to vary by about 4 days. The orbit of exoplanet TOI-4504 d does not cause a transit event but if its orbit were such that it did then the orbital period would vary by up to 6 days. 

Illustration of NASA’s Transiting Exoplanet Survey Satellite. Credit: NASA’s Goddard Space Flight Center

The lead author fo the paper, PhD student Michaela Vítková from the AI CAS in Czech Republic said “We were surprised to see such a large amplitude of the variations in the transit times of TOI-4504 c.”  The results of the study relied upon data not only from TESS but also from FEROS (Fibre-fed Extended Range Optical Spectrograph) on the 2.2m telescope at ESO’s La Silla observatory in Chile. The planetary system is a complex one with another 10 Earth-mass planet on an inner orbit that takes 2.4 days to complete one trip around the star.

The study reveals yet again what a fascinating study exoplanetary systems are. TOI-4504 is a great example of how varied the systems and their planets can be. The orbital resonances of planets ‘c’ and ‘d’ make for a fascinating system that would benefit from further study.

Source : Violent dance of massive gas giant planets

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