Discovery of Exoplanet Perplexes Astronomers

  (© NASA/JPL-Caltech, Artist rendering of Gas Giant orbiting star)

While a sub-class of exoplanets given the name ‘Hot Jupiters’ is well known to astronomers, a new exoplanet has been discovered that resembles a Hot Jupiter, but displays unique properties not shared by these previously studied exoplanets.

Hot Jupiters are large, hot, gas giants that have small orbits that usually last 10 days or less and were the first exoplanets orbiting sun-like stars to be discovered in 1995. Now, almost thirty years later, we are discovering a young, Jupiter-like planet with distinct characteristics, namely its density. Planet HD 114082 b is being called a ‘super Jupiter’ and has a diameter similar to that of Jupiter, but recent data suggests that the mass of the exoplanet is about 8x Jupiter’s. Since this newly studied exoplanet is a gas giant, we would generally expect its density to be comparable to that of the gas giants we’re most familiar with, however this does not appear to be the case. For reference, Saturn is our solar system’s least dense planet at 0.687g/cm­³, and Jupiter has a density of 1.34g/cm³, approximately one-fourth of Earth’s. Comparatively HD 114082 b’s density is estimated to be twice Earth’s.

Exoplanet HD 114082 b is located in the Centaurus constellation, the same constellation the three-star Alpha Centauri system is found and orbits the star HD 114082, which is nearly 1.5x the radius and mass of our sun with an effective temperature 800-900 K higher. Astronomers have determined the exoplanet is 310 lightyears away from Earth, has an orbital period of 110 days, and a semi-major axis of 0.51 AU. This orbital period is much longer than that of a Hot Jupiter, much shorter than our Jupiter’s, and is instead comparable to that of Mercury at 88 days. It has been approximated to be around 15 million years old, making it far denser than other planets at similar ages that have been observed in the past.

 It was first discovered by the radial velocity method, which was also used to determine its mass, and the transit method was used to determine the planet’s radius. Radial velocity uses the wobble of the star, an effect from the gravity of the orbiting exoplanet, to quantify the orbital period, and from this the mass of the orbiting planet can be calculated using Kepler’s third law. The transit method of planetary detection and measurement involves measuring the baseline luminosity of a star and comparing the reduction of luminosity as the planet passes between its star and the measuring instrument. The amount of light blocked by the planet allows us to infer the radius of the planet.

            Light Curve graph of HD 114082 b as it transits its parent star (Max Planck Institute for Astronomy)

 

Similar to Hot Jupiters, the location of this exoplanet in relation to its star is unexpected and does not fall within the parameters of the currently accepted nebular hypothesis. From our current understanding of planetary formation, we would expect larger gaseous planetary bodies to form and orbit further away from their stars, just as Jupiter does in our own solar system. Comparatively, we expect heavier, denser bodies to form closer to their stars, where their rocky and metal cores form as the heavier material condenses at the higher temperatures facilitated by the star. In the case of Hot Jupiters, we suspect that these exoplanets form further away from their star and migrate over time inwards. Considering the attributes of HD 114082 b do not fall into a well-understood category, this seems to be an unexplored area in which more research will need to be conducted to reach a plausible conclusion as to how this planetary body came to be, whether it formed near its star or migrated to its current orbit.

A co-author on the release of these findings, Ralf Launhardt, is quoted with stating, “All we can say is that we still don’t understand the formation of giant planets very well.” Overall, the qualities exhibited by this exoplanet are seemingly incompatible, it’s a dense gas giant, which sounds like an oxymoron, orbiting relatively near its star. Since this development in the field of Astronomy is still new, it is unclear what the existence of exoplanet HD 114802 b implies in regards to planetary formation at this time.

 

Work Cited:

1.       Giant exoplanet has astronomers puzzled. Max-Planck-Gesellschaft. (2022, November 25). Retrieved November 27, 2022, from https://www.mpg.de/19503964/giant-exoplanet-has-astronomers-puzzled

2.       Lea, R. (2022, November 26). Weird young super-jupiter challenges theories of planet formation. Space.com. Retrieved November 27, 2022, from https://www.space.com/weird-super-jupiter-planet-very-dense

3.       Planet HD 114082 b. The Extrasolar Planet Encyclopaedia - HD 114082 b. (n.d.). Retrieved November 27, 2022, from http://exoplanet.eu/catalog/hd_114082_b/