The remnant core of a gas giant has been discovered orbiting a distant star offering a unique look into the interior of a planet. The discovery was made by planetary scientists from the University of Warwick and the results were published in Nature.
An unusual discovery
Researchers from the department of Physics from the University of Warwick reported the first time discovery of an exposed core of a planet in the journal Nature. The exposed core, named TOI 849 b, of a gas giant is located in the vicinity of a star similar to our own almost 730 light years away. TOI 849 b orbits very close to its host star that a year is merely 18 hours and its surface temperature is approximately 1800K (1526 Celsius). This discovery offers a rare opportunity to study the interior and composition of a planet.
TOI 849 b discovery was made by NASA’s Transiting Exoplanet Survey Satellite (TESS) during a survey of stars. The gas giant core was discovered in the ‘Neptunian desert’ – a term used by astronomers for a region close to stars where we rarely see planets of Neptune’s mass or larger. The researchers postulated that the object’s mass is 2 to 3 times greater than Neptune while being extremely dense at the same time.
The transit signal for the discovery was confirmed and refined using observations with ten telescopes of the Warwick-led Next-Generation Transit Survey (NGTS), based at the ESO research center in Chile. TOI 849 b was studied using HARPS (High Accuracy Radial velocity Planet Searcher) instrument, at the ESO ‘s La Silla Astronomical Observatory in Chile. HARPS uses Doppler effect to determine the mass of exoplanets by looking at their ‘wobble’ – small movements towards and away from us that register as tiny shifts in the star’s spectrum of light.
Dr. David Armstrong lead author of the study said: “TOI 849 b is a massive planet, much larger in size than we expected and very dense for something the size of Neptune. This points towards the fact that this planet would have had a very unusual history. TOI 849 b has also astonished us due to its location, as we don’t see planets with this mass at these short orbital periods.”
“TOI 849 b, being the most massive terrestrial planet has a density similar to earth. It is expected that a planet this size to have accumulated huge quantities of hydrogen and helium during its formation, growing into something similar to Jupiter. The reason we don’t see hydrogen and helium gases lets us know this is an exposed planetary core.”
TOI 849b, possibility of being a gas giant core
According to the researchers, there are two hypothesis as to why we are looking at a planet’s core, rather than a typical gas giant. The first theory suggests that TOI 849 b was once similar to Jupiter but lost almost all of its outer gas by various means. These could include “tidal disruption” (when planet being ripped apart from orbiting too close to its star, or a collision with another planet). Large-scale photoevaporation of the atmosphere could also play a role, but can’t account for all the gas that has been lost.
On the other hand, TOI 849 b could be a failed gas giant i.e. as the core of the gas giant formed something went wrong and it never formed an atmosphere. This could have resulted if there was a gap in the disc of dust that the planet formed from, or if it formed late and the disc ran out of material.
Dr. Armstrong adds: “One way or another, TOI 849 b either used to be a gas giant or is a failed gas giant.
This discovery is unique and could enlighten scientists to study the core of planets which we can not do in our own solar system. The chemical compositions of the TOI 849 b could be measured using telescopes, as it orbits near to its star, so any remaining atmosphere around it constantly replenished from the core. By measuring that atmosphere, scientists could get key insights regarding the composition of the core itself.
First exposed planetary core discovered allows glimpse inside other worlds
Peter Thorley (press release)| July 1, 2020 | University of Warwick, UK
NOTE: Image credit & copyright – University of Warwick/Mark Garlick