Around 730 light-years away, around a star very similar to our Sun, astronomers have found a really strange exoplanet.
It is only a little bit smaller than Neptune, which could indicate a gaseous planet … but it is more than twice as massive as Neptune, with a density comparable to Earth and Venus.
This super-dense surprise suggests that the exoplanet is rocky, but well above the usual upper size limit for rocky planets. Which in turn means that it could indeed be something very rare – a so-called chthonic planet, the core of a gas giant, whose atmosphere has either been removed.
This is a hypothetical class of planets because the discovery of a planet has never been confirmed before.
The planet in question is called TOI-849b and orbits a sun-like star called TOI-849. If we find out exactly what it is, it could help us to better understand what is in the dense atmosphere of gas and ice giants like Neptune and what processes of formation these impressive planets have.
“TOI 849 b is the most massive terrestrial planet ̵
“This is the first time we have discovered an intact exposed gas giant core around a star.”
TOI-849b was found by a survey performed using NASA’s Transiting Exoplanet Survey Satellite (TESS), the space telescope for exoplanet hunting. TESS searches for exoplanets by staring at stars and using its sensitive instruments to search for regular, weak light dips that indicate that something big like a planet is passing in front of the star.
How much and how often the light from the star dims allows astronomers to calculate things like the size of the planet and the proximity to the star. TOI-849b is very close to its star – it whips every 18 hours. Such proximity would make it extremely hot, with a surface temperature of around 1,800 Kelvin (1,530 degrees Celsius or 2,780 degrees Fahrenheit).
This closeness to its star makes the exoplanet a special category – very few planets in Neptune size have been found near their stars, creating a so-called hot Neptune desert.
This alone would be remarkable, but then the team made follow-up observations using Doppler spectroscopy.
When a planet orbits a star, it exerts a slight gravitational pull on the star, causing the star to wobble a little in place. Doppler spectroscopy measures how the light of the star changes when it shakes. If the mass of the star is known, astronomers can calculate the mass of the planet based on how much the star shakes.
In this way, the team calculated the mass of the exoplanet – approximately 39.1 times the mass of the earth and 2.3 times the mass of Neptune. This leads to a density of 5.2 grams per centimeter of cubes – very close to the 5.24 g / cm³ of Venus and the 5.51 g / cm³ of earth.
“Although this is an unusually massive planet, it is far from the most massive one that we know of,” said Armstrong.
“But it is the most massive we know for its size and extremely dense for something the size of Neptune, which tells us that this planet has a very unusual history. The fact that its mass makes it a strange one Location is also helpful – we are attracting In these short orbital times, I see no planets with this mass. “
Which leads to the conclusion that we are looking at a chthonic planet. Although it’s still a mystery how it came about.
It is possible that TOI-849b has formed with a huge gas atmosphere similar to that of Jupiter and somehow later removed.
We know that gas planets next to their stars can lose their atmosphere due to the incredible heat. And one of the few other hot Neptunes ever discovered, Gliese 3470 b, loses its atmosphere at an unbelievable rate that is evaporated by the heat of its star.
This process would not take into account the total atmospheric loss calculated for TOI-849b, but other events could have played a role, such as collisions with other large objects.
The other possibility is that TOI-849b started to form as a gas giant but didn’t have enough material – either because it formed late in the evolution of the planetary system when there was very little material left in the star’s protoplanetary disk, or because it formed a gap in the disc where there wasn’t enough material to create an atmosphere.
The team plans to monitor its research with observations to determine if TOI-849b still has atmosphere. This could help determine the composition of the core yourself.
“In one way or another, TOI 849 b was either a gas giant or a ‘failed’ gas giant,” said Armstrong.
“It is a premiere that tells us that planets like this exist and can be found. We have the ability to look at the nucleus of a planet in a way that we cannot do in our own solar system. There are still big ones Unanswered Questions About the nature of Jupiter’s nucleus, for example, weird and unusual exoplanets give us a window into planet formation that we have no other way of exploring. “
The research was published in nature.