Gas giant exoplanet discovered, twice as dense as Earth

(ORDO NEWS) — The recently suspended exoplanet has deeply puzzled astronomers.

By taking measurements of a very young Jupiter-sized exoplanet called HD-114082b, scientists found that its properties do not match either of the two popular models for the formation of gas giant planets.

Simply put, she is too heavy for her age.

“Compared to currently accepted models, HD-114082b is about two to three times too dense for a young gas giant just 15 million years old,” explains astrophysicist Olga Zakhozhay from the Max Planck Astronomical Institute in Germany.

Orbiting about 300 light-years away, the star HD-114082, the exoplanet has been the subject of an intense data-gathering campaign.

HD-114082b is only 15 million years old. It is one of the youngest exoplanets ever discovered, and understanding its properties could provide clues to how planets form, a process that is not fully understood.

Two types of data are needed to comprehensively characterize an exoplanet based on the impact it has on its parent star. The transit data is a record of how the light of a star dims when a spinning exoplanet passes in front of it. If we know how bright the star is, this faint dimming could reveal the exoplanet’s size.

Radial velocity data, on the other hand, shows how much a star wobbles in place in response to the motion of an exoplanet. gravity tug. If we know the mass of a star, then the amplitude of its oscillations can give us the mass of an exoplanet.

For nearly four years, the researchers have been collecting observations of the radial velocity of HD-114082. Using combined transit and radial velocity data, the researchers determined that HD-114082b has the same radius as Jupiter but 8 times the mass of Jupiter.

This means that the density of the exoplanet is about twice the density of the Earth and almost 10 times the density of Jupiter.

Due to the size and mass of this young exoplanet, it is unlikely to be an extra-large rocky planet; the upper limit for them is about 3 Earth radii and 25 Earth masses.

Rocky exoplanets also have a very small density range. Above this range, the body becomes denser, and the planet’s gravity begins to hold onto a significant atmosphere of hydrogen and helium.

HD-114082b greatly exceeds these parameters, which means that it is a gas giant. But astronomers just don’t know how it happened.

“We think there are two possible ways for giant planets to form,” says MPIA astronomer Ralph Launhardt. “Both occur within a protoplanetary disk of gas and dust distributed around a young central star.”

These two methods are called “cold start” or “hot start”. It is believed that during a cold start, an exoplanet is formed, stone by stone, from the debris of a disk orbiting a star.

The pieces are attracted first electrostatically and then gravitationally. The more mass it gains, the faster it grows until it becomes massive enough to cause uncontrolled accretion of hydrogen and helium, the lightest elements in the universe, resulting in a massive shell of gas around the rocky core.

Given. gases lose heat as they fall towards the planet’s core and form an atmosphere, this is considered a relatively cool option.

Hot start is also known as disk instability and is thought to occur when a swirling region of instability in the disk directly collapses on its own under the force of gravity. The resulting body is a fully formed exoplanet without a rocky core where the gases retain more of their heat.

Exoplanets experiencing a cold start or a hot start should cool at different rates. producing distinct characteristics that we should be able to observe.

The properties of HD-114082b do not match the hot start model, the researchers say; its size and mass are more in line with core accretion. But even then, he is still too massive for his size. Either it has an unusually flimsy core, or something else is going on.

“It’s too early to abandon the idea of ​​a hot start,” Launhardt says. “All we can say is that we still don’t understand the formation of giant planets very well.”

This exoplanet is one of three planets known to us younger than 30 million years for which astronomers have received measurements of radius and mass. So far, all three seem to be inconsistent with the disk instability model.

Clearly, three is a very small sample size, but three out of three suggests that perhaps kernel augmentation may be the more common of the two.

“While more of these planets are needed to confirm this trend, we think theorists need to start rethinking their calculations,” says Zahozhay.

“It’s amazing how the results of our observations are taken into account in the theory of planetary formation. They help improve our knowledge of how these giant planets grow and tell us where the gaps in our understanding lie.”

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