A newly discovered planet has the diameter of Jupiter but eight times its mass, giving it twice the density of Earth despite being composed mostly of gas. Not only have these characteristics of this “super Jupiter” puzzled astronomers, but they could also challenge current theories about planet formation.
The exoplanetwhich lies about 310 light-years outside the solar system in the constellation Centaurus, orbits around a sun star and is only 15 million years old, making it a relative child in cosmic terms and compared to our 4.6 billion year old planet. A team of astronomers have been able to measure both the diameter and the mass of this gas giant – nicknamed “super Jupiter” because it is more massive than its solar system namesake – making it the youngest such planet for which such measures have never been made.
And these statistics are strange. Explaining how this planet, designated HD 114082 b, came to be eight times the mass packed into a Jupiter-as the diameter may require updating models of planetary formation that allow gas giants to possess unusually large solid planetary cores.
“Compared to currently accepted models, HD 114082 b is about two to three times too dense for a young gas giant just 15 million years old,” said Olga Zakhozhay, an astronomer at the Max Planck Institute for Astronomy in Germany and lead author of the new research, said in a statement.
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The diameter and mass of HD 114082 b give it a density twice that of Earth — surprising given that it is a gas giant composed mainly of hydrogen and helium, the lightest elements in the universe.
The exoplanet revolves around its star at a distance that is half that between Earth and the sun, completing an orbit every 110 Earth days, an orbit comparable to that of Mercurythe planet closest to the sun.
A Recipe for a Weird Super-Jupiter
A gas giant like HD 114082 b could form in two possible ways, both occurring in the protoplanetary disk, a disk of gas and dust that collapses to form planets.
The first formation mechanism, the core accretion model, involves a protoplanet beginning life as a solid, rocky core accumulating more and more material. Once this core reaches critical mass, its gravitational influence pulls the surrounding gas towards it, causing the core to accumulate hydrogen and helium in a runaway process that gives rise to a giant planet.
The second mechanism, the disk instability model, involves the collapse and growth of dense, gravitationally unstable plates of the protoplanetary disk to form a gas giant lacking a rocky core.
These formation patterns differ in the rate at which the accumulated gas cools, leading astronomers to describe planets as having a “hot” (core accretion) or “cold” (disk instability) start. Scientists currently favor the hot-start model, but the two approaches should lead to observable differences, thereby directing scientists to the correct training model.
In gas giants, this key feature is size: since hot gas occupies a larger volume than cold gas, smaller gas giants may have formed from a “cold” start, while that larger gas giants like HD 114082 b more likely formed by core accretion. The difference in size caused by the two potential origins is expected to be particularly pronounced among younger worlds, becoming less and less measurable over hundreds of millions of years as the planet cools and the gas contracts.
Although the hot start is the generally expected model, the density of HD 114082 b appears to defy what astronomers would expect from a basic accretion model, favoring the underdog, cold start, or model instead. disk instability. Some older exoplanets discovered by other teams of astronomers also favor this cold model, but the team behind the new research warns not to discard hot start planet formation models just yet. .
Alternative explanations for HD 114082 b’s small size and large mass that rescue the critical mass model include the idea that the exoplanet simply has an unusually large rocky core buried at its heart or that astronomers have not yet another accurate picture of how quickly the gas enters. an infant gas giant cools.
“It is far too early to abandon the notion of a hot start,” Ralf Launhardt, an astronomer at the Max Planck Institute for Astronomy and co-author of the new research, said in the release. “All we can say is that we still don’t fully understand how giant planets form.”
Star Oscillation Reveals Exoplanet HD 114082 b
HD 114082 b was spotted as part of the Radial Velocity Survey for Planets Around Young Stars (RVSPY) program, operated using the 2.2-meter telescope at the European Southern Observatory’s (ESO) La Silla site in Chile . The program aims to discover the population of hot, hot and cold giant planets around young stars.
Astronomers use data collected by RVSPY to look for changes in the spectrum of starlight that indicate a “wobble” caused by an orbiting exoplanet. Known as the radial velocity method, this technique can also reveal the mass of a planet, but to measure the size of the world, astronomers must observe it as it crosses or “transcends” the face of its star. , causing a small drop in light output.
This method of transit can also help refine the exoplanet’s orbital period around its star, but it is limited to planets that actually cross the face of their star as seen from Earth. Fortunately, HD 114082 b is such a world, which the team confirmed with NASA’s Transiting Exoplanet Survey Satellite (TESS) which hunts exoplanets.
“We already suspected a near frontal configuration of the planetary orbit from a dust ring around HD 114082 discovered several years ago,” Zakhozhay said in the statement. “Still, we felt lucky to find an observation in the TESS data with a nice transit light curve that improved our analysis.”
So far, HD 114082 b is one of only three giant planets less than 30 million years old for which astronomers have determined both masses and sizes. All of these planets seem incompatible with core accretion.
Although this is a very small dataset, the team thinks these planets are unlikely to be outliers and point to a larger trend.
“Although more such planets are needed to confirm this trend, we think theorists should start re-evaluating their calculations,” Zakhozhay said. “It’s exciting to see how our observational results feed into the theory of planet formation. They help improve our knowledge of the growth of these giant planets and tell us where the gaps in our understanding lie.”
The team discoveries were published Friday, November 25 as a letter to the editor in the journal Astronomy & Astrophysics.
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