A group of scientists led by Ukrainian astrophysicist Olga Zakhozhay, who has been working in Germany since the beginning of the full-scale war, discovered the youngest exoplanet and calculated its mass and size. Senior researcher of the Institute of Physics of the National Academy of Sciences of Ukraine Anton Senenko reported this on his Facebook page and added:
“This news should be all over the Ukrainian media, because, to be honest, such discoveries do not happen so often. All the more by domestic scientists in the conditions of a full-scale war.”
The results of the research are published in the form of a letter to the editor in the journal Astronomy & Astrophysics.
HD 114082b is 15 million years old, making this super-Jupiter the youngest exoplanet for which astronomers have been able to determine its radius and mass. Although its size corresponds to the diameter of Jupiter, its mass is eight times that of Jupiter. The combination of these quantities is difficult to agree with the generally accepted models of the formation of planets. A possible solution to this puzzle may require updating formation models to account for the planet’s unusually large solid core.
“Compared to currently accepted models, HD 114082 b is about two to three times too dense for a young gas giant with only 15 million years of age,” says Olga Zakhozhay.
The resulting mean density of that gas planet amounts to twice that of Earth – which is truly remarkable. After all, Earth is a rocky planet with an iron-nickel core, and not made of hydrogen and helium, the lightest elements in the Universe that make up Jupiter almost entirely.
“HD 114082 b is currently the youngest known gas giant planet with an established mass and radius,” Zakhozhay notes. As a result, it promises astronomers new discoveries in the case of the formation of gas giants.
“We think that giant planets can form in two possible ways,” Ralf Launhardt, Olga’s co-author, says. “Both occur inside a protoplanetary disk of gas and dust distributed around a young central star.”
The first process, known as “core accretion”, involves the accumulation of a solid core of rocky material at the first stage. Once it reaches a critical mass, its gravitational force pulls in the surrounding gas, causing it to accret hydrogen and helium in an accelerated process to form a giant planet.
The second mode, called “disk instability”, features gravitationally unstable parcels of dense gas that collapse directly to grow into a giant planet without a rocky core.
At first glance, HD 114082 b does not meet the expectations of astronomers: the combination of its mass and size is incompatible with the picture of a hot start. Instead, it seems to fit the cold start scenario better.
Olga Zakhozhay and colleagues also found that HD 114082 b orbits its Sun-like parent star for 110 days at a distance of about 0.5 AU. One astronomical unit is the average distance between the Sun and the Earth.
HD 114082 b is one of three young giant planets under 30 million years old with known masses and sizes. And all of them are probably inconsistent with the most common hot start models. Although astronomers are looking at statistics with a low number of cases – three out of three – it seems unlikely that all these planets are deviations from the accepted patterns.
“While more such planets are needed to confirm this trend, we believe that theorists should begin re-evaluating their calculations,” Zakhozhay points out. “It’s exciting how our observational results feed back into planet formation theory. They help improve our knowledge about how these giant planets grow and tell us where the gaps of our understanding lie.”