A Gas Giant Exoplanet Has Been Discovered With Twice The Density of Earth - ScienceAlert

After taking measurements of a very young Jupiter-sized exoplanet named HD-114082b, scientists have found that its properties don't neatly match either of the two popular models of gas giant planet formation.

This young exoplanet's size and mass mean that it's highly unlikely to be a super large rocky planet; the upper limit for those is around 3 Earth radii and 25 Earth masses.

In a cold start, the exoplanet is thought to form, pebble by pebble, from debris in the disk orbiting the star.

The more mass it gains, the faster it grows, until it's massive enough to trigger runaway accretion of hydrogen and helium, the lightest elements in the Universe, resulting in a massive gaseous envelope around a rocky core.

A hot start is also known as disk instability, and it's thought to occur when a swirling region of instability in the disk directly collapses in on itself under gravity.

The properties of HD-114082b don't fit the hot start model, the researchers say; its size and mass are more consistent with core accretion.

"All we can say is that we still don't understand the formation of giant planets very well.".

The exoplanet is one of three we know of that are younger than 30 million years, for which astronomers have obtained radius and mass measurements.