New measurements reveal the true nature of the young 'hot Neptune' HIP 67522 b

Star system: HIP 67522 | Distance from the Sun: 417 light years

Scientists have conducted a detailed follow-up study of the young planet HIP 67522 b to pin down its exact size and weight. Located in a star system only 17 million years old—a mere blink of an eye compared to our 4.5-billion-year-old solar system—this planet is roughly the size of Neptune but significantly less dense.

 By measuring how the planet's gravity tugs on its parent star, researchers determined it has a much lower mass than expected for its size. This suggests the planet is surrounded by a massive, bloated atmosphere of hydrogen and helium that hasn't yet cooled or shrunk, offering a unique 'time machine' view into how giant planets like Uranus or Neptune might have looked shortly after their birth.

Scientific study

A precise mass and radius for the young Neptune HIP 67522 b (external link)