Recent research has shed light on how super-Earths and sub-Neptunes form. This discovery comes from studying four young planets around a star called V1298 Tau, located about 350 light-years away. These planets are massive, with sizes ranging from five to ten times that of Earth.
The V1298 Tau system has a relatively young star, about 23 million years old, and was first discovered by astronomers using data from the Kepler space telescope in 2019. A team led by John Livingston from the Astrobiology Center in Tokyo later studied the planets’ characteristics using a method called “transit timing variations.” This method enables scientists to figure out the mass of the planets based on how their gravitational pull affects each other during transits—when they pass in front of their star.
Interestingly, super-Earths are rocky planets larger than our Earth, while sub-Neptunes are smaller, partially gaseous worlds. These types of planets are the most common discoveries among exoplanets. Nonetheless, our solar system lacks both, which poses a mystery for astronomers. Why are these common planets missing here?
When the V1298 Tau planets transit, they block light from their star, which helps determine their sizes. Their close orbits lead to gravitational interactions, causing variations in timing. This helps researchers calculate each planet’s mass and density, revealing that they have low densities.
Notably, the atmospheres of these planets are evaporating into space due to extreme heat from radiation emitted by their star. Trevor David from UCLA noted that this is the first time scientists have measured the low densities of these planets, affirming theories about their evolution. The intense radiation causes the atmospheres to expand and, ultimately, be stripped away, a process called photoevaporation.
Predictions suggest this atmospheric loss will continue for another 100 million years. The inner planets may completely lose their atmospheres and evolve into rocky super-Earths. The outer planets, while currently larger, also risk losing their atmospheres but might develop into mini-Neptunes.
These insights reveal a potential future for planetary systems. “What’s exciting is that we’re seeing a preview of a typical planetary system,” said Livingston. The findings highlight the evolution of planetary types that are most common in our galaxy, providing a clearer understanding of how such planets develop over time.
The study was published in the journal Nature on January 7.
