Astronomers have observed a unique planetary system 350 light-years away that reveals how the most common types of exoplanets—super-Earths and sub-Neptunes—are formed. A team of researchers, led by John Livingston, studied four young planets orbiting a sun-like star called V1298 Tau, finding that these worlds are actively evaporating under intense stellar radiation. The discovery offers a rare glimpse into the early stages of planet evolution, explaining why these planets dominate the galactic landscape while remaining curiously absent from our own solar system.
The V1298 Tau System: A Planetary Nursery
The V1298 Tau system is remarkable because it’s young—only 23 million years old—and its four planets orbit extremely close to their star. These worlds, discovered in 2019, have radii between five and ten times that of Earth, making them unusually large for their proximity to a star. The research team used “transit timing variations” (TTVs) to measure each planet’s mass. TTVs occur because planets tug on each other gravitationally, causing slight delays or accelerations in their orbits, which astronomers can detect when observing the planets passing in front of their star.
The Role of Stellar Radiation
The measurements confirmed that these planets have exceptionally low densities and are losing their atmospheres to space through a process called photoevaporation. This happens when extreme ultraviolet light and X-rays from the star heat the planets’ atmospheres, causing them to expand and eventually be stripped away by the stellar wind. The inner two planets are on track to become rocky super-Earths, while the outer two may evolve into mini-Neptunes, depending on how much atmosphere they retain.
“By weighing these planets for the first time, we have provided the first observational proof… They are indeed exceptionally puffy, which gives us a crucial, long-awaited benchmark for theories of planet evolution.” — Trevor David, Flatiron Institute
Why This Matters: The Missing Planets of Our Solar System
Super-Earths and sub-Neptunes are the most common type of planet discovered outside our solar system. Yet, our own planetary neighborhood lacks one of these worlds. Understanding how they form may explain why. The V1298 Tau system provides a potential answer: intense radiation whittles down larger, gas-rich planets into smaller, rocky or partially gaseous bodies. This process likely explains why many exoplanet systems, like TRAPPIST-1, are packed with similarly sized planets in close orbits.
This research is significant because it gives us a preview of how many planetary systems will eventually look. The observed planets are in the process of becoming the most common worlds in the galaxy, offering unprecedented insight into their formative years. In about 100 million years, the V1298 Tau planets will likely resemble the super-Earths and sub-Neptunes that astronomers have already detected around other stars.
