Astronomy Fluffy planets provide new clues to planet formation
An international research team has "weighed" four young planets. According to the scientists, the giant celestial bodies are surprisingly light.
07.01.2026, 17:00
SDA
Their density is among the lowest ever measured, as the Geneva-based research team reported on Wednesday in the journal Nature. According to the researchers, the results help to understand how planets form.
The four planets orbit the 10 to 30 million-year-old star V1298 Tau in the constellation Taurus. This makes the planetary system extremely young in cosmic terms. By comparison, our solar system is around 150 to 460 times older, with an age of 4.6 billion years. If the solar system were a human 46 years old, then V1298 Tau would be around one to four months old.
"Fluffy" planets
Planets cannot be weighed directly, of course. Instead, researchers determine their mass indirectly by measuring the effect a planet has on its surroundings. For the new study, the researchers measured how strongly the planets attract each other as they orbit their star, thereby minimally delaying or accelerating their passages in front of the star. From these small time shifts, they calculated how heavy the planets are.
According to this, they are around 4.7 to 15.3 times heavier than the Earth. And this despite the fact that they are significantly larger: There would be room for around 130 Earths in the smallest and over 1000 Earths in the largest of the planets studied. In the study, the researchers describe the planets as "fluffy".
Planets will shrink
The results support a certain theory of planet formation: the low mass and density indicate a so-called "boil-off" scenario. In this scenario, some of the young planets lost their bloated atmosphere after the rapid disappearance of the gas and dust disk, which led to rapid cooling and low density.
The researchers assume that the planets will not retain their current shape. They will cool and contract over billions of years.
The Geneva Astronomy Observatory was involved in the study from Switzerland. The lead author of the study is John Livingston from the National Astronomy Observatory of Japan.
