Four planets orbiting a newly born star in our galaxy are so light that they have the density of polystyrene, and could provide a key missing link in helping us understand how the most common planetary systems form.
Solar system is unusual when compared with most other planetary systems in the Milky Way, which typically contain planets larger than Earth but smaller than Neptune. Astronomers have found hundreds of planetary systems like these, but almost all of them are formed around stars that are billions of years old, making it difficult to explain how they take shape.
Now, a team led by John Livingston at the Astrobiology Center in Tokyo, Japan and Erik Petigura at the University of California, Los Angeles has identified four tightly clustered planets that appear to have formed recently, given that they orbit a young, 20-million-year-old star called V1298 Tau.
“We are seeing a young version of a type of planetary system we see all over the galaxy,” says Petigura.
V1298 Tau and its four planets were first discovered in 2017, but little was known about the planets themselves. The researchers used telescopes in space and on Earth to observe them for five years, looking for subtle variations in the time it took for each planet to complete an orbit and pass in front of the star due to the gravitational forces of attraction among the four worlds. By measuring these small differences, they could more accurately calculate each planet’s radius and mass.
