Key takeaways
- Planets larger than Earth but smaller than Neptune are the most common kind in the galaxy, but because our solar system lacks such a planet, scientists don't know much about how they form.
- Astronomers have now witnessed four baby planets in the V1298 Tau system in the process of becoming super-Earths and sub-Neptunes.
- Despite being 5 to 10 times Earth's radius, the planets had masses only 5 to 15 times Earth's. This means they are very low-density, comparable to Styrofoam, whereas the Earth has the density of rock.
Thanks to the discovery of thousands of exoplanets to date, we know that planets bigger than Earth but smaller than Neptune orbit most stars. Oddly, our sun lacks such a planet. That's been a source of frustration for planetary scientists, who can't study them in as much detail as they'd like, leaving one big question: How did these planets form?
Now we know the answer.
An international team of astrophysicists from UCLA and elsewhere has witnessed four baby planets in the V1298 Tau system in the process of becoming super-Earths and sub-Neptunes. The findings are published in the journal Nature.
"I'm reminded of the famous 'Lucy' fossil, one of our hominid ancestors that lived 3 million years ago and was one of the 'missing links' between apes and humans," said UCLA professor of physics and astronomy and second author Erik Petigura. "V1298 Tau is a critical link between the star- and planet-forming nebulae we see all over the sky, and the mature planetary systems that we have now discovered by the thousands."
