Scientists have finally worked out where the common planets actually come from

Scientists have finally worked out where the most common kinds of planets come from.

In recent years, the discovery of thousands of exoplanets – or worlds around other stars – has shown us that most of them are bigger than Earth but smaller than Neptune. That is surprising because our solar system doesn’t have one of its own, meaning that the planets are both incredibly common and very difficult to study.

That has made their origin somewhat mysterious. Until now, researchers have struggled to understand where these planets actually come from.

Now, however, researchers have watched a set of four baby worlds as they grow into exactly these sorts of planets. They hope that could allow us to better understand these common but mysterious worlds.

“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 Erik Petigura, who worked on the research.

“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.”

Planets are formed when clouds of gas and dust in space are squashed together by gravity, creating a young star and a swirl of material around it that is known as a protoplanetary disk. Planets then form out of that material, through a messy process that can leave them growing or shrinking when they are young.

“What’s so exciting is that we’re seeing a preview of what will become a very normal planetary system,” said John Livingston, the study’s lead author from the Astrobiology Center in Tokyo, Japan. “The four planets we studied will likely contract into ‘super-Earths’ and ‘sub-Neptunes’—the most common types of planets in our galaxy, but we’ve never had such a clear picture of them in their formative years.”

The work is described in a new paper, ‘A young progenitor for the most common planetary systems in the Galaxy’, published in the journal Nature.