Density, not radius, separates rocky and water-rich small planets orbiting M dwarf stars.

Gaining a clearer picture of exoplanets

31 May 2023

Distinguishing planets based on their density rather than size provides a better way of classifying them.

Small, cool stars known as red dwarfs often have planets orbiting around them, some of which may be habitable. These planets fall into two categories, based on whether they have a small or large radius.

Now, a researcher from University of La Laguna and a collaborator have shown that classifying these planets based on their density provides a clearer picture.

The pair analysed 34 planets orbiting red dwarfs based on density and found that they could be classified into three types: rocky, water rich and gas rich.

They proposed that rocky planets could be birthed within the snow line—where it is cold enough for volatile compounds to form grains of ice. In contrast, water-rich worlds form outside it but then migrate to within it.

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References

1. Science 377, 1211–1214 (2022). doi: 10.1126/science.abl7164