The seven rocky planets orbiting the red dwarf star TRAPPIST-1, about 40 light-years away, have remarkably similar densities. Similar properties provide clues about their formation.
TRAPPIST-1 is the largest cluster of Earth-sized planets found in a star system. Previous calculations have shown that the planets are the size and mass of the Earth and that they must be rocky or Earth – as opposed to gas dominated by Jupiter and Saturn. According to The New Paper published in the Journal of Planetary Science, it provides the most accurate density measurements ever for any group.
The most accurate scientists know the density of a planet, which can place great limits on its structure. The densities of the eight planets in our own solar system vary widely. Seven TRAPPIST-1 planets have similar densities – values not exceeding three percent.