Seven distant, rocky planets may be made of the same material

The densities of seven potentially rocky planets orbiting a star 40 light-years away are surprisingly similar, according to a new study.

Why it matters: The finding is unusual because the planets in our solar system have different densities. Scientists can use the new data to home in on whether these planets, that appear similar in some ways to our own but form differently, might be suitable for life.

What they found: Seven planets orbiting the red dwarf star TRAPPIST-1 appear to all have similar densities, according to a new study in the Planetary Science Journal.

• That measurement suggests the planets have similar ratios of iron, magnesium, oxygen, silicon and other materials.
• These planets are about 8% less dense than they would be if they had compositions like Earth's, according to NASA.
• "The TRAPPIST-1 system is fascinating because around this one star we can learn about the diversity of rocky planets within a single system," Caroline Dorn, an author of the paper, said in a statement. "And we can actually learn more about a planet by studying its neighbors as well, so this system is perfect for that."

Yes, but: These planets appear to be rocky instead of enveloped in a thick, gaseous atmosphere, but not much is known about their potential habitability.

• All seven of the TRAPPIST-1 planets orbits are within what would be Mercury's orbit around our Sun.
• While at least three of the planets orbit in an area where water could exist on their surfaces, it's not clear how conducive a red dwarf star would be to hosting life, as they are thought to be more volatile stars than our relatively mild Sun.