NASA has been studying a red dwarf star called TRAPPIST-1, home to the largest group of Earth-sized planets ever found in a single solar system. TRAPPIST-1 is about 40 light-years away, and the seven rocky planets are an excellent example of the variety of planetary systems in the universe. A new study was published this week showing that all of the planets in the stellar system have a remarkably similar density.
NASA scientists believe that the similar density could mean they all contain roughly the same ratio of materials, including iron, oxygen, magnesium, and silicon. NASA does note that if that theory is correct, the ratios would be notably different than Earth’s as TRAPPIST-1 planets are approximately eight percent less dense than they would be if they had the same makeup as our planet.
The discovery has led to a few hypotheses on what mixture of ingredients could make up the planets. Some planets orbiting TRAPPIST-1 have been known about since 2016 when discovered by the NASA Transiting Planets and Planetesimals Small Telescope or TRAPPIST. NASA performed subsequent observations using the retired Spitzer Space Telescope and ground-based telescopes.
Spitzer observed the system for over 1000 hours before its decommissioning in January 2020. NASA has used most tools at its disposal to study the planetary system, including Hubble and Kepler. All the scientific scrutiny led NASA to believe that seven TRAPPIST-1 planets have density values that differ by no more than three percent.
The difference between those planets and Earth is about eight percent, said to be significant on a planetary scale. TRAPPIST-1 planets could have lower iron densities, with the study speculating a density of around 21 percent compared to 32 percent on Earth. The study also theorizes that the planets may not have solid iron cores. NASA admits the answer could be a combination of both scenarios, including some oxidized iron.