There are Seven Rocky Planets in the TRAPPIST-1 System and They’re Surprisingly Similar

The TRAPPIST-1 system has long be studied by exoplanet hunters due to its unique quantity of planets that happen to also be Earth sized. In a recent paper, a team of scientists led by Erik Agol at the University of Washington, dove into more detail on the density of the seven known planets in the system, and, surprisingly, found that they were all very similar.

All seven planets were all found to be around 8% less dense than the Earth. Many planets have been found that were of similar density.  But there has never been a system found with the same consistency of density of the TRAPPIST-1 system.  The paper’s authors offer up three different explanations for why this might be the case.

First, there could be slightly less iron in them compared to the Earth.  Since most of the Earth’s iron is found in its core, this would imply that the core of these TRAPPIST worlds would have a smaller core than that of Earth.

Second, the planets could be completely covered in rust (iron-oxide), much as Mars is.  Unlike on Mars, this rust could go all the way to its core, meaning that the iron inside the core of the seven planets could actually be completely made out of rust – a bit of a strange thought.

But even more intriguing than the idea of a planet with a rusty core is the basis of the third hypothesis – a large percentage of the mass of the planets could be accounted for by water.  The three inner stars in the system are too close to the star at the system’s heart to hold on to any liquid water.  However, much like Venus, if the planets had a heavy atmosphere it is possible they could maintain water-heavy clouds.

MORE of the story and 2 more associated images plus another VIDEO / click image