An international team of astronomers reported this week that the seven rocky planets of the nearby TRAPPIST-1 system had low-density compositions and possibly shockingly similar.
New, more accurate mass estimates of these rocky, low-mass planets orbiting the cold red dwarf star TRAPPIST-1 show that this strange solar system is radically different from our group.
“These planets could have accumulated directly from the protoplanetary disk around a star cooler than the sun,” said Eric Asfaug, a planetary geophysicist at the University of Arizona who was not part of the study.
The international team of researchers used 1,000 hours of observation time on NASA’s now-turned-off Spitzer Space Telescope to make their observations. Their findings, she reported on The Journal of Planetary Sciences, He showed that this strange solar system – about 40 light-years away in the constellation Aquarius – formed in completely different conditions than our own solar system.
If these planets had merged directly from their star’s protoplanetary disk, rather than a more violent and random recurring accretion process, Asfog says he wouldn’t be surprised that they ended up with a lower density.
That’s because the kind of gigantic collision buildup that we think made Earth, Venus, Mars, Mercury and the Moon a wasted process and a portion of the low-density material was discarded in each collision (from a few percent to tens of percent), Asfog says.
“The TRAPPIST-1 system may in this sense resemble the ancestral bodies from which Earth and Venus were ultimately built, given that they are less dense because they have never experienced these gigantic impacts,” said Asfog.
Even if the individual terrestrial planets from TRAPPIST-1 and the Solar System look very similar in terms of mass and size, the entire system architecture is completely different, Simon Grimm, one of the paper’s co-authors and an astrophysicist at the University of Bern, tells me. Estimates of the new mass indicate that the densities of all seven planets are much more similar than we previously thought, he says.
As for their actual books?
The fact that these planets are less dense than the terrestrial planets in our solar system suggests a different composition to be sure, Asfog says. Whether this is due to a lack of iron available to condense up to the core, or more water mixed into the shell and mantle, he says.
NASA says the TRAPPIST planets could have a composition similar to that of Earth – and made up of the same proportions of iron, oxygen, magnesium and silicon found on our planet. The fundamental difference appears to be that the TRAPPIST planets simply lack Earth’s abundance of iron. Or, perhaps the iron in TRAPPIST planets is saturated with oxygen levels higher than Earth’s, resulting in iron oxide (or rust). NASA says this hypothetical supplemental oxygen will also reduce the planets’ density.
However, the team reports that the three deeper planets of the TRAPPIST system are severely lacking water. Martin Torbett, an astrophysicist at the University of Geneva and co-author of the study, told me that the waters were unlikely to harbor TRAPPIST-1b, TRAPPIST-1c and TRAPPIST-1d (at any stage) at all.
“To those three [inner] Planets, so the habitability potential is not very good, ”Turbett said.
But Turbett says that although the three inner planets may be biological wastelands, three of the system’s four outer planets still offer some hope for habitability.
NASA’s upcoming James Webb Space Telescope (JWST) will likely be able to monitor these planets’ atmospheres and make major advances in determining their potential habitability, says Turbet.