The Drunk Monk and the Seven Novitiates

Last week, NASA announced the discovery of seven(!) planets orbiting a relatively nearby (40 light years away) and very small (about the size of Jupiter) star.  The system was called TRAPPIST-1, after a Belgian telescope that first discovered the system in 2016, and that was itself named for (or, rather, acronymed to honor) the Belgian style of brewing made famous by the sect of Benedictine Monks called Trappists.  Because this is such an interesting discovery, I want to take a temporry detour form my previous post to talk about this.

Not only were seven (well, a minimum of six) planets discovered in the system, but all of them have diameters very similar to Earth's.  Furthermore, because the planets' orbits are so close together, their masses can be estimated by measuring the effect each has on the others' orbits.  The team found that the masses of these planets also were very similar to Earth.  This implies they have similar densities, which means they are likely made up of roughly the same bulk materials (i.e., are probably rocky bodies with dense inner cores and probably a small but not negligible amount of water).  That is, they are probably not big gas giants like Jupiter, they are bodies that likely have solid surfaces.

However, the method the team used to measure the mass is prone to large uncertainties.  A similar technique was used to infer the existence of Pluto before it was discovered, and to estimate its mass after it was discovered.  Most of the headlines surrounding Clyde Tombaugh's discovery of Pluto in 1931 report the discovery of a planet "bigger than Earth."  In fact, the New York Times, possibly referring to a -- by then outdated -- pre-discovery estimate of its mass, reported that it "may be bigger than Jupiter."  Over time, the measurements improved, and the likely mass of Pluto became smaller and smaller.  As the New Horizons spacecraft sped toward the planet in the early 21st Century, one astronomer even went so far as to jokingly suggest that the trend indicated that Pluto might entirely disappear by the time the spacecraft arrived!  In the case of the Trappist-1 planets, these uncertainties mean that three of the planets could actually be smaller than Mars; two of the planets could actually be twice as massive as the Earth.  Such large variations in basic properties will have tremendous effects on the types of planets these truly are, and how likely they might be able to support life.

Part of the reason for the uncertainty in the masses of these planets is the inability to continuously monitor them.  They are very faint, and only a handful of powerful telescopes can detect them.  There is much competition to obtain time on these telescopes.  So, the team had to make do with short observations taken a few days at a time, spread over many months, and then piece those observations together to find any repetitions of changes in the observed stellar brightness that would indicate planetary motion.  When it comes to searching for planets using transits, it is best to just star continuously at the stars, and wait for the characteristic dimming.  Fortunately, this system lies in a part of the sky that can (now) be observed using the Kepler Space telescope, whose job is specifically to do just that.  In a few months, we might have much more and much better information about these planets!

Perhaps the most interesting aspect of the discovery so far is that the planets are observed to be almost in resonance.  I'll describe what that means in more detail another time; but in brief, it means that the orbital periods are integer multiples of each other.  In this case, the 1st planet orbits five times for every three of the 2nd planet; eight times for every three of the 3rd; twelve times for every three of the 4th; and eighteen times for every three of the 5th.  In our Solar System, three of the four largest moons of Jupiter also are in resonance with each other, but in a much simpler 1:2:4 ratio (for every orbit of Ganymede, Europa orbits twice, and Io four times).  The existence of resonance tells us two things.  First, the planets likely migrated through their star system to arrive at their current locations; resonances are particularly harmful places to try to build a planet.  Second, these planets might be interacting with each other and their star to heat each others' interiors through tidal interactions.  This process makes Io the most volcanically active planet in the Solar System, and may be responsible for the existence of a vast reservoirs of liquid water beneath the surface of Europa and deep in the core of Ganymede.  In fact, a rough calculation suggests that each of these bodies experiences tidal heating that is far larger than what Io experiences.  Even if these planets cannot support atmospheres, there is a high probability that the subsurfaces of these bodies can support life.  Or, it could be that each of these planets is turning itself inside out, like that of Kal-El's Krypton.

The team that discovered these planets have mentioned that they'd like to see them named for Belgian Trappist Style beers.  Since it is unlikely we'll be able to narrow down a list to seven Trappist Beers, I propose instead to name the planets for their ultimate eponymous influence, the Trappist Monks themselves and their practices.  The Trappists take three vows, and practice several disciplines.  So, the planets would be named: Stability, Fidelity, Obedience, Tranquility, Dexterity, Vegetarian, and (rarely seen) Sobriety.