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  In fact, the New York Times, possibly referring to a -- by then outdated -- pre-discovery estimate of its mass, reported that it "may be bigger than Jupiter."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.

Why is the Solar System like a Carousel?

...and not more like a moth-infested light bulb?

Someone who is like a brother to me asked me this question recently (well, I may have rephrased it slightly).  I thought it would be a good idea to write up my response as a blog post. 

As it turns out -- in a manner of speaking -- the planets actually resemble both.  To understand what I mean by this, let's think about the formation of a star like the Sun and its Solar System of planets.

Most stars begin as a huge cloud of gas and dust.  Due to gravity, every molecule in the cloud tugs a little on every other molecule, but on average, the tugs mostly balance out.  Except on the edge of the cloud, that is.  You're right, I never said the cloud had an edge.  But, face it, if it didn't have an edge, then this cloud we're talking about is the whole Universe, not a star; and that's an entirely different prospect.  So, this cloud has boundaries, and you will respect them.

If you were a molecule on the edge of this cloud, because all of the molecules are on one side of you, and none are on the other, you will feel a gravitational pull toward the center of the cloud.  It's just like standing on the surface of the Earth.  But, there is no "surface" on the edge of this cloud.  So, instead of feeling your weight supported by the solid surface, you begin to fall through the cloud.  If you were to dig a hole under your feet through the center of the Earth and out the other side, you could experience the same sensation as this molecule (legal disclaimer: please do not dig a hole from your backyard through the center of the Earth and then jump in; if you do, then @wwwheniheard claims no responsibility for what may, literally, befall you).  If you do that on Earth, you'll fall and fall, picking up speed until you reach the center of the Earth.  When you reach the center of the Earth, because you are now falling VERY quickly, you'll zoom right on past.  As soon as you do, however, because there is now more mass behind you than in front for you, you start slowing down.  If we assume the Earth is perfectly uniform, then you'll come to a stop just as you reach the surface at the antipode (this is an awesome word to drop into a casual conversation: Google it).  If you don't grab hold of the ledge, the next thing you'll see is the tiny mouth of your cave fading in the distance as you again fall through the Earth back to your starting point.

Of course, if you did this on Earth, most of the time, the other end of the tunnel would be under water, and the ocean would flood into the hole from the other side.  As you fell, you'd eventually crash into this massive flood, and would very quickly cease to fall, and cease to live.  Of course, even if you were lucky enough to live in a place where there is land at your antipode, then air molecules would rush in to fill the void you've created.  As you fall, you'll encounter all of these air molecules.  And each one you bumped into would slow you down just a little bit.  This is called air drag.  Skydivers are very thankful for this aspect of physics.

Now, back to the cloud of gas and dust.  If you are very lucky, though it may take a while, you will fall all the way to the other edge (oh, did I not mention we are assuming it is a spherical cloud?  Yeah, I'm a physicist, that's all we know), just as you did in the Earth example.  But, the cloud is very big and you have very many molecular friends.  You're going to run into one of them, and then another, and then another.  And, just as in the Earth case, when you reach the other side, you'll find that you can't quite make it to the edge.  So, you now are trapped inside the cloud, closer to then center than where you started.  Now, imagine this happening to EVERY molecule in the cloud, and you can see that, eventually, we'll start to have a crowd near the center.

That's when things start getting interesting....

Adventures in Kanjiland, Part 2

Well, one thing that trying to learn the Kanji has helped me with is remembering the names of the train stations.  And knowing these names reveals a bit about the history of the area I think, or at least shows how much Japan has changed in the last hundred years or so.  For example, the city nearest where I live is called Machida (町田).  It essentially means town-town.  However, that is not too unusual a name when you consider that the town grew up around a large rail station at the confluence of two major and growing rail lines.  My housemate tells me that Machida station is today among the ten most popular transfer points in the Tokyo area rail system.

I take the train to ISAS passing through Kobuchi (古淵), which means "old wasteland," on my way to Fuchinobe (淵野辺), which means "edge of the wasteland." In other words, it seems this trainline was truly a road to nowhere.  However, on the other side is Sagamihara (相模原) station, which is the namesake of the city containing all of these stations.  Its name represents the fact that this was once a massive USA Army base, after WWII.  There still is an Army base in Sagamihara, in Camp Zama.  Many years ago, large portions of the base were returned to Japan; these areas now house Fuchinobe, Kobuchi, ISAS, etc.

I've also learned some new Japanese words thanks to the Kanji!  Walking to or from ISAS, I pass a large sign at a Nissan dealership.  It reads, 中古車.  I recognized all three: 中 is "middle," 古 is "old," and 車, is "vehicle."  Hmm, middle-old vehicle... middle aged car?  Ah, "Used Car", chu-u-ko-sha!  It was a used car dealership.  Another I found nearby was 大売出.  The first was big ('dai'), the last was out ('dashi'), the middle I had to remind myself was sale ('uru').  Ah, "Big Sell Out"!  Or, rather, dai-uri-dashi, a Clearance Sale!  

Hmm, maybe the vocabulary I learn by reading billboards isn't the most useful after all....