RIP Theia, you crashed with Earth to create the Moon (maybe)
February 6, 2016 11:01 AM   Subscribe

 
Just a heads up, next month we're probably safe this time.
posted by sammyo at 11:10 AM on February 6, 2016 [1 favorite]


One thing I miss about college is journal access through the university library.
posted by double block and bleed at 1:02 PM on February 6, 2016


I find this super exciting, not least because of the science fight that might occur due to the difference in findings around the isotopes by the two teams (science fights being great for producing lots of data and research), but because I would consider Earth's formation and early development - its planetary evolution - the big question of geology* due to how so many of the other big questions naturally follow:

Why is Earth the only planet dominated by plate tectonics? What are the full relationships between core dynamics, geomagnetism, interior and surface composition of all layers, including convection, heat/cooling processes (how did the earth cool itself prior to plate tectonics?) and radiogenic element abundance? Behavior of all the above? Water? Full understanding of: early crust formation; hotspot sourcing (shallow or deep?); large igneous provinces/flood basalts; polar wander; paleomagnetism (reversals and core dynamics - are they related? why do superchrons - long periods where the polarity does not change, like the Cretaceous long normal - occur?); earthquakes and volcanic prediction; understanding fault formation/activation; and layer boundary relationships and behavior. Then there's allllll the questions in plate tectonics (so many!): crust stratification/ductility/strength, plate boundary relationships, mountain building process questions, plate movement questions (like mantle drag); dynamic topography; and the interplay of climate and tectonics. . . and possibly my favorite of all the questions, which is why and how events occur contrary to or outside of Earth's many cyclical processes (as well as questions around many of those cycles themselves - the earth is really wonderfully episodic). So many questions that a better understanding of how the planet evolved will contribute to in some real ways. (And working on these questions will also contribute to planetary evolution understanding, of course.) It's exciting to see some new ideas and data inserted into the flow. And of course, more answers will lead to more questions, just tremendous fun all the way around.

Of course, understanding how and what occurred in the early solar system does have different meaning for other people.

*Not leaving out other big questions which involve geology like life and climate change - I just consider those questions big questions in science overall. Questions surrounding life, and life on other planets, could also be helped tremendously by understanding planetary evolution. And planetary evolution is helped by astrophysics and chemistry. . . really, everything is related.
posted by barchan at 1:13 PM on February 6, 2016 [24 favorites]


This is super interesting, but I keep getting distracted by what a dumb name Theia is. Too many vowels.
posted by Pater Aletheias at 1:24 PM on February 6, 2016 [8 favorites]


I've always thought that the Giant Impact Hypothesis was one of the wildest generally-accepted hypotheses in all of science. You're telling me that a Mars-sized planet hit Earth, liquefied
it, and splashed out to make the Moon? And that's why our Moon is so huge? And that therefore the Earth as we know it contains significant amounts of another planet, all mixed in from the collision? Not what I would have guessed.
posted by Anticipation Of A New Lover's Arrival, The at 1:28 PM on February 6, 2016


... what a dumb name Theia is. Too many vowels.
posted by Pater Aletheias

βλέπω τι κάνατε εκεί.
posted by Greg_Ace at 1:31 PM on February 6, 2016 [15 favorites]


Not what I would have guessed.

Sir George Darwin, son of Charles Darwin, was an English astronomer who championed the theory that the Moon was once part of the Earth, until it was pulled free to form a satellite (Google books preview of a Boys Life article from 1951 -- small print, but you can zoom in for a better read).
posted by filthy light thief at 1:42 PM on February 6, 2016 [1 favorite]


MetaFilter: βλέπω τι κάνατε εκεί.
posted by benito.strauss at 2:09 PM on February 6, 2016 [1 favorite]


This is super interesting, but I keep getting distracted by what a dumb name Theia is. Too many vowels.
posted by Pater Aletheias

Don't let the people here in Aiea hear you say that. ALL vowels, baby.....ALL vowels.
posted by KillaSeal at 8:55 PM on February 6, 2016


So where did the rest of Theia end up? Earth/Moon just suck the debris back by gravity? Or are there asteroids that we think were part of Theia?

Super interesting, thanks for posting!
posted by kisch mokusch at 11:52 PM on February 6, 2016


So where did the rest of Theia end up? Earth/Moon just suck the debris back by gravity? Or are there asteroids that we think were part of Theia?

Gravity would imply most of it landed here, but there are asteroids in near-Earth orbits (the Apollos, Atens and Amors asteroids) It is likely that if the Theia Impactor Hypothesis is true, that some if not most of those are leftover from the impact -- ones with perihelion or aphelion close to exactly 1AU would be the most likely.

The theory that Theia was originally at one of the Earth's trojan points (L4 or L5) is interesting, because we know of one object that is, 2010TK7. It has a diameter of about 300m. The implication is if something could pull the much more massive Theia out of L4/L5 and into an Earth intersecting orbit, something could pull that out, and a 300m asteroid would make one hell of a hole. Thankfully, 2010TK7 inclination (20&deg*) means it's very unlikely it would hit the Earth. But there may be other objects we haven't spotted yet -- we didn't spot this one until 2010.


* From the point of view of the sun, 2010TK7 is on an orbit similar to Earth's, but inclined at 20° from the ecliptic and precessed forward to the L4 point. From the point of view of the Earth, 2010TK7 appears to orbit the L4 point, which moves along the Earth's orbit with the Earth. You see similar oddities with orbits around the Earth -- they orbit the Earth in simple ellipses, but when you take into account the Earth's rotation, the ground track of the satellite can do some weird things -- including geosynchronous orbits, where the ground track hardly moves at all.
posted by eriko at 6:02 AM on February 7, 2016 [4 favorites]


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