Toffee planets: hard sci-fi with a crispy outer shell and gooey center
February 13, 2020 11:01 AM   Subscribe

The Geology of Toffee Planets (PDF): A world with a lithosphere too thin to subduct (or with no lithosphere at all) could not support plate tectonics, with implications for heat loss, style of volcanism, atmospheric composition, and the frequency with which new reactive minerals reach the surface. Bodies with masses sufficient to yield thin lithospheres, then, might host tectonic and volcanic features similar to those that characterize the Venus lowlands [21] or Archean Earth [22], with high-standing terrain the exception, not the rule. This inference can be tested by efforts to search for exoplanet topography [23]. “Toffee Planets” Hint at Earth’s Cosmic Rarity -- Exoplanets with stretchy, flowing rock may be bereft of plate tectonics—and of complex life (Scientific American)
posted by filthy light thief (9 comments total) 12 users marked this as a favorite
 
Note: "hard sci-fi" is my editoralizing on the topic, of which I am not anywhere near expert enough to editorialize. I don't mean to diminish the research in this area. On re-reading the title, I realize it might be dismissive, and that wasn't my intent.
posted by filthy light thief at 11:04 AM on February 13


Just think of how many fossils you wouldn't ever be able to find.
posted by Made of Star Stuff at 11:31 AM on February 13 [1 favorite]


IDK, I only read the puff piece and not the PDF: it seems they are talking about the kind of planets that can be directly imaged from Earth, which are larger than Earth. There's a scaling "law" which, IIRC, says that for every object in the Universe of size X, there are 10 objects that are X/3 in size. That is to say, more like Earth than these "super Earths" being talked about. "Super Earths" might not be conducive to the kind of geochemistry that leads to life. OK! But that's not necessarily what we care about! IOW, this is no evidence of Earth's "cosmic rarity" at all!
posted by Aardvark Cheeselog at 11:32 AM on February 13 [4 favorites]


While this sort of thing is very relevant to my scientific interests (my dissertation was on the global resurfacing of Venus), reading just the title here made me think it was going to be about a particular kind of science fiction: it *looks* hard (rigid crust), but if you poke it even a little, you find that the crust is thin and the interior is much softer.
posted by Four Ds at 12:36 PM on February 13 [1 favorite]


Yeah, I instantly regretted the framing from the title.


IOW, this is no evidence of Earth's "cosmic rarity" at all!

Interesting, thanks! I was looking for peer-review of the research article, but finding none, I figured the next best thing would be to link to all the articles cited in my pull-quote in the OP, but your insight is even better. I couldn't find the law-type thing you mentioned, but I found Ask Ethan: How Many Planets Did NASA’s Kepler Miss? (Medium article), where Ethan Siegel, a NASA columnist, notes that "the vast majority of [planets] discovered are larger than Earth and closer than Earth to their parent star, which might simply be because those are the easiest ones to find."
posted by filthy light thief at 1:26 PM on February 13 [1 favorite]


Neat!

There are some serious selection effects to be aware of (and help you not despair):

(1) Orbital period: all of the planets in the study are much close to their stars than Mercury, with orbital periods of ~2-13 days, because those are the planets that are both easiest to discover (using transits from Kepler/K2/TESS, which have strong biases toward shorter periods because their time series are only so long), and also easiest to follow up on, since you need multiple orbits to measure the mass. So perhaps it's as simple as being close to a star = lots more radiation = lithosphere takes longer to cool = no crunchy chocolate shell for alien bugs to grow on.

(2) Size: although we have detected a handful of exoplanets smaller than Earth, they're much harder, so our sample is very incomplete. There seem to be more things smaller than Earth than areEarth sized, insofar as we can correct for detection biases (which is tough).

In conclusion: the current smallest exoplanets may be toffee icebergs floating on top a vast sea of smaller planets, about which we know very, very little (sample size: our solar system).

(Too bad the diamond planet is probably not a thing, or you could have a very seasonally appropriate post.)
posted by puffyn at 1:28 PM on February 13 [3 favorites]


Are there chocolate planets?
posted by Cardinal Fang at 11:55 PM on February 13


How did you find this document? I can't find other submissions to this conference.
posted by neuron at 7:26 AM on February 14


This is apparently from last year's LPSC meeting, all of the abstracts for which are here.

It doesn't appear that the authors have published a paper yet, from a search of ADS.
posted by puffyn at 7:33 AM on February 14 [1 favorite]


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