3318: Earth Sized Planets

Earth Sized Planets

|< < Prev #3318 (October 30, 2026)

Title text: It probably has an icy mantle over the real silicate geology, but I'm hoping something weird happened to burn off most of the water like with Io.

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Explanation

This is one of 60 incomplete explanations: This page was created recently on a ROCKY, EARTH-SIZED PLANET. Don't remove this notice too soon. You can help by editing the explanation!

Cueball and Ponytail are discussing the possibility of the new Vera C. Rubin Observatory discovering an Earth-sized object in the far reaches of the Solar System, as one of several so far unsupported hypothetical candidates as the next Planet Nine, or Ten, that might be on the cusp of being discovered. It would have to be very distant, however, since gravitational effects of an Earth-sized object in the vicinity of Pluto should already have been detected.

Cueball is intrigued by Ponytail's initial imagery, of a planet similar to Earth but with internal heat to make up for the limited heat it would be able to receive from the Sun. In his mind, this leads straight to the exciting possibility that it might even harbor life. Ponytail, being a geologist, has another objective in mind. She is more excited by the idea that it might have plate tectonics, which none of the other terrestrial planets have to any significant degree (excluding, perhaps, some of the moons of the gas giants, especially those where there is a possibly mobile ice surface rather than rocky plates such as Earth has).

The title text continues with the geologist's bias towards being interested in rock-based situations (i.e. silicates) by dismissing the presence of water-ice (a possible hint of the presence of liquid water, an assumed prerequisite for life). Though they expect there to be a layer of ice, they would rather that this would somehow go away in order that the 'real surface' could be studied properly. Ironically, based on our current understanding of plate tectonics, the lack of water would prevent "normal" (i.e. earth-like) plate tectonics. Water is needed to lubricate subduction zones, without it oceanic plates could not slide under the continental plates.

This comic may have been inspired by the actual discovery of an "enormous dwarf planet" by the VCRO, although this is still far from being an Earth-sized planet.

Transcript

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[Cueball and Ponytail are walking side by side.]

Ponytail: If there's an earth-sized object in the outer solar system, the Rubin Observatory should find it soon.

[Cueball and Ponytail continue to walk, Ponytail raises her left hand a bit.]

Ponytail: If it's Earth-sized, it might have a rocky surface and internal heat.

[They stop, and Ponytail turns to face Cueball, raising her arms above her head.]

Ponytail: If it has a rocky surface and internal heat, it might have-

Cueball: Life?

Ponytail: Plate tectonics!

[They continue walking. Ponytail's hands are out in front of her.]

Cueball: You geologists have weird priorities.

Ponytail: Earth just can't be the only one!

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Discussion

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F1RST P0ST. sorry, CANT RESIST! 73.132.167.116 21:23, 30 October 2026 (UTC)

anyway, I THINK that the person would prefer life forms? 73.132.167.116 21:24, 30 October 2026 (UTC)

Which "the person"? Cueball might. Ponytail clearly doesn't. That's the point. (PS., sure you can resist. Whether or not you actually will do.) 2.98.68.172 21:29, 30 October 2026 (UTC)

There is ample evidence that intelligent life doesn't exist in the observable universe, so I'd settle for plate tectonics anytime. Wait, is subduction a form of negging ? 2001:861:3F07:A020:B7EE:F04E:FD87:56BE 22:05, 30 October 2026 (UTC)

"ample evidence"^{[actual citation needed]} 2.98.68.172 23:35, 30 October 2026 (UTC)

We haven't found any on the third planet from our own sun. 2603:8081:9700:1224:0:0:0:3 01:08, 31 October 2026 (UTC)

That may or may not be true but, if it is, it doesn't prove that it doesn't exist elsewhere. In fact, might prove that it does, given the possibility it would only make itself known to us if it was not intelligent enough to keep us at arms length or further. (But the completely serious point is that absence of evidence is not the same as evidence of absence, ample or otherwise.) 2.98.68.172 02:28, 31 October 2026 (UTC)

I was under the impression that water or a similar solvent/lubricant is actually required for plate earth style tectonics? Otherwise the plates can't slide freely. 2600:100E:B0A6:584F:0:52:1CE9:9401 23:50, 30 October 2026 (UTC) DaveK

It's very much a case of "as far as we know", as counter-examples/supporting examples of actual tectonics aren't really there. What causes non-tectonic bodies (that might have been) to not be tectonic therefore is a less nice comparison to work out what does facilitate it, as the nearest non-working equivalent will still have active vulcanism, just not any tectonic action. Cryovolcanoes aside, you're restricted to the likes of Io for that, seemingly without water anywhere like the amount that would replicate Earth (but smaller), but how much this really leads to "no water, therefore no tectonics" is... unknown at present.

Also, the presence or absence of ice above a surface may not necessarily be significant marker of how much lubricating-water there is. Sub ice-sheet liquid oceans might be the closest we have with our surface-oceans (and minimal, only polar, ice-sheets), but the ice-topped "moons with oceans" don't obviously have tectonics, despite the same potential for some of that water to leach down into the subduction zones that we are still far from knowing whether they have.

IOW, maybe it is required. Maybe it's just an aid that prevents tectonics from seizing up quite so easily as it might otherwise. And we have so much more data about Earth to try to identify layers (and what is in those layers), plus current activity. I think we've gotten seismometers onto three non-Earth bodies, plus tried to interpolate subsurface conditions by the changes in magnetic flux/etc, around a few more (mostly moons, within the range of "hard, rocky bodies"). The relative understanding from such things just can't be considered comparable.

I'm sure there's a lot more we'll learn, as time gone by, of course. Maybe that will confirm that water is (semi?)uniquely capable of sustaining tectonics, but we can't be so clear cut about that right now. "Best guesses" might suggest so, of course. 2.98.68.172 00:50, 31 October 2026 (UTC)
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