How to Detect Things Through Lava

Question

I'm coming up with an alien species that can swim through magma.
Assuming that all necessary body parts are somehow protected from/immune to the magma, what would be feasible senses for it to use to find its way around while submersed in the molten rock? Echolocation? Smell? Electromagnetism (like that of the tiger shark (and I think) the platypus)? I'm guessing that eyesight might not be a viable option, as the liquid magma that the species would be trying to see through would still nonetheless be rock, but if versions of eyesight (such as ultraviolet vision) would be viable options, then I'd prefer to use them.

Thank you!

Answer 1

Sight based on forming images from photons would indeed be completely pointless, but basically everything else is on the table.

• Taste/smell: most magmas have a lot of dissolved volatile molecules like water, carbon dioxide, hydrogen sulfide, etc. Especially the less-viscous ones that would be easier (not easy, but easier) to swim through. Also lots of metal ions. And low diffusion rates mean that chemical trails will stick around longer.

• Hearing and echolocation: passive hearing is no problem. Magma transmits pressure waves just fine. Active sonar is more difficult, but if we handwave a creature that can live in magma in the first place, being able to efficiently couple to that medium for producing directed sound is a small extra step.

• Active electroception: easy to do, excellent for identifying the type of magma you are surrounded by via its dielectric constant and conductivity, as well as finding other organisms nearby which disrupt that signal, and possibly even communicating with them.

• Passive magnetoception. Good for navigation, possibly also for local environmental sensing via the magnetic distortion induced by nearby materials.

• Thermoception: detecting absolute temperature and thermal conductivity are both easy, and potentially useful.

• Graviception: it's hard to imagine a biological creature being sensitive enough to map masscons with gravity sensors, but detecting the direction of gravity and your relative orientation is easy.

• Absolute pressure detection. Can use similar mechanisms as hearing, but with different intent. Something like a fish's lateral line allows determining absolute depth and detecting low-frequency waves induced by other stuff moving nearby.

• And, of course, there's always touch and internal proprioception.

Answer 2

• The analogue for echolocation in earth sciences would be reflection seismology, in which a shock wave is generated and the acoustic reflections give information about the surroundings. Like echolocation, it is very coarse information, only identifying large-ish things that are nearby.
• Smell is rather implausible. The diffusion rate through lava would be low and it's unclear what compounds would survive lava temperatures long enough to even be detected.
• In terms of electromagnetism, the creature could use an analogue of ground-penetrating radar, but note that the ranges are very short ( a handful of meters under the best circumstances) and depend on both the the conductivity of the lava the creature exists in and the frequencies used.

Answer 3

The most plausible way to "sense" something in lava seems to be echolocation: sonic waves bouncing off the interfaces between the lava and the other body, possibly at frequencies outside the range of noise produced by flowing lava, just for the signal to not be drown into noise.