NASA’s InSight detects Phobos using its seismometer during solar eclipses | Hacker News Reader

NASA’s InSight detects Phobos using its seismometer during solar eclipses

ethz.ch

59 pointssohkamyung15 comments

Very neat article. Nasa and ETH Zurich noticed the Martian moon Phobos during the eclipse using a seismometer. The effect is tiny, but their hypothesis is that this is caused by the top level of ground rapidly cooling. The effect can be used to determine the material of the ground. Separately, this can help determine Phobos' orbit more accurately.

> “This tilt is incredibly small,” Stähler notes. “Imagine a 5- franc coin; now, push two silver atoms under one edge. That’s the incline we’re talking about: 10-8.” As slight as this effect was, it was still unmistakable.

That is incredible sensitivity. How does one calibrate something, or also not suspect the instrument is affected by other environmental variables?

Considering the Moon could have a similar (but stronger due to totality) effect on Earth during a Solar eclipse, could the Moon cause an earthquake?

This seems to be caused by heat, not the gravity. The article includes a story about a lamp being left on in a mine that caused enough thermal expansion to be measured by a seismometer.

Presumably the solar eclipse could be measured as well.

I did mean the heat, not gravity. A Solar eclipse on Earth blocks all direct sunlight for about 10 minutes. My question is would that be enough to cause an earthquake, by suddenly cooling an area of the planet.

I also realise the night blocks sunlight for way longer, but maybe this is different because the effect is spread out. During eclipse we have the planet all around the area of eclipse heated up and a comparatively small area not being heated in the middle.

I suspect, without having any real clue, that you’d see greater localized extremes in temperature with a pop—up thunderstorm.

I’d have a hard time believing earthquakes could result from that (although the science & engineering in this article are enough to make me believe just about anything is possible).

Do lightning strikes/thunderclaps register on seismometers? Apparently yes: [1][2]

[1] https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/91JD...

[2] https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2007...

So do rivers and animal migrations.

http://www.geologypage.com/2019/11/studying-the-snowmelt-epi...

https://pubmed.ncbi.nlm.nih.gov/25618038/

https://www.researchgate.net/publication/251437544_Seismic_w...

https://abcnews.go.com/Technology/DyeHard/elephants-predict-...

Apparently particularly energetic soccer cheers are also easily detected by seismometers. Here is one example:

https://www.huffingtonpost.ca/entry/fans-cheering-world-cup-...

Earth is mostly water and large portions of land are covered vegetation and the atmosphere could serve as a larger thermal buffer. It could be that on mars that the surface is more connected structurally and has a much thinner crust, local cooling could have a much larger affect.

If my hypothesis are true, I think it would show that meteor impacts would cause longer spherical ringing. In a quick search I can't tell if there are multiple seismometers on mars, which would make it much easier to infer the structure of the core and the crust.

(disclaimer, just a dog on the internet)

https://en.wikipedia.org/wiki/Tectonics_of_Mars

No for a few reasons. The article mentions that the change in heat gradient only reaches a depth of a few micrometers. The time of eclipse here on earth is ~30 sec (just as on Mars which is interesting) but I agree that total temp change should be greater. From hooke's law you could estimate the stress change caused by the temp induced strain (10^8 from the article) by making assumptions about the material and thermal properties. This would depend on rock type, local structure and sediment type and distribution. Not to mention we have all this pesky vegetation here on earth which would reduce total temp change by preemptively shading the earths surface. The isotherm due to the highest (seasonal) temperature changes on earth is somewhere between 0-50m.

Second, earthquakes tend to occur deeper in the subsurface since the surface is a free boundary where stresses are minimized. Surface ruptures result from shallow earthquakes, such as the one from the 2019 Ridgecrest sequence. The depth of the Ridgecrest earthquake was ~10km.

Lastly, the the local stress change would probably be smaller than those imposed by the moon (few kPa), and tidal stress change does not correlate with earthquake event times here on earth.

Best case would be a huge temperature swing (few ~100deg) over the hottest bare rock on earth for an hour rather than a 30 second eclipse.

Wow, Phobos has a seismometer? Neat!

NASA's InSight lander is located on the surface of Mars. There are no synthetic objects on Phobos (please correct me if I'm wrong).

Phobos has a seismometer?

This is huge news, as it's a positive sign of intelligent life having evolved there.

God forbid! A joke on the internet?

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