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Comment by praveenscience | Hacker News Reader

14 points·praveenscience··7 comments

Saved you a click: "During an eclipse, the ground cools," said seismologist Martin van Driel of ETH Zurich. "It deforms unevenly, which tilts the [seismometer]" a small amount.

The phenomenon is boring, but the ability to measure it is pretty mind-blowing:

> "Imagine a 5- franc coin; now, push two silver atoms under one edge. That's the incline we're talking about: 10^-8."

Imagine a headline writer who wrote like this. I would click the dang story just out of respect and with the idea that an author like that is worth reading generally. If the headline is that informative how great would the content be?

Duplicate: https://news.ycombinator.com/item?id=24383060

Eh. This is sadly a clickbait headline with a murder-mystery writeup.

The seismometer on the lander (sitting on Mars) registered a tiny tilt:

> “But we didn't expect this seismometer reading; it's an unusual signal," Stähler said. "Imagine a 5- franc coin; now, push two silver atoms under one edge. That's the incline we're talking about: 10^-8."

Their theory is that the ground got cooler in the shadow, and therefore the instrument shifts slightly. So nothing “strange happens”, it just took them a while to debug it.

tl;dr: the shadow cast by Phobos during an eclipse affects the ground of Mars just a tiny bit.

I think the choice of an object in this comparison is interesting, altough it doesn't affect the result that much, of course. The 5-franc coin is ridiculously big: measuring 31.45 mm (1.24 inch) in diameter and weighing 13.2 g, it's one of the largest circulating coins in the world.

If I'm understanding this correctly, whenever Mars goes through a solar eclipse, the Mars InSight lander picks up something on its seismometer, indicating some ground activity (like a minor earthquake, etc)?

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