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Astronomers Spot a Planetary 'Suicide'

(www.science.org)
19 points rbanffy | 1 comments | 12 Apr 25 11:29 UTC | HN request time: 0s | source
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mrkstu ◴[13 Apr 25 03:25 UTC] No.43669848[source]▶
Can someone explain the orbital mechanics of these sentences?:

The constant stretching of such tidal deformation would create friction within the planet that would soak up some of its orbital energy, causing it to edge closer to the star.

How exactly does the energy of tidal energy being expressed inside the planet affect its speed relative to its host star? There is no external friction in empty space so how does the speed disappear?

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alganet ◴[13 Apr 25 04:21 UTC] No.43670071[source]▶
Think of a very unbalanced car wheel. It wobbles, interferes with the smooth road and eventually reduces the speed of the system.

A planet that stretches and contracts in orbit also wobbles, which does something similar to its orbit. Loss of speed often results in lowered orbit, and thus more wobbling, in a feedback loop.

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heavenlyblue ◴[13 Apr 25 09:34 UTC] No.43671441[source]▶
An unbalanced car wheel is hitting the road harder to it stops, an unbalanced planet is still flying in empty space, where does the energy go then?
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1. alganet ◴[13 Apr 25 15:45 UTC] No.43673614[source]▶
Part of the energy is transformed into heat as the planet mass is deformed. In the same way an unbalanced wheel tire heats up faster. This is the internal friction part.

Part of it is transfered to the mass being orbited. In the same way a wobbling wheel makes the road vibrate a little bit. This is the gravitational part.

It's not a perfect metaphor, but it should be enough to visualize what happens.