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trgui
2008-Apr-08, 03:25 PM
When a terrestrial planet is young is it larger than when it is old?

I know that young gas giants are larger than when they are old.

Is this also with terrestrial planets?

Can't seem to find an answer to this question :doh::confused:.

Please,if anyone could help me I would appreciate it.

Ilya
2008-Apr-08, 03:31 PM
My guess is: yes, but only by a very small amount.

Gas giants are made of fairly compressible stuff, so as they cool off they shrink noticeably. Terrestrial planets are far less compressible, so as they cool off they also shrink, but not much.

John Mendenhall
2008-Apr-08, 04:21 PM
Check the recent Mercury flyby pictures, they think the scarps are shrinkage caused.

trgui
2008-Apr-10, 06:57 PM
My guess is: yes, but only by a very small amount.

Gas giants are made of fairly compressible stuff, so as they cool off they shrink noticeably. Terrestrial planets are far less compressible, so as they cool off they also shrink, but not much.

Thanks,that is the answer I was looking for :dance::clap:.


Check the recent Mercury flyby pictures, they think the scarps are shrinkage caused.

Thank you too :clap:.

Eroica
2008-Apr-11, 02:56 PM
My guess is: yes, but only by a very small amount.I disagree. Terrestrial planets are continually accreting meteoritic matter, so they are increasing in mass, which would offset the contraction due to cooling.

And are they cooling? I heard somewhere that the Earth is losing internal heat at the same rate that radiogenic decay is generating more...:think:

Noclevername
2008-Apr-13, 05:00 AM
I disagree. Terrestrial planets are continually accreting meteoritic matter, so they are increasing in mass, which would offset the contraction due to cooling.


In very, very tiny amounts compared to the planet's overall mass. For most of the planet's existence, heat is the deciding factor. Only after nearly all cooling is complete does the slow accretion of meteoric debris outweigh it.

Eroica
2008-Apr-13, 02:53 PM
The Earth is also tectonically active, so there is the complicated matter of how much high-density minerals in the mantle are being converted into lower-density minerals in the crust.