Heavenly body which rises when hot (7)

I believe the answer is:

mercury

I believe this clue is a double definition.

'heavenly body' is the first definition.
(Mercury is an example)

'which rises when hot' is the second definition.
(mercury rises in a thermometer)

(Other definitions for mercury that I've seen before include "Element, symbol Hg" , "First rock from the Sun - Hg" , "one in distant orbit?" , "Atomic number 80" , "Planet nearest the sun" .)

I've seen this clue in The Guardian.

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