Salvage extremely rare celestial object (7)
I believe the answer is:
reclaim
'salvage' is the definition.
(I've seen this before)
'extremely rare celestial object' is the wordplay.
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'celestial object' becomes 'claim' (I can't justify this - if you can you should give a lot more credence to this answer).
'rare' with its middle removed is 're'.
're'+'claim'='RECLAIM'
Can you help me to learn more?
(Other definitions for reclaim that I've seen before include "civilize" , "'Make useful again, land say (7)'" , "Recover (materials/land) for subsequent use" , "Get back (eg from the sea)" , "From sea, rescue" .)