Jupiter shrinks by about two centimetres every year.
Why it is true
The planet's huge mass generates strong gravitational compression, and the slow loss of internal heat causes the gas giant to slowly contract over time.
Source: Astrophysics
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.