The Aerosmith rocker's Massachusetts estate in Duxbury -- consisting of more than 7 acres of land and a 7,181 sq. foot palace of a home -- is currently under contract with someone who's ready to make a deal and claim the property for themselves very soon, we're told.

The price Joe was asking -- a cool $4.5 million. And you can bet JP and his wife, Billie, are cleaning up on profit -- they reportedly snapped up this place back in the late '80s, and have done quite a bit of work to turn it into the paradise you see here.

The 5-bed, 8-bath home is as picturesque as you can imagine a countryside retreat could be -- in addition to the massive number of rooms, there are a ton of amenities too.

For starters, there's a whole detached stone front carriage house that stands alone from the main house, and there's also a 3-stall barn with a tack room ... plus a marsh and pond nearby. So, yeah ... we're talking serious "Green Acres" vibes here.

On top of that, there's a pool, a rooftop garden, 3 fireplaces, a game room, a media room, a state-of-the-art kitchen and incredible vaulted ceilings -- not to mention the fact this place is totally gated and offers the utmost privacy.

And did we bring up the gorgeous nature all around???