Production engine from the Mars Viking spacecraft program used for the first landing on Mars... 45 years ago.

Constructed from Beryllium, Columbium, and stainless steel by North American Rockwell/Rocketdyne, the engine provided propulsion to take the Mars-bound orbiter with its attached lander to Mars and an orbital insertion around the planet. The engine was produced by Rocketdyne for the Jet Propulsion Laboratory (JPL) and includes gimbal attachments which allowed the engine to be adjusted on a rotational axis for in-flight course corrections. The beryllium thrust chamber was derived from the Minuteman ballistic missile program.

"As close to a flown engine from the project as you will find." — https://www.cnet.com/news/buy-a-spare-mars-viking-lander-rocket-engine/ More info and photos below. Part of the FV Space Collection.

NASA sent two Viking spacecraft to Mars in the summer of 1976, and each comprised of an orbiter, which photographed the surface, and a lander, which studied the surface and conducted several experiments. The whole spacecraft orbited the planet for approximately one month, using the images relayed back to mission control to identify a landing site.