When somebody asks Brad Pitt what he did this summer, here’s how he should respond: “Resuscitated my acting career!”

Although the movie star’s best days seemed well behind him, he has, out of nowhere, delivered a pair of stellar performances these past few months: as a devilishly funny stuntman in “Once Upon a Time in . . . Hollywood,” and now as a futuristic American astronaut in the gripping “Ad Astra.”

With the latest film, we trade laughs for gasps. His hardened character, Maj. Roy McBride, wades around in a state of emotional paralysis as if on heavy mood stabilizers. His dad disappeared on a mission to Neptune 20 years earlier, and now he’s so steely he makes Spock look like a blubbering hot mess.

When Earth begins to reel from a series of power surges, it’s discovered that the damaging outages are a result of antimatter explosions emanating from the eighth rock from the sun — Neptune. Pops (Tommy Lee Jones), the space administration believes, is still alive — and Roy must blast off on a secret mission to Mars, which is in close enough range to send Dad a message and stop the antimatter experiments.

On his journey, we witness one of the most compelling cinematic visions of where mankind is going. There are no “Back to the Future Part II” rehydrated Pizza Hut meals here; the realism and practicality of this world are striking.

Take the human settlement on the moon: It kinda looks like Penn Station. It’s mostly dingy concrete, there are escalators and, naturally, a Subway sandwich shop. The settlement is totally believable. Roy gets there by taking a commercial flight with Virgin airlines, and one of film’s best lines happens when he asks for a pillow and blanket. “That’ll be $125,” says the flight attendant, not batting an eye.

Director James Gray’s style harks back to classic space movies, such as “Alien” and “Star Trek II: The Wrath of Khan,” that played around with the vastness of the stars, and made it seem like there was nowhere lonelier. “Ad Astra” also has an old-school visual panache, with deep-colored, dramatic lighting that’s regrettably fallen out of fashion.

Gray also employs a canny blend of genres. Early on, we assume we’re in for a pretty straightforward space flick — here’s your mission, strap in — and then it segues into a psychological thriller with several exciting action sequences, one involving a monkey. Another, set among the rocky rings of Neptune and featuring what amounts to a metallic boogie board, is tough to buy into, however.

Roy meets a few companions along the way — Liv Tyler, Donald Sutherland and Ruth Negga play peripheral parts — but this movie should really be called “Brad Astra.” Pitt almost never leaves the frame, and his character’s unraveling is expertly paced, and treated so subtly, even in his many narrations. It’s a very adult role for someone we often forget is an adult — and easily the most welcome comeback of the year.

Next up: Angelina Jolie in “Maleficent.”