Opher believes that the influence of the sun’s magnetic field may warp the heliosphere into the shape of a ‘‘croissant.’’ At its plump center, interstellar matter presses in closer than previously thought — which would mean we are less isolated from the rest of the galaxy than we believe.

Last Sept. 29, a Thursday, Larry Zottarelli awoke before 7, as he did most weekdays, and dressed quietly so as not to disturb his sleeping wife. He raked a comb through his silver hair, donned trifocals and a calculator watch and drove to the office. He brewed his first mug of coffee in the efficiency kitchen and carried it to his desk. He’d been on the job for 40 years; the next day would be his last. A printed-out email taped to his computer hutch had instructions for handing in his badge and parking pass and collecting his final paycheck. He had cleared out most of his belongings, except two gallon-size Ziploc bags, in which he had sealed the plastic arms of his office chair to protect them from disintegrating under the daily weight of his elbows. Sitting facing the door, backed by a windowless, conch-pink brick wall, he brought to mind a hermit crab wearing a seashell.

Later that morning, when Zottarelli entered the conference room to attend his last daily flight-team briefing, his colleague Adans Ko, 58, was arranging takeout containers of dim sum on the table for a celebration. He threw an arm around his shoulders and said, ‘‘Larry is going to give me a kiss today!’’ Matsumoto, who was holding a camera, said, ‘‘O.K., look at me.’’ She was making a photo album for him. When the party broke up, I found Zottarelli’s replacement, Lu Yang, at her desk. I asked her if he had given her any specific advice. ‘‘Whatever the problem, you go there and solve it,’’ she said, and laughed.

In retirement, Zottarelli told me, he would like to see Florida again. He wonders how it has changed. In his garage is a 1954 Swallow Doretti, a fixer-upper. ‘‘It probably needs new brakes,’’ he said. I asked him if there was anywhere he liked to drive for fun. ‘‘No,’’ he replied. ‘‘Not anymore.’’

I had stopped by his office to say goodbye and ask him what he planned to do with his newfound freedom. I pictured him in the Doretti, flying down the Pacific Coast Highway, wind in his hair. But he seemed to be in no mood for talking. I wished him well and turned to go. Then he spoke. ‘‘I expect my second stroke will be on the 17th of November,’’ he said ruefully, gesturing toward his empty wall calendar. ‘‘Life expectancy is five to seven years at my age on retiring, so —’’ He paused. ‘‘That was humor, I guess. I’m not looking forward to being even older. Got no choice in the matter.’’

I asked if he ever found himself thinking about the billions of years that the Voyagers will circle the center of the galaxy, long after our sun has exploded, scattering more stardust throughout the universe. ‘‘Of course,’’ he said. ‘‘I was raised in the Roman Rite. I’m pretty much an atheist. But what is the meaning of life? It’s not Monty Python, O.K.?’’

Had he reached any conclusions about what it is? ‘‘Well, on Earth, yeah,’’ he said. ‘‘One species always prepares the way for the next generation — that’s all.’’