News from the edge of the solar system

Artist’s concept drawing of NASA’s Voyager 1 spacecraft entering interstellar space (NASA/JPL-Caltech)

Artist’s concept drawing of NASA’s Voyager 1 spacecraft entering interstellar space (NASA/JPL-Caltech)

Two years ago, the first human-made object left the solar system. That was Voyager 1. Right now, in late August and early September, it’s also the anniversary of the launching of both Voyagers, way back in 1977. If ever there was an epic journey worthy of Homer, it’s this.

These spacecraft were built to study Jupiter and Saturn and their larger moons. To accomplish this, they were designed to last five years. But we all knew that a rare geometric arrangement of the outer planets would unfold from 1977 to 1989, which could let a spacecraft visit every planet beyond Mars. This layout of Jupiter, Saturn, Uranus and Neptune only happens once in 175 years. A precisely aimed craft could swing from one world to the next, using each one’s gravity as a slingshot. Even Pluto was attainable.

But could any spacecraft last long enough to reach all those planets? Congress said flat-out “no” to the notion of going to Pluto. Even designing a craft to last long enough to reach Neptune was thought to be too expensive. Therefore the Voyagers were funded to fly past Jupiter and Saturn only.

But as we received stunning images and breathtaking surprises – at Jupiter in 1979, then Saturn in late 1980 and early ’81 – the additional attempted flybys of Uranus and Neptune were approved. Actually, the extended mission was funded for just Voyager 2, which already suffered from a broken main radio and a worrisome temperamental backup. Sadly, Voyager 1’s deliberate close passage past Saturn’s moon Titan gave it a trajectory that made further planets unattainable. Thus, Voyager 2’s five-year shelf life was now stretched to 12, with fingers crossed. But the craft kept working. We got our first (and still the only) close-up images of green Uranus in 1986 and blue Neptune in 1989.

The end? No way. Thanks to their RTGs, their plutonium-based electrical generators, the ships had enough power to study the “solar wind” as it blew past them, and to seek the edge of the solar system where that wind would be theoretically stopped cold by incoming particles from interstellar space.

Several years ago, the Sun’s particles no longer zoomed past the Voyagers, which instead outraced them. Voyager 1 sensed the heliopause – the boundary at the end of the Sun’s magnetic influence – and entered Interstellar Space, two years ago this week. As Voyager 1 leaves the solar system by rising above the ecliptic plane at an angle of about 35 degrees, it travels 320 million miles farther away annually. Voyager 2 is meanwhile leaving at a downward angle of 48 degrees and a speed of 290 million miles a year. Both spacecraft are expected to return valuable data until roughly the year 2035.

The Voyagers each famously carry a phonograph record in the form of a 12-inch gold-plated copper disk. It will be 40,000 years before the first Voyager passes within a light-year of any star. Should an alien civilization somehow ever find it and figure out how to use the enclosed needle, and play the disk at a speed of 16 2/3 revolutions per minute, they’ll see 115 images of Earth, including autumn foliage from our region. They’ll also hear a 90-minute selection of music of various cultures, from Bach to Chuck Berry, and a potpourri of natural sounds such as wind, surf and birds. Also a “Hello” in 55 languages including Akkadian, which was spoken 6,000 years ago, just in case they visited us back then and still remember the formalities. (That’s not actually why Akkadian was included.)

With all the world’s problems and the pseudoscience that one keeps seeing, it’s hard not to remain in love with the Voyagers. I fondly pat my blue hippie airplane after every landing, when she has kept my passengers and me alive for decades now. But no love affair with a material object can compare with what I – and many others – still feel for those amazing Voyagers.

Happy anniversary, you two.

Want to know more? To read Bob’s previous “Night Sky” columns, visit our Almanac Weekly website at HudsonValleyAlmanacWeekly.com.

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