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Why Didn't Voyager Visit Pluto?
Flash Modin writes: NASA built the twin Voyager spacecraft for a rare planetary alignment that put Jupiter, Saturn, Uranus, and Neptune within reach at once. Originally, Voyager 1 was programmed to see Pluto in 1986, but managers targeted Saturn's planet-like moon Titan instead. That choice made Pluto impossible by vaulting Voyager 1 from the orbital plane. Interestingly, Voyager 2, which couldn't reach Pluto, made the case for New Horizons by revealing Neptune's moon Triton as a kidnapped Pluto. "I'm very glad that they chose not to go to Pluto in 1986," says New Horizons head Alan Stern. "We'll do a better job at Pluto with modern instruments than they would have, and they did a much better job at Saturn..."
The original "Planetary Grand Tour" project would have visited Pluto, but it relied on a planetary alignment that would have to have started in 1976 or 1977. It was originally announced as a single craft, which became four before it was cancelled (I don't remember that, but for a brief history, see https://en.wikipedia.org/wiki/...). This was replaced by the two Voyager satellites launched in 1977. The later launch date made Pluto harder to visit, but it was still possible.
Why Didn't Voyager Visit Pluto?
Why is this asked as a question, when the summary does in fact have the answer? Why not just headline it thus:
Why Voyager didn't visit Pluto
Then I'd be less likely to mistake it for another speculative piece of guff from a professional blog writer, which we already have plenty of.
systemd is Roko's Basilisk.
How do you think these decisions are made? Carl Sagan was involved with basically every NASA planetary mission (including Apollo) from 1960 through Voyager and Viking. He proposed that Titan might have a lot of hydrocarbons (it does) a thick atmosphere (it does), haze (check) and maybe a biosphere (the jury is still out). (He did propose a strong greenhouse for Titan, and struck out there. The surface is not as balmy as he hoped.) As far as I can remember, no one was proposing a biosphere for Pluto (we didn't even know Pluto had a moon at that point). The decision to do a Titan close approach was rational, and (while it certainly wasn't his decision alone) his advocacy for it carried a lot of weight.
Technically the Pluto-Charon system is not a primary with a satellite, but a double system. The center of mass of the system is not within either body, but in the space between them. Anyway, several asteroids have been found to have tiny satellites, so owning a satellite doesn't count for much anyway.
I believe Voyager 1 still hasn't passed pluto if projected back down onto its orbital plane.
Voyager 1 is almost 20 billion miles away from us now, and is traveling about 35 degrees out of the ecliptic. Some really rough trigonometry shows that if you project that down onto the ecliptic, it's still about 16 billion miles away from the Sun, which is almost three times the length of the long axis of Pluto's entire orbit.
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One of the things accomplished by taking Voyager I behind Titan was a direct measurement of the thickness and density of Titan's atmosphere. They did this, btw, by measuring how much of the probe's signal was absorbed before it was completely occluded and by how long it took the signal to come back to normal strength after it came out on the other side. And to show you how good the navigation was, closest approach was less than two radii out, meaning that if it had been cut in half, Voyager would have collided with Titan instead of just passing closely. I know this, because I spent some time at JPL in the mid 1980s and am slightly acquainted with the man who came up with the idea and did most of the work involved.
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