Thread by @mcnees

The Voyager 2 spacecraft launched #OTD in 1977. It is currently 11.8 billion miles from Earth, hurtling through interstellar space at about 35,000 mph with respect to the sun.
Image: NASA/JPL-Caltech

Voyager 2 is so far from Earth that round trip for a signal is over 35 hours. Only its twin Voyager 1 (which launched a few weeks later but took a more direct route out of the solar system) is further. You can see a live mission status for both craft here:
voyager.jpl.nasa.gov/mission/status/

You can also see the Solar System from Voyager 2's perspective using @NASA's interactive "Eyes on the Solar System."
eyes.nasa.gov/apps/orrery/#/…

Voyager 2 is the only spacecraft to have visited all four of the giant planets: Jupiter, Saturn, Uranus, and Neptune. NASA had originally planned a "Grand Tour" that would use four probes to explore the five (at the time) outer planets.

That plan was scrapped over cost and replaced with two Voyager probes. The idea was to investigate Jupiter and Saturn. If the first probe worked out okay, the second would be directed on to Uranus and Neptune. So Voyager 2 more or less carried out the Grand Tour.
Image: NASA

Here's a timeline of the mission and a view of the probes' paths through the outer Solar System.
Image: NASA

Those trajectories led both probes out of the heliosphere. Voyager 2 punctured the hot, dilute bubble of plasma associated with the solar wind in 2018, entering a transitional region where the colder, denser medium of interstellar space begins to dominate.
jpl.nasa.gov/news/voyager-2…

By the way, NASA / JPL have a great collection of Voyager posters and infographics that are free to download and print. I’ve seen these three framed and they look fantastic.
voyager.jpl.nasa.gov/downloads/

Alight, let's do some greatest hits from the Grand Tour that began #OTD in 1977.

Voyager 2's flyby of Jupiter took place in 1979, a few months after Voyager 1 passed through. Here are images it captured of Jupiter, Io, Europa, and Ganymede.
Images: NASA / JPL

It sent back remarkable views of the planet and the faint ring system first spotted by Voyager 1. A tiny moon, now named Adrastea, was found lingering near the edge of the main ring. It was the first natural satellite of a planet discovered by a space probe.
Images: NASA / JPL

Adrastea is the small, faint dot near the center of this image sent back by Voyager 2. It is probably the main contributor of material – blown off by small impacts – to the main ring.
Image: NASA / JPL / Wikimedia

And here is an animation of volcanic plumes on Io, built from images Voyager 2 captured during the 1979 flyby. Voyager 1 saw them a few months earlier.
Animation: Calvin Hamilton
solarviews.com/cap/jup/ioplum…

Voyager 2's closest approach to Saturn took place in August of 1981, almost a year after Voyager 1's visit. It passed within about 60,000 miles and sent back detailed images of the planet, its moons, and structures in its rings.
Images: NASA / JPL

Look at this lovely, trailing ribbon of cloud in an eastward-moving jetstream. Thirty years later, when Cassini looked, the wavy structure had dissipated.
Image: NASA / JPL
photojournal.jpl.nasa.gov/catalog/PIA013…

Voyager 2 was the first and still only craft to visit Uranus. It passed by in 1986, discovering numerous moons, two new rings, and a very odd magnetic field.
Image: NASA / JPL

(The existence of a ring system was already known, revealed by a little flicker of starlight just before and after an occultation in 1977.)

https://twitter.com/mcnees/status/1237367386510110723

I've always loved this final image of a crescent Uranus that Voyager 2 captured as it left the system on its way to Neptune.
Image: NASA/JPL

Voyager 2 made its closest approach to Neptune in 1989. It discovered five moons, several rings, and three dramatic atmospheric features seen here: a "Great Dark Spot," a bright patch of cloud nicknamed "Scooter," and a "Dark Spot 2" with bright, central core.
Image: NASA / JPL

Just five years later, when the Hubble Space Telescope looked for the Great Dark Spot, it had disappeared. A similar storm, dubbed the "New Great Dark Spot," appeared in 2016.

Again, I'm a sucker for these crescent views. Here is Neptune and its moon Triton (which, despite being in the foreground of the image, still appears much smaller) three days after closest approach.
Image: NASA / JPL

Like its twin, Voyager 2 carried a gold-plated phonograph record containing sounds and images of life on Earth. The covers are made of aluminum and electroplated with Uranium-238 so any civilization discovering these artifacts can estimate their age.
Image: NASA/JPL

The audio contents of the golden record were uploaded to @SoundCloud a few years ago. @NASA's “Greetings to the Universe” playlist contains greetings in 55 different languages. The English recording is a 6yo Nick Sagan, son of Carl Sagan and Linda Salzman.
soundcloud.com/nasa/sets/gold…

And here is a playlist with the “Sounds of Earth” tracks from the golden records carried by the Voyager probes:
soundcloud.com/nasa/sets/gold…

(Here is an adult Nick Sagan reflecting on the recording back in 2013 when Voyager 1 left the heliosphere.)
agupubs.onlinelibrary.wiley.com/doi/pdf/10.100…

Besides the audio tracks, the album contains 115 encoded images. Many of the images are under copyright that prevents sharing them, but you can see a gallery here:
voyager.jpl.nasa.gov/galleries/imag…

The images on the record’s cover include instructions for how to play it, and a cosmic map that pinpoints the probe’s origin. The map is the same as the plaques on the Pioneer probes.

A depiction of the hyperfine transition in neutral hydrogen appears in the lower right corner. This emits a photon with a characteristic wavelength of 21 cm and a frequency of 1,420 MHz. Distances and frequencies shown on the map use these as base units.

A diagram in the lower left quadrant indicates the position of Earth relative to 14 pulsars. The period of each pulsar, in units of the inverse hyperfine frequency, is indicated in binary along its line.

The periods of the pulsars, which are given to very high precision, change in a predictable way. So any civilization that discovered the probe should be able to determine where it came from, even in the far-flung future.

So, what's everyone's favorite Voyager 2 image?

BTW, I didn't know that recording was Nick Sagan until just now. I looked it up because he sounds just like Christopher Shea, who voiced Linus in "A Charlie Brown Christmas." I wondered if maybe Shea had recorded the message!