Beyond the Sun’s Reach: Voyager Reaches The Edge of Interstellar Space

Voyager is at the edge of the heliosphere’, going farther than any other craft before it or since. The space probe, of a modest 722 kg, launched in 1977 by NASA to probe nearby planets, had exceeded all expectations long ago, as it crossed the orbit of Neptune at its farthest point on 14th February 1990 (a romantic coincidence?). It is now at the edge of the imaginary sphere of Sun’s influence the edge at which particles from the Sun can resist those coming from interstellar medium.

Voyager 1

Voyager: A Brief History

Voyager 1 was launched on 5th September, 1977. Its sister, Voyager 2, was launched two weeks later on 20th September. Its primary mission was to photograph Jupiter and its moons along with the Saturnian system.

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Voyager carries on itself a golden audio-video record disc, in the event that it is discovered by some form of intelligent life. The disc has photos of the male and the female human forms, of various other lifeforms on Earth, audio records of greetings from US and Russian state-heads and those by children. It also contains recordings of various sounds of Earth that of a whale, a baby crying and of various pieces of music.

Cover for the Golden Disc aboard each of the two Voyagers

Tryst with Jupiter

Voyager 1 reacher Jupiter early January 1979 and made its closest approach on 5th March. The photos revealed tantalizing details about both Jupiter and its moons. Most of the, now legendary, tales about Jupiter and its moons come due to Voyager. It closely observed the storms on Jupiter, especially the Great Red Spot, and measured its magnetic field. The photos of Io revealed volcanic activity not known before, while those of Ganymede revealed a frozen world the largest ice cover in the Solar System.

Jupiter - one of the first photos from Voyager 1
The Great Red Spot on Jupiter
A Plume on Io, the volcanic moon of Jupiter
Time lapse photo of Jupiter by Voyager 1
Jupiter with its moons. A collage formed with Io on the upper left, Europa at the center, Ganymede on the lower center and Callisto on the lower right

Sojourn to Saturn

Saturn was supposed to be the last stop for Voyager. It picked up a close view of Titan, Saturn’s largest moon, after Pioneer 11 had detected a thick cloud cover. Voyager picked up brilliant images of Saturn, its rings and of Titan’s thick atmosphere. This was the end of the Grand Tour’, but Voyager, which was over-engineered’, kept on going. The extended mission included sending it to Uranus, Neptune, Pluto and, maybe, beyond.

Saturn: Observed by Voyager through UV and green filters
Titan: Note the thick atmosphere that appears blue in reflected sunlight

Uranus and Neptune

Voyager revealed Uranus and Neptune to be frigid gaseous worlds with a blue atmosphere made predominantly of ammonia and methane. It explored the Uranian ring system, photographed the Great Dark Spot’ of Neptune and flew further out.

Uranus from Voyager 2
Neptune: Note the dark spot in the middle of the blue. That's the Great Dark Spot

The Pale Blue Dot: Our Home

On 14th February, 1990, Voyager officially left the Solar System. It turned its camera back onto the planets and photographed the entire planetary family from the distance. One of these photos was that of Earth, which was a blue dot suspended in a sunbeam the famous Pale Blue Dot.

The Family of Planets - from beyond the Solar System
The Pale Blue Dot. Great poets and warriors, saints and sinners, happiness and sadness have originated on that single pixel suspended in sunbeam.

This is the pale blue dot we claim home. The late Carl Sagan was lyrical in his famous lines about the Pale Blue Dot on the wildly popular TV series Cosmos‘ and his inspired book by the same name.

Look again at that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was … every teacher of morals, every corrupt politician, every “superstar,” every “supreme leader,” every saint and sinner in the history of our species lived there–on a mote of dust suspended in a sunbeam.

Our posturings, our imagined self-importance, the delusion that we have some privileged position in the Universe, are challenged by this point of pale light. Our planet is a lonely speck in the great enveloping cosmic dark.

Here’s a small clipping taken from featuring Sagan. Don’t miss it for the world the warm tingling in your spine is a feeling unrivaled. Lose yourself in it.

Onto the Great Beyond

Voyager transmits to the Deep Space Network, each transmission taking 16 hours to reach. It crossed the termination shock’ boundary, the region in which the solar wind’s magnetic influence drops to near zero in 2004. Scientists were waiting for it to cross the edge of the heliosphere the region where the solar wind sharply changes direction. (Heliosphereis thus the sphere’ which the solar winds fill up.)

Now that Voyager has gone there, scientists find the area to be utterly calm. They find the solar wisps mingling with the interstellar particles. What’s the big deal you ask? The sun is wading through a sea of particles produced by nearby supernovae and other energetic phenomenon. The heliosphere keeps out their influence. Precious little is known about this forbidden limit; maybe Voyager will shed some light.

Voyager will continue. Calculations say that it will have enough batteries to last it till 2025, and by then it will be far out of range of radio communication. It is expected to pass the constellation Camelopardalis in another 40,000 years (Remember Newton’s First Law of Motion?).

The Great Beyond Beckons…

(All images credited to JPL/NASA)

Published by

Debjyoti Bardhan

Is a science geek, currently pursuing some sort of a degree (called a PhD) in Physics at TIFR, Mumbai. An enthusiastic but useless amateur photographer, his most favourite activity is simply lazing around. He is interested in all things interesting and scientific.