Happy Birthday: Mystery Planet Neptune is One Year Old Since Discovery

It’s humbling to take a walk in someone else’s shoe for a day; it’s awesome to take a walk on another planet for a year. Neptune, since its discovery on 24th September, 1846, will complete one revolution on 12th July, 2011, marking one complete year for the planet. We wish it a very happy new year.

Predicted before, observed later

Neptune is the farthest planet known to Man (especially with the exclusion of Pluto).


At an average distance of 4.4 billion kilometres, Neptune represents the brink of human knowledge as far as planets go. Precious little is known about Neptune’s atmospheric composition, moons and any ring system that it might have. Completely invisible to the naked eye and only just visible with a ground-based telescope, it took Hubble for us to get a good view of Neptune. However, most of what we know about Neptune comes from the data and photos sent back by Voyager on its extended mission. Neptune orbits the Sun in an orbit so large that each year of Neptune is 164.8 Earth years.

Neptune was the second planet, after Uranus, to be deduced from astronomical observations, before being directly observed. Astronomers noticed a strange tug on the planet Uranus and were puzzled. Either Newton’s gravitation law was wrong or there was another body, at least half the size of Uranus, present in the vicinity. By the 1780’s, when this anomaly was discovered, the laws of Newton were on such a strong foundation that astronomers concluded the latter. The French mathematician Urbain Le Verrier predicted the exact position of this unknown body and Johann Gottfried Galle first saw it using the telescope at the Berlin Observatory at the exact spot in which it was supposed to be. A dot of blue had vindicated Newton’s laws again! The day was 24th September, 1846.

So what do we know about Neptune?

Neptune’s atmosphere has been of great interest. The composition is similar to that of Uranus mainly methane and ammonia. However, there has been photographed The Great Dark Spot’, a giant storm raging on the planet, akin to the larger and better known Great Red Spot’ of Jupiter. Voyager 2 photos showed the extent of the storm when it passed by the planet in 1989; data collected lead astronomers to speculate that the wind speeds must be more than 1900 kmph (more than 1200 mph).

Neptune's Great Dark Spot, as captured by Voyager (Credit: NASA)

Great interest lies in Neptune’s rings. The ring system is faint, was only visible when Voyager got really close and blocked out the reflected light from Neptune. The rings appear as thin, dark bands with quite high amounts of dust in them. Scientists conclude that there might be a lot of organic material in the rings, making them appear dark.

Rings of Neptune. Note the arcs on the Adams ring

A peculiar feature of a ring, called the Adams ring, is the presence of numerous arcs on it. Scientists, till date, know nothing about the formation or stability or composition of these arcs.

Neptune is as dark and mysterious as it gets. Further missions, like the Voyager, will help shed some light on this faraway dark world. For now, as far as we’re concerned, Neptune is just a year old.

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 youtube.com 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)