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.

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.