In 1781 Sir William Herschel discovered the planet Uranus, an event that doubled the size of the solar system. After extensive observation, astronomers soon realized that its orbit was inconsistent and, moreover, was being disturbed by the gravitational force of an unknown object. They soon set out to find that object by calculating the amount by which it affected the orbit of Uranus. Using Sir Isaac Newton's Law of Gravity, astronomers had been able to study the gravitational interactions between planets in some detail. Deviations from the predicted motions were easily noticed, and the probable location of the perturbing object could be fairly easily estimated.
In 1841, John Couch Adams, a twenty-two-year-old astronomy and mathematics student, used these principles to conclude that the irregularities of Uranus's orbit were caused by another planet further away from the Sun. He had first assumed that the planet tugging Uranus was in the same plane of orbit as Uranus and was about the same size. He also used the Bode-Titius rule, a quirky and basically meaningless mathematical formula used to calculate the mean distance between planets, to roughly pinpoint the mystery planet's location.
Adams carefully waded through the collected data on Uranus since its discovery. In September 1845 he presented his astronomy professor with a paper correctly predicting the position of the unknown planet for October 1, 1845. Adams, however, met with a series of setbacks after this point. Instead of asking a major observatory to look for the planet, his professor gave Adams a letter of recommendation to the Astronomer Royal, Sir George Airy (1801-1892). After several miscommunications, Airy finally received Adams's paper, but dismissed the young astronomer's calculations, believing that Uranus's irregular orbit represented flaws in Newton's theory of gravity.
At the same time, the French astronomer Urbain Leverrier (1811-1877) had completed his own calculations concerning the location of the unknown planet affecting Uranus. Leverrier's calculations, published a few months after Adams presented his paper, came within one degree of Adams's prediction. Airy, upon reading of Leverrier's work, asked the director of the Cambridge Observatory, the Reverend James Challis (1803-1882), to look for the mystery planet using Adams's data. However, Challis investigated a much larger area of the sky than necessary and lacked the most current astronomical maps of the day. As a result, he was unable to pinpoint the planet.
By then, Leverrier had enlisted the help of Johann Galle (1812-1910) at the Prussian Observatory in Berlin. On September 23, 1846, Galle looked through the telescope while a student, Heinrich d'Arrest (1822-1875), sat nearby with a star chart. Galle called out the stars in his field of view, and d'Arrest checked them off on the chart: the mystery planet was discovered within one hour. Leverrier named the planet Neptune, after the Roman god of the sea, due to its blue-green appearance. Leverrier was initially credited with the work that led to the discovery, but due to the efforts of Sir John Herschel (1792-1871), the son of Uranus's discoverer, Adams was given his proper share of recognition.
Over the next century, small findings about Neptune trickled in. Within a few weeks of the planet's discovery, English astronomer William Lassell (1799-1880) discovered its largest moon, Triton, named for Neptune's mythical son. Its orbit proved surprising: it moved around Neptune in the reverse direction compared to other planets' satellites and in the opposite direction in which Neptune itself revolves on its own axis. In 1948 Gerard Kuiper (1905-1973) discovered a second Neptune satellite, a faint, small body that he named Nereid.
Information concerning the remote planet's environment revealed a sister world to Uranus. It was another gas giant, but it wasn't tipped over on its axis like Uranus.
The late twentieth century saw a rapid increase in our understnading of Neptune. In 1972 an infrared instrument at Mauna Kea Observatory in Hawaii found feeble heat coming from the planet just as was found for Jupiter and Saturn. Neptune passed in front of a star in 1977, giving astronomers a chance to see if the planet had a ring system. The event revealed invisible rings of dark, opaque material circling the planet.
Finally, in 1989, Voyager 2 flew by Neptune on the last stop of its "Grand Tour" of the outer solar system, giving astronomers a wealth of data about Neptune. Instead of the featureless face of Uranus, Neptune showed cloud markings like Jupiter, including its own storm called the Great Dark Spot. The planet's rings were found to be clumpy, with alternately thicker and thinner sections. Neptune's interior appears to be similar to that of Uranus, with a rocky core surrounded by a watery mantle and a thick atmosphere primarily composed of hydrogen and helium with some methane.
Voyageralso found several small moons and discovered that Triton, Neptune's largest moon, has an atmosphere with haze layers, clouds (possibly volcanic plumes), and arid wind streaks like those found in the atmosphere of Mars. Scientists are trying to determine how an apparently dead, frozen moon remains geologically active today. Astronomers now believe Triton was captured long ago from an independent orbit around the sun after crashing into an earlier Neptunian moon. This would explain its reverse orbit around the planet.
In the late 1990s, new observations of Neptune with the Hubble Space telescope revealed that it is a very dynamic planet. The Great Dark Spot, observed by Voyager 2, had disappeared, distinguishing it from the apparently similar but much longer-lived spot on Jupiter. Additionally, observations of Neptune's clouds showed them to be whipping around the planet at speeds up to 900 mph, clearly being driven by ferocious winds. This presented analysts with quite a puzzle. Atmospheric turbulence and wind currents receive their impetus from solar radiation. One can explain high winds in the atmospheres of the inner planets, where the sunlight is relatively strong. But on Neptune, where the sunlight is about 400 times feebler than at Earth, such tremendously energetic atmospheric currents are difficult to explain. Although we have looked at Neptune close-up with Voyager, and with the most modern space instrumentation available, it still presents us with many unanswered questions.
This is the complete article, containing 1,006 words
(approx. 3 pages at 300 words per page).
