Take a moment to consider Neptune. The eighth planet in our solar system, the planet farthest from the Sun, and the third most massive planet in our solar system. Also one of the least visited, and consequently one of the least understood planets in our solar system. Neptune was discovered in 1846. Forty years later, in 1886, astronomer Sir Robert Ball wrote ‘Besides this brief sketch of the discovery of Neptune, we have little to tell with regard to this distant planet. With a good telescope and a suitable magnifying power we can indeed see that Neptune has a disc, but no features on that disc can be identified’.
Neptune (Credit NASA)
Unfortunately in the last 126 years not much has changed. Due to its enormous distance from Earth (~ 30 Astronomical Units) Neptune remains little more than a blurry disk in the eyepiece of the most powerful ground based telescopes. In the past astronomers studied Neptune by examining the planet as it occulted, or passed in front of the light of another object, usually a star, allowing scientists to calculate its diameter, chemical composition, and temperature. The opportunity to study the gas giant only improved when Voyager flew by Neptune in 1989, and the Hubble Space Telescope was launched in 1990.
Voyager 2 launched in 1977, and reached Neptune on the 25th of August 1989 (click here for an impressive animation of the Voyager 2 flyby of Neptune). Although Voyager 2 began imaging the planet from about 35,000,000 million miles out, most of the data we have today is from a 24 hour period, during which Voyager 2 passed 4,500 kilometres above Neptune’s north pole at an eye watering 67,000 km per hour. During the trip to Neptune Voyager gathered about 5 trillion bits of information or about .5 of a Terabyte of data. That doesn’t sound much now, but back in 1977 the 3 computers on the Voyager spacecraft had a combined memory of 68Kb, so Voyager sent back almost 15 million times more data that could be stored in it’s memory!!
