Make your own free website on
Atmosphere on
[ Main I Statistics I Atmosphere I Moons I Missions I Other Info I Images I Links ]

Neptune's Atmosphere
Written by Dane Atkinson

INTRO: In August of 1989, Voyager 2 was the first and only ship so far to fly by Neptune. This was the only time we really were able to observe the interesting atmosphere of Neptune.

COMPOSITION AND COLOR: It's atmosphere consists of 85% hydrogen, 13% helium, and 2% methane. The icy particles of methane are the cause of Neptune's blue appearance because it absorbs wavelengths of red light and transmits the reflected blues.

CLOUDS AND STORMS: It was also recorded to have the greatest wind speeds compared to any other planet in our solar system, reaching speeds of 2000 km/hour. This causes Neptune's features like clouds to form and dissipate over several hours.

Neptune's largest storm, The Great Dark Spot is an Earth-sized hurricane spinning counter-clockwise in the thick methane atmosphere of Neptune. The shape, size, and location of this spot vary greatly over time: It disappears and re-appears occasionally.

Horrendous winds near this spot were measured by Voyager 2 to be about 1,500 miles per hour. This is the strongest recorded wind in our solar system. Scientists believe this storm is caused by a difference in temperature with the heat-producing core and the frigid cloud tops. The fastest winds in the solar system sweep them "backward" around the planet (in a direction opposite to Neptune’s
direction of spin). Other storms that are smaller than the Giant Dark Spot include the Scooter and Dark Spot Two.

CORE COMPOSITION: Beneath these strong clouds is a mantle of ice and gas. Neptune has a magnetic field, which is tilted more than 50° to the rotation axis. Neptune also has it's own large internal heat source, as the planet emits nearly three times as much heat as it receives from the Sun. How does a cold planet like this produce most of it's own heat? Possibly it is
due to a highly active electro-magnetic field or possibly some totally unknown cause. Different groups of scientists believe that Neptune's core structure is composed of either rocky material or liquid ice about the mass and/or size of Earth.

TEMP: Infrared measurements made by Voyager 2 indicated a higher temperature of at least minus 218 deg C (minus 360 deg F). Thus Neptune, like Jupiter and Saturn but unlike Uranus, appears to have an internal energy source.