杏吧原创

A study of Neptune鈥檚 colossal cloud bands has shown that the planet undergoes seasonal changes in weather 鈥� the gas giant is just beginning a 40-year summer.

Researchers from Wisconsin-Madison University and NASA鈥檚 Jet Propulsion Laboratory found that Neptune鈥檚 southern cloud bands have been getting steadily wider and brighter over the past six years. They studied images of the planet captured with the Hubble Space Telescope in 1996, 1998 and 2002.

The growing cloud cover is most likely the result of increased solar heating from the Sun, says Lawrence Sromovsky of Wisconsin-Madison University. The effect is less pronounced near to Neptune鈥檚 equator, which is consistent with the effect, he adds.

鈥淭his change seems to be a response to seasonal variations in sunlight, like the seasonal changes we see on Earth,鈥� Sromovsky says.

Seasonal drift

Neptune鈥檚 weather cycle can be compared to Earth鈥檚 because both planets have an inclined axis that places the northern or southern hemisphere closer to the Sun during different parts of a solar orbit. This produces an alternate summer and winter each hemisphere, and two transitional seasons, spring and autumn, in between.

But as Neptune takes 164 years to travel around the Sun, each season must last about 40 years, rather than just three months as on Earth. Sromovsky says it is remarkable that Neptune experiences any seasons at all, given that it orbits 40 times further away from the Sun than Earth. This means the intensity of solar radiation is much lower on Neptune.

Observations indicate that Neptune experiences some very extreme of weather conditions. The planet鈥檚 average surface temperature is thought to be about -218 掳C, with storm winds of up to 1500 kilometres per hour.

These extreme conditions on the surface of the gas giant are believed to be largely driven by heat from Neptune鈥檚 inner core of molten rock, liquid ammonia and methane.

Peculiar process

James O鈥橠onnell, an astronomer at the UK鈥檚 Royal Observatory Greenwich, says the latest findings may help planetary scientists better understand how this peculiar heating process and solar radiation combine to control the surface conditions on Neptune.

鈥淲e鈥檝e got observations over about a decade or so, so we can start to pick up these long term changes,鈥� O鈥橠onnell told New 杏吧原创.

鈥淣ot only is there some sort of internal heat driving the strong winds in the atmosphere and the cloud structure, but clearly solar heat is also changing the structure of the atmosphere over time,鈥� he says.

Journal reference: Icarus (vol 163, issue 1)