Washington: NASA’s Cassini spacecraft has found that Saturn emitted gradually less energy each year from 2005 to 2009, but its southern hemisphere consistently emitted more energy than its northern one.
On top of that, energy levels changed with the seasons and differed from the last time a spacecraft visited in the early 1980s.
The results could help scientists understand the nature of Saturn’s internal heat source.
“The Cassini CIRS data are very valuable because they give us a nearly complete picture of Saturn,” said Liming Li of Cornell University in Ithaca, N.Y.
“This is the only single data set that provides so much information about this planet, and it’s the first time that anybody has been able to study the power emitted by one of the giant planets in such detail,” Li said.
The planets in our solar system lose energy in the form of heat radiation in wavelengths that are invisible to the human eye.
“In planetary science, we tend to think of planets as losing power evenly in all directions and at a steady rate. Now we know Saturn is not doing that,” said Li.
Instead, Saturn’s flow of outgoing energy was lopsided.
This effect matched Saturn’s seasons: during those five Earth years, it was summer in the southern hemisphere and winter in the northern one. (A season on Saturn lasts about seven Earth years.) Like Earth, Saturn has these seasons because the planet is tilted on its axis, so one hemisphere receives more energy from the Sun and experiences summer while the other receives less energy and is shrouded in winter.
In the study, Saturn’s seasons looked Earth-like in another way: in each hemisphere, its effective temperature, which characterizes its thermal emission to space, started to warm up or cool down as a change of season approached.
“The effective temperature provides us a simple way to track the response of Saturn’s atmosphere, as a system, to the seasonal changes,” said Li.
The emitted energy for each hemisphere rose and fell along with the effective temperature. Even so, during this five-year period, the planet as a whole seemed to be slowly cooling down and emitting less energy.
“The differences between Saturn’s northern and southern hemisphere and that fact that Voyager did not see the same asymmetry raise a very important question: does Saturn’s internal heat vary with time?” said Li.
“The answer will significantly deepen our understanding of the weather, internal structure and evolution of Saturn and the other giant planets.”