Almost like a light bulb, which is gradually reduced current Saturn for the past four years emits less energy in the infrared range, and its southern hemisphere is much "lighter" than the north, according to an article published by the American and British scientists in the Journal of Geophysical Research-Planets .
Researchers led by Li Limin (Liming Li) from Cornell University (USA) analyzed data from the infrared emission of Saturn, obtained in recent years automated probe "Cassini» (Cassini). As it turned out, the planet constantly dims: over the last four years of its radiated power has fallen by 2%, and the effective temperature of — 0.5%.
"The fact that Saturn radiates more than twice as much energy as it receives from the sun, was a mystery to us more than a decade. What generates this excess energy? Our study — the first step in the analysis, "- said co-author Kevin Baines (Kevin Baines) of the Jet Propulsion Laboratory of NASA.
Data received from the infrared spectrometer (CIRS) on board the "Cassini" the researchers also compared with the information obtained as a result of passage of the probes, "Voyager", visit around Saturn in 1980 and 1981. This information, combined with data on the amount of solar heat that gets the planet could help scientists eventually understand the nature of the energy source in the interior of Saturn.
All the planets in the solar system emit energy in the invisible infrared. "We thought that the planets radiate energy evenly and equally in all directions. Now we know that Saturn behaves differently, "- says Li Limin.
As shown by "Cassini", the southern hemisphere of Saturn emits about one-sixth more energy than the northern one. This effect corresponds to the change of time — in the past five years in the northern hemisphere of Saturn was the "winter" and "summer" — in the south. As on Earth, the seasons on Saturn caused by tilting the axis of rotation of the planet, which is why one hemisphere of the planet receives from the sun more energy than others.
Saturn's equinox, when both hemispheres are equally illuminated by the sun, was in August 2009.
Observations "Cassini" showed that the effective temperature — a measure of the radiated heat — the northern hemisphere of the planet gradually fell from 2005 to 2008 and began to grow in 2009. In the southern hemisphere, the effective temperature fell from 2005 to 2009.
The entire planet on the whole observation period "Cassini" cool slowly, reducing the flow of radiation energy. To analyze the changes one Saturnian year (about 30 Earth years) ago, the researchers turned to data collected by the "Voyager" in the early 1980s. However, as it turned out, whereas no significant difference in emission between the two hemispheres of the planet almost was not.
Scientists believe that these differences are due to the weather on Saturn.
"Changes in the energy flow associated with Saturn's cloud cover. When you change the area of the clouds, so does the amount of radiation passing into space. These values can be changed in a single season and from year to year. But to fully understand what is happening on Saturn, we need the second half of the picture: the amount of energy absorbed by the planet, "- says study co-author Amy Simon-Miller (Amy Simon-Miller), head of the Laboratory of planetary systems in the Center of NASA Goddard.
Scientists plan to take the next step, by comparing data from different instruments on board the "Cassini". In particular, the spectrometer will help determine the amount of energy reflected clouds of Saturn. Comparing these data with information about the flow of solar energy, we can calculate the amount of energy absorbed and ultimately determine what the source of the internal energy of the planet.
The mission of "Cassini — Huygens" — a joint project of the U.S. space agency, Europe and Italy to study Saturn. Space probe "Cassini" the descent vehicle "Huygens" was launched in 1997 and reached the planet's orbit July 1, 2004. "Huygens" has studied the atmosphere and surface of Titan, a moon of Saturn, and "Cassini" after the separation of the unit continued to study the planet and its satellites.
In late September, "Cassini" began a new phase of its mission, called "Solstice» (Solstice): the term of the device extended until 2017, and the probe will give scientists their first opportunity to examine in detail all the seasonal period of Saturn.
In early November, the probe has failed, resulting in the "Cassini" moved to "safe mode" in which it ceases to transmit scientific data and transmits only the information about his condition. "Cassini" programmed so that it goes into safe mode every time you create a situation that requires intervention from Earth.
Scientists expect to resume normal operation of the machine on November 24.