So what of those winds? They are undeniably fierce, and this may have something to do with temperature. For Uranus and Neptune it is possible that they are different ages or, more likely, the event that turned Uranus onto its side may have jumbled its interior structure and/or released heat faster," said Simon. "On the gas giants there may be significant amounts of helium rain, changing the amount of heat released. How quickly they release depends on the interior structure and composition, cloud layers, convection and so on and that can be rather complicated." "How much heat a planet radiates depends mostly on how old it is and how quickly or slowly it releases that heat," said Amy Simon, a NASA senior scientist for Planetary Atmosphere Research at the NASA Goddard Space Flight Center. It could also be an issue of Uranus being an old-timer and Neptune a younger pup. "The burps are convection, which may happen in discrete episodes separated by long time periods, but we may not know if it works this way for sure unless we see one of these convective episodes take place." "We may just be seeing Uranus in a quiescent period, whereas Neptune has burped more recently," said Tollefson. There is a possibility that heat is not released from the interior at a steady rate but instead comes in "burps". "The question becomes, why does Neptune have an internal heat source but Uranus does not?" "Something must have stunted this process on Uranus - perhaps due to a collision in its early history that knocked the planet on its side," said Tollefson. Yet there is no clear reason why Uranus does not have much of an internal heat source - or any at all. "As the planet slowly gravitationally contracts, the material falling inward changes its potential energy into thermal energy, which is then released upwards out of the planet." "The extra heat source on Neptune is largely due to gravitational contraction," said Joshua Tollefson, also of the University of California, Berkeley. The heat contracts out of the primitive solar nebula - an effect known as the Kelvin-Helmholtz contraction. "Yet that unusual result is associated with the fact that Uranus does not have a significant internal heat source." Neptune is finding a way to warm itself up to the level of Uranus, while the latter is unable to generate any extra heat other than that gleaned from the sun.īut just what is an internal heat source? In simple terms it is heat left over from the birth of the solar system when these planets were formed. Uranus is the one that is out of place," Del Genio said. "The progression of temperature as you go farther away from the sun shows Jupiter to be the warmest of the gas giants, Saturn next, then Neptune. Related: A Mysterious Glow Warms Rings of Uranus " Jupiter and Saturn also emit almost twice as much heat as they absorb, but Uranus does not," Del Genio said. That's because Neptune is not unusual in this case. And this is where things become rather intriguing. "Voyager's measurements show Neptune emits more than twice as much heat as it absorbs from the sun, while Uranus does not," Anthony Del Genio of the NASA Goddard Institute for Space Studies (GISS) told All About Space. What this similarity in temperature suggests is that Neptune is warmer in terms of how much heat it emits in comparison to the amount of heat it absorbs from the sun. But since Neptune receives less solar illumination because it's farther from the sun, this shouldn't be the case. In doing so we find that Neptune isn't actually hotter than Uranus in real terms - they're essentially at the same temperature. "We can only measure temperatures in the outermost layers," said Michael Wong, a planetary scientist at the University of California, Berkeley, via email.
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