"New Images Yield Clues to Seasons of Uranus"
The atmospheres of distant planets like Uranus were previously impossible to study in detail until improvements in imaging technology, optics, and the large ground-based telescope Keck II. Now researchers are able to study the seasonal changes that influence astonishing weather conditions. The study also examines how the sun influences the planet's weather.
The study was conducted by Sromovsky and Pat Fry and William Ahue of UW-Madison, the study and Heidi B. Hammel of the Space Science Institute, Imke de Pater of UC-Berkeley, Kathy Rages and Mark Showalter of the SETI Institute, and Marcos van Dam of the Keck Observatory.
Sromovsky says the study is challenging because the seasons change so slowly and Uranus is so far away. Uranus has huge changes in the distribution of solar heating due to the extreme tilt, an unusually large 98 degrees from its orbit plane. During a year the poles of the planet get more sunlight that the equator. Seasons change so infrequently because Uranus has an 84 year orbit.
However, in 2007 Uranus reached its equinox, when the sun is directly over the equator and the little sunlight the planet gets is distributed evenly over the northern and summer hemispheres. The last time this happened scientists didn't have the technology to see any features of the planet, so this time gave scientists their best opportunity to study the seasonal dynamics of Uranus.
Uranus has a blue-green atmosphere of hydrogen, helium and methane and has a ring system. It also has some of the strangest cloud features in the outer solar system. Because the planet lacks a measurable internal heat source and the sun's warmth is 400 times less than it is at the Earth, parts of Uranus can reach below 360 degrees fahrenheit. This is why "Although both hemispheres were symmetrically heated by sunlight at equinox, the atmosphere itself was not symmetric, implying that it was responding to past sunlight instead if current sunlight, a result of Uranus's cold atmosphere and long response time," explains Sromovsky.
The most recent Keck II images show changes in the brightness of cloud bands in the planet's northern and southern hemispheres. Also, there are changes in the discrete cloud features; a massive vortex that had been oscillating in Uranus's southern hemisphere began drifting north and may soon dissipate. The new images showed Uranus' winds can achieve speeds of up to 560 miles per hour.
