Weizmann Institute researchers and their colleagues set an upper limit for the thickness of jet streams on these two giant planets.
The weather forecast for Uranus and Neptune has been the same since the discovery of strong atmospheric winds in the 1980s by the Voyager II spacecraft. But now a team of Israeli and American scientists say winds on the surface of Uranus and Neptune don’t cover the entire planets. New research at the Weizmann Institute of Science, the University of Arizona and Tel Aviv University, which was published online in Nature, shows that the hurricane-like wind patterns seen on the surface can extend only so far down on these two worlds. The vertical extent of these winds has been a major puzzle – one that influences our understanding of the physics governing the atmospheric dynamics and internal structure of these planets. a team led by Dr. Yohai Kaspi of the Weizmann Institute’s Environmental Sciences and Energy Research Department realized they had a way, based on a novel method for analyzing the gravitational field of the planets, to determine an upper limit for the thickness of the atmospheric layer. Kaspi and his co-authors calculated, for the first time, the gravity signature of the wind patterns and created a wind-induced gravity map of these planets. By computing the gravitational fields of a large range of ideal planet models – ones with no wind – a task conducted by team member Dr. Ravit Helled of Tel Aviv University – and comparing them with the observed gravitational fields, upper limits to the meteorological contribution to the gravitational fields were obtained. This enabled Kaspi’s team, which included Profs. Adam Showman and Bill Hubbard of the University of Arizona, and Prof. Oded Aharonson of the Weizmann Institute, to show that the streams of gas observed in the atmosphere are limited to a “weather-layer” of no more than about 1000 km in depth, which makes up only a fraction of a percent of the mass of these planets. Kaspi hopes the team’s findings will be useful in the analysis of another set of atmospheric circulation patterns that will be closely observed soon: those of Jupiter.