Is the orbit of Uranus unusual

View inside Uranus and Neptune

The violent winds in the atmospheres of Uranus and Neptune that can be observed from outside only rage in a zone a maximum of one thousand kilometers deep. This is shown by the exact analysis of the planet's gravity field. By earthly standards that may seem like a lot, but for the two planets, which are around 50,000 kilometers in diameter, it is only a comparatively thin zone. The currents are therefore not circulations that reach deep into the interior of the planets, according to the research team in the journal "Science".

Schematic representation of the winds on Neptune

Yohai Kaspi from the Weizmann Institute of Science in Rehovot, Israel, and his colleagues evaluated the orbit of Voyager 2 to take a look inside the two planets, which are always covered by a thick cloud cover. The American space probe had passed Uranus in 1986 and Neptune in 1989. "Two types of mass anomalies come into question as the cause of measurable disturbances in the gravitational field," explain the researchers: "the rapid rotation, which leads to the planets flattening, and density fluctuations due to fast winds."

As the shape of the planet is known, Kaspi and his team were able to deduce the depth of the winds, which can reach speeds of up to 1,600 kilometers per hour, from the orbital disruptions of the spacecraft: “The dynamics are limited to a thin layer of weather that reaches a maximum of a thousand kilometers on both planets . ”However, that does not necessarily mean that the winds are driven by solar radiation from outside. The researchers emphasize that at Neptune the heat flux from the interior is 1.6 times greater than the inflow from the sun.

For Jupiter and Saturn, which also have strong atmospheric currents, Kaspi and his colleagues have not yet been able to carry out such an analysis. The reason for this is that the winds of the two giant planets vary considerably more with latitude than those of Uranus and Neptune, which leads to additional disturbances in the gravitational field. However, the researchers hope that sufficiently accurate measurements at Jupiter will be possible with the Juno probe, which will reach the planet in 2016. At Saturn, they are relying on the Cassini probe, which will be guided into a polar orbit around the planet after the end of its successful mission in 2017.