Two new studies underline that astronomers are still looking for an accurate assessment of the length of a day on Venus and Saturn.
Venus:
Obscured by clouds, it does not present a readily visible surface feature, such as a crater, which could have been a reference point for measuring its rotation period.
In 1963, when radar observations broke through the cloud cover, Venus revealed that it rotates in a direction opposite to that for most planets.
Studies based on the Magellan spacecraft’s observations concluded that the correct rotation period is 243.0185 days, with an uncertainty of about 9 seconds. Subsequent measurements have, however, given inconsistent values.
Saturn:
A gas giant, by definition, it has no solid surface features for scientists to track.
For Jupiter, scientists figured out the rotation period by observing patterns in radio signals from there. Saturn has defied such attempts. It emits only low-frequency radio patterns that are blocked by Earth’s atmosphere.
A new study led by Duane Pontius of Birmingham-Southern College, US, looked at Jupiter. A key difference is that unlike Jupiter, Saturn has a tilted axis and, therefore, seasons like Earth. Thus, the rotation period cannot be determined from the radio signals.
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