Nature reminds us that Neptune’s about to complete its first orbit since it was discovered:
Next week, Neptune will complete its first full orbit of the Sun since it was discovered in 1846.
The blue planet, the farthest out in the Solar System, remains one of Earth’s most mysterious neighbours, but scientists now know one thing that they hadn’t for the past 165 years: the precise length of its day.
Earlier estimates had set that figure at about 16 hours and 6 minutes. But, in a paper in Icarus1, Erich Karkoschka, a planetary scientist at the University of Arizona in Tucson, now pegs it at 15 hours, 57 minutes and 59 seconds.
Determining the day length of rocky bodies such as Mars or Mercury is easy, because scientists can look at their surfaces, in photos or radar images, and track the motion of easily identifiable features.
But Neptune is made mostly of thick clouds of gas, so it has no visible surface. The only visible features are storms, the apparent motion of which results from a mixture of the planet’s rotation and shifting weather fronts.