Jupiter's Rotation

[p1t1o]

If Jupiter is made largely of fluid - there is a possibility of a solid core, but this is uncertain - at least the upper several  thousand kilometres are fluid, and we can only observe a fraction of this.

Not only that but of the layers we can see, they can rotate in either direction, at varying speeds.

Taking all of that, how can we say that Jupiter "rotates". It has a "day" length of around 10 hours. Which part is rotating once every 10 hours? This band? That band? Do we have some kind of handle on what the deeper masses are doing? 

In other words, how do you measure the rotation of a swirling ball of fluid?

[Scotius]

Probably just like we chose Greenwich as a point 0 of time measurement. Astronomers picked a feature on the Jovian equator, measured the time until it showed up again, and said "Jupiter makes one rotation in 10 hours." Bam. Done.

[sevenperforce]

25 minutes ago, p1t1o said:

If Jupiter is made largely of fluid - there is a possibility of a solid core, but this is uncertain - at least the upper several  thousand kilometres are fluid, and we can only observe a fraction of this.

Not only that but of the layers we can see, they can rotate in either direction, at varying speeds.

Taking all of that, how can we say that Jupiter "rotates". It has a "day" length of around 10 hours. Which part is rotating once every 10 hours? This band? That band? Do we have some kind of handle on what the deeper masses are doing? 

In other words, how do you measure the rotation of a swirling ball of fluid?

The official rotation of Jupiter is the rotational period of its magnetosphere, because this represents the bulk of the mass of the planet. This was also the first rotational period to be accurately measured, since it could be measured via radiotelescopes. Parts of the surface orbit faster than this; parts orbit slower.

[YNM]

1 hour ago, p1t1o said:

Taking all of that, how can we say that Jupiter "rotates". It has a "day" length of around 10 hours. Which part is rotating once every 10 hours? This band? That band? Do we have some kind of handle on what the deeper masses are doing? 

I think the blunderbus attempt is made for this. I've heard that you can actually measure it from down here, by pinging radar off it and see the shift in frequency. Given the low accuracy, I guess it just ends up being the average "tropical" "top" layers. EDIT : Look the post above.

It is well known that the layers and latitudes rotates differently and there are models of it, just like for The Sun.

53 minutes ago, Scotius said:

Astronomers picked a feature on the Jovian equator, measured the time until it showed up again, and said "Jupiter makes one rotation in 10 hours." Bam. Done.

They'd notice the inexactness very quickly I think. Even sunspot measurements were known to show the varied rotational speed of Sun's surface, back when sunspots were all we could see on it.

Edited March 12, 2018 by YNM

[p1t1o]

54 minutes ago, sevenperforce said:

The official rotation of Jupiter is the rotational period of its magnetosphere, because this represents the bulk of the mass of the planet. This was also the first rotational period to be accurately measured, since it could be measured via radiotelescopes. Parts of the surface orbit faster than this; parts orbit slower.

Asked and answered, noice

 

[kerbiloid]

Jupiter has 3 rotation coordinate systems at once.

I (T = 9^h30^m) for equatorial visual surface (abs(latitude) <9°)
II (T = 9^h56^m) for visual surface at other latitudes
III for magnetosphere.

Saturn has two: for visual surface and for magnetosphere.

http://www.springer.com/gb/book/9783540672210