The Great Red Spot by Voyager 1

Sorry for the gigantic image, but it was just too cool to pass up (Edit: The image has been resized to fit better. NASA loves to show things at uber-resolution, unfortunately that doesn't work too well when showing it in a blog. The full res image can be found at APOD). Courtesy of today's APOD we have an exquisite picture of Jupiter's Great Red Spot taken by Voyager 1 as it passed by in 1979. To be honest this picture looks more like a painting than an actual image of a real event, but such is the way of many astronomical images.

The Great Red Spot is an incredible storm that has been raging for over 400 years on Jupiter. No one is quite sure how it started or why it is so long lived. It is huge though being so large that two Earths could easily exist inside of it, with winds topping out at about 400 km/h.

While it looks like a giant hurricane, the Great Red Spot is actually anticyclonic. This means the Great Red Spot rotates the wrong way with respect to the expected Coriolis forces. Instead the Great Red Spot is a fantastic example of a classic fluid instability called the Kelvin-Helmholtz instability. In this instability you have two fluids adjacent to each other, each flowing in opposite directions. This forms a shear layer between the two fluids. If one perturbs the boundary between the fluids, one creates and instability which will grow mixing the fluids. This mixing pattern can form into a stable configuration known as a cat's eye, of which the Great Red Spot is an excellent example. Simulations of this instability can be found here.

The probe that took these pictures, Voyager 1, is now long gone from Jupiter. It is now on a trip out of the Solar System and is investigating other interesting astrophyisical fluid dynamics. In this case it is looking at how the wind generated by our Sun interacts with the surrounding Interstellar Medium (ISM). Currently Voyager 1 has entered what is known as the Heliopause. In this region the Solar wind slows down and stops as it interacts with the ISM. This creates a contact discontinuity between the Solar Wind and the ISM. When Voyager 1 leaves this area it will finally enter into interstellar space for the first time. This will be our first chance to directly probe what interstellar space look like rather than relying on telescopes. Voyager 2 is also on the same path and will join its sibling out in interstellar space soon after Voyager 1 gets there.

On a side note, in my previous post I mentioned Endeavour's impending launch. The launch has been delayed due to a heater malfunction. The earliest date for a retry won't be until May 8th. However, that is subject to change as any further problems are found. Once a firm date is set I will try to post a note here.