Jupiter Today | 18 December 2015 | Velocity Audio

Let's start with the sound of the relative velocities:

Velocity Audio | 18 December 2015

Here are the positions of the four Galilean moons of Jupiter as they orbit the planet over the next 24 hours.  This view is looking down on the system, and the moons are moving counterclockwise.  The blue line pointing towards the left is the line of site to Earth.  The red line pointing left is the line of site to the sun.

Here are the relative velocities between the four moons (six combinations):

The y-axis shows the velocity in kilometers per minute.  Negative values represent moons moving towards one another, positive values represent moons moving away from one another.  So for example, the blue line representing the relative velocity between Ganymede and Callisto shows that they are moving toward one another at a pretty constant velocity of 300-ish km/min.  Looking at the orbit plot above, you can see that Ganymede is "catching up" to Callisto just as the velocity plot shows.

Line color code:

• Cyan - Io / Europa
• Pink - Io / Ganymede
• Yellow - Io / Callisto
• Green - Europa / Ganymede
• Red - Europa / Callisto
• Blue - Ganymede / Callisto