Mass of objects is decreased, making them more easily displaced.
This is probably the easiest Skull to obtain next to the Blind skull. At the start of the level, look directly behind you for an Elite. Right behind the Elite is a tunnel (hard to miss). Go through the tunnel and continue walking straight until you pass a bridge, which is to your right. Beyond the bridge there is a narrow ledge jutting out of the cliff face ahead. Jump onto this. Hug the wall (just enough room for you to walk) until you get to the end of the cliff, and you will see the Sputnik skull floating in the air.
When activated, the Sputnik skull causes most objects to have severely reduced mass, meaning that they often go flying disproportionately far from seemingly minor melee attacks or explosions. Said objects often have a tendency to splatter players.