Asteron, called Telstar (テルスター) in the Japanese manual, is a starfish-shaped badnik from the 16-bit version of Sonic the Hedgehog 2 found in Metropolis Zone. Asteron is found in the walls and normally can't be destroyed. When you approach, they begin to flash, then explode, with spikes flying in five different directions.
The enemy reappeared in Sonic Pocket Adventure's Gigantic Angel Zone, and Sonic 4's Mad Gear Zone. In Mad Gear, they twirl before they explode, making them easier to spot.