And the answer is...

Shuttle

Charon is unusually large for a moon; it is almost half the size of Pluto!

Pluto and Charon
Pluto and Charon

Shuttle

The StarChild site is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), within the Astrophysics Science Division (ASD) at NASA/ GSFC.

StarChild Authors: The StarChild Team
StarChild Graphics & Music: Acknowledgments
StarChild Project Leader: Dr. Laura A. Whitlock
Curator: J.D. Myers
Responsible NASA Official: Amber Straughn