Astronomy Picture of the Day . New Horizons at Io . ... Credit: NASA , JHU/APL , SwRI - Additional Processing: Sean Walker Explanation: Spewed from a volcano , a complex plume rises over 300 kilometers above the horizon of Jupiter's moon Io in this image from cameras onboard the New Horizons spacecraft. The volcano, Tvashtar , is marked by the bright glow (about 1 o'clock) at the moon's edge, beyond the terminator or night/day shadow line. ... Publications with keywords: volcano - Io . ...