After Messenger Spacecraft's Successful Orbital Burn, Mercury Now Has Its First-Ever Satellite
Last night, NASA's Messenger probe fired its thrusters and became the first man-made satellite ever to orbit Mercury. It's a major achievement for NASA and planetary researchers who hope to learn more about the formation and evolution of Earth-like rocky worlds, in this solar system and beyond. Mercury was hurtling through space 96 million miles from Earth when its main thruster fired for 15 minutes starting at 8:45 p.m. eastern time, slowing it down by 1,929 miles per hour. It needed to move slowly enough for wee Mercury's gravitational field to pull it in. It can be difficult to insert a spacecraft into orbit around another world, as evidenced by Japan's failed attempt to send the Akatsuki craft into orbit around Venus last winter. Akatsuki's thrusters failed early in its insertion burn, causing it to overshoot the planet and enter a solar orbit. Japanese researchers hope to try again in six...