Next Wednesday Oct. 9, the Juno spacecraft will make an extremely close approach to Earth as part of a gravity assist maneuver to boost to it to Jupiter. The probe was launched on Aug. 5, 2011 on a mission to look deep inside the planet below the swirling clouds that make Jupiter a favorite target for beginning astronomers.
Juno will focus on the composition of Jupiter’s core, how much water saturates its lower level clouds, clock wind speeds at great depth and examine the planet’s vast magnetosphere, a bubble of magnetism spun to high speed by Jupiter’s rotation and laced with subatomic particles that buzz like angry bees. Most of particles are spewed by volcanic eruptions from the moon Io and spawn powerful auroras.
Most spacecraft launched these days are not sent directly to their targets but loop by planets like Earth and Venus to pick up additional speed free of charge. Well, not exactly free. As Juno slingshots by Earth it will gain energy and velocity from the encounter but rob Earth of a tiny bit of its orbital energy. A gravitational assist both changes the direction of a spacecraft and pumps up its speed, saving time and propellant.
Video of Juno’s flyby of Earth on Oct. 9
A gravity assist can speed up a spacecraft if it flies with the movement of the planet or decelerate if it flies against the direction of its movement.
Will we see it? Probably not. The spacecraft’s closest approach occurs while in Earth’s shadow off the southern coast of Africa. The ground-track then heads northeast toward India before turning west to cross southern Europe. Observers there might catch it in binoculars if they know exactly where to look.
The spacecraft buzzes over North America the night of Oct. 9-10. It will be departing Earth’s vicinity at that time and probably be too faint for small telescopes but not for astrophotographers and amateurs with larger scopes.
NASA’s next Mars mission called MAVEN (Mars Atmosphere and Volatile EvolutioN) had been put on hold during the U.S. government shutdown. This raised the possibility that it might have missed its launch window (Nov. 18 – Dec. 7) depending on how long it the impasse might continue. But earlier this week it was determined that the mission provided a crucial communications link to help relay signals from Earth to the Curiosity and Opportunity rovers, making the spacecraft available for emergency funding. We’re back in business!
MAVENwill begin orbiting Mars next September to study its current climate to shed light out how the planet evolved into its current cold, dry state. Nice to get some good news.