Look! It’s a bird, it’s a plane, it’s … Juno! The Juno spacecraft will make an extremely close pass of Earth en route to its ultimate goal, the planet Jupiter. At 4:21 p.m. Central Daylight Time the probe will pass just 347 miles (559 km) from the ground while sailing over the southern tip of Africa at the incredible speed of 25 miles per second relative to the sun.
The close shave is deliberate – Juno will pick up an additional 16,330 mph of speed as it steals a bit of Earth’s orbital energy during the flyby. NASA’s been using “gravitational assist” since the Mariner 10 flybys of Venus and Mercury in 1973. Outer planet probes Voyager 1 and 2 leapfrogged their way across the solar system thanks to speed boosts from Jupiter, Saturn, and in the case of Voyager 2, Uranus. The method saves time and reduces energy requirements for space missions. Best of all – it’s free!
Juno won’t be twiddling its thumbs during the flyby. NASA has programmed it to make a movie of the Earth-moon system showing the Earth spinning on its axis – the first time ever we’ll see our planet rotating from a distance. The craft will also make brief studies of Earth’s magnetosphere, the protective magnetic envelope surrounding the planet.
No one’s sure how bright the spacecraft might become. Most estimates I’ve seen put it around magnitude 9 at closest approach, making it easily visible in a small telescope if you know exactly where to look.18 minutes after its closest approach, Juno leaves Earth’s shadow and comes into view for observers in Europe and Asia, when it will be moving through the constellation Perseus. By then it will have faded to about magnitude 14 but possible glints from its large solar panels could create brighter flares.
When darkness falls over North America Juno will still be in Perseus but a magnitude fainter. That’s a tough find for visual observers with larger scopes but within reach of amateur astrophotographers. Again, these estimates are approximate. Juno could be brighter or dimmer.
Since most of us won’t be able to see this faint flyby from our backyards, others have generously come to the rescue. The Slooh telescope in the Canary Islands will broadcast live video of Juno tonight beginning at 8:30 p.m. CDT. Ham radio operators can also say hello to the probe in Morse cod by participating in Say ‘HI’ to Juno!
Amateur astronomer Scott Degenhardt will webcast Juno live from his home in New Mexico during two time slots: 1:45-2:45 a.m. and 4:15–5:15 a.m. tomorrow morning Oct. 10. Scott mentioned in an e-mail that bad weather might be coming, so if he’s offline, you’ll know why.
Learn more about the Juno mission in this video
Once Juno departs the Earth’s vicinity it’s in for a long cruise to Jupiter nearly half a billion miles away. Not until it enters Jupiter orbit in July 2016 will Juno see another planet so close. Click HERE to find out more its mission.