Bakersfield Night Sky – July 2, 2016
By Nick Strobel
Two days from now, on July 4, the Juno spacecraft will arrive at Jupiter. It will fire its main engine for 35 minutes starting at 8:18 p.m. and loop over Jupiter’s north pole to slow Juno’s speed by 1212 mph, so Jupiter can capture it. It will burn through 785 kilograms of fuel during that 35-minute burn. In this capture orbit, Juno will get within 2900 miles of the cloud tops at the equator.
That 8:18 p.m. time is actually when we receive the radio signal from Juno that it has fired its engines. Because of Jupiter’s distance from us (540 million miles), the radio signal from Juno will have been traveling for 48 minutes and 19 seconds, so Juno will actually have started to fire its main engine at 7:30 p.m.
The first couple of polar orbits will be very large ones that take 53 days to execute. After testing all of the systems in Jupiter’s environment, the Juno team will drop Juno in mid-October into smaller 14-day orbits for the science observations. The first few of the science orbits will have Juno come within about 2600 miles of the cloud tops, speeding by at about 60 km per second (or 216,000 mph) at closest approach as it ducks under Jupiter’s very powerful and deadly radiation belts. Its very elliptical orbit will carry Juno out to about 1.7 million miles where Juno will transmit its data back to us and also sample Jupiter’s magnetic field far from the planet.
The last few of the science orbits will have Juno get within about 4900 miles and also flying through part of the radiation belts as it dives in to closest approach. There will be 32 science orbits for the mission. After the last science orbit, Juno’s rocket will fire again to have Juno crash into Jupiter, burning up in Jupiter’s atmosphere on October 16, 2017, after a year’s worth of science observations.
You can watch NASA TV on July 4 for the Jupiter Orbit Insertion (JOI) coverage at www.nasa.gov/nasatv starting at 7:30 p.m. or you can ride along with Juno in realtime using the “Eyes on the Solar System” app at http://eyes.nasa.gov/juno .
Being the most massive of the planets in the solar system, Jupiter was probably the first of the planets that formed and contains the original material from the solar nebula before strong winds from the just-formed sun blew the original light material away. Jupiter’s gravity also played a significant role in shepherding material around in the inner solar system where the Earth and other terrestrial planets were forming. Of particular importance are water and carbon compounds that are critical to life.
Juno will be able to determine if Jupiter has a core of elements heavier than helium and that will tell us about what initiated the formation of Jupiter. Juno will be especially interested in how much water is in Jupiter because that will tell us quite a bit about how the planets got the elements heavier than helium and how Earth got its oceans and hydrogen-carbon compounds. That’s because the various formation theories make significantly different predictions on the amount of water that Jupiter would end up with.
Here are the other science objectives of the Juno mission. Juno will map Jupiter’s gravitational and magnetic fields to help us understand Jupiter’s interior structure and dynamical properties. Juno will map variations in Jupiter’s atmospheric composition, temperature, cloud opacity and dynamics to depths up to 1000 Earth atmospheres of pressure. Juno will measure and explore the three-dimensional structure of Jupiter’s magnetic field at a variety of distances with special attention to the poles where the aurorae are. More about Juno can be found at www.missionjuno.swri.edu and nasa.gov .
Besides JOI and Independence Day festivities, July 4 is also aphelion day when we’re as far from the sun as we will get all year. We’ll be 94,512,904 miles from the sun. That clearly shows that our distance from the sun is not the reason for the hot days of summer.
On the evening of next Saturday, July 9, the telescopes of the Kern Astronomical Society will be pointed at Jupiter and other objects such as a fat crescent moon, Mars, Saturn, globular clusters, open clusters, and bright nebulae for you to look at. The free public star party is at Panorama Park near where Linden Avenue meets Panorama Drive. A map is posted on the KAS website at kernastro.org . Observations begin shortly after sunset and go until 10 p.m. The star chart below shows the sky for the free public star party.