Like the Roman god the planet is named for, Jupiter is shrouded in clouds. And as the story goes, only Juno, Jupiter’s wife, will be able to peer in. Enter the NASA Juno mission.
On July 4 (EDT), the Juno spacecraft completed its five-year trek from Earth to get into orbit around the Solar System’s largest planet. This is much easier said than done. Since Juno was travelling too fast for Jupiter’s gravity to ensnare it when it got there, the spacecraft fired its engine for 35 minutes and slowed considerably. Juno also had to perform complex manoeuvres to keep itself stable (and not break apart like Japan’s Hitomi did in February), and steer clear of Jupiter’s moons, its strong magnetic field and the harmful radiation surrounding it. And Juno had to do all this within a 35-minute window. If it had missed, Jupiter’s radiation would’ve killed the probe and the $1.1-billion mission would’ve ground to a tragic, premature halt. As it happened, the orbital insertion manoeuvre was flawless.
It’s no wonder then that the team behind the achievement was overjoyed when it was all over. In fact, a NASA scientist had proclaimed that this was ‘the hardest thing’ NASA had ever done – beyond its famed Pluto fly-by last year or even the first manned moon mission in 1969. Now, Juno will orbit Jupiter twice over 106 days in a large, loopy orbit before settling into a 14-day orbit in mid-October. That’s also when the science mission will begin in earnest. In the meantime, a group of NASA scientists took to reddit to answer questions about the mission. A curated version, edited for clarity, follows.
What specific theories about Jupiter are you most looking forward to confirming?
I’m most interested in finding out what lurks beneath Jupiter’s clouds. It’s mind-blowing to think that we don’t yet know what the interior is of the largest planet in the solar system. Is it rocky? Is it metallic? We just don’t know. But that’s exciting, and it’s why we explore. –Stephanie L. Smith, social media lead at NASA’s Jet Propulsion Laboratory (JPL), Pasadena
I’m really excited about measuring the global water abundance! The amount of water in Jupiter should tell us a lot about how and where the planet formed. The leading theory right now involves large chunks of ice initially, possibly with the planet drifting inward after initially forming much farther from the Sun. The water abundance should teach us a lot about those formation theories. –Steve Levin, Juno project scientist
Could you elaborate on what we could learn about Earth with new information we may obtain?
Our understanding of how solar systems form is in some chaos (pun intended) due to all the exoplanets we’re finding. Understanding when and where Jupiter formed (e.g. by looking at the water abundances) will help us understand when and where Earth formed with respect to our Sun. –Jared Espley, Juno program scientist
Does Jupiter’s massive gravitational pull make it more difficult to keep a probe in orbit?
Actually, Jupiter’s massive gravitational pull helps to keep our probe in orbit. When we fired our main engine last night, we were moving at 54.1 km/sec. After firing our main engine, we were moving away from Jupiter at 53.7 km/sec. That’s still really fast! But that really small decrease in orbital speed was enough to put us into a 53 day orbit (instead of a Jupiter flyby). Jupiter’s pull is so strong, it would be very challenging now to get out of orbit. This wasn’t what I initially expected when the navigators explained to me but it does help demonstrate how different things are when you are around such a massive planet. –Rick Nybakken
Can you talk more about the reason Juno has to be intentionally destroyed? Also, from the pre-orbit press release there was a question about the possibility of sending an image back from under the clouds before it disintegrates. How likely could this really be?
Re deorbiting: We think Jupiter’s icy moon Europa has a subsurface ocean of liquid water; and because everywhere on Earth that we’ve found water, we’ve also found life, this is a good place for us to search. However, we don’t want to go looking for life in the universe only to find that we brought it with us from Earth. We have to abide by something called Planetary Protection. (It’s like the Prime Directive, but real.)
So, to keep Juno from ever running the risk of crashing into Europa and contaminating it, we will deorbit the spacecraft into Jupiter.
Re pictures: Images from under the clouds would be amazing. Whether or not the spacecraft could still transmit them is another matter. We might not have the right attitude during deorbit to do that.
While the main goal of the mission is to study the planet’s origin and structure, we will take as many images of the moons as we can. –Steve Levin
Do you plan to release the raw images taken with JunoCam to the public soon? Will there be an approach similar to the release of Cassini or Curiosity raw images?
The approach movie images will be released soon. Images from Orbit 1 will not be released immediately, because we’ll be doing lots of testing of the camera operations then, but from Orbit 2 and onward, our policy will be to release all images in a format that can be read immediately as soon as we get them and this initial processing step is done. –Glenn Orton, NASA-JPL senior research scientist
If you had to send a command in ‘real time’ how long would it take one byte of data to reach Juno?
Right now, it would take a bit more than 45 minutes for a command to reach Juno. That’s how long it takes for radio waves (or light) to reach Jupiter from Earth. Earth and Jupiter both move, of course, so the “one way light time” will change.
Do your antennas have to account for this relative motion when sending or receiving data? Is the frequency shift significant?
Yes. The big radio antennas from NASA’s Deep Space Network have to take into account both the motions of Jupiter, Earth, and the spacecraft in order to point in the right direction and track at the right frequency. –Steve Levin
What kind of radiation protection do the electronics on Juno have?
The predominant protection is the titanium vault that houses our critical electronics – the “brains” of the spacecraft. This vault has walls up to 1/2 inch thick and weighs approx. 400 lbs empty. The vault reduces the radiation these electronics are exposed to over the life of the mission from 20,000,000 rad to 25,000 rad and allows us to survive the full 16 months of our science mission. External sensors are outside the vault and have a side wall of tantalum or tungsten to provide them sufficient shielding to operate for our 16 month science mission. –Rick Nybakken