Juno provides new data on Jupiter; readies for primary science mission

by Chris Gebhardt

The Juno spacecraft has beamed back stunning images from its recent – and closest – approach to Jupiter, swinging to within 4,200 km (~2,610 miles) of the largest planet in our solar system. The approach sets the stage for the primary aspect of Juno’s science mission – an extended, polar orbit survey the Jovian giant to help us better understand Jupiter and aspects of outer solar system development.

Post orbit insertion activities:

After launching from the Cape Canaveral Air Force Station aboard a United Launch Alliance Atlas V 551 rocket on 5 August 2011 at 12:25 EDT, Juno enjoyed a relatively issue free cruise to Jupiter, arriving at the Jovian system on 4 July 2016.

With Juno in autopilot mode, the spacecraft’s onboard computers began the anticipated 35min 03sec Jupiter Orbit Insertion (JOI) burn at 22:30 EDT – with confirmation of JOI burn commencement arriving through the Deep Space Network at 23:18:19 EDT after a travel time of 48 minutes 19 seconds across a distance of 869 million km (540 million miles).

Screen Shot 2016-07-02 at 14.42.28Juno’s computers completed the JOI burn at 23:05:02 EDT – just one second off the predicted burn time.

Despite the one second discrepancy in predicted vs. actual burn time, Juno settled perfectly into its initial 53.5-day capture orbit.

After JOI burn, Juno reduced its spin rate from five rotations per minute – needed for stabilization during the burn – to its nominal stabilization rate of two rotations per minute before then reorienting itself to aim its solar panels back toward the sun.

Unlike all previous missions to the outer solar system, Juno utilizes solar power instead of nuclear energy from Radioisotope Thermoelectric Generators (RTGs).

Because of its operational distance from the sun, Juno is fitted with three solar panels measuring 2.7 m (9.8 ft) in width by 8.9 m (29 ft) in length for a total power generation capability at Jupiter of 486 W, dropping to 420 W at the end of the mission due to radiation degradation.

Screen Shot 2016-07-02 at 14.43.29A prime reason that Juno is able to use solar panels instead of RTGs comes from the significant advancements in solar cell technology over the past several decades and makes Juno the farthest solar-powered mission in the history of space exploration.

Following JOI and reorientation, Juno’s science teams slowly brought the spacecraft’s science systems and JunoCam back online.

Juno’s instruments and cameras were not active during the JOI burn due to spacecraft orientation, power conservation requirements (Juno was on battery power during the JOI burn), and a desire to simplify the orbit insertion procedure as much as possible.

Unlike the immediate previous outer solar system planetary encounter – New Horizons with dwarf planet Pluto on 14 July 2015 – Juno’s orbital mission did not necessitate a need to have its science instruments functioning upon its arrival.

Instead, the instruments were powered up after Juno attained a stable capture orbit around Jupiter, and Juno’s science teams used the craft’s first orbit to calibrate the instruments ahead of the first close approach to the planet.

In fact, the initial 53.5-day orbit suited Juno’s science instruments well, since they were designed for close-up investigation of the planet and not long-range observations – the only kind possible during a vast majority of the capture orbit period.

Closest approach:

By 31 July at 12:41 PDT (15:41 EDT), Juno reached apojove – the farthest point in its orbit of Jupiter – at a capture orbital distance of 8.1 million km (5 million miles) from the giant planet.

At this point, Jupiter’s gravity took hold of Juno and began pulling the craft back toward the planet.

2016-09-03-141602At the same time as Juno reached apojove, its science teams confirmed that all of the craft’s instruments were fully functional and ready for the first close science encounter with Jupiter.

“We’re in an excellent state of health, with the spacecraft and all the instruments fully checked out and ready for our first up-close look at Jupiter,” said Rick Nybakken, Juno project manager at NASA’s JPL ahead of the milestone.

After 26 and a quarter days of return flight, Juno performed its first and closest approach to Jupiter for the entire mission (less its planned end-of-mission plunge into the planet) with an active suite of science instruments and cameras.

2016-09-02-233109The encounter came on 27 August with the time of closest approach occurring at 06:44 PDT (13:44 UTC) when Juno passed about 4,200 km (2,610 miles) above Jupiter’s upper cloud features.

“Early post-flyby telemetry indicates that everything worked as planned and Juno is firing on all cylinders,” said Mr. Nybakken.

Moreover, according to Scott Bolton, principal investigator of Juno from the Southwest Research Institute in San Antonio, “We are getting some intriguing early data returns.  It will take days for all the science data collected during the flyby to be downlinked and even more to begin to comprehend what Juno and Jupiter are trying to tell us.”

2016-09-03-142842That data started to arrive back on Earth, including some unique views of Jupiter’s north pole taken by JunoCam during the flyby from 25 to 29 August.

“First glimpse of Jupiter’s north pole, and it looks like nothing we have seen or imagined before,” added Mr Bolton. “It’s bluer in color up there than other parts of the planet, and there are a lot of storms.

“There is no sign of the latitudinal bands or zone and belts that we are used to – this image is hardly recognizable as Jupiter. We’re seeing signs that the clouds have shadows, possibly indicating that the clouds are at a higher altitude than other features.”

The Jovian Infrared Auroral Mapper (JIRAM), supplied by the Italian Space Agency, also acquired some remarkable images of Jupiter at its north and south polar regions in infrared wavelengths.

2016-09-03-142749“JIRAM is getting under Jupiter’s skin, giving us our first infrared close-ups of the planet,” added Alberto Adriani, JIRAM co-investigator from Istituto di Astrofisica e Planetologia Spaziali, Rome.

“These first infrared views of Jupiter’s north and south poles are revealing warm and hot spots that have never been seen before. And while we knew that the first-ever infrared views of Jupiter’s south pole could reveal the planet’s southern aurora, we were amazed to see it for the first time.

“No other instruments, both from Earth or space, have been able to see the southern aurora. Now, with JIRAM, we see that it appears to be very bright and well-structured. The high level of detail in the images will tell us more about the aurora’s morphology and dynamics.”

Juno is now on its second capture orbit swing around Jupiter – which won’t bring the craft back into proximity with the gas giant until 19 October.

2016-09-02-233300On that day, Juno’s teams will fire the craft’s engine once more to alter the orbit from the initial 53.5-day capture orbit to the primary 14-day science orbit.

Once in a stable science orbit, Juno will execute 34 polar orbits of Jupiter, providing excellent coverage and information regarding the planet’s cloud formations, interior, and magnetosphere.

As with all missions that hold the risk of contaminating potentially habitable worlds, Juno’s mission is currently scheduled to come to an end on 20 February 2018 when the probe will once again fire its engine to send it on a destructive dive into Jupiter’s atmosphere.

At first, it was widely stated by NASA that there was no ability to extend Juno’s mission beyond that 20 February 2018 date.

However, at the post-orbit insertion news conference on 5 July, Juno’s science teams seemed to hesitantly – yet optimistically – confirm that 20 February 2018 is not set in stone, and the mission could be extended based on fuel consumption rates and radiation degradation to the spacecraft.

Harmonic resonance – Juno captures an unprecedented film:

Juno’s primary science mission won’t begin for another month, and, while it promises to bring exciting discoveries about Jupiter, the craft has already contributed a significant observation of stellar systems.

For centuries, astrophysicists and the many in the general public have heard of harmonic resonance among celestial bodies.

2016-09-03-143200Harmonic resonance – often referred to colloquially as orbital resonance – is a mathematical ratio balance in the orbital periods of certain celestial bodies.

While harmonic resonance does not occur in obvious ways within the inner solar system, the outer solar system is rife with such balance, seen especially with the Trans-Neptunian Objects/Kuiper Belt Objects (TNO and KBO) and Neptune.

Neptune and a number of the TNOs/KBOs orbit in a 3:2 resonance with each other – including Neptune and dwarf planet Pluto.

Coming back into the solar system, a close example of harmonic resonance can be found between three of Jupiter’s four primary moons: Ganymede, Europa, and Io – which orbit in a 1:2:4 resonance with each other.

2016-09-03-143349However, while harmonic resonance is a well known, understood, and logical pattern, we have never been able to directly observe and/or film this resonance because we’ve never been able to look down or up at the solar system or the planets.

That is, we have never been able to do this until Juno.

During Juno’s approach to Jupiter for orbit insertion, JunoCam captured for the first time what Galileo first discovered – by observing Jupiter – in 1611.

Looking down on the Jovian system, JunoCam captured a complete orbital harmonic dance of the Jovian moons.

While not a discovery, it nonetheless provided a view of what our solar system – and likely what countless other stellar systems – looks like.

(Images, NASA and L2 including render from L2 artist Nathan Koga – The full gallery of Nathan’s (SpaceX Dragon to MCT, SLS, Commercial Crew and more) L2 images can be *found here*)

(To join L2, click here: //www.nasaspaceflight.com/l2/)

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