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Arrival: Juno in Orbit

People in the space business always joke about the stress levels at any launch, but if you’re keeping tabs on a billion dollar spacecraft like Juno, I’d say the arrival can create just as many, if not more, gray hairs. Plenty of people are breathing easier this morning after Juno’s successful 35-minute engine burn and entry into orbit around Jupiter, confirmation of which came in just before midnight Eastern US time (03:53 UTC on July 5). Congratulations to the entire team.

All of this was part of a sequence of arrival events — Juno’s orbit-insertion phase (JOI) — that included spinning up the spacecraft from 2 to 5 revolutions per minute as an aid to stability, along with attitude changes in anticipation of the main engine burn, which began at 23:18 EDT. The latter decreased the spacecraft’s velocity by 542 meters per second to make orbital capture possible. Juno has already been turned again to allow its solar cells to work at full capacity.


Image: The Juno team celebrates at NASA’s Jet Propulsion Laboratory in Pasadena, California, after receiving data indicating that NASA’s Juno mission entered orbit around Jupiter. Rick Nybakken, Juno project manager at JPL, is seen at the center hugging JPL’s acting director for solar system exploration, Richard Cook. Credit: NASA/JPL-Caltech.

I always love control room photos when things are going well, remembering especially the New Horizons team last summer, images of which mingled joy with astonishment at what the doughty spacecraft was seeing. Juno is now in a 53.5 day orbit in preparation for an eventual 14-day orbit that will be achieved after a final engine burn on October 19. It’s at that point that the mission’s primary science collection period begins.

In this Cornell University news release, Jonathan Lunine, a member of the university’s Carl Sagan Institute, likens Juno’s work at Jupiter to an older discipline here on Earth, one that can help us understand the earliest days of the Solar System. What sort of materials, for example, did Jupiter take in as it grew into the gravitational behemoth it is today?:

[Jupiter is] a unique record for the outer solar system of what these protoplanets might have been like. We’re doing the astronomical equivalent of ‘broken pottery’ archaeology, trying to piece back together the original molecules and ice grains that got evaporated and dissociated inside Jupiter billions of years ago.”

We’ll have the opportunity to look at Jupiter in a number of new ways. The Galileo probe was unable, for example, to measure the water abundance in Jupiter beneath the clouds, but Juno’s microwave radiometer should be able to provide that measurement. Water abundance, in turn, tells us something about the materials that Jupiter absorbed early in its life, And by extension, we can apply this knowledge to the numerous gas giants we’re finding around other stars.

But it’s also going to be fascinating to learn whether or not the giant planet has a solid core. Juno’s gravity experiment will bring the spacecraft to within a few thousand kilometers of the cloud tops, allowing a measurement of the gravity field accurate enough to make the call. Bear in mind that the Cassini probe will burn up in Saturn’s atmosphere in 2017. During its final close flybys inside the rings, the same gravity experiment can be run. Says Lunine:

“[Cassini] will be passing just above the cloud tops like Juno does at Jupiter, underneath the rings of the planet, which will be pretty spectacular. The chance to be able to measure the core for both Jupiter and Saturn is really a tremendous opportunity.”

Bear in mind that even before Juno got to Jupiter, a number of science operations were already in progress, including work with the Jupiter Energetic Particle Detector Instrument (JEDI) to investigate the interplanetary medium as the spacecraft approached. Based at the Johns Hopkins University Applied Physics Laboratory, the JEDI team has been looking at ‘upstream ions,’ as explained by Dennis Haggerty, APL’s instrument scientist for the JEDI investigation:

“Jupiter is a very leaky planet. It has a unique particle identity, especially in terms of sulfur — which is not found in high numbers in the solar wind — and we’ve seen particles from Jupiter ‘upstream’ of the planet from missions including Voyager, Galileo and New Horizons.”

More in this APL news release, which describes the JEDI instrument and its upcoming work on Jupiter’s aurorae, which have a power density ten times greater than Earth’s, and an overall power that is greater by a factor of 100. JEDI will help explain how this system is energized.


Image: This artist’s concept depicts NASA’s Juno spacecraft above Jupiter’s north pole. Launched in 2011, the Juno spacecraft will arrive at Jupiter on July 4, 2016. As part of its instrument suites, it carries three Johns Hopkins APL-built Jupiter Energetic Particle Detector Instrument (JEDI) units to study the giant planet from an elliptical, polar orbit. Juno will repeatedly dive between the planet and its intense belts of charged particle radiation, coming only 5,000 kilometers (about 3,000 miles) from the cloud tops at closest approach. Juno’s primary goal is to improve our understanding of Jupiter’s formation and evolution. Credit: NASA/JPL-Caltech.

What Lies Beneath

Juno invariably calls up memories of Arthur C. Clarke’s A Meeting with Medusa, a 1971 novella that Greg Benford mentioned in a conversation this past weekend. It’s been many years since I’ve read it, but I may have to revisit the work now that Alastair Reynolds and Stephen Baxter have produced a sequel, a timely arrival given the Juno activities. The Medusa Chronicles evidently presents Clarke’s character Howard Falcon with a host of new challenges, but I’ll want to refresh my memory of the Clarke before tackling it.

In Clarke’s tale, Falcon skippers a balloon craft making a slow descent through Jupiter’s upper atmosphere, where he runs into enormous life-forms, one the Medusa of the title. And here we go back to another Cornell physicist who changed our view of Jupiter, Edwin Salpeter. I’ll send you to Larry Klaes’ fine 2009 essay Edwin Salpeter and the Gasbags of Jupiter for a more detailed look, but I do want to at least mention Salpeter’s work with Carl Sagan on life in the atmospheres of gas giants on the morning of the Juno arrival.


The duo produced a paper titled “Particles, Environments, and Possible Ecologies in the Jovian Atmosphere” that appeared in The Astrophysical Journal in late 1975. Sagan would go on to discuss such life-forms in the popular TV series Cosmos. Let me quote Larry on the kinds of life Sagan and Salpeter imagined:

Sagan and Salpeter envisioned three main types of Jovian creatures. There were sinkers, small organisms which were constantly falling towards the deadly deep, dense, and hot layers of the planet but always managed to survive long enough to produce offspring that would stay up in the more habitable air layers to repeat their cycle of life. The other aerial residents of Jupiter were known as floaters, which Sagan would later describe as being “kilometers across, enormously larger than the greatest whale that ever was, beings the size of cities.” Floaters were seen as drifting across the vast alien sky in great herds, looking like a collection of immense balloons, which in essence there were, using the lighter elements of Jupiter’s atmosphere to stay aloft.

Image: Physicist Edwin Salpeter, whose work with Carl Sagan brought the idea of airborne life in Jupiter’s clouds to a wide audience.

Throw a class of hunter species into the mix and you have a vibrant and violent ecology, one that, the paper pointed out, could have been detected by the Voyager probes’ cameras if a floater of this sort existed and were high enough up in the cloud deck to be seen. Presumably Juno’s views will be spectacularly better, so perhaps some scrutiny of its imagery in search of unusual moving objects could be advocated. In any case, it’s a shame that Clarke, Sagan and Salpeter couldn’t be here to witness Juno’s arrival and the abundant imagery to follow of a realm they once imagined so vividly.


Comments on this entry are closed.

  • Michael Spencer July 6, 2016, 7:00

    And it is a shame as well, Paul, that upon Juno’s demise several years hence the outer planets will be devoid of mankind’s presence for the first time since the 70’s.

    • Paul Gilster July 6, 2016, 15:02

      A sobering thought, that’s for sure. We’ve been feasting on mission news these past two summers, but we’ve got to keep new missions in the pipeline!

  • Michael July 7, 2016, 6:35

    Here is some more info on Juno’s science and orbital danamics, a clever orbit to aviod those pesky radiation belts.


  • john walker July 7, 2016, 19:15

    Kinda late with this one, but I just discovered thi unusual protective shielding on Juno: http://mashable.com/2016/07/05/juno-orbiting-jupiter-legos/#7Cnu1R5Wg8qA :)

  • ljk July 7, 2016, 20:25

    Sagan and Salpeter have been alerting scientists and the public alike since 1975 that space probe cameras going back to the Voyagers could image the floaters, which would be just large enough to resolve.

    Perhaps the presence of Juno and a more open attitude towards finding alien life will inspire at the least a collective group of amateurs to examine every usable image from every Jupiter probe with a decent camera to search for floaters. What does one have to lose? And perhaps something else outside of new living neighbors could be discovered about the Jovian atmosphere in the process.

    Here is a very recent news item addressing the possibility of life forms in Jupiter’s atmosphere, namely the Sagan-Salpeter floaters, hunters, and sinkers as seen in the original Cosmos:


    This is the scene in Cosmos redone via CGI to make the creatures mobile:


    The Planetary Society had a blog piece about this famous painting by the artist himself, Adolf Schaller, here:


  • ljk July 7, 2016, 20:33

    Ben Bova’s 2000 SF novel Jupiter deals with huge native life forms that exist in the layer of water that may girdle the planet. There were also aerial creatures in his novel, but Bova focused on the aquatic ones.

    My question is: Will Juno be able to determine if Jupiter has a liquid water layer and if so, does that mean another opportunity for life forms?

    Sagan said decades ago that Jupiter was one of the best places in the Sol system to find life. He may not have realized just how right he was.

    Here is an interview with Bova on the subject of his aquatic Jovial life forms:


    To quote from the Bova interview:

    AM: You say that Jupiter may be the most likely place to find extraterrestrial life, since the planet has organics, water and energy. Yet Jupiter is rarely seen as a likely place for life by most astrobiologists. Do you have any thoughts about what sort of creatures could exist there?

    BB: Most scientists ignore Jupiter because of the enormous difficulties of exploring the planet. However, in my novel “Jupiter” I postulated a biosphere that included airborne species below the Jovian cloud deck, and gigantic aquatic species in the planet-wide ocean that girdles Jupiter.

    In his 2001 novel series, Clarke briefly discussed the life forms that dwelled in the atmosphere of Jupiter until the Monolith Aliens turned Jupiter into a star. The aliens knew the floaters existed, but decided that the Europan life forms had a better chance of evolving into an intelligent species so they went ahead and lit up Jupiter and bye bye floaters.

    Kind of scary how the Monolith ETI got to decide who deserved to live and evolve, eh?

  • ljk July 7, 2016, 21:45

    Don’t hold your breath about seeing many Juno images of Jupiter any time soon:


  • Brian Schmidt July 9, 2016, 12:25

    I’ve thought that planetary protection policies give insufficient credit to the possibility of life on gas giants. We’re very careful not to contaminate Mars, but we’ve dropped one atmospheric probe into Jupiter and will do more on other gas and ice giants without anything near the same level of protection.

    Destroying spacecraft by running them into the atmosphere isn’t a problem, the heat will sterilize them, but slowed-down atmospheric probes are different.

    What’s especially egregious is that Earth bacteria transferred to Mars could survive for years, maybe longer, but they’re inactive under Mars conditions. Bacteria sent to the gas giants could start growing and reproducing instantly, becoming an alien and invasive form of sinkers that Sagan mentions. Doesn’t strike me as a good idea.

  • Mark July 19, 2016, 7:45

    On the subject of Arthur C. Clarke’s “Encounter With Medusa,” there is one book already written that was pretty clearly inspired by the story and it is Timothy Zahn’s “Manta’s Gift.” He’s more of an action space opera writer, but the book is really wonderful and fun, I’d call it SF stretched to the limit and it does take place mostly in the clouds of Jupiter with all the attendant exo-ecosytems. I recommend it.

  • ljk August 11, 2016, 9:28

    Juno has finally sent more images of Jupiter, but don’t bother trying to find the floaters in them just yet:


    I wonder how the three little Lego figures are doing? Are Jupiter and Juno getting along? Does Galileo feel awkward in their company? And to think they almost sent actual pieces of the real Galileo Galileo to Jupiter:


    Which would not have made much sense as Juno will eventually burn up in the Jovian atmosphere, so there will be nothing for future space archaeologists to find.

  • ljk August 23, 2016, 8:52

    JunoCam “Marble Movie” data available

    Posted by Emily Lakdawalla

    2016/08/22 21:56 UTC

    Since a few days after entering orbit, JunoCam has been taking photos of Jupiter every fifteen minutes, accumulating a trove of data that can be assembled into a movie of the planet. This first orbit of Jupiter was a very long one, taking Juno more than 10 million kilometers away.

    Because JunoCam is a wide-angle camera, Jupiter appears tiny from such a great distance. Fortunately, Jupiter is colorful enough that it’s not featureless, even when it appears so small; you can see its red belts and occasionally the red spot show up in the photos. The JunoCam team is calling the movie taken from this first long orbit the “Marble Movie,” because that’s what Jupiter looks like, a little rolling marble.

    The JunoCam team has released the first month’s worth of Marble Movie data in two large chunks. Space imaging enthusiast Gerald Eichstädt has developed an automated routine to process those chunks of data, producing thumbnails, which means I can now post one of my browse indexes to all the data.


  • ljk August 25, 2016, 17:34

    Juno makes its first really close dive this Saturday:


    To quote:

    “Not only will Juno’s suite of eight science instruments be on, the spacecraft’s visible light imager — JunoCam will also be snapping some closeups. A handful of JunoCam images, including the highest resolution imagery of the Jovian atmosphere and the first glimpse of Jupiter’s north and south poles, are expected to be released during the later part of next week.”

    Be sure to check the images for floaters!

  • ljk August 29, 2016, 13:02

    One big close-up photo and lots of little far away ones here:


  • ljk August 30, 2016, 10:12

    What is it going to take for those who run these space missions to realize just how important it is to excite as well as inform the public (and politicians) about exploring other worlds?


    You want interest and support? Put a camera on your space probe and show off its images. When the US was first exploring Venus with robot vessels, they didn’t think they needed a camera on Mariner 5 in 1967 because there would be nothing to show due to the planet being completely cloud covered. Mariner 10 showed the error of that thinking in 1974 and a lack of images is one reason that Mariner 5 is barely remembered these days. This despite the fact that the probe confirmed what Mariner 2 had found at Venus five years earlier (a world shockingly hostile to life) and was also the first probe to work in tandem with a Soviet explorer, Venera 4, albeit not deliberately.

    Mariner 5 also helped determine that the Soviet drop lander did not reach the surface of Venus intact (the air pressure levels were underestimated and Venera 4 was crushed like an egg miles above the ground), despite the claims by the probe’s owners. They even went so far as to declare that Venera 4 had landed on a very high (12 miles) mountain! Later observations would show that Venus has one of the relatively flattest surfaces of all the terrestrial worlds. Of course the Soviets could still claim the first direct examination of the Venusian atmosphere, which turned out to be mostly carbon dioxide and not nitrogen as predicted. Now imagine the even bigger coup the Soviets could have had if Venera 4 carried a camera.

  • ljk September 2, 2016, 17:14