Jupiter's ammonia plumes run deep, Juno finds
With each flyby, the NASA spacecraft tells us more about our solar system's biggest planet. But it poses questions too, writes Richard A. Lovett.
Despite suffering two glitches on its 19 October close flyby of Jupiter, NASA’s Juno spacecraft is already starting to redefine our understanding of the giant planet, scientists said at a meeting of the American Geophysical Union, on 13 December in San Francisco, California.
Better yet, two days earlier the spacecraft had completed another close flyby with no additional glitches, although mission controllers again decided not to risk using the spacecraft’s engine – which malfunctioned before the previous flyby – for a burn that would have shortened its orbit from 53 days to 14.
Also to be on the safe side, the 11 December flyby was completed with one of the spacecraft’s instruments turned off, after determining that the Jovian Infrared Aural Mapper (JIRAM) instrument was responsible for a computer reboot that had prevented the spacecraft from collecting data on the flyby in which the engine malfunctioned.
“The problem was diagnosed, but the patch has not yet been installed,” says the mission’s principal investigator, Scott Bolton.
Still, he adds, the mission has successfully collected another round of data to be added to that which it accumulated on its first close passage of the gas giant on 27 August: “We’re not exactly in the orbit we had planned [but] I can tell you that the results are pretty exciting."
Some of these results came from the spacecraft’s microwave radiometer, which uses microwave emissions escaping from as deep as 300 to 400 kilometres beneath the cloud tops. Not only does this map the “roots” of Jupiter’s enormous cloud bands and storms, but it will determine abundances of gases such as ammonia and water.
One of this instrument’s finds, says Michael Janssen of NASA’s Jet Propulsion Laboratory in Pasadena, California, is that ammonia concentrations in Jupiter’s atmosphere vary with latitude and depth.
Of particular interest is a zone near the equator where the atmosphere is ammonia-rich all the way from the top of the atmosphere to the depths. “We have a giant plume of ammonia,” he says.
What exactly might produce such a plume is still the subject of speculation, Janssen says. In some ways, it looks like a type of circulation pattern called a Hadley cell, in which gases rise in one part of the atmosphere and descend in another.
“But if you’re pumping ammonia up, it’s got to return [to the depths] somewhere,” he says.
And so far, there’s no sign of a descending plume elsewhere.
“Welcome to the new Jupiter,” Janssen says, adding: “We have a lot of work to do.”
Other scientists have found additional intriguing results. Steve Levin, another Juno scientist from JPL, says Jupiter’s magnetic field has proved stronger and more variable from one latitude to another than expected.
Future close approaches will allow scientists to build 3-D maps not only of that field but also of Jupiter’s radiation belts, radio emissions, ionosphere and gravity field.
And of course, there are pictures. Some will be dramatic close-ups, posted via JunoCam, an instrument designed in part to let the public download images and enhance or adapt them freely.
But the spacecraft also carries four “star tracker” cameras, says Jack Connerney, of NASA Goddard Spaceflight Centre, Greenbelt, Maryland. These cameras were designed for navigation, but they can also be programmed to spot non-stellar objects.
Already they have identified dozens of such objects, Connerney says — though it is too early to specify exactly what these objects are.
Some, he says, appear to be small satellites orbiting in Jupiter’s rings. Others may be similar objects orbiting outside of the ring plane. Still others may simply be bright flashes from material blown off of Juno’s solar panels by micrometeorite impacts.
“We’re not really prepared to sort through those yet,” Connerney says. “We have to figure out if it’s a small thing close to the spacecraft or a big thing far away. It’s a big job because there’s so many of them.”
Meanwhile, the spacecraft is now moving away from Jupiter before diving in again for its next close passage on 2 February. It’s still undetermined whether it will remain on its current 53-day circuit or fire the engine to shorten its orbit.
“You might be hearing from us in little bursts every 53 days,” Levin says, “or you might start hearing from us more often.”