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By Emily Lakdawalla

New Horizons is approaching Jupiter!

Jan. 18, 2007 | 14:04 PST | 22:04 UTC

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There was a press conference this morning on New Horizons' upcoming encounter with Jupiter. The spacecraft is barreling down on the giant planet for a February 28 flyby, and Jupiter already looks pretty big in New Horizons' windshield:

Jupiter and Io
New Horizons snapped this view of Jupiter and Io on January 8, 2007, seven weeks before the spacecraft would make its closest approach to the giant planet. New Horizons scientists had planned to study the turbulent wake to the northwest of the Great Red Spot during the flyby, but this photo shows that the weather in that region of Jupiter has calmed, with little cloud activity. Credit: NASA / JHUAPL / SwRI

Amir Alexander will be posting a detailed story on this later today; I thought I'd focus on what was said about the plans for science during the encounter.

There is plenty to study at Jupiter. There is the planet itself; its aurorae; magnetosphere; a large family of moons, including the four giant Galilean satellites Io, Europa, Ganymede, and Callisto; and a small family of rings. New Horizons will approach from, I believe, below the plane of the ecliptic, but not very far off that plane, and pass through Jupiter's ring plane on March 1, three days after closest approach.

I jotted down just a few of the science activities mentioned by John Spencer and Alan Stern during the press conference. They will include:

Infrared studies of the atmosphere (infrared can see to some depth in Jupiter's atmosphere)
Studies of the Great Red Spot and the turbulent wake region to its northwest
Studies of Oval BA (a.k.a. the Little Red Spot or Red Junior)
Searches for new satellites
Measurements of the three-dimensional structure of the rings, enabled by the ring plane crossing
A flight straight down the magnetotail
Searches for changes in surface patterns on Io
Observations of stellar occultations by the moons to study their atmospheres
Studies of topography on Europa by capturing images with low-angle solar illumination

Of these, there are several "firsts" or "best-ever" observations planned. The science team seemed most excited about the flight down the magnetotail, because no spacecraft has ever flown such a trajectory down the magnetotail of any giant planet. And Jupiter's is a big one; it may stretch 6 astronomical units, to the orbit of Saturn. The studies of Jupiter's ring system and searches for close-in moons will be the most detailed ever; Galileo was unable to do much ring system studies because of its communication problems.

Here's the geometry of the flyby at closest approach:

Click to enlarge >

New Horizons Jupiter encounter trajectory
New Horizons flies by Jupiter on February 28, 2007, passing within 2.3 million kilometers (1.4 million miles) of the giant planet, just outside the orbit of the outermost large moon, Callisto. Unfortunately, all four of the Galilean satellites will be on the far side of Jupiter from New Horizons at closest approach, but the encounter still offers plenty of opportunities for studying the moons, rings, planet, magnetosphere, and space environment. Credit: NASA / JHUAPL / SwRI

Currently on approach, New Horizons has already grabbed two movies of Jupiter's rotation, each consisting of 11 images. They released a movie made from one of these 11-image observations; they "tweened" the images to create a smoother animation. You can download the movie in MPEG (3.5 Mb) or Quicktime (7 Mb) formats from their website.

There are more than 700 observations planned, each of which may include several images or other measurements. Surprisingly to me, this is a great deal more than they have planned for the Pluto encounter. Alan explained that they plan to use the Jupiter encounter to "exercise the spacecraft hard enough that we will turn up any remaining vulnerabilities in either ground or flight systems." John said that one of the reasons there were so many observations was that they are testing out a variety of modes for the instruments, and will use what they learn from this encounter to fine-tune their choices of instrument modes for the Pluto encounter.

It will be a while before much data comes back. The spacecraft will occasionally return data to Earth on approach, but during the closest approach the spacecraft will spend most of its time pointed at science targets, sending only housekeeping data back to Earth. The science data will be saved on the solid-state recorders and be spooled back beginning in March, while New Horizons' outbound observations continue; they plan to have all the data on the ground by the summer, when they'll be getting ready to hibernate the spacecraft until they begin to approach Pluto.

John acknowledged the fact that their small science team -- only a few dozen people, a paltry number compared to the hundreds available to the Voyager teams during their flybys -- owed a debt to two different groups of amateurs. First, amateur astronomers' observations of the positions of the Great Red Spot and Oval BA over time helped them predict where the spots would be over time -- they are always moving, so this is not a trivial problem. John said that the amateurs' forecasts of spot positions have been very accurate. He also acknowledged the help of armchair mission planners who were asked on a public forum: this is New Horizons' trajectory, when will there be opportunities to take pictures that will be particularly scenic? John confirmed that they'll be implementing several of the suggestions that amateurs made. (You can read that discussion here.)

All in all, it's going to be an exciting few months. It would be exciting enough if it were just New Horizons passing by Jupiter. But Alan and John have another reason for excitement. Both scientists are not only on New Horizons, but also on Rosetta -- in fact, they work on the same instrument on both spacecraft, an ultraviolet imaging spectrometer called ALICE (similar to the UVIS instrument on Cassini, on which John is also an investigator). Alan sent me an email last week saying, "The Rosetta Mars encounter is the same week as the New Horizons Jupiter encounter. Both are flybys. Has this ever occurred before? Has a given PI or team ever had the same instrument passing two planets the same week? I wish I were a better historian to really know. Anyway, we're busy. Space exploration is is IT!"

I agree! To share some of the excitement of this encounter period, I've asked John to serve another stint as a guest blogger in this space the week of February 5. Stay tuned for that!