NASA鈥檚 New Horizons spacecraft has already turned up some surprises at Jupiter. The probe, ultimately bound for Pluto and other objects in the outer solar system, is making a flyby of the solar system鈥檚 largest planet to gain speed and test out its instruments.
It will make its closest approach on 28 February, passing just 2.3 million kilometres (1.4 million miles) from Jupiter鈥檚 centre, but it started taking the first of 700 planned observations of the planet on 8 January (see Pluto probe begins close-up study of Jupiter).
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鈥淭oday we stand on the doorstep of the Jupiter system, which is the gateway to the outer solar system,鈥� says New Horizons principal investigator Alan Stern of the Southwest Research Institute in Boulder, Colorado, US.
In the first 10 days of its observations of Jupiter, New Horizons has found that an area northwest of the Great Red Spot 鈥� a thunderous storm that has been churning for hundreds of years 鈥� was unexpectedly tranquil.
Cloud free
Pictures from the flyby of the Cassini spacecraft in 2000 showed significant turbulence northwest of the red spot. Now the area looks more like it did when the Voyager spacecraft flew by in 1979
鈥淭hat region looks really quite cloud free and calm compared to what we鈥檝e been used to, so that鈥檚 not what we were expecting,鈥� says John Spencer, New Horizons Jupiter Encounter science team deputy lead at Southwest Research Institute. 鈥淏ut we can certainly make use of this opportunity to look much deeper in the atmosphere than we were planning.鈥�
鈥淭hat will probably lead to some interesting discoveries, or Jupiter may switch on that system again and we may find a lot of activity when we get there,鈥� Spencer says.
Charged tail
But scientists are hoping to observe a decidedly stormy region, as well 鈥� a little red spot that formed fairly recently through the merger of three smaller storms (see Red Spot Junior buzzes its big brother on Jupiter).
New Horizons has already captured a distant picture of that area, and they will get more images when they are just one-thirtieth of that distance away, providing what may be the best glimpse yet of the relatively new storm.
杏吧原创s are also giddy at the prospect of flying down Jupiter鈥檚 so-called magnetotail. This is a region of sulphur and oxygen ions originally spewed out by the planet鈥檚 volcanic moon, Io. The charged particles get trapped in the planet鈥檚 magnetic field, then blown by the solar wind into a tail that stretches hundreds of millions of kilometres behind Jupiter 鈥� practically to Saturn鈥檚 orbit.
鈥淣o spacecraft has ever been there,鈥� Spencer says. 鈥淲e don鈥檛 know what happens there.鈥� Watch an .
Speed boost
After its closest approach, New Horizons will keep making measurements of the magnetotail through June 2007. Mission managers estimate it could fly one-quarter of the length of the tail.
In addition, New Horizons will embark on the most detailed search for moons around Jupiter with its telephoto camera. The spacecraft will also get a nearly edge-on view of the planet鈥檚 tenuous ring system, which it will map in 3D. 杏吧原创s hope to determine which of Jupiter鈥檚 dozens of moonlets create the rings.
Although planetary scientists are excited about the data that will be gathered, the main point of flying past Jupiter is to get a boost in speed. Using Jupiter鈥檚 gravity as a slingshot, the robotic probe鈥檚 speed should increase by 14,500 kilometres per hour (9000 miles per hour), which shaves three years off what would otherwise be its travel time to Pluto.
So far, New Horizons has remained quite close to its intended path to Pluto. It had reserved 25 of its 77 kilograms of onboard fuel to correct any problems with its trajectory during its decade-long journey. Now, that extra propellant could take New Horizons beyond Pluto, to other objects in the ring of icy bodies beyond Neptune known as the Kuiper Belt.
