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Planetary News: New Horizons (2007)New Horizons to Test its Mettle during Fly-By of JupiterBy Amir Alexander18 January 2007
Exactly a year after its launch on January 19, 2006, New Horizons is fast closing in on Jupiter, the first target on its near decade-long journey. On February 28 the spacecraft will approach to within 2.3 million kilometers (1.4 million miles) of Jupiter before speeding along on to its way to the edge of the solar system. Overall, between now and the end of June, New Horizons will conduct around 700 separate observations of the giant planet. New Horizons’ encounter with the king of the planets is a byproduct of its trajectory, which will take it to Pluto in 2015. As it swings by Jupiter, the planet’s enormous gravitational pull will give the spacecraft a boost that will increase its speed by 9000 miles per hour (5600 kilometers per hour) relative to the Sun. This gravity assist will cut a full three years from New Horizons’ journey, bringing it down to a mere 9 years. While this may sound like a long time, it is in fact a remarkably speedy voyage. The spacecraft’s 13 month journey to its close encounter with Jupiter is the shortest ever, and almost six times faster than the orbiter Galileo’s journey from 1989 to 1995. This makes New Horizons the fastest spacecraft ever launched. New Horizons’ journey thus far has not only been very fast, but also very precise. This is essential, explained Alan Stern of the Southwest Institute in Boulder, Colorado, who is the project’s Principal Investigator. In order to get the gravity assist from Jupiter that will send it on to Pluto, the spacecraft needs to pass through a “window” only 500 miles (800 kilometers) wide. Passing through that precise location in space after launching from Earth, 500 million miles away, said Stern, is a challenging feat in itself. It is equivalent to hitting a target in Central Baltimore, from a position in downtown Washington D.C. he said, using a local analogy. So far, New Horizons has lived up to everything that was expected of it and more. Only three times this past year did the spacecraft require any corrections to its trajectory, and these were very minor. “You could walk the kind of corrections we’ve made” said Glen Fountain, New Horizons project manager at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland. He went on to explain that the fuel saved on the trajectory maneuvers will provide the spacecraft with a plentiful reserve for any contingencies that may arise in the coming years of its long flight. In addition to providing an essential gravity assist, the Jupiter encounter will also serve as a live dress rehearsal for the Pluto encounter, which is still more than eight years away. “We have an incredible opportunity to conduct a real-world encounter stress test, to wring out our procedures and techniques, and to collect some valuable science data” said Stern. In testing both the spacecraft and the team under stress conditions, New Horizons will actually make twice as many observations of Jupiter as it is expected to make of Pluto and its moons in 2015. The observations, explained John Spencer of the Southwest Research Institute, deputy leader of the New Horizons Jupiter encounter Science Team, were designed specifically to complement rather than repeat observations made by the seven spacecraft that had visited Jupiter in the past (Spencer will be a guest blogger on Emily Lakdawalla's blog in the week beginning February 5). Accordingly, New Horizons will study Jupiter’s ring system, and look for moons that are orbiting among the rings and are likely responsible for their presence. Four such moons are currently known, but more are suspected. New Horizons will also take a close look at Jupiter’s four giant “Galilean” moons, focusing particularly on Europa’s icy surface and Io’s numerous volcanoes.
The spacecraft will also take a close look at the “Little Red Spot” – a giant storm that has been raging on the surface of Jupiter for the last two years. This, by Jupiter standards, is a very short time for a storm. In fact, the Little Red Spot was born from the conjunction of three smaller storms that have been stirring things up for more than 40 years. The famous Great Red Spot, the most prominent and familiar feature on the face of Jupiter, is a storm that has already lasted for hundreds of years. But as New Horizons scientists found out, even an old and familiar feature like the Great Red Spot is not without surprises. In planning for the encounter, the New Horizons team expected to take close pictures and measurements of a highly turbulent area bordering the northwest side Great Red Spot. This turbulence had been observed by several spacecraft, most recently by Cassini-Huygens which flew by Jupiter in 2000. But when Stern and his colleagues studied the preliminary pictures of Jupiter taken by New Horizons in the past few weeks they found no trace of the turbulence. The supposedly turbulent area appeared as clear as it had been during the Voyager encounters more than a quarter century ago. This does not mean that the planned observations will be wasted, explained Spencer. The tranquility of the region will enable the spacecraft’s instruments to penetrate deeper into the cloud cover, and study the different layers of the Jovian atmosphere in far greater detail than would have been possible otherwise. Perhaps most intriguing to scientists will be New Horizons’ study of the long tail of Jupiter’s magnetosphere. This “magnetotail,” is made up of charged particles generated buy Jupiter’s fierce magnetic field. Instead of being spread evenly around the planet, however, the particles are blown “outwards” – away from the Sun – by the solar wind, forming a tail that scientists estimate might be 5 astronomical units (AU) long, with each AU marking the average distance of Earth from the Sun. Following its close encounter with Jupiter on February 28 New Horizons will fly along about one fifth of the magnetotail, giving scientists their first sustained look of a magnetotail of a giant planet.
New Horizons will not transmit the data it collects immediately to Earth, but rather store it on board on digital recorders. In March, the spacecraft will begin transmitting this information back to Earth, providing scientists with data and images that will occupy them for years to come. This is especially the case because New Horizons is expected to be the only spacecraft that will visit Jupiter between the Cassini encounter in 2000 and the Juno mission scheduled for 2016. “It’s the only train going there” said Stern. Once the encounter and the transmissions are over, New Horizons will enter its long hibernation, waking up only occasionally to conduct checks on its systems. But eight years from now, as it approaches Pluto and its moons, New Horizons will again be wide awake, ready to explore those regions of our solar system where no spacecraft has gone before. |
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