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Planetary News: New Horizons (2006)

New Horizons Snaps First Picture of Jupiter

By Amir Alexander
27 September, 2007

More than eight months into its epic journey, New Horizons is now cruising through the outer borders of the asteroid belt at a dazzling 70,000 kilometers per hour (45,000 miles per hour). The spacecraft is still almost nine years away from its flight through the Plutonian system in the summer of 2015, but only a few months from its closest encounter with the giant Jupiter on February 28, 2007. During the fly-by, Jupiter's massive gravitational pull will grab a hold of the spacecraft, and hurl it outwards to the far reaches of the solar system, shortening its overall flight-time by several years. In the meantime, New Horizons will have a chance to conduct some close observations of Jupiter, the first since the orbiter Galileo made its final plunge into the planet in 2003. The New Horizons team has been working hard getting ready for the encounter, preparing around 500 separate observations and measurement of our giant neighbor.

The first of these came on September 4, When LORRI, the "Long Range Reconnaissance Imager" took its first picture of Jupiter. Less than a week before, on August 29, LORRI took its "first light" picture in space, of star cluster Messier 7. Now LORRI was ready for a more challenging feat, capturing the image of a planet from a distance of 291 million kilometers (181 million miles). The results were spectacular. Not only is the planet and its familiar contours clearly visible, but so are its moons, Io and Europa, casting their shadows on the Jovian surface.

LORRI took the picture with the Sun almost directly behind it, meaning that Jupiter was exceedingly bright, 40 times brighter, in fact, than Pluto will be on New Horizons' closest approach. This meant that in order to capture Jupiter's image, Lorri's light-sensitive cells had to be exposed for only the briefest time, to avoid an overload. Indeed, one of the reasons the New Horizons team decided to take the image in the first place was to test how well LORRI would operate with such a short exposure time. The final image, taken with an exposure of only 6 milliseconds, fully confirmed their high expectations for the instrument. "LORRI's first Jupiter image is all we could have expected" said a satisfied Andy Cheng of Johns Hopkins University's Applied Physics Laboratory (APL), who is the Principal Investigator for LORRI.

LORRI is composed of a telescope with an 8.2 inch (20.8 centimeter) lens that focuses on a charged-coupled device (CCD). Since similar devices are used in ordinary digital cameras, LORRI can be thought of as a camera with a long telescopic lens. When New Horizons approaches Pluto in the summer of 2015, LORRI will provide the first pictures of the planet and its moons, and later on the highest resolution images. At closest range, LORRI's resolution will be 125 times greater than in its first Jupiter image, enabling it to distinguish objects as small as 50 meters across on Pluto's surface.

For the next few months, as it covers the hundreds of millions of miles separating the asteroid belt from the orbit of Jupiter, New Horizons will make no further observations of the giant planet. Then, in early January of next year, with Jupiter looming near, observations will resume, reaching a crescendo during the closest approach to the planet in late February. After that things will gradually quiet down, though measurements of Jupiter's magnetosphere will continue for some months to come.

And then – nothing but the sounds of silence, as New Horizons streaks through billions of miles of empty space, to the edge of the solar system.

New Horizons' first image of Jupiter
New Horizons' first image of Jupiter
This image was taken by New Horizons' LORRI instrument on September 4, 2006, from a distance of 291 million kilometers (181 million miles). Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute