Today on Galileo
August 12, 1999
Closest approach to Jupiter is first on the flyby schedule. The spacecraft flies within 7.3 Jupiter radii (523,000 kilometers, 325,000 miles) of the planet's center at 03:39 am PDT [see Note 1]. Next on the schedule is closest approach to Europa, occuring at 12:53 pm PDT at a distance of 212,000 kilometers (132,000 miles). Finally, closest approach to Ganymede occurs at 7:53 pm PDT at a distance of 835,000 kilometers (530,000 miles).
Today's observation schedule starts with a six hour recording performed by the Fields and Particles instruments. The recording is one in a series of four being performed during each encounter of the Perijove Reduction Campaign (Galileo's previous two encounters, this encounter, and Galileo's next encounter). During these encounters, the spacecraft's Perijove distance, or closest distance to Jupiter for a given orbit, is reduced from orbit to orbit. These recordings will provide valuable high resolution data describing the inner magnetosphere and Io torus environment. The instruments will make measurements of the magnetic fields and particles interactions wiithin these regions, including measurements of radio signals and electromagnetic waves. These measurements will contribute to the study of the dynamic processes within the Jupiter magnetosphere and Io torus. The Io torus is a region of intense plasma and radiation activity, in which there are strong magnetic and electric fields. Constantly replenished by the volcanic activity on Io, it is a vital part of the Jovian magnetosphere.
In a related observation, the Plasma Wave instrument performs an observation dedicated to the detection of Chorus emissions. The Chorus signal is seen in the electromagnetic fields measured by the Plasma Wave instrument when plasmas are being accelerated due to a particularly efficient type of wave-particle interaction. In detecting and analyzing Chorus emissions, scientists hope to understand a significant process by which energy is transferred from Jupiter's magnetic field into plasmas within the Io torus and from there into outer portions of the magnetosphere.
The Solid-State Imaging camera performs the first few remote sensing observation of today's schedule. The camera peforms a total of eight observations during the day, six focusing on Io, and two on Amalthea, one of Jupiter's inner moons. Five of the camera's observations of Io are part of a campaign of ten observations designed to monitor volcanic plume activity on the moon. Volcanic activity seen in these images will be compared to measurements of the Io torus taken by the Fields and Particles instruments to determine if there is any relationship. The camera's remaining observation of Io is performed around noon PDT and is designed to provide additional data on the size and shape of the volcanic moon. During the day, the camera makes two observations of Amalthea. The observations will provide the best spatial resolution ever obtained of Amalthea for the portions imaged (up to 8.5 kilometers, 5.3 miles, per picture element). The images will enhance studies of the shape of this inner moon.
The Near-Infrared Mapping Spectrometer makes six observations today, four of features in Jupiter's atmosphere and two of Europa. Two of the Jupiter observations capture data describing a white oval. White ovals are long-lived storms that form between two adjacent zonal jet streams. The other two observations take a look at a spot that is unusually darker than other spots in Jupiter's atmosphere. The spot appears to be more devoid of clouds and warmer than neighboring spots, suggesting to scientists that winds around this feature are travelling in a clockwise direction, unlike the colder Great Red Spot and white ovals that have counter-clockwise winds. The Near-Infrared Mapping Spectrometer observations will describe this winds near this spot and allow scientists to verify the models that explain this interesting behavior. Of the Europa observations, the first captures a region known as Belus Linea. The region is characterized by large concentrations of dark surface materials. The second observation captures a global view of one of Europa's hemispheres. In both of these observations, the Near-Infrared Mapping Spectrometer obtains spectral and spatial measurements of Europa's surface. The spectral data contains information describing the light reflected from the different materials on the surface. Each material reflects a unique spectra which allows scientists to identify the given material. In conjunction, the spatial data will allow scientists to determine how these materials are distributed on Europa's surface.
The Ultraviolet Spectrometer instrument completes today's observing schedule. In one observation, the instrument takes a look a Io while it is eclipsed from the sun by Jupiter. The observation is designed to capture auroral activity on Io, which is more easily observed while the moon is in darkness.
Note 1. All times listed correspond to the Pacific Time zone (currently daylight time) and spacecraft event time. Radio signals indicating that an event has occurred on the spacecraft reach the Earth 33 to 50 minutes later, depending on the time of year. Currently, Pacific Daylight Time (PDT) is 7 hours behind Greenwich Meridian Time (GMT), and it takes radio signals 38 minutes to travel between the spacecraft and Earth.
For more information on the Galileo spacecraft and its mission to Jupiter, please visit the Galileo home page.
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