Today on Galileo
30 Jan 1999
(Source: Jet Propulsion Laboratory)
Today at 4 pm PST [see Note 1], Galileo starts the eighth encounter of the Galileo Europa Mission. The encounter features a close flyby of Jupiter's icy moon Europa, the ninth in a series that started with the last flyby of Galileo's primary mission. This flyby is also the last Europa flyby of the Galileo Europa Mission, and will occur tomorrow, Sunday, just after 6 pm PST. The spacecraft will be executing encounter commands through next Wednesday, but most of the encounter activity takes place on Sunday and Monday. During this time, the spacecraft is approximately 836 million kilometers (519 million miles) from Earth. At that distance, it takes radio signals approximately 46 1/2 minutes to travel from the spacecraft to Earth.
To kick off the encounter, the fields and particles instruments resume their survey of the inner portions of Jupiter's vast magnetosphere. This survey has been repeated for almost every encounter of Galileo's mission at Jupiter, allowing scientists to study the long term variations in the plasma, dust, and electric and magnetic fields that comprise the magnetosphere. The survey is scheduled to continue through Monday.
Four remote sensing observations are performed today-two by the near-infrared mapping spectrometer and two by the ultraviolet spectrometer. Both near-infrared observations are designed to obtain measurements of the composition and thermal properties of Jupiter's atmosphere. Similar observations have been repeated during previous orbits, allowing the science community to map variations over time. By looking at the same location on Jupiter at different times, with different viewing geometries, it is possible to extract information on the properties of Jupiter's cloud layers. The depths of the different cloud layers, and their thickness, can be assessed in this way.
The ultraviolet spectrometer takes the encounter's first look at Europa. Its first observation gathers measurements of Europa's surface that will give scientists clues as to how the surface has been affected by external phenomena such as meteors and high-energy particles which bombard the surface. In the second observation, the instrument will look for atmospheric emissions, which might be due to venting. Such outgassing events are an expected feature of ice volcanism. If detected, they would provide scientists with indirect evidence of internal activity within Europa, and would strengthen the case for liquid water there.
For more information on the Galileo spacecraft and its mission to Jupiter, please visit the Galileo home page:
http://www.jpl.nasa.gov/galileo Note 1. All times listed correspond to the Pacific Time zone (currently standard 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, this time is 46 1/2 minutes. Currently, Pacific Standard Time (PST) is 8 hours behind Greenwich Meridian Time (GMT).