# Europa

Freedom lies in being bold. - Robert Frost

Jupiter II

## Table of Contents

- Europa (This page)
  - Europa Statistics
  - Views of Europa
- Hubble Finds Oxygen Atmosphere On Jupiter's Moon Europa
- The Discovery of the Galilean Satellites
- Jupiter's Europa Harbors Possible "Warm Ice" or Liquid Water
- Statement by Goldin on the New Galileo Images Of Europa

Europa [yur-ROH-pah] is a strange looking moon of Jupiter with a large number of intersecting features. It is unlike Callisto and Ganymede with their heavily cratered crusts. Europa has almost a complete absence of craters as well as almost no vertical relief. As one scientist put it, the features "might have been painted on with a felt marker". There is a possibility that Europa may be internally active due to tidal heating at a level one-tenth or less that of Io. Models of Europa's interior show that beneath a thin 5 km (3 miles) crust of water ice, Europa may have oceans as deep as 50 km (30 miles) or more. The visible markings on Europa could be a result of global expansion where the crust could have fractured, filled with water and froze.

## Europa Statistics

    Discovered by ................ Simon Marius & Galileo Galilei
    Date of discovery ...................................... 1610

    Mass (kg) ........................................... 4.8e+22
    Mass (Earth = 1) ................................. 8.0321e-03
    Equatorial radius (km) ................................ 1,569
    Equatorial radius (Earth = 1) .................... 2.4600e-01
    Mean density (gm/cm^3) ................................. 3.01

    Mean distance from Jupiter (km) ..................... 670,900
    Rotational period (days) ........................... 3.551181
    Orbital period (days) .............................. 3.551181
    Mean orbital velocity (km/sec) ........................ 13.74

    Orbital eccentricity .................................. 0.009
    Orbital inclination ................................... 0.470°

    Escape velocity (km/sec) ............................... 2.02

    Visual geometric albedo ................................ 0.64
    Magnitude (Vo) ......................................... 5.29

## Views of Europa

Europa (GIF, 593K)
This is one of the highest resolution images of Europa obtained by Voyager 2. It shows the smoothness of most of the terrain and the near absence of impact craters. Only three craters larger than 5 km in diameter have been found. (Credit: Calvin J. Hamilton)

Europa From a Distance (GIF, 39K)
This view of Europa was taken by Voyager 2 and shows a bright, low-contrast surface with a network of lines which crisscross much of its surface. (Credit: Calvin J. Hamilton)

Natural and False Color Views of Europa (JPEG, 71K)
This image shows two views of the trailing hemisphere of Europa. The left image shows the approximate natural color appearance of Europa. The image on the right is a false-color composite version combining violet, green and infrared images to enhance color differences in the predominantly water-ice crust of Europa. Dark brown areas represent rocky material derived from the interior, implanted by impact, or from a combination of interior and exterior sources. Bright plains in the polar areas (top and bottom) are shown in tones of blue to distinguish possibly coarse-grained ice (dark blue) from fine-grained ice (light blue). Long, dark lines are fractures in the crust, some of which are more than 3,000 kilometers (1,850 miles) long. The bright feature containing a central dark spot in the lower third of the image is a young impact crater some 50 kilometers (31 miles) in diameter. This crater has been provisionally named 'Pwyll' for the Celtic god of the underworld. (Courtesy: NASA/JPL)

False Color Image of Minos Linea Region (JPEG, 139K)
False color has been used here to enhance the visibility of certain features in this composite of three images of the Minos Linea region on Jupiter's moon Europa taken on 28 June 1996 Universal Time by the Galileo spacecraft. Triple bands, lineae and mottled terrains appear in brown and reddish hues, indicating the presence of contaminants in the ice. The icy plains, shown here in bluish hues, subdivide into units with different albedos at infrared wavelengths probably because of differences in the grain size of the ice. The composite was produced using images with effective wavelengths at 989, 757, and 559 nanometers. The spatial resolution in the individual images ranges from 1.6 to 3.3 kilometers (1 to 2 miles) per pixel. The area covered, centered at 45N, 221 W, is about 1,260 km (about 780 miles) across. (Courtesy: NASA/JPL)

Galileo Near-Infrared Image of Europa (JPEG, 47K)
The Near Infrared Mapping Spectrometer (NIMS) on the Galileo spacecraft imaged most of Europa, including the north polar regions, at high spectral resolution at a range of 156,000 km (97,500 miles) during the G1 encounter on June 28 1996. The image on the right shows Europa as seen by NIMS, centered on 25 degrees N latitude, 220 W longitude. This is the hemisphere that always faces away from Jupiter. The image on the left shows the same view point from the Voyager data (from the encounters in 1979 and 1980). The NIMS image is in the 1.5 micron water band, in the infrared part of the spectrum. Comparison of the two images, infrared to visible, shows a marked brightness contrast in the NIMS 1.5 micron water band from area to area on the surface of Europa, demonstrating the sensitivity of NIMS to compositional changes. NIMS spectra show surface compositions ranging from pure water ice to mixtures of water and other minerals which appear bright in the infrared.

Europa's Broken Ice (JPEG, 80K)
Jupiter's moon Europa, as seen in this image taken June 27, 1996 by NASA's Galileo spacecraft, displays features in some areas resembling ice floes seen in Earth's polar seas. Europa has an icy crust that has been severely fractured, as indicated by the dark linear, curved, and wedged-shaped bands seen here. These fractures have broken the crust into plates as large as 30 kilometers (18.5 miles) across. Areas between the plates are filled with material that was probably icy slush contaminated with rocky debris. Some individual plates were separated and rotated into new positions. Europa's density indicates that it has a shell of water ice as thick as 100 kilometers (about 60 miles), parts of which could be liquid. Currently, water ice could extend from the surface down to the rocky interior, but the features seen in this image suggest that motion of the disrupted icy plates was lubricated by soft ice or liquid water below the surface at the time of disruption.

This image covers part of the equatorial zone of Europa and was taken from a distance of 156,000 kilometers (about 96,300 miles) by the solid-state imager camera on the Galileo spacecraft. North is to the right and the sun is nearly directly overhead. The area shown is about 360 by 770 kilometers (220-by-475 miles or about the size of Nebraska), and the smallest visible feature is about 1.6 kilometers (1 mile) across. (Courtesy: NASA/JPL)

Europa's Active Surface (JPEG, 157K)
A newly discovered impact crater can be seen just right of the center of this image of Jupiter's moon Europa returned by NASA's Galileo spacecraft camera. The crater is about 30 kilometers (18.5 miles) in diameter. The impact excavated into Europa's icy crust, throwing debris (seen as whitish material) across the surrounding terrain. Also visible is a dark band, named Belus Linea, extending east-west across the image. This type of feature, which scientists call a "triple band," is characterized by a bright stripe down the middle. The outer margins of this and other triple bands are diffuse, suggesting that the dark material was put there as a result of possible geyser-like activity which shot gas and rocky debris from Europa's interior. The curving "X" pattern seen in the lower left corner of the image appears to represent fracturing of the icy crust and infilling by slush which froze in place.

The crater is centered at about 2 degrees north latitude by 239 degrees west longitude. The image was taken from a distance of 156,000 kilometers (about 96,300 miles) on June 27, 1996, during Galileo's first orbit around Jupiter. The area shown is 860 by 700 kilometers (530 by 430 miles), or about the size of Oregon and Washington combined. (Courtesy: NASA/JPL)

Dark Bands on Europa (JPEG, 483K)
Dark crisscrossing bands on Jupiter's moon Europa represent widespread disruption from fracturing and the possible eruption of gases and rocky material from the moon's interior in this four-frame mosaic of images from NASA's Galileo spacecraft. These and other features suggest that soft ice or liquid water was present below the ice crust at the time of disruption. The data do not rule out the possibility that such conditions exist on Europa today. The pictures were taken from a distance of 156,000 kilometers (about 96,300 miles) on June 27, 1996. Many of the dark bands are more than 1,600 kilometers (1,000 miles) long, exceeding the length of the San Andreas fault of California. Some of the features seen on the mosaic resulted from meteoritic impact, including a 30-kilometer (18.5 mile) diameter crater visible as a bright scar in the lower third of the picture. In addition, dozens of shallow craters seen in some terrains along the sunset terminator zone (upper right shadowed area of the image) are probably impact craters. Other areas along the terminator lack craters, indicating relatively youthful surfaces, suggestive of recent eruptions of icy slush from the interior. The lower quarter of the mosaic includes highly fractured terrain where the icy crust has been broken into slabs as large as 30 kilometers (18.5 miles) across.

The mosaic covers a large part of the northern hemisphere and includes the north pole at the top of the image. The sun illuminates the surface from the left. The area shown is centered on 20 degrees north latitude and 220 degrees west longitude and is about as wide as the United States west of the Mississippi River. (Courtesy: NASA/JPL)

Jupiter Io Ganymede

##### Author: Calvin J. Hamilton.