Europa:

Europa

Introduction: Over the past few weeks the Kingdown Community School’s Astronomy Club have been researching the icy moon of Jupiter, Europa. We have conducted a number of experiments that include:

  1. Could life survive on Europa and
  2. How are the cracks on Europa’s surface formed.

We have conducted experiments into these issues; we have tested the durability of different plants in frozen and cold conditions, and have heated a sheet of ice to develop different conclusions about the surface of Europa. But before we could perform these experiments we have carried out some background research into the moon itself. All the research is listed below. At this point we would just like to thank all the website owners for their contribution to our project.

Background Research:

Europa is the sixth of Jupiter's known satellites and the fourth largest; it is the second of the Galilean moons. Europa is slightly smaller than the Earth's Moon. Europa was a Phoenician princess abducted to Crete by Zeus, who had assumed the form of a white bull, and by him the mother of Minos. Discovered by Galileo and Marius in 1610.  Europa and Io are somewhat similar in bulk composition to the terrestrial planets: primarily composed of silicate rock. Unlike Io, however, Europa has a thin outer layer of ice. Recent data from Galileo indicate that Europa has a layered internal structure perhaps with a small metallic core. But Europa's surface is not at all like anything in the inner solar system. It is exceedingly smooth : few features more than a few hundred meters high have been seen. The prominent markings seem to be only albedo features with very low relief.

There are very few craters on Europa; only three craters larger than 5 km in diameter have been found. This would seem to indicate a young and active surface. However, the Voyagers mapped only a fraction of the surface at high resolution. The precise age of Europa's surface is an open question.

The images of Europa's surface strongly resemble images of sea ice on Earth. It is possible that beneath Europa's surface ice there is a layer of liquid water , perhaps as much as 50 km deep, kept liquid by tidally generated heat. If so, it would be the only place in the solar system besides Earth where liquid water exists in significant quantities.

Europa's most striking aspect is a series of dark streaks crisscrossing the entire globe. The larger ones are roughly 20 km across with diffuse outer edges and a central band of lighter material. The latest theory of their origin is that they are produced by a series of volcanic eruptions or geysers.

Recent observations with HST reveal that Europa has a very tenuous atmosphere (1e-11 bar) composed of oxygen. Of the 61 moons in the solar system only four others (Io, Ganymede, Titan and Triton) are known to have atmospheres. Unlike the oxygen in Earth's atmosphere, Europa's is almost certainly not of biologic origin. It is most likely generated by sunlight and charged particles hitting Europa's icy surface producing water vapor, which is subsequently split into hydrogen and oxygen. The hydrogen escapes leaving the oxygen.

The Voyagers didn't get a very good look at Europa. But it is a principal focus of the Galileo mission. images from Galileo's first two close encounters with Europa seem to confirm earlier theories that Europa's surface is very young; very few craters are seen, some sort of activity is obviously occurring. There are regions that look very much like pack-ice on polar seas during spring thaws on Earth. The exact nature of Europa's surface and interior is not yet clear but the evidence is now strong for a subsurface ocean.

Galileo has found that Europa has a weak magnetic field (perhaps 1 / 4 of the strength of Ganymede's). It varies periodically as it passes through Jupiter's massive magnetic field. This is very strong evidence that there is a conducting material beneath Europa's surface, most likely a salty ocean.

Europa Quick-Look Statistics

Discovery: Jan 7, 1610 by Galileo Galilei

Diameter (km): 3,138

Mass (kg): 4.8e22 kg

Mass (Earth = 1) 0.0083021

Surface Gravity (Earth = 1): 0.135

Mean Distance from Jupiter (km): 670,900

Mean Distance From Jupiter (Rj): 9.5

Mean Distance from Sun (AU): 5.203

Orbital period (days): 3.551181

Rotational period (days): 3.551181

Density (gm/cm³) 3.01

Orbit Eccentricity: 0.009

Orbit Inclination (degrees): 0.470

Orbit Speed (km/sec): 13.74

Escape velocity (km/sec): 2.02

Visual Albedo: 0.64

Surface Composition: Water Ice

Europa Orbiter

As part of NASA's Ice and Fire Preprojects, planning has begun on a mission to send a spacecraft to Europa to measure the thickness of the surface ice and to detect an underlying liquid ocean if it exists. Using an instrument called a radar sounder to bounce radio waves through the ice, the Europa Orbiter sciencecraft would be able to detect an ice-water interface, perhaps as little as 1 km below the surface. Other instruments would reveal details of the surface and interior processes. This mission would be a precursor mission to sending "hydrobots" or remote controlled submarines that could melt through the ice and explore the undersea realm.

Icepick – the Europa Ocean Explorer

 

 

 

 

 

 

Ice pick: the Europa Ocean Explorer project is an effort to generate a design for a future mission to Jupiter's moon Europa. The spacecraft's mission would explore the liquid water oceans that may exist beneath Europa's surface. The project is organized by the Europa Ice Penetrator Internet Committee (IcePIC).

 

Misson Data

  • Launch: December 2001. Europa Survey: June 2009 Sample Return to Earth: January 2014
  • Power source: Solar (Photovoltaic)
  • Instrumentation: Camera Sample collector: Aerogel Capture System, low density silica foam.
  • Weight: 20 kg. Construction: hollow copper ball, softball-sized (approx. 10 cm. diameter).
  • Impact speed: 10 km sec – 2 Upon intercepting Europa, the Impactor would be released via Ice Clipper.
  • Impact speed of 10 km sec - 2 and trajectory designed to eject plume of material from Europa's surface. Ice Clipper would intercept eject at 50 km altitude above Europa and capture material using aerogel collector. During return trip to Earth, Ice Clipper would perform analysis of captured material Upon arrival at Earth, re-entry vehicle containing Europa sample would separate from Ice Clipper, enter Earth's atmosphere and land with the aid of parachutes
  • Cost: $255 Million

 

C urrent Galileo Mission data are giving us the closest views of Jupiter's icy moon, Europa, since Voyager images first revealed the surface 20 years ago. The icy crust is smooth and blocky, with a banded and broken-puzzle appearance. Europa's outer shell, intriguing to geologists and astrobiologists alike, has been cited as evidence supporting a subsurface-ocean hypothesis. Two articles in a recent Galileo Mission special section of the Journal of Geophysical Research (Planets) review the water-ice surface, major geologic units, and the search for current geologic activity on Europa. Ronald Greeley (Arizona State University) and colleagues from universities, NASA, U. S. Geological Survey, and the National Optical Astronomy Observatories provide an extensive compilation of Europa's primary geologic units as a framework for further mapping of the surface. In another analysis of Galileo images, Cynthia Phillips of the University of Arizona (now at the SETI Institute) and colleagues from ASU, Brown, and JPL look for changes on the surface of Europa since Voyager. They also look for evidence of current geologic activity in the form of active plumes. Not finding proof of surface change and plumes, they give estimates of surface age and surface alteration rates on Europa.

Europa's Major Geologic Units

Europa's geologic history is written in its crisscrossed surface. The straight and curved bands and mottled bright and dark patches looking like jig-saw-puzzle pieces. Defining and characterizing the surface units is the first step in reading the geologic history of Europa's whole body, inside and out. Since the Voyager Mission, planetary scientists have divided the surface of Europa into general geologic units. Traditionally, a geologic unit is defined as a three-dimensional body of material (it has a thickness that extends below the surface) distinguished by its physical features and time of formation. Looking at images of Europa, planetary geologists have used surface shapes, textures, forms, layers, color, and relative brightness to define geologic units. The five primary terrain types now recognized in Galileo images of Europa are plains, chaos, band, ridge, and crater materials.

Structural features on Europa mapped by the team include troughs, strike-slip faults, lineaments, depressions, and domes. All of these resulted from internal activity (tidally-driven tectonism and "ice-water" volcanism.).


The Interior of Europa
This cutaway view shows the possible internal structure of Europa. It was created by using a mosaic of images obtained in 1979 by NASA's Voyager spacecraft. The interior characteristics are inferred from gravity field and magnetic field measurements by the Galileo spacecraft. Europa's radius is 1565 km, not too much smaller than our Moon's radius. Europa has a metallic (iron, nickel) core (shown in gray) drawn to the correct relative size. The core is surrounded by a rock shell (shown in brown). The rock layer of Europa (drawn to correct relative scale) is in turn surrounded by a shell of water in ice or liquid form (shown in blue and white and drawn to the correct relative scale). The surface layer of Europa is shown as white to indicate that it may differ from the underlying layers. Galileo images of Europa suggest that a liquid water ocean might now underlie a surface ice layer several to ten kilometers thick. However, this evidence is also consistent with the existence of a liquid water ocean in the past. It is not certain if there is a liquid water ocean on Europa at present.

Europa - The Past and Future
It is believed that oceans once existed on the surface of Europa. Since liquid water existed in the past, could life have formed and even exist today? The primary ingredients for life are water, heat, and organic compounds obtained from comets and meteorites. Europa has had all three. From the images and data collected by the Galileo spacecraft, scientists believe that a subsurface ocean existed in relative recent history and may still be present beneath the icy surface. Europa's water should have frozen long ago, but warming could be occurring due to the tidal tug of war with Jupiter and neighbouring moons.

 

 

Ridges on Europa
This view of Europa shows a portion of the surface that has been highly disrupted by fractures and ridges. This picture covers an area about 238 kilometers (150 miles) wide by 225 kilometers (140 miles), or about the distance between Los Angeles and San Diego. Symmetric ridges in the dark bands suggest that the surface crust was separated and filled with darker material, somewhat analogous to spreading centers in the ocean basins of Earth. Although some impact craters are visible, their general absence indicates a youthful surface. The youngest ridges, such as the two features that cross the center of the picture, have central fractures, aligned knobs, and irregular dark patches. These and other features could indicate cryovolcanism, or processes related to eruption of ice and gases.

 

Natural and False Color Views of Europa
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.

Galileo Near-Infrared image of Europa
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
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.

 

Europa's Active Surface
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
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.

Comparing Europa to Io

Similarities in composition:

In contrast to most of the moons in the outer solar system, Io and Europa may be somewhat similar in bulk composition to the terrestrial planets, primarily composed of molten silicate rock. Recent data from Galileo indicates that Io has a core of iron (perhaps mixed with iron sulphide) with a radius of at least 900 km. Some of the hottest spots on Io may reach temperatures as high as 2000 K though the average is much lower, about 130 K. These hot spots are the principal mechanism by which Io loses its heat. The energy for all this activity probably comes from tidal interactions between Io, Europa, Ganymede and Jupiter. These three moons are locked into resonant orbits such that Io orbits twice for each orbit of Europa which in turn orbits twice for each orbit of Ganymede. Though Io, like Earth's Moon always faces the same side toward its planet, the effects of Europa and Ganymede cause it to wobble a bit. This wobbling stretches and bends Io by as much as 100 meters (a 100 meter tide!) and generates heat the same way a coat hanger heats up when bent back and forth.

Comparing Europa with the other four Galilean Moons

Group

Name

Diameter (km)

Mass (kg)

Mean orbital
radius (km)

Orbital period

2

Io

3632

8.92×10 22

421,600

1.76 days

Europa

3138

4.8×10 22

670,900

3.55 days

Ganymede

5262

1.49×10 23

1,070,000

7.16 days

Callisto

4820

1.08×10 23

1,883,000

16.69 days

 

 

 

Life in the Ice?

The following research is an insight to how life can survive in frozen conditions, as this article is about the theory of a worldwide ice cap that may have formed millions of years ago!

An except from ‘The Snowball Earth’ by Paul F. Hoffman and Daniel P. Schrag August 8, 1999

"Many lines of evidence support a theory that the entire Earth was ice-covered for long periods 600-700 million years ago. Each glacial period lasted for millions of years and ended violently under extreme greenhouse conditions. These climate shocks triggered the evolution of multi-cellular animal life, and challenge long-held assumptions regarding the limits of global change.."

Organisms could survive in extreme cold conditions such as  "psychrophilic" (cold-loving) organisms of the kind living today in the intensely cold and dry mountain valleys of East Antarctica. Under conditions not too different from those on a "snowball" Earth, various prokaryotic organisms, including cyanobacteria, and certain eukaryotic algae, occupy habitats including snow, porous rock, and the surfaces of dust particles encased in floating ice."

This study of ‘Snowball Earth’ seems to support the hypothesesis that Europa may indeed be able to support life.

This research led us to try some experiments in the lab to look at the nature of ice and also how temperature affects the growth of living things.

The Experiments:

  1. Cracking

We researched into how the surface of Europa may have become cracked, and we have come to this conclusion, convection currents formed by black smokers, cause hot water to rise to the surface of Europa, and crack the ice. The images below show how we performed our experiment:

We observed layers of ice, noting how cracking had occurred in the freezing process. Here were also variations in thickness and surface frosting. We heated a tray of ice and observed that water moved freely under the surface.

We believe that by comparing the ice cap to the crust on the Earth, that the moon Europa, is a representation of the Earth’s ‘inner self’. Convection currents of liquid beneath the ‘icecrust’ could possibly move the ice and therefore many different aspects could form from icequakes - mirroring to the movement of the tectonic plates, comprising the Earth’s crust, due to convection currents in the magma.

 

2) Plant life in the ice

In the other experiment that we performed we examined whether life could survive in sub zero temperatures. We researched the growth of algae and bacteria in sub-zero temperatures, such as cyanobacteria, and eukaryotic algae but we were unable to study these in the lab conditions at school. We therefore opted to examine the growth of simple duckweed and cress, which could be measured easily at school.

We measured the rate of growth of cress seeds and duckweed at temperatures of 18 o C, 4 o C and -15 o C, to compare warm, cold and frozen conditions, in water. We examined growth and appearance and found that the ‘green’ plants cannot photosynthesise in the dark. Growth continued in warm conditions and, to a lesser extent in cold conditions, although in an etiolated state. Prolonged etiolation resulted in the formation of mould. With the frozen samples we found that these living organisms can survive at cold temperatures but then enter a type of stasis where growth does not occur. See images below.

We think that the ice on Europa could preserve life, bacterial or otherwise. Perhaps life on meteorites or comets could be preserved in the frozen material in the moon’s surface.

If ‘undersea’ convection currents are generated from heat nearer to the moon’s core, then it is possible that the liquid material could provide an environment in which this life could develop.

We have enjoyed our study of Europa but, as with most studies, there are still many questions to answer.

  • How thick is the surface ice?
  • Is there liquid water below? The proposed Europa Orbiter spacecraft might find out.
  • What are the surface streaks?
  • How were they formed?
  • Why is the surface so smooth?
  • Is Europa being heated by tidal friction like Io and how much?
  • Is there any volcanism, perhaps hidden beneath the ice? The possible presence of liquid water and volcanism on Europa could result in life-supporting conditions.

Perhaps with more exploration and data in the future these questions will be answered.

 

 

 

Sources of information

6 January 1997: "Scientists Eager to Break the Ice on Europa" Space News

Europa Ice Clipper Science Summary - and excerpt from the Discovery Mission proposal to NASA[ Aerogel info from the JPL Stardust Home Page ]

jpl.nasa.gov/galileo/europa/

http/galileo.jpl.nasa.gov/moons/europa.html

www.the-planet-jupiter.com/europa-moon/europa-pictures.html

solarsystem.nasa.gov/features/planets/jupiter/europa.html

en.wikipedia.org/wiki/Galilean_moon

http/ wiki/Image:Galilean_satellites.