Tuesday, June 26, 2012

Europa, The Frozen Ocean

The Moon Europa as seen by the Galileo probe, via NASA.
Between 1609 and 1610, using his improved telescope design, Galileo Galilei observed four bodies orbiting Jupiter.  These bodies, later named the Galilean Moons, are the largest satellites of the Jovian System (Jupiter and its moons).  The second of these moons and the smallest of the first four observed, Europa has become one of the focal points for the search for life outside of Earth.

Despite most sources giving credit to Galileo for its discovery, Europa and the other three Galilean Moons were also likely discovered at the same time by Simon Marius.  Originally Galileo named the moons the Medician Stars, partly out of his initial uncertainty of their nature and as a way of faltering his future patrons.  Marius, however, named the moons according to the suggestion of fellow astronomer Johannes Kepler, invoking the names of the mistresses of Zeus (who was later renamed Jupiter according to Roman mythology), a tradition that has been used in the naming of all of Jupiter's moons since.

Europa was named after a Cretan moon goddess who was absorbed into Greek mythology as a Phoenician Princess who was abducted and raped by Zeus as he took the form as Bull.  Sought out by Zeus for her beauty, the Jovian moon of Europa follows in the steps of its namesake.

The first human probe to observe Europa was Pioneer 10 in 1973 and was followed the next year by Pioneer 11.  The first images of this sixth moon of Jupiter were grainy and lacked any distinguishing detail.  It wasn't until 1979 when the first Voyager probe passed by that images detailed enough to discern surface features were available.  It was with these first images that scientific curiosity and debate surrounding Europa bloomed.

While studying images obtained from both Voyager 1 and 2, certain anomalous features were noticed.  The most striking were striations that seemed to cover the moon.  Named Lineae, these features reached widths of 20 kms (12 mi) across and hundreds to thousands of kilometers in length. 

Europa with its prominent Lineae, via NASA.
To confound things further, the surface of Europa was surprisingly smooth.  Few craters were observed which suggests that the surface is constantly being remade.  In the cosmic shooting gallery that is the solar system, craters are a common feature.  The older the visible surface, the more craters that will be observed as only changes in surface features will wipe away craters that form.  A quick look at Mercury or our own moon Luna and you will see how a geologically inactive body collects craters.  Europa, on the other hand, has very few craters and those few that do exist are visibly 'young'.  Combined with Europa having a very high reflectivity, or albedo, at 0.64, the surface of the moon can be estimated to be between 20 and 180 million years.  In comparison, regions of the Martian surface have been dated to around 3.3 billion years.

These and other unexpected features seen by future missions such as the the Galileo mission to the Jovian system and the New Horizon probe as it passed by Europa on its way to visit Pluto suggested that the source of the strange features was ice, water ice.  But these surface structures suggests something more then just a cold frozen moon.  The renewing of the surface and the formation of the long Lineae lent credence to the hypothesis that there was liquid water hidden beneath the icy surface.  Not just a little water, but a vast, possibly global ocean.

But with an average surface temperature of 110 K (−160 °C; −260 °F) at the equator, how could there be a subsurface ocean of liquid water?  The answer seems to come from the same process that causes the tides here on Earth.  As Europa and the other Jovian moons orbit Jupiter, they are pulled on gravitationally at different rates at different times.  Similar to the processes that cause the nigh constant volcanism on the innermost of the Galilean Moons of Io, Jupiter's gravity causes tidal forces that heat up the plant.  This could, potentially, cause volcanism akin to the deep ocean hydrothermal vents on Earth.

The 'Ice Rafts' of the Conamara Chaos, via Wikipedia Commons.
With such internal heating, a warm, liquid water ocean is likely to exist.  This isn't a fringe idea either, it has become the leading hypothesis to explain the observable features of Europa.  The liquid ocean has been calculated to have an average depth of 100 km (over 62 miles) with depths up to 170 km (over 105 miles).  This liquid ocean would exist below a cold, hard cap of ice reaching 10 -30 km (6 - 19 miles) slowly becoming a more ductile warm ice before eventually becoming the liquid water below.  This warm ice would be capable of moving up into any cracks that form in the hard surface ice, creating the Linaea.  Still further evidence from the chaoses suggest that there may even be liquid water 'lakes' trapped in the ice.

The amount of water that can be found on Europa is staggering.  If one takes the average depth of 100 km, there is a volume of 3 × 1018 miles cubed of liquid water.  This is over two times the amount of water that can be found here on Earth.

Europa next to Earth, along with the comparable spheres of water contained by each, via NASA.
In the search for life elsewhere in our solar system, Mars tends to steal the show in the popular media.  With its relatively close proximity, potential for human colonization, and its history of once possessing large quantities of liquid water on the surface, it is understandable.  Liquid water seems to be the key for life as we know it.  Everywhere on Earth that it is found, life can be observed as well.  This being considered, Europa seems to be one of the best sites for the future search for life and the astronomical community knows this.  While there have been many probes proposed to visit Europa, most have fallen through until JUICE.

JUICE is the somewhat tortured acronym for the planned European Space Agency (ESA) probe known as the JUpiter ICy moon Explorer.  Planned for a 2022 launch, JUICE would reach the Jovian system in 2030 where it will serve out at least a three year mission to visit Europa and two other of the Galilean moons, Callisto and Ganymede.  Like Europa, Callisto and Ganymede also appear to have liquid water as well as the observed water ice.  While all have the potential for harboring conditions that could be conducive to life, Europa is seen as the most likely to contain such an environment due to its larger amounts of water, hotter internal environments and a far more dynamic surface.

Artist rendition of the JUICE probe, via ESA.
As a final boost to the potential for the development of life is the oxygen content of Europa.  Oxygen is, as far as we know, required for the development of complex life and was directly responsible for the explosion of multicellular life here on Earth.  Based on new calculations by Richard Greenberg, there could be enough oxygen to support a biomass of around 3 billion kilograms if such multicellular life had developed on Europa.  Even better, the proliferation of oxygen most likely occurred later in its existence which would be required for the formation of life based on how life progressed here on Earth.

Complete Dictionary of Scientific Biography. New York: Charles Scribner's Sons, 2007. ISBN 0-684-31559-9.

Geissler, Paul E.; Greenberg, Richard; et al. (1998). "Evolution of Lineaments on Europa: Clues from Galileo Multispectral Imaging Observations".

McFadden, Lucy-Ann; Weissman, Paul; and Johnson, Torrence (2007). The Encyclopedia of the Solar System. Elsevier. pp. 432. ISBN 0-12-226805-9.

Schmidt BE, Blankenship DD, Patterson GW, & Schenk PM. (2011) Active formation of 'chaos terrain' over shallow subsurface water on Europa. Nature, 479(7374), 502-5. PMID: 22089135

Cosmos Magazine. http://www.cosmosmagazine.com/news/3069/jupiter-moon%E2%80%99s-ocean-rich-oxygen.

Hartmann, William K., and Gerhard Neukum. "Cratering Chronology and the Evolution
of Mars." Space Science Reviews 96 (2001): 165-194.
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Friday, June 15, 2012

The Kakapo

Evolution is a strange thing.  Change the selective pressures on a species a bit and it will take take any path to survival it can, no matter how absurd.  Familiar body plans begin to diverge and change and every so often, these adaptations add up to what can only be called odd.

Approximately 85 million years ago, the microcontinent of Zealandia -the tectonic plate containing New Zealand- split from the super continent East Gondwana.  As it did so, the resident organisms became isolated from their mainland relatives.  One group of birds, the ancestors to the New Zealand Parrots (superfamily Strigopoidea) became trapped on the islands.  While most of the parrot species retained a recognizable, if unique form, one species adapted itself to its new environment in the most unexpected of ways.

Enter Strigops habroptila, more commonly known as the Kakapo.  The Kakapo is what a parrot would look like, if it were to be described by someone who had only the vaguest idea of what one was.  Instead of flying through the trees seeking food in the light of the sun, the Kakapo prefer to run about the underbrush at night using their wings for little more then as a means to fall a bit slower.

When flight is no longer an issue, neither is size.
Meaning Night Parrot in Maori, the Kakapo is a rotund bird that inhabits both the underbrush and trees.  An avid climber, it has not lost its preference for high places despite the lack of any native land predators that could threaten the bird.  The only native predators are diurnal (active during the day) birds of prey which have helped push the species towards its flightless and nocturnal nature to escape the threat.

While flightless birds tend to be relatively uncommon, the Kakapo is even more so as no other known species of parrot, living or extinct, has lost the ability to fly.  Since weight is of little concern for the Kakapo any longer, it has been able to grow into the heaviest of all parrots, weighing up to 8 lbs (3.5 kg).  Instead of flight, they will use their strong legs to 'jog' about.  While not exceedingly fast, they are able to cover a few kilometers a night if need be, as can be seen both when females leave their nest in search of food and during the mating season.

Generally solitary, the Kakapo only gathers for breeding purposes.  The mating rituals of the Kakapo also set it aside as it is the only flightless bird to have what is known as a lek mating system.  A lek is a gathering of indiviudals in an area for breeding purposes.  When available food is abundant, the males will leave their territories to gather around hilltops and ridges specifically for breeding.   Here they will compete with other males to attract females.  Each male attempts to control their own patch of ground that is typically seperated by around 160 ft (50 m) from any other male.  While direct confrontation does occur between males, females tend to pick mates based on the loudness of the males calls.  During mating seasons, the males will let out a series of loud 'booms' that can be heard for miles.  The males call out on average 1,000 times an hour for 6 to 7 hours each night.  After finding a mate, the female will leave the lek and retains no connection to the male.

Kakapo chicks, courtesy TerraNature.org.

While the Kakapo was once revered by the Maori and even kept as pets due to their calm and curious nature, the species now faces an uncertain future.  As humans began to arrive on New Zealand, they brought with them new species that began to threaten the Kakapo.  Starting with rats brought to the island by the Maori's Polynesian ancestors and continuing to include domestic cats and stoats, the introduction of mammalian predators along with changes to the environment led to a dramatic drop in the Kakapo population. 

Now critically endangered, only 126 individuals survive in both captivity and the wild.  While there have been multiple attempts at reintroduction of Kakapo to various islands with minimal predators, success has been limited.  This is not helped by the fact that Kakapo typically breed only once every 3 to 4 years.  Since the start of programs to save the Kakapo, its plight has gained a certain amount of attention with multiple books and television programs being made about the dying species.  While its future is uncertain, continued research and breeding programs have made it possible for the Kakapo to, at the very least, hold on for a bit longer.  If you wish to aid in the survival of this unusual species, the Kakapo Recovery Program accepts donations to help maintain the future of the Kakapo.
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