New and ongoing discoveries by two interplanetary probes indicate oceans underneath miles of ice on distant moons.
NASA launched the New Horizons spacecraft in 2006, sending it on track for Pluto with a due date in July 2015. The journey will total over 3 billion miles. Pluto lives on the outskirts of the Solar System in the neighborhood of the Kuiper Belt. The Kuiper Belt houses multitudes of frozen objects believed to be leftover bits from the creation of the Solar System. Over 1600 have been catalogued thus far.
New Horizon will explore Pluto and its moons as well as some of the ice worlds in the Kuiper Belt. These far away objects have been largely untouched since the solar system was born billions of years ago. They could hold information about the origins and evolution of the solar system and planets.
Pluto temperatures average -387 F (-233 C) on a good day. The landscape is icy and dim perhaps similar to Arctic regions on Earth. The Sun probably appears as just a bright point in the sky and daytime on Pluto is likely darker than a stormy day on Earth. The Pluto sky, though, would be clear enough to see thousands of stars even in the daytime.
New Horizons is looking for evidence of a sub-surface ocean on Pluto. The outer surface of Pluto appears to be a thin nitrogen shell over water ice. Researchers believe the presence or absence of a bulge in the surface at the planet’s equator will provide this evidence. A bulge could be 10 km tall.
A bulge will indicate no ocean lies underneath, because liquid water moving over time would have reduced or eliminated the bulge. If New Horizons sees evidence of stretching of the surface due to temperature changes, however, that would be more indicative of an ocean. If an ocean exists on Pluto, potassium and other isotopes undergoing radioactive decay and emitting heat would probably maintain it. Potassium ions would be most likely to occur in a rocky planetary core, and would need to occur at about 1/10 the rate of that found in meteorites from the early Solar System. Researchers believe this is a good possibility for existing on Pluto.
The nature of the ice on the surface will also influence whether an ocean exists. Ice that is slushier and resists flowing would suck the heat out of the water beneath, causing the ocean to freeze. A more solid shell would hold in heat and maintain the ocean.
A planet wide ocean might be beneath 100-120 miles (165-200 km) of ice. The ocean itself might be from 60 to 105 miles (100 to 170 km) deep with an average depth of 100 miles (165 km). The planet might also have geysers similar to those found on Saturn’s moon Enceladus and Neptune’s moon Triton.
New Horizon Status Update – Late May 2013
New Horizons will pass within 7750 miles of the surface of Pluto, providing high-resolution photos and mapping of the planet that currently appears as a blurry mix of brown and gold. Even images from farther away will be 10 times better than the best of those from the Hubble Space Telescope. Ridges and valleys of 260 feet (80 m) should be distinguishable. Water is necessary for life as we know it, and scientists are finding it farther out into the solar system than expected.
As of late May 2013, New Horizons was approximately 2.6 billion miles from the sun and about 600 million miles away from Pluto. Arrival at the distant world is under 700 days away. New Horizons has been underway over 2700 days since launch. It is currently involved in a wake-up period after 100 days in hibernation. It is undergoing a thorough annual checkup and software updates in addition to approach and close-encounter rehearsals.
In August, the ship will go back to sleep for several more months. The navigation team has determined the ship is on course, and no fuel needs to be spent making course corrections. This summer, the ship will be close enough to photograph Pluto separately from Charon, its largest moon. The first week of July is the 35th anniversary of the discovery of Charon.
Saturn and Jupiter’s Moons and the Cassini Spacecraft
Jupiter’s moons Europa, Ganymede and Callisto may have liquid oceans under their icy surfaces, and Saturn’s moon Titan probably has underground water. It may also have a ocean of ammonia-enriched water below the surface in addition to liquid methane surface lakes and seas. Enceladus, another moon of Saturn, appears to have liquid water below the surface enhanced by giant geysers of water vapor, organic particles and ice particles erupting from fissures near the South Pole. The Cassini spacecraft has directly sampled these eruptions. Some asteroids may even have liquid water under their surfaces.
Mike Brown and Kevin Hand of the Jet Propulsion Laboratory have announced the ice surface of Europa contains the same chemicals as the ocean underneath the surface. Future exploration of the moon could answer questions about life in that ocean just by analyzing the surface.
Brown and Hand detected magnesium sulfate on one side of the moon, and surmise the surface contains other salt compounds that could only come from its ocean. The pair will use the same ground-based telescopes to examine Ganymede and perhaps Europa. Plans are in the works for the European Space Agency to send a mission to the Jovian system in 2030, including flybys of Europa, Ganymede and Callisto.
Saturn’s Moon Dione
Other interesting news from distance iceballs includes that from the Cassini orbiter visiting Saturn’s moon Dione. Instruments onboard Cassini have found hints of a particle stream coming from the moon as well as images of features similar to the geysers on Enceladus. Images showed evidence of a possible liquid or slushy layer under the hard ice crust of Dione.
A surface feature called Janiculum Dorsa, a mountain ridge approximately 800 km long and 0.6-1.2 miles (1-2 km) tall appears to sit atop a part of the Dione crust that flexes by approximately 0.3 mile (0.5 km). This suggests the icy crust was warm when the ridge formed, and the best way to get that heat is through the presence of a subsurface ocean during the ridge’s creation.
Tidal pulls from Dione’s orbit – the stretching and squeezing as it gets closer to and farther away from Saturn in the orbit – and an icy crust capable of moving independently from the core of the moon could also produce the heat. From a distance, the moon appears like nothing so much as a boring ice cue ball. Close up images of the Janiculum Dorsa ridge indicate the moon may still be geologically active today. It is a feature similar to those on Enceladus that houses the geysers. Dione could be a fossil of a world once like geyser moon Enceladus, or a weaker copy of Enceladus according to scientists at JPL.
Dione has a diameter of 698 miles (1123 km) and is the fourth largest moon of Saturn. It is the 15th largest moon in the solar system, and orbits Saturn at approximately the same distance between Earth and her moon. It is one of 53 named satellites of the ringed planet. The moon is 1.48 as dense as water, indicating it has a dense core surrounded by ice. The average temperature on Dione is -302F (-186C). These temperatures cause the ice surface to behave much like rock.
Cassini also detected a faint oxygen atmosphere on Dione, equivalent to the oxygen density 300 mi (480 km) above Earth. Dione orbits with the same side always facing Saturn, a position referred to as “tidally locked.” The Earth’s moon orbits the same way in relation to Earth. Dione’s gravity keeps Helene and Polydeuces, two smaller moons, locked into their orbital positions as the three travel around Saturn together.
Dione also influences the orbits of Enceladus and Mimas, two of Saturn’s larger moons. Scientists are still puzzling over why Enceladus became so geologically active with geysers and geologic activity, while Dione did not move as quickly.
Regardless, scientists are discovering that subsurface liquid oceans are fairly common on these ice satellites. Other worlds of high interest for the presence of liquid water include dwarf planets Ceres and Pluto, and Pluto’s moon Charon.
Read More about the exploration of the far solar system, the search for life off Earth, and the space missions mentioned in this article: