After a few days of suspenseful drama, NASA held its press briefing on Thu April 13, 2017, announcing new discoveries about ocean worlds in the Solar system beyond Earth.
Speculations were high that the announcement would deal with Enceladus, Saturn’s moon, which was earlier discovered to have water-rich plumes venting from the south polar region, that shoot geyser-like jets of water vapor, carbon dioxide, methane and ammonia and ice particles into space.
The Cassini spacecraft, now on its last few orbits around Saturn, performed a flyby on October 28, 2015, passing as close as 49 km and through a plume of Enceladus, sniffing at and analyzing molecules.
New analysis of that data has now shown that the plume contains Hydrogen molecules (H2) (about 1%). This provides strong evidence of hydro-thermal activity at the bottom of Enceladus’s sub-surface ocean, which can provide support for microbial life.
Ocean Worlds in the Solar System
Here is a quick review of solar system bodies known or suspected to harbor oceans. Surprisingly, the solar system contains an unexpectedly large amount of water.
Object |
Description |
Ocean Type |
Estimated Depth |
Surface High Temp. |
Europa |
Jupiter moon |
Sub-surface salt water |
100 km |
-160 C |
Encedalus |
Saturn moon |
Sub-surface salt water |
65 km |
-201 C |
Titan |
Saturn moon |
Icy shell
Sub-surface ammonia + water
Surface methane lakes
|
< 100 km
200 km
|
-179 C |
Callisto |
Jupiter moon |
Sub-surface salt water |
150–200 km |
-108 C |
Ganymede |
Jupiter moon |
Sub-surface salt water
Ice layer at surface and bottom
|
800 km |
-113 C |
Pluto |
(Dwarf) Planet |
Sub-surface water |
100 to 180 km |
-218 C |
Ceres |
Dwarf Planet |
Sub-surface water |
? |
-38 C |
Triton |
Neptune Moon |
Sub-surface water |
? |
-235 C |
By comparison, the deepest parts of Earth’s oceans lie 11 km below the surface.
Enceladus
Enceladus is the sixth-largest moon of Saturn. In 2005, the Cassini spacecraft made multiple close flybys of Enceladus, revealing its surface and environment in greater detail. Cassini discovered water-rich plumes venting from the south polar region. Cryovolcanoes near the south pole shoot geyser-like jets of water vapor, other volatiles, and solid material, including sodium chloride crystals and ice particles, into space, totaling about 200 kg per second. Some of the ejected material escapes into space and and creates Saturn’s E ring. Measurements indicate a sub-surface global ocean tens of km deep. en.wikipedia.org/…
Both Enceladus and Europa have warm cores, caused by periodic gravitational stretching of the moons in elliptical orbits around their giant mother planets. Geophysical models indicate that tidal heating is a main heat source for Enceladus, perhaps aided by radioactive decay and some heat-producing chemical reactions.
The News on Enceladus
From www.nasa.gov/…
NASA's Cassini spacecraft discovered hydrogen in Enceladus’s plume of gas and icy particles. Hydrogen can be a source of chemical energy that could be useful for microbes, if any exist there. The finding also provides further evidence that warm, mineral-laden water is pouring into the ocean from vents in the seafloor. On Earth, such hydrothermal vents support thriving communities of life in complete isolation from sunlight. Enceladus now appears likely to have all three of the ingredients scientists think life needs: liquid water, a source of energy (like sunlight or chemical energy), and the right chemical ingredients (like carbon, hydrogen, nitrogen, oxygen).
The presence of ample hydrogen in the moon's ocean means that microbes – if any exist there – could use it to obtain energy by combining the hydrogen with carbon dioxide dissolved in the water. This chemical reaction, known as "methanogenesis" because it produces methane as a byproduct, is at the root of the tree of life on Earth, and could even have been critical to the origin of life on our planet.
Cassini is not able to detect life, and has found no evidence that Enceladus is inhabited. Future missions to this icy moon may shed light on its habitability.
Here is a NASA video describing the exciting discovery about Enceladus -
Europa
The briefing also described new Hubble Space Telescope observations of the plumes of Europa which were first observed in 2014.
The newly imaged plume rises about 100 km above Europa’s surface, while the one observed in 2014 was estimated to be about 50 km high. Both correspond to the location of an unusually warm region that contains features that appear to be cracks in the moon’s icy crust, seen in the late 1990s by NASA's Galileo spacecraft. Researchers speculate that, like Enceladus, this could be evidence of water erupting from the moon’s interior.
Europa has long been hypothesized to contain a water ocean beneath a thin icy surface, which could conceivably harbor life. Heat from tidal flexing causes the ocean to remain liquid and drives ice movement similar to plate tectonics, allowing surface chemicals and organic molecules of meteoric origins to enter into the ocean below, helping make it more conducive to life.
Water Worlds
Here is another interesting NASA video describing other Oceans in the Solar system -
Future Missions
NASA's Europa Clipper mission, which is planned for launch around 2022, will orbit around Jupiter and make close flybys over Europa. It will provide further details on the plumes, their composition and the geology and chemistry of Europa’s surface.
NASA's Europa Lander Project will send a spacecraft to land on Europa and explicitly search for evidence of life. Launch around 2024-2025, landing in 2031. The Trump administration proposed budget does not include funding for this project. See www.space.com/…
ESA's Jupiter Icy Moons Explorer, will be launched around 2022 and will reach Jupiter in 2030. It will fly-by Europa and Callisto multiple times before moving into orbit around Ganymede in 2033.
Several other projects are on the drawing board for missions to Saturn and its moons, including rovers for underwater exploration. But nothing is imminent.
Here is a video of new robots being developed by NASA for exploring icy worlds such as Europa and Enceladus.
NASA Budget in the Time of Trump
The Trump proposed 2018 budget axes the Europa Lander project, the Asteroid Redirect Mission, and four NASA Earth-science projects: The Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) satellite, which would monitor Earth's oceans and atmosphere; the Orbiting Carbon Observatory-3 (OCO-3), which would track atmospheric carbon-dioxide levels from the International Space Station (ISS); the Climate Absolute Radiance and Refractivity Observatory (CLARREO) pathfinder, another instrument that would be installed on the ISS; and the Deep Space Climate Observatory (DSCOVR).
Congress will have the final say on the budget. Let’s call our congressional reps and demand that our tax dollars to be used for science, not wars.
References
- NASA news release — www.nasa.gov/…
- Journal paper — Cassini finds molecular hydrogen in the Enceladus plume: Evidence for hydrothermal processes — science.sciencemag.org/...
- NASA twitter site — twitter.com/...
- Ocean Worlds Beyond Earth — nasa.tumblr.com/…
- Europa Lander report — solarsystem.nasa.gov/…
- Earth Life May Have Originated at Deep-Sea Vents — www.space.com/…
- Earlier diary on Europa — www.dailykos.com/...