What Heats the Bottom of the Enceladus Moon’s Ocean to 194 Degrees Fahrenheit?

— “We think that the temperature at least in some part of the ocean
must be higher than 190 degrees Fahrenheit. If you could swim a little bit
further from the really hot part, then it could be comfy.”

– Sean Hsu, Ph.D., Laboratory for Atmospheric and Space Physics, Univ. of Colorado

— “[For such heat] the most exciting possibility is that there’s ongoing chemical reactions between the rock inside Enceladus and the water.”

– Bill McKinnon, Ph.D., Planetary Scientist, Washington Univ.-St. Louis

 

Reposted January 1, 2024 – March 27, 2015 Boulder, Colorado – In 2014, NASA reported that gravity-measuring devices on its Cassini spacecraft showed there was an enormous body of liquid water directly below the south pole of Enceladus, one of Saturn’s 31 moons and the sixth largest.

Measurements from NASA’s Cassini spacecraft suggest that Saturn’s moon, Enceladus, which has jets of water vapor and ice gushing from its south pole, also harbors a large interior ocean with hydrothermal activity beneath an ice shell, as this illustration depicts. (Courtesy NASA/JPL-Caltech)
Measurements from NASA’s Cassini spacecraft suggest that Saturn’s moon, Enceladus, which has jets of water vapor and ice gushing from its south pole, also harbors a large interior ocean with hydrothermal activity beneath an ice shell, as this illustration depicts. (Courtesy NASA/JPL-Caltech)

Now comes news that the bottom of the Saturn moon’s ocean must be heated very hot in order to produce silica particles that have now been confirmed in space around Saturn and Enceladus. This surprising new data about ongoing hydrothermal activity on Enceladus was published in the March 11, 2015, issue of Nature, by postdoctoral researcher, Sean Hsu, Ph.D., at the Laboratory of Atmospheric and Space Physics (LASP) at the University of Colorado in Boulder. Dr. Hsu and his colleagues have found that microscopic grains of silica detected near Saturn are most likely bursting out from the watery geysers on Enceladus.

Illustration of water ice geysers erupting on the surface of Enceladus, one of Saturn's 31 moons, the sixth largest and only moon so far confirmed by a NASA gravity study in 2014 to have a large body of fluid water, an ocean, beneath its south pole. Artist's concept © 2006 by Joe Bergeron.
Illustration of water ice geysers erupting on the surface of Enceladus, one of Saturn’s 31 moons, the sixth largest and only moon so far confirmed by a NASA gravity study in 2014 to have a large body of fluid water, an ocean, beneath its south pole. Artist’s concept © 2006 by Joe Bergeron.

Dr. Hsu said: “It’s very exciting that we can use these tiny grains of rock, spewed into space by geysers, to tell us about conditions on — and beneath — the ocean floor of an icy moon.” What he and his colleagues have discovered shocked not only them, but all planetary scientists: the ocean bottom of Enceladus must be very hot.

Saturn's moon Enceladus is one of the brightest objects in our solar system because it is covered in water ice that reflects sunlight.
Saturn’s moon Enceladus is one of the brightest objects in our solar system because it is covered in water ice that reflects sunlight.

LASP March 11, 2015 Press Release: “This is the first clear indication of an icy moon having hydrothermal activity — in which seawater infiltrates and reacts with a rocky crust, emerging as a heated, mineral-laden solution that produces silica. The finding adds to the tantalizing possibility that Enceladus, which displays remarkable geologic activity including geysers, could contain environments suitable for living organisms.”

This image of water geysers spouting from Saturn's moon Enceladus was taken by NASA's Cassini orbiter in October 2007. Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA.
This image of water geysers spouting from Saturn’s moon Enceladus was taken by NASA’s Cassini orbiter in October 2007. Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA.

Hydrothermal activity would mean there is an energetic heat source in Enceladus’s core interacting with rocks that are heating the Saturn moon’s ocean. And that could mean some kind of life on the ocean floor as Earth has marine life at hot vents in this planet’s oceans. A radioactive core could explain lots of heat, but so far the LASP computer model data doesn’t add up to the amount of  radioactive material that would be needed.

Measurements from NASA’s Cassini spacecraft suggest that Saturn’s moon Enceladus, which has jets of water vapor and ice gushing from its south pole, also harbors a large interior ocean with hydrothermal activity beneath an ice shell, as this illustration depicts. Graphic by NASA/JPL-Caltech.
Measurements from NASA’s Cassini spacecraft suggest that Saturn’s moon Enceladus, which has jets of water vapor and ice gushing from its south pole, also harbors a large interior ocean with hydrothermal activity beneath an ice shell, as this illustration depicts. Graphic by NASA/JPL-Caltech.

This surprising news follows an extensive, four-year analysis of data from the Cassini spacecraft, computer simulations and laboratory experiments. From their close examination, the researchers determined the tiny grains of silica most likely form when hot water containing dissolved minerals from the moon’s rocky interior travels upward, coming into contact with cold water near the icy surface and vents outward  from Enceladus’s frozen crust. According to the LASP research, the temperatures required for interactions to produce these tiny silica grains would have to be at least 194 degrees Fahrenheit (90 degrees Celsius) at the bottom of the Enceladus ocean.

Hot core of Enceladus (chemistry unknown) heats rocky ocean floor that interacts with liquid ocean through hydrothermal vents on ocean bottom that are at least 194 degrees F. (90 degrees C.). That hot water rises to the Saturn moon's icy crust and vents out in water vapor plumes that have been photographed many times by NASA's Cassini spacecraft. Illustration by NASA.
Hot core of Enceladus (chemistry unknown) heats rocky ocean floor that interacts with liquid ocean through hydrothermal vents on ocean bottom that are at least 194 degrees F. (90 degrees C.). That hot water rises to the Saturn moon’s icy crust and vents out in water vapor plumes that have been photographed many times by NASA’s Cassini spacecraft. Illustration by NASA.

One of the astrophysicists working on the discovery of silica particles ejected from the many vents of water ice from Enceladus is Sascha Kempf, Ph.D., a research associate at LASP after working at the Max Planck Institute in his home country of Germany. Dr. Kempf first began working on the dust instrument aboard the Cassini spacecraft orbiting in the Saturn system and was stunned when they identified silica particles in the dust around Saturn. On Earth we know silica as quartz sand that evolves from the chemistry of water interacting with rocks.


Interview:

Sascha Kempf, Ph.D., Research Associate at Laboratory for Space Physics (LASP), University of Colorado, Boulder, Colorado: “This was a big mystery because we couldn’t understand what is the source of these (silica) particles. And we were even more surprised when we realized that the composition of these particles is silica and not water ice.

TO HAVE SILICA, YOU WOULD HAVE TO HAVE HAD SOME SORT OF WATER INTERACTION?

Right. These particles are formed from sub-surface water, which is in contact with a rocky core. What our measurements says is that the temperature of the ocean at the bottom of the ocean is 194 degrees Fahrenheit. The temperature of the water at the surface of this ocean is about 0 degrees Centigrade (32 degrees F.)

BECAUSE THERE HAS BEEN COOLING FROM THE 194 DEGREES F. AT THE BOTTOM TO THE ICY SURFACE AT THE TOP?

Right, absolutely so.

WHAT IS THE PROCESS THAT WOULD PRODUCE THAT TEMPERATURE IN A BODY THAT IS ONLY 500 KILOMETERS  (311 miles) IN DIAMETER?

That is a good question. I would really like to answer the question if I would know the answer. (laughs) So, this process is not really understood. And the energy source for maintaining the jet activity on this moon was a big mystery from the beginning. You’re absolutely right, the body is too small to really understand that this energy can be provided by an interior process. But, this is what the data is telling us — that there needs to be a temperature of 194 degrees Fahrenheit at least at the interface between the rocky core and the sub-surface ocean in order to allow such particles to form in the sub-surface ocean water.

DR. KEMPF, WHAT PROCESS DO YOU THINK IS OCCURRING AT THE CORE OF ENCELADUS THAT COULD POSSIBLY PRODUCE 194 DEGREES FAHRENHEIT WATER AT THE BASE OF THE OCEAN?

The process which is generally considered for warming rocky cores is radioactive decay. The models we have for the amount of such material in the rocky core of Enceladus is not working out close to the amount of energy that we observe to be generated in order to maintain the temperature at the interface.

SO, WHAT YOU ARE SAYING IS THAT RADIOACTIVITY AS WE KNOW IT IN THE CORE OF THE EARTH THAT CREATES THE HEAT IN OUR PLANET, YOU DO NOT FIND DATA THAT IS GOING TO SUPPORT  THAT RADIOACTIVITY IS RESPONSIBLE  INSIDE OF ENCELADUS?

Not really. It’s very hard to understand why the moon is so efficient in generating heat to have such a high temperature at the core water interface. So the answer for this, I cannot provide to you. And I think no one can right now.

RIGHT. IS THERE ANY HYPOTHESIS THAT YOU THINK MIGHT BE MORE LIKELY THAN ANOTHER?

Not really because it’s already hard to understand where the energy is coming from to prevent the ocean from freezing. But now we have to have even more energy available to maintain such a  high temperature at the core ocean interface. So the problem to explain the activity of Enceladus gets even more challenging.

SO WHAT DO YOU SPECULATE MIGHT BE BEHIND THIS?

In order to maintain such a high temperature of the rocky core, the only way to do this is to have sufficient amount of radioactive material in the rocky core to generate so much energy. I cannot think of any other process.

OK, THEN THAT MAKES SENSE, BUT WHY DO YOU THINK THAT THE DATA IS NOT SUPPORTING ENOUGH RADIOACTIVE CORE MATERIAL TO PRODUCE THIS HEAT?

I’m not really sure I can speculate about it. Now we really have difficulties to understand the formation of Enceladus. If these are the constraints for the heat outputs after 4.6 billion years of the formation of the moon itself. So one way to do this is to have a larger rocky core relative to the ice crust of the moon. The model we had before we got the first good data from this moon, were not predicting this.

 

Marine Life Is Found Around Hot Water
Vents of Earth Oceans

Deep-sea hydrothermal vents on Earth lie more than a mile and a half below the sea surface, in total darkness. Yet the searing hot vents support a thriving ecosystem that includes thousands of species of microbes and dozens of species of animals, from blind shrimp to giant tubeworms.

How can such a large variety of life exist in total darkness? The organisms that make up a vent ecosystem may seem strange and exotic, but they might be a clue to the range of alien life we might find in the Enceladus warmed ocean and other cosmic bodies.

A well-developed ecosystem at a hydrothermal vent in the Pacific Ocean includes tubeworms (with the red plumes) and mussels (the yellow shellfish). Image by divediscover.
A well-developed ecosystem at a hydrothermal vent in the Pacific Ocean includes tubeworms (with the red plumes) and mussels (the yellow shellfish). Image by divediscover.

IF THERE IS WATER COMING OUT OF THE HEATED CORE OF ENCELADUS OUT OF VENTS IN THE BOTTOM LIKE WE HAVE HERE ON EARTH WHERE THERE ARE VARIOUS KINDS OF TUBE WORMS AND LIFE THAT SEEM TO THRIVE IN HIGH TEMPERATURES AND EVEN SULFUR, THEN WHAT IS YOUR OWN PERSPECTIVE ON THE LIKELIHOOD THAT WE WILL DISCOVER THAT THERE IS SOME KIND OF LIFE WHERE THESE VENTS ARE WARM AND WARMING THE WATER GOING TOWARDS THE ICY SURFACE OF ENCELADUS?

Enceladus is definitely one of the best candidates for finding life in the solar system. And you are exactly right. We have the temperatures. We have energy available. We have probably complex organics in the ocean water. We have liquid water. So that is a place that we should check if we want to find life in this solar system. But in order to get conclusive evidence about biological material, we need to have better instruments — instruments with higher resolving power. And for that reason, we need to have a mission dedicated for finding life on Enceladus by having more capable instruments and to take data samples from the gas and the dust particles to identify such (living) compounds.

COULD YOU DESCRIBE YOUR FEELING AS A SCIENTIST WHEN YOU WERE FACING DATA THAT THIS ENCELADUS MOON OF SATURN, ONLY 500 KILOMETERS IN DIAMETER, WOULD HAVE AN OCEAN EQUAL TO THE GREAT LAKES ON EARTH AND AT THE BOTTOM, THE BOTTOM TEMPERATURE OF THAT WATER HAS TO BE 194 DEGREES FAHRENHEIT IN ORDER TO EXPLAIN THE SILICA.

In all honesty, this is not what we expected to observe. And there is one Cassini flyby left and I am really looking forward to the close flyby, which will happen this year around August 2015, I guess. So we have the optimum flyby conditions for this last flyby. This will be the closest flyby ever traversing the plumes (jets of water ice that vent from Enceladus). This will provide us with unique data about the dynamical structure of the plume, about the density profile, about the composition of the ice particles, and the composition of the gas. Because we are now much, much closer to the surface. We will collect more material and so our sensitivity will be higher and I’m really looking forward to the data provided by this upcoming flyby. What kind of surprises this data will offer to us?

 

Cassini Will Fly Close to the Enceladus
Plumes in August 2015

This is an artist concept of Cassini spacecraft making its August 2015 close flyby about 31 miles (50 km) from the ice water venting from the Enceladus ocean. Image credit: NASA/JPL
This is an artist concept of Cassini spacecraft making its August 2015 close flyby about 31 miles (50 km) from the ice water venting from the Enceladus ocean. Image credit: NASA/JPL

HOW CLOSE WILL IT GET?

We will do a flyby that will be approximately 50 kilometers (31 miles) at the closest approach. This time we will be 50 kilometers within the plumes and this is really exciting!

THIS WILL REINFORCE ALL OF THE RESEARCH THAT YOU HAVE DONE UP TO THIS DATE WITH MORE DATA?

Absolutely so.

WHEN WILL THERE BE ANOTHER MISSION SPECIFICALLY DESIGNED TO INVESTIGATE WHETHER OR NOT THERE IS SOME KIND OF LIFE ASSOCIATED WITH THIS WARMER WATER IN THE ENCELADUS OCEAN?

So this depends on the size of the mission. If NASA decides to send a spacecraft just to verify if there is evidence for life in the Enceladus plumes, then such a mission can probably be launched around 2020.

WHAT YOU ARE SAYING IS IF THE MONEY AND WILLINGNESS IS THERE TO GET ANOTHER MISSION LAUNCHED IN 2020, WHICH WOULD BE FIVE YEARS FROM NOW, IT WOULD HAVE BETTER INSTRUMENTS, MORE REFINED INSTRUMENTS FOR ANALYZING EMISSIONS THAT MIGHT TELL YOU ONCE AND FOR ALL WHETHER THERE IS EVIDENCE OF LIFE  UNDERNEATH THE ICY CRUST OF ENCELADUS DOWN IN THE WARMER OCEAN?

Yes, with higher quality instruments, we can do a much better job of identifying such agents in the gas phase and the ice particles.

HOW LONG WOULD IT TAKE IF THERE IS A LAUNCH IN AUGUST OF 2020 TO GET TO ENCELADUS?

This depends on the way how you launch. With the biggest launches, you can probably send such a spacecraft on a direct route to the planets. But it’s much more likely that we will do excursions into the inner solar system to acquire the energy of flybys from Venus and Earth to go to Saturn. This is a very long process. Cassini took seven years to get to Saturn. I would expect for such an Enceladus mission, it would be of similar length.

DURING THOSE SEVEN YEARS OF TRAVEL FOR THE SPECTROMETER MISSION, THEY MIGHT BE ABLE TO GET THINGS CLEARED OFF THAT BY 2030, WE MIGHT BE ABLE TO LAUNCH A LANDER.

That’s what I think, right. You know, space exploration is a very slow progress. But eventually, we will do this.”


More Information:

For further information about solar system mysteries, please see these reports in the Earthfiles Archive:

  • 03/01/2013 —Strange Martian Moon Phobos – Could Its Dust Have Evidence of Life?
  • 06/20/2007 —Update: What Is the Moving Light in Saturn’s Rings? Answer: Opposition Effect
  • 10/19/2005 —Saturn’s Icy Moon, Dione, Up Close
  • 03/25/2005 —Glow of Distant Worlds Seen For First Time
  • 02/17/2005 —Iapetus and Enceladus: Baffling Moons of Saturn
  • 06/11/2004 —Cassini Spacecraft Will Rendezvous with Saturn July 1, 2004

Websites:

“Saturn Moon’s Ocean May Have Hydrothermal Activity,” March 11, 2015, Laboratory for Atmospheric and Space Physics, Univ. of Colorado Boulder:
http://lasp.colorado.edu/home/blog/2015/03/11/saturn-moon-hydrothermal-activity/

Enceladus: http://en.wikipedia.org/wiki/Enceladus

“NASA Space Assets Detect Ocean inside Saturn Moon,” April 3, 2014: http://www.nasa.gov/press/2014/april/nasa-space-assets-detect-ocean-inside-saturn-moon/

Deep-sea Hydrothermal Vent Life On Earth:
http://www.divediscover.whoi.edu/expedition15/hottopics/ecosystems.html

 

 

 


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