The water world

Coming hard on the heels of an encouraging paper about the possibilities of near-light-speed travel, at which we might potentially have probe data from the nearest star to the Sun in ten years or so, we have an even more encouraging study of a place right here in the Solar System that might be worth looking at as a home of extraterrestrial life.

The place is Enceladus, the sixth largest moon of the planet Saturn.  It's a pretty decent-sized object, about one-seventh the diameter of the Earth.  Flyby data from the spacecraft Cassini in 2014 showed that it's a curious place, with a liquid water ocean capped by a shell of solid ice.  There are geysers coming up through cracks in the surface, and Cassini was able to sample the spray and confirm that it is, indeed, water.

Enceladus [Image is in the Public Domain courtesy of NASA/JPL and the Cassini probe]

But it's kind of a topsy-turvy world even so.  Here on the Earth, oceans are warmest at the top and coolest at the bottom; the deep parts of the ocean are the most stable ecosystems on Earth, always completely dark, under crushing pressure, and about four degrees Celsius (the temperature at which water is densest).  On Enceladus, it's the other way around; coldest on top, where it's in contact with the undersurface of the ice cap, and warmest at the bottom, where it's in contact with the core of the moon.  There's no land surface; the oceans on Enceladus are estimated at thirty kilometers deep (contrast that to an average three kilometers for Earth's oceans).

The upside-down temperature structure on Enceladus is what makes it an excellent place to look for extraterrestrial life, but to see why, we'll need to take a brief digression for a physics lesson.

One of the main drivers of ocean currents -- the movement of water not only horizontally, but vertically -- is convection, which is fluid flow because of differences in density.  One of the best-studied examples, which I described more fully in a post a few weeks ago, is the Atlantic Conveyor (known to scientists as the Atlantic Meridional Overturning Circulation), in which evaporation from the warm Gulf Stream as it flows north cools the water and makes it more saline, both of which have the effect of increasing its density.  Eventually, the blob of water becomes cool and saline enough that it exceeds the density of the water surrounding it, and it sinks.  This usually occurs in the North Atlantic southwest of Iceland, and that draw-down is what pulls more warm water north, keeping the whole system moving.

This has multiple effects, two of which concern us here.  The first is that it acts as a heat transfer mechanism, warming the air (and the land near it) and giving the American Northeast, the Maritimes of Canada, Iceland, and northwestern Europe the temperate climate they have, which otherwise would be a lot more like Siberia.  Second, the water carries with it nutrients of various sorts, and redistribution of those nutrients forms the basis of phytoplankton growth and the food chain.  (The most obvious example of this latter effect is the El Niño Southern Oscillation, in which upwelling of nutrient-laden water off the coast of Peru supports a huge population of fish -- until an El Niño year, when warm water flowing east blocks the upwelling, and the entire food chain collapses.  The four-year lots-of-fish to no-fish cycle was observed as far back at the seventeenth century, when the Spanish rulers of Peru noted that the collapse often started in midwinter, and gave it the name El Niño, which refers to the baby Jesus.)

So as long as you have alterations in density, a fluid will move.  It's what drives all weather, in fact; ground heating raises the temperature of air, lowering its density and making it rise, generating a low-pressure system that draws in more air to replace what's moving aloft.  This causes wind, and if the air has moisture, it'll condense out as it rises and cools, causing rain and/or snow.

Of course, the water drawn down by the sinking of the Gulf Stream near Iceland (or the air moving upward because of warming) is only half the picture.  It's got to come back somehow, and both the atmosphere and ocean are filled with convection cells, swirling, more-or-less circular currents following the motion both vertically and horizontally.  And once again -- to return to why the topic comes up -- these redistribute not only heat, but (in the case of water), nutrients.

On Enceladus, the pattern is upside down as compared to Earth's oceans.  Water in contact with the underside of the ice shell cools and eventually sinks, drawing warmer water up from near the center of the moon.  This mixing stirs the pot, and any potential nutrient chemicals don't just settle out on the bottom.  Thus, Enceladus is a prime candidate for extraterrestrial life of some sort.

To be sure, it'd be different from what we have here on Earth.  A lot different.  Despite the cracks and geysers, the ice shell on Enceladus is thick and pretty much solid, so any living things under there would never come into contract with direct rays of the Sun (as dim as they'd be out there).  The only energy source would be the warmth of the core, so there'd be no photosynthesis, only chemosynthesis, perhaps similar to the weird organisms near Earth's hydrothermal vents in the deep oceans.  

Even so, it's a prime spot to look for signs of life.  And unlike Proxima Centauri, the nearest star, which in a best-case scenario would require ten years for an outward-bound near-light-speed probe and returned signal back on Earth, the same round-trip to Enceladus would take on the order of three hours.  

Once again highlighting that the universe is freakin' huge.

If we can develop near-light-speed travel, maybe the first thing to do is to send some probes to explore our own Solar System more thoroughly.  Not only Enceladus, but a similar water-world moon of Jupiter, Europa, which is even closer.  I'd say the likelihood of finding intelligent life on either one is slim to none, so I wouldn't be looking for anything like the super-tech civilization on a planet orbiting Vega in the movie Contact, but I think there's an excellent chance that there's something living down there, even if it turns out to be only as complex as bacteria.

But even so.  How cool would that be?  A life form completely unrelated to anything we have down here.  And if we did find life on Europa or Enceladus, it would really bolster the hunch I've had for years, which is that life is common in the universe.

And I, for one, would settle for that in a heartbeat.

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The sad truth of our history is that science and scientific research has until very recently been considered the exclusive province of men.  The exclusion of women committed the double injury of preventing curious, talented, brilliant women from pursuing their deepest interests, and robbing society of half of the gains of knowledge we might otherwise have seen.

To be sure, a small number of women made it past the obstacles men set in their way, and braved the scorn generated by their infiltration into what was then a masculine world.  A rare few -- Marie Curie, Barbara McClintock, Mary Anning, and Jocelyn Bell Burnell come to mind -- actually succeeded so well that they became widely known even outside of their fields.  But hundreds of others remained in obscurity, or were so discouraged by the difficulties that they gave up entirely.

It's both heartening and profoundly infuriating to read about the women scientists who worked against the bigoted, white-male-only mentality; heartening because it's always cheering to see someone achieve well-deserved success, and infuriating because the reason their accomplishments stand out is because of impediments put in their way by pure chauvinistic bigotry.  So if you want to experience both of these, and read a story of a group of women who in the early twentieth century revolutionized the field of astronomy despite having to fight for every opportunity they got, read Dava Sobel's amazing book The Glass Universe: How the Ladies of the Harvard Observatory Took the Measure of the Stars.

In it, we get to know such brilliant scientists as Willamina Fleming -- a Scottish woman originally hired as a maid, but who after watching the male astronomers at work commented that she could do what they did better and faster, and so... she did.  Cecilia Payne, the first ever female professor of astronomy at Harvard University.  Annie Jump Cannon, who not only had her gender as an unfair obstacle to her dreams, but had to overcome the difficulties of being profoundly deaf.

Their success story is a tribute to their perseverance, brainpower, and -- most importantly -- their loving support of each other in fighting a monolithic male edifice that back then was even more firmly entrenched than it is now.  Their names should be more widely known, as should their stories.  In Sobel's able hands, their characters leap off the page -- and tell you a tale you'll never forget.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Halting the conveyor

The Irish science historian James Burke, best known for his series Connections and The Day the Universe Changed, did a less-well-known two-part documentary in 1991 called After the Warming which -- like all of his productions -- approached the issue at hand from a novel angle.

The subject was anthropogenic climate change, something that back then was hardly the everyday topic of discussion it is now.  Burke has a bit of a theatrical bent, and in After the Warming he takes the point of view of a scientist in the year 2050, looking back to see how humanity ended up where they were by the mid-21st century.

Watching this documentary now, I have to keep reminding myself that everything he says happened after 1991 was a prediction, not a recounting of actual history.  Some of his scenarios were downright prescient, more than one of them down to the year they occurred.  The Iraq War, the catastrophic Atlantic hurricane barrage in 2005, droughts and heat waves in India, East Africa, and Australia -- and the repeated failure of the United States to believe the damn scientists and get on board with addressing the issue.  He was spot-on that the last thing the climatologists themselves would be able to figure out was the effect of climate change on the deep ocean.  He had a few misses -- the drought he predicted for the North American Midwest never happened, nor did the violent repulsion of refugees from Southeast Asia by Australia.  But his batting average still is pretty remarkable.

One feature of climate science he went into detail about, that beforehand was not something your average layperson would probably have known, was the Atlantic Conveyor -- known to scientists as AMOC, the Atlantic Meridional Overturning Circulation.  The Atlantic Conveyor works more or less as follows:

The Gulf Stream, a huge surface current of warm water moving northward along the east coast of North America, evaporates as it moves, and that evaporation does two things; it cools the water, and makes it more saline.  Both have the effect of increasing its density, and just south of Iceland, it reaches the point that it becomes dense enough to sink.  This sinking mechanism is what keeps the Gulf Stream moving, drawing up more warm water from the south, and that northward transport of heat energy is why eastern Canada, western Europe, and Iceland itself are as temperate as they are.  (Consider, for example, that Oslo, Norway and Okhotsk, Siberia are at the same latitude -- 60 degrees North.)

[Image is in the Public Domain courtesy of NASA/Goddard Space Flight Center]

Just about any high school kid, though, has heard about the Gulf Stream, usually in the context of the paths of sailing ships during the European Age of Exploration.  What many people don't know, however, is that if things warm up, leading to the melting of the Greenland Ice Sheets, it will cause a drastic drop in salinity at the north end of the Gulf Stream, making that blob of water too fresh to sink.

The result: the entire Atlantic Conveyor stops in its tracks.  No more transport of heat energy northward, putting eastern Canada and northwestern Europe into the deep freeze.  The heat doesn't just go away, though -- that would break the First Law of Thermodynamics, which is strictly forbidden in most jurisdictions -- it would just cause the south Atlantic to heat up more, boosting temperatures in the southeastern United States and northern South America, and fueling hurricanes the likes of which we've never seen before.

Back in 1991, this was all speculative, based on geological records from the last time something like that happened, on the order of thirteen thousand years ago.  The possibility was far from common knowledge; in fact, I think After the Warming was the first place I ever heard about it.

Well, score yet another one for James Burke.

A paper this week in Proceedings of the National Academy of Science describes research by Johannes Lohmann and Peter Ditlevsen of the University of Copenhagen indicating the that based on current freshwater output from the melting of Arctic ice sheets, that tipping point from "saline-enough-to-sink" to "not" might be too near to do anything about.  "These tipping points have been shown previously in climate models, where meltwater is very slowly introduced into the ocean," Lohmann said, in an interview with Gizmodo.  "In reality, increases in meltwater from Greenland are accelerating and cannot be considered slow."

The authors write -- and despite the usual careful word choice for scientific accuracy's sake, you can't help picking up the urgency behind the words:

Central elements of the climate system are at risk for crossing critical thresholds (so-called tipping points) due to future greenhouse gas emissions, leading to an abrupt transition to a qualitatively different climate with potentially catastrophic consequences...  Using a global ocean model subject to freshwater forcing, we show that a collapse of the Atlantic Meridional Overturning Circulation can indeed be induced even by small-amplitude changes in the forcing, if the rate of change is fast enough.  Identifying the location of critical thresholds in climate subsystems by slowly changing system parameters has been a core focus in assessing risks of abrupt climate change...  The results show that the safe operating space of elements of the Earth system with respect to future emissions might be smaller than previously thought.

The Lohmann and Ditlevsen paper is hardly the first to sound the alarm.  Five years ago, a paper in Nature described a drop in temperature in the north Atlantic that is precisely what Burke warned about.  In that paper, written by a team led by Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research, the authors write, "Using a multi-proxy temperature reconstruction for the AMOC index suggests that the AMOC weakness after 1975 is an unprecedented event in the past millennium (p > 0.99).  Further melting of Greenland in the coming decades could contribute to further weakening of the AMOC."

Once again, the sense of dismay is obvious despite being couched in deliberately cautious science-speak.

Even if the current administration in the United States explicitly says that addressing climate change is one of their top priorities, they're facing an uphill battle.  Baffling though it is to me, we are still engaged in fighting with people who don't even believe climate change exists, who understand science so little they're still at the "it was cold today, so climate change isn't happening" level of understanding.  (To quote Stephen Colbert, "And in other good news, I just ate dinner, so there's no such thing as world hunger.")  Besides outright stupidity (and apparent inability to read and comprehend scientific research), there's the added problem of elected officials being in the pockets of the fossil fuel industry, the money from which gives them a significant incentive for keeping the voting public ignorant about the issues.

Until we hit the tipping point Lohmann and Ditlevsen warn about.  At which point the effects will be obvious.

In other words, until it's too late.

If the Atlantic Conveyor shuts down, the results will no longer be arguable even by climate-change-denying knuckle-draggers like James "Senator Snowball" Inhofe.  The saddest part is that we were warned about this thirty years ago by a science historian in terms a layperson could easily understand, and -- in Burke's own words -- we sat on our hands.

And as with Cassandra, the character from Greek mythology who was blessed with the gift of foresight but cursed to have no one believe what she says, we'll only say, "Okay, I guess Burke and the rest were right all along" as the world's climate systems are collapsing around us.

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 Many of us were riveted to the screen last week watching the successful landing of the Mars Rover Perseverance, and it brought to mind the potential for sending a human team to investigate the Red Planet.  The obstacles to overcome are huge; the four-odd-year voyage there and back, requiring a means for producing food, and purifying air and water, that has to be damn near failsafe.

Consider what befell the unfortunate astronaut Mark Watney in the book and movie The Martian, and you'll get an idea of what the crew could face.

Physicist and writer Kate Greene was among a group of people who agreed to participate in a simulation of the experience, not of getting to Mars but of being there.  In a geodesic dome on the slopes of Mauna Loa in Hawaii, Greene and her crewmates stayed for four months in isolation -- dealing with all the problems Martian visitors would run into, not only the aforementioned problems with food, water, and air, but the isolation.  (Let's just say that over that time she got to know the other people in the simulation really well.)

In Once Upon a Time I Lived on Mars: Space, Exploration, and Life on Earth, Greene recounts her experience in the simulation, and tells us what the first manned mission to Mars might really be like.  It makes for wonderful reading -- especially for people like me, who are just fine staying here in comfort on Earth, but are really curious about the experience of living on another world.

If you're an astronomy buff, or just like a great book about someone's real and extraordinary experiences, pick up a copy of Once Upon a Time I Lived on Mars.  You won't regret it.

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