Mission buzz

It has been a while since I posted. Without promising too much, I hope to make more time for this blog. One issue was that I focused on polished pieces (at least for me!), which take a while to do. From now on, I would like to also have normal posts too. What is funny is that I write every day in little notebooks that will never see the light of day--even I seldom read them again. These writings do, however, clear my head a bit and make it easier to focus on what I often consider my real work. There is no reason, however, that these daily writings (similar to Julia Cameron's "morning pages" in her book The Artist's Way) cannot be posted. Occasionally, they may even hold a real idea.

My main motivation to restart this is what seems to me to be a rise in excitement for space. Last fall's The Martian movie is part of it--as well as the prior year's Interstellar and Neil Degrasse Tyson's Cosmos series. But there is more than that. There has been a spate of discoveries and missions that are making space fun. Gravity waves are real and will soon be used in a new kind of observatory. There is a new fundamental particle that was hypothesized to exist and now is known to be real. Pluto and Charon no longer are simply a dwarf planet and its largest moon, but now are complex worlds. A couple rovers are chugging along on Mars; meanwhile, a spacecraft purposely crashed into Mercury last year, one has been tailing a comet, one is circling the dwarf planet Ceres (formally the largest asteroid), and one is preparing to dive in-between Saturn's rings. Meanwhile, Voyager 1 slipped out of the Solar System into interstellar space. All of this is happening while new companies are working with NASA to launch rockets into close, mundane orbits so that NASA can focus on heavy rockets and the exciting stuff. Or so we thought--now there are companies hoping to mine asteroids and one hoping to launch to Mars by 2018.

With all this buzz, space news can be seen everywhere. The magazine Glamour recently spotlighted four women astronaughts with their sights on Mars. The President is talking about Mars missions and flowing water on Mars. NASA just fielded its largest number of applications hoping  to become astronaughts ever.

It has become a thing.

Where it will lead and what the timelines are for our return to deep space (loosely being defined by me as being out of a close Earth orbit) are hard to define yet. But, it feels like we are building towards something big. And this time it isn't a simple military push to see who can build the biggest rocket*. This time, the excitement and expectations of society is pushing this. New missions, including a manned mission to Mars, are starting to feel inevitable.


* Here, I am being a little unfair--for instance, a huge amount of good science was done and continues to be done with samples returned from the Apollo missions.

The paradigm of the snow line (1)

 

Saturn's Rings (photo from NASA's Cassini probe)

Saturn is very unlike the Earth. For one thing, its rings are made of almost pure water ice. Rings like that wouldn't last long in our neck of the Solar System. In daytime, the surface of the Moon can reach over 100 degrees Celsius, the boiling point of water on earth at sea level (at night, it gets below -200 Celsius). Water ice exposed to sunlight here wouldn't last very long. But out where Saturn is, water ice persists through the centuries that we've observed it. 

The Sun--with the help of atmospheric greenhouse gases keeping the average temperature of the Earth above freezing--keeps things toasty here near Earth. Exposed ice out from the Sun, past Mars, and into the Asteroid Belt does not last very long. Frozen comets traveling near the sun thaw and spew off water vapor and dust. However, once we pass a certain point in the Asteroid Belt, water ice is finally stable. This is the snow line; it is perhaps one of the simplest ideas but most profound-in-result structures in the Solar System. 

The snow line in our solar system isn't really that much different from snow lines on earth. Near the equator, the snow line is far up in elevation above the heat radiating surface and above the greenhouse gases that hold heat in. The further from the equator that you go, the lower the snow line gets until "up" in Greenland and "down" in Antarctica, the snow line is practically at sea level. This is the land of perpetual ice where the average temperature is below freezing. 

In space, the snow line seems set where it is between Mars and Jupiter. However, as the Solar System has changed from a disk of gas and dust to the aged system of today, the snow line's distance from the sun has changed through time. Even now, it slowly is moving outwards from the Sun as it slowly gets brighter (since the Cambrian explosion of life, the Sun has gotten about 10% more luminous).

Why do we care where the snow line is, that its location has changed through time, and that it exists at all? Why am I calling this blog "The paradigm of the snow line" (besides the rhyming of the words)? It seems mundane that the further that one goes from a heat source, the colder it becomes, correct?

In one way, the snow line defines the make up of our solar system. The gas giants--Jupiter, Saturn, Uranus, Neptune--are very different from the smaller terrestrial planets. The asteroid belt straddles the snow line, which is fortunate as tidal forces from the gas giants kept larger bodies from forming and melting, which preserved the very material that makes up the planets for us to study. 

In the next few posts, except when news interrupts the process, I want to explore the snow line and its ramifications. I'll get into ideas about the pre-solar nebula, how planets formed, and the role of the snow line in that process. What did the snow line have to do with where gas giants are located? When we see a gas giant planet very close to a star, does that mean that the snow line didn't affect its formation? Or does that say something about that solar system that is very different from our own, a place where huge planets can spiral inwards and probably destroy terrestrial planets that may have been there? 

This is a big topic, but understanding it is as big a thing as it is to understand that, on Earth, the mantle convects and drives plate tectonics, a mechanism that explains or affects the majority of processes that occur on Earth's surface. The snow line isn't a mechanism; it's simply a place that the defines the stability of water. But it's more than saying that "here Saturn's rings are stable" and "here they are not stable". Without the snow line, would Saturn itself exist?

Space Coasts

Ganymede, in natural light. Image captured by NASA’s Galileo spacecraft, 1996. From https://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=9003

Space coasts

Recently I was in central Florida, east of Orlando, to visit family. This area is near Cape Canaveral and the Kennedy Space Center. The barrier island has a long sandy beach where waves break onto fossil-filled ledges at low tide, a Walmart, low slung condos, schools of fish playing under piers, small beach bars, Patrick Air Force Base, and Space Coast Credit unions sprinkled up and down highway A1A. This is America’s Space Coast. It’s small town; it’s high tech.  From Cape Canaveral, SpaceX just tested a new rocket type where the first section, can make its way back to the surface, hover, and land .

In the Solar System, there are no other Space Coasts. Earth is in the “sweet spot”, the habitable zone around our star where water can exist as a liquid. Some scientists looked at the topography of Mars and say that there used to be similar coastlines there surrounding a northern ocean, although it remains to be proven.  Like Earth, Mars is also in the habitable zone, but most of its atmosphere bled into space long ago and liquid water is rare and ephemeral.   

Even though we know of no other surface water oceans (Titan, a moon of Saturn, has big lakes of liquid methane), there is evidence for layers of liquid water inside a growing number of bodies in the Solar System. Europa, a moon of Jupiter, has been long thought to have an ocean under its icy surface—if you ever watched the 1960s classic movie 2001, then you know its significance. Other bodies which may have of water within it include the dwarf planet Ceres with its water geysers, Jupiter moons Ganymede and Callisto (in addition to Europa), Saturn moons Titan and Enceladus, and, perhaps, Neptune’s Triton. Ganymede is not a small body—it is larger than Earth’s moon and the planet Mercury.

Cartoon of the results of Vance and other authors showing the interlayering of liquid water and different ice types or polymorphs. From http://www.huffingtonpost.com/2014/05/03/jupiter-moon-ganymede-ocean-life_n_5252853.html

In the journal Planetary and Space Science, Vance and other authors have modeled water’s behavior inside Ganymede. The authors, assuming that water is brackish with salts like magnesium sulfate (Epsom salt), calculate that Ganymede may have more than one ocean layer sandwiched between layers of water ice (see Figure). These ice layers are most likely different versions of the ice that we are familiar with. On the figure Ice I is ice that we are familiar with, ice that floats on water. Higher ices are stable at in the high pressures deep in the Ganymede ocean or in terrestrial lab experiments.

One of the more interesting findings is that liquid water, like on Earth, may lie on top of silicate rock deep within Ganymede. This is important as early terrestrial life may have begun in this setting on Earth, where some minerals provided the fuel to run chemical reactions.

Unlike Florida’s Space Coast, there are no palm trees blowing in the breeze and no waves breaking in the distance. On Ganymede, the meeting of ocean and land occurs in the dark at the bottom of a multi-layered ocean. But does life gather at this interface at the Ganymede equivalent of a beach-side bar? Without visiting, we won’t be able to prove if oceans or a tacky t-shirt shop can be found.

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References:

Huffington Post article: http://www.huffingtonpost.com/2014/05/03/jupiter-moon-ganymede-ocean-life_n_5252853.html

Planetary and Space Science: http://www.sciencedirect.com/science/article/pii/S0032063314000695

Earth hydrosphere #2? What really can be said about the ringwoodite discovery

Earth hydrosphere #1 and a big floating hunk of the cryosphere too. (From http://inter3.kuicr.kyoto-u.ac.jp/album/KH94-4/FH000153.jpg)

Earth has a well known hydrosphere--the oceans that make it up cover two-thirds of the planet. But there may be another hydrosphere deep underground. Recently, a mineral that had only been seen in impact - shocked meteorites, ringwoodite, was discovered in a terrestrial diamond¹. Pearson and other workers wrote in the journal Nature that this diamond is thought to have originated in the transition zone between the upper and lower mantle--a zone long known by geologists from a change in earthquake seismic wave behavior as they pass through the earth.

Ringwoodite is a high pressure version or polymorph of olivine, which is a common mineral in basalt. It has the same composition as olivine, but the atoms are arranged differently to be more stable at high pressures found in Earth's mid-mantle. Although only one ringwoodite grain has now been found from the Earth, it is commonly found in meteorites. This is because many asteroids experienced collisions in the 4.5 billion years they've orbited the sun; these collisions produce high shock pressure that allows olivine to recrystallize as ringwoodite. Below is an image showing an incidence in a meteorite where recrystallization from olivine to ringwoodite was incomplete. The box on the left image is blown up on the right image (Ol is olivine; Rgt is ringwoodite.):

 Image credit: Feng et al., 2011 (http://ammin.geoscienceworld.org/content/96/10/1480.abstract)

Ringwoodite had been predicted to be stable deep within the Earth for decades², and the presence of water has also been hypothesized, but remained controversial. The authors not only have confirmed a terrestrial ringwoodite, but the finding of water (1.4 to 1.5% with uncertainties "as large as 50%") allow one to make predictions of the hydration of Earth's transition zone. The authors claim that the area local to where the ringwoodite formed (and presumably where the diamond grew around it, preserving it) is about 1% hydrated.

The discovery of a ringwoodite mineral on earth is a significant achievement. The discovery that it hosts water is also very exciting. Furthermore, showing that diamonds and the kimberlite source that brought all the material to the surface must have originated in the transition zone is a very significant result. If other grains are found elsewhere, perhaps it can be shown that the transition zone is pervasively hydrated. It could also show that a volatile rich zone deep in the mantle may be linked to diamond formation and explosive kimberlite eruptions (Water is often linked to vulcanism; one reason is that it lowers the melting temperature of rock). It must be stressed, however, that only one 40 micron diameter ringwoodite grain has been discovered.

Unfortunately, the announcement of this discovery has been accompanied by hyperbole. The University of Alberta, where the first author is from, extrapolates the local area surrounding a tiny 40 micron mineral grain to Earth's entire transition zone: "We show that a special region of the Earth, between 400 and 700km, known as the 'transition zone', is an oasis of water in an otherwise very dry deep interior."³ Sci-News.com states "The first land discovery of ringwoodite confirms the presence of huge water reservoirs beneath the surface of the Earth." Other news outlets, from CBC to BBC to Fox News, have announced similar claims.

There are inklings that the transition zone may be hydrated--for example, seismic waves behave peculiarly in the area that could be explained by pervasive hydration. Many workers (some referenced in the Pearson paper) have given evidence that point to a hydrated transition zone and its role in a deep water cycle. The work by Pearson and his co-authors offers one more link, an exciting link, that the mantle's transition zone may be hydrated at least locally. However, extrapolating interpretations made from a single observation to Earth's entire mantle transition zone is not valid. More samples, preferably from wide-ranging locations, are needed to make such a claim. 


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Correction: The amount of water reported was mistakenly first written as 2.5 +/- 50%. The actual number is recorded as "clearly indicative of significant H2O content, and are consistent with a minimum estimate between 1.4 and 1.5 wt% H2O, derived by integrating the spectra in Fig. 2 (see Methods section on FTIR spectroscopy). Although the uncertainty in these estimates may be as large as 50%..." 


1. Pearson et al. Hydrous mantle transition zone indicated by ringwoodite included within diamond. Nature. 507, 221-224 (2014)  http://www.nature.com/nature/journal/v507/n7491/full/nature13080.html

2. Ringwood, A. E. & Major, A. The system Mg2SiO4-Fe2SiO4 at high pressures and
temperatures. Phys. Earth Planet. Inter. 3, 89–108 (1970)

3. Hydrous mantle transition zone indicated by ringwoodite included within diamond, University of Alberta Department of Earth and Atmospheric Sciences, http://easweb.eas.ualberta.ca/page/hydrous-mantle-transition 

Mars isn't static!

One of the old stories has always been that things in space are never changing. The stars were fixed to the celestial sphere and stayed in place like a light fixture with a few thousand bulbs. What made the planets different from the stars was their movement. We now know that stars aren't static either: their light changes, some blow up, some have planets moving around them, some orbit one another, and some whip around our galaxy's center at incredible rates due to the giant black hole there.

Even though we know that the Solar System isn't unchanging, it still is surprising to see a change. Jupiter got walloped by a comet in 1994 and telescopes caught each explosion. The moons Enceladus around Saturn and Io around Jupiter erupt occasionally and the plumes can be seen in space. And now, researchers at NASA have caught a subtle change on Mars. Something common on Earth was captured on mostly dry Mars: a gully changed course.

"A comparison of images taken by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter in November 2010 and May 2013 reveal the formation of a new gully channel on a crater-wall slope in the southern highlands of Mars" http://www.jpl.nasa.gov/news/news.php?release=2014-086

Scientists do not know what time of year that the gully changed.In the area on Mars where this gully lies (Southern Highlands), however, gullies often change in the winter when it is far too cold for liquid water to exist. Martian winters get so cold that carbon dioxide may condense out of the atmosphere and be involved with gully formation. Or perhaps liquid (probably salty, because it didn't freeze in the very cold martian air) water was involved. Either way, this new gully is a good reminder to us that Mars, like Earth, is not static. It's a world where things happen.

Water's connection to us

There's something about water. Sure, we know it is essential to life. It facilitates chemical reactions, either carrying ions or participating itself. It is everywhere on earth--traces of it can be found from the poles to the Atacama Desert, deep in the earth to high in the atmosphere. But there's more to it than its role in biology, meteorology, geology, chemistry. In the desert water brings cool wind and a scent that makes the heart leap--for a desert dweller truly knows the blessing that water is, the Prodigal Son come back, life for the land. In Tucson, the smell and sound of rain brings people to the windows, or sends them outside to hear it, to feel it on their faces. In New Mexico, nineteen Pueblos celebrate the rare rains and artists make a living photographing storms and rainbows in the desert landscape. Elsewhere, even in humid climes, people construct ponds on their land, fountains in their plazas, and build homes in flood zones to be near the whispers and ripples and cascades of water. Vacationers go to the beach and bask by the ocean, the roaring waves themselves soothe bathers by their rhythmic movements.

Our world's connection to water, humanity's connection, is profound. For thousands of years we've revered both the sun and rain for the life they give our fields and us. Our reverence our water and reliance on it is hard-wired in us. A thirst in our genes. It is dear to us.

Though we recognize its value, water is quite common both at home and in space. The Moon has small amounts in its crust. Mars has ancient river valleys where water once flowed, and gullies where it may flow now. Ice lies at the poles and what seem to be ancient shorelines are visible. Further  away, some asteroids show signs of water--from light reflecting off their surface (or emitted really) to jets of vapor coming off like a geyser in Yellowstone. Jupiter's moons are full of it, one with an ice-covered world ocean that reminds us of home. Saturn's beauty is owed to billions of chunks of ice orbiting in an incredibly thin sheet. One of these rings, a faint one, begins in a small icy moon that consistently sends water plumes off its South Pole. Even further away, water makes up much of the moons of Uranus and Neptune, the dwarf planets, asteroids, and comets that lie even further away.  Beyond the furthest icy body, we can see water's fingerprint associated with other stars and gassy nebulae. Water, one of the drivers of life, is everywhere.

That a substance so useful and essential for us is so common, is comforting. The focus of this blog is water in the solar system. This is a broad place, everything in our normal experience except the stars themselves are fair game. Penguins and polar bears roam this realm, as do planets, moons, asteroids, and even dust. Where it is, what does it do, how, and why? It is a shaper of our neighborhood and, we are realizing, necessary for further human exploration beyond the earth.