Setting Foot on Titan

September 30, 2015 ~ J.S. Pailly ~ Leave a comment

Titan has held a special place in the hearts and minds of Sci-Fi authors for decades. Initially it was because the thick, opaque atmosphere made Titan a moon on mystery. No one knew what might be hidden on the surface. It seemed like the kind of place where anything could happen.

Unraveling Titan’s mysteries has only increased this large moon’s allure. Chemically speaking, Titan couldn’t be more alien to us, yet it looks eerily familiar. The lakes and rivers, mostly situated in the northern hemisphere, bear an uncanny resemblance to features seen on Earth.

A world both familiar yet alien: sounds like the perfect setting for a science fiction adventure to me. So what would it be like to set foot on the surface of Titan? In 2005, the Huygens probe (a joint mission by NASA and ESA) landed on the surface of Titan, collecting data all the way through its descent and for about 90 minutes after touchdown.

Based on measurements by two impact penetrometers, it seems Huygens landed on a surface of hardened crust atop a layer of softer, perhaps moister material. Scientists at the time compared it to crème brûlée. Of course, this crème brûlée is infused with methane, ethane, butane, etc; so it probably doesn’t taste very good.

Assuming the Huygens landing site is typical of surface conditions in general (which it may or may not be), walking on Titan might feel a little like slogging through mud. The hardened upper crust is probably not thick enough to support your weight, even in the reduced gravity.

Regarding weather, it doesn’t so much rain on Titan as drizzle. Picture a gloomy, overcast day here on Earth with the air heavily saturated by mist. Now drop the temperature to -180 C (-290 F), turn the clouds from grey to dull orange, and change the misty, drizzly precipitation from water to liquid methane. That would be normal weather conditions on Titan.

There is some evidence of heavier rainstorms from time to time, perhaps heavy enough to cause flash flooding, but this appears to be rare compared to the amount of rain and flooding we get here on Earth. I wouldn’t worry too much about this.

Today’s post marks the end of our month-long visit to Saturn and its moons. As the 2015 Mission to the Solar System continues, we can now turn our attention to one of the strangest, most enigmatic planets in the Solar System: Uranus.

Links

Titan Unveiled: Saturn’s Mysterious Moon Explored by Ralph Lorenz and Jacqueline Mitten.

Rare Rains on Titan from Astrobiology Magazine.

Molecular Monday: Life on Titan

September 28, 2015September 28, 2015 ~ J.S. Pailly ~ 6 Comments

For today’s Molecular Monday post, I had planned to continue my investigation of water. However, the 2015 Mission to the Solar System has just brought us to Titan, Saturn’s largest moon, and Titan’s potential biochemistry demands some special attention.

So we’ll continue studying water in the next Molecular Monday post.

Titan is a lot like Earth, except it’s also a lot different than Earth. Both have air and bodies of liquid on their surfaces, but on Titan, the air doesn’t contain oxygen, and the liquid is not water.

Titan’s atmosphere is 95% nitrogen, with methane constituting most of the remaining 5%. Exposure to sunlight causes the methane molecules to break apart and recombine into other, more complex hydrocarbons, which drizzle down to the moon’s surface.

Liquid methane and liquid ethane also exist on Titan’s surface, forming eerily Earth-like rivers and lakes. The largest, known as Kraken Mare, is located near the north pole.

It seems unlikely that Titan’s lakes are home to enormous sea monsters. The available chemicals would probably limit the size and complexity of Titanian life forms to microbes.

Compared to life on Earth, or even theoretical life on Mars, Europa, or Enceladus, Titan’s microbes would be weird. Really weird. They could still be carbon-based, but they’d have to substitute liquid methane and/or ethane for water. They’d also have to perform cellular respiration without oxygen, perhaps using hydrogen instead.

The breakdown of methane by sunlight produces, among many other things, molecular hydrogen (H₂) and acetylene (C₂H₂). According to David C. Catling’s book Astrobiology: A Very Short Introduction, microbes on Titan could derive energy from these two chemicals via the following chemical formula.

C₂H₂ + 3H₂ –> Energy + 2CH₄

The 2CH₄ byproduct is two molecules of methane. If true, this would conveniently explain how Titan replenishes the methane in its atmosphere, which is continuously being broken down and recombined by sunlight.

Whether or not life exists on Titan, the possibility of hydrogen-breathing aliens opens up some intriguing possibilities for science fiction. Especially since hydrogen is far more common in our universe than oxygen.

P.S.: Titan also apparently has a subsurface ocean of liquid water, just like Europa, Ganymede, or Enceladus, where more traditional organisms could exist. So Titan may have two viable habitats supporting two very different forms of alien life.

Sciency Words: Specular Reflection

September 25, 2015 ~ J.S. Pailly ~ 3 Comments

Sciency Words is a special series here on Planet Pailly celebrating the rich and colorful world of science and science-related terminology. Today, we’re looking at the term:

SPECULAR REFLECTION

A specular reflection is a reflection off a smooth, mirror-like surface, such as glass, polished metal, or a tranquil body of water. The opposite of a specular reflection is called a diffuse reflection, where light strikes a surface and scatters in multiple directions.

Specular reflections are rare in nature. Few surfaces have the perfect, mirror-smooth finish that makes this phenomenon possible. Pools of liquid water are really the best example. Well, pools of liquid—it doesn’t necessarily have to be water.

In the field of planetary science, specular reflections have become extremely important in relation to Titan, Saturn’s largest moon. For a long time, scientists thought Titan might have liquid on its surface. Not liquid water—Titan’s too cold for that—but perhaps liquid hydrocarbons, specifically a mixture of liquid methane and ethane.

And so when the Cassini spacecraft entered orbit of Saturn in 2004, the search was on for Titan’s liquids. Titan’s hazy atmosphere makes it almost impossible to view the moon’s surface in visible light, so Cassini made its observations in other wavelengths, from infrared to radio frequencies.

Dark regions were soon identified on Titan’s surface. Were they lakes of hydrocarbons? No one could be sure until 2008, when Cassini bounced radiowaves off a suspected lake in the southern hemisphere; the radiowaves bounced back, just like a specular reflection.

In 2009, Cassini was again observing Titan in infrared when a glint of sunlight bounced off another suspected lake, this time in the northern hemisphere. Again, it was just like a specular reflection.

Sp10 Titan Sparkles — Cassini continues to investigate Titan’s other… peculiarities.

In fact, these specular reflections turned out to be surprisingly bright. Titan’s lakes must be extremely smooth and still, with hardly any waves at all. This suggests that either Titan’s weather is oddly tranquil or that the methane/ethane mix in these lakes is more viscous than we expected, more like honey than water.

Earth and Titan are the only places in the Solar System where liquid anything flows on the surface. As a result, these two worlds have a surprising amount of stuff in common, from erosion to weather patterns, and maybe even life. More on that next week.

In the meantime, who’s up for a swim?

Links

Smoothness of Titan’s Ontario Lacus: Constraints from Cassini RADAR Specular Reflection Data from Geophysical Research Letters.

Sunlight Glint Confirms Liquid in Titan Lake Zone from NASA.

Saturn Moon’s Mirror-Smooth Lake “Good for Skipping Rocks” from New Scientist.

Saturn’s Funny Hexagon

September 24, 2015 ~ J.S. Pailly ~ 3 Comments

“The most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘Eureka!’ but ‘That’s funny…”

– Isaac Asimov

In the 1980’s, Voyager 1 and Voyager 2 flew past Saturn, collecting data and snapping lots of photos to send back to Earth. One of the features discovered during that mission was a near prefect hexagon-shaped cloud formation at Saturn’s north pole.

In 2009, the Cassini spacecraft confirmed that the hexagon was still there, apparently unchanged after 30 years, and began collecting more data and taking more pictures.

Scientists aren’t 100% sure what causes this hexagon (some wise thinkers on the Internet have proposed a connection to the satanic rituals of the Illuminati). The best theoretical model at the moment seems to be that differing wind speeds in Saturn’s atmosphere have generated a standing wave with six peaks and six troughs (on the sixth planet, making 666… Oh no! The Internet was right!)

Similar hexagonal standing waves have been created in the laboratory.

Researchers also created ovals, triangles, octagons, and other shapes using standing waves, suggesting that there may be more planets out there with geometric cloud formations in their atmospheres.

But the really important thing to know is that, based on infrared imagery, it appears the hexagon is rooted deep into Saturn’s interior structure. The hexagon’s rotation may directly correspond to the rotation of Saturn’s presumably solid, possibly metallic core.

If that’s true, then the hexagon may provide planetary scientists an easy way to study Saturn’s interior, and perhaps a way to learn about the interior structures of gas giants in general. All thanks to a rather odd, rather funny observation of Saturn’s north pole.

Links

Saturn’s Hexagon Recreated in the Laboratory from the Planetary Society.

Science Shot: Mysterious Hexagon May Reveal Length of Saturn’s Day from Science Magazine.

Enceladus’s Wet, Watery Secret

September 21, 2015September 21, 2015 ~ J.S. Pailly ~ 3 Comments

I owe one of Saturn’s moons an apology. Enceladus is on the shortlist of places in the Solar System that might support life, but I never took Enceladian life seriously. You see, Enceladus is really small. I mean really, really small. A mere 300 miles across.

For some time now, we’ve known Enceladus has liquid water beneath its surface. The cryovolcanos in the south polar region make it pretty obvious. You can see them erupting in the totally legit Hubble image above.

But how much water is there, and how long has it been liquid? Could an object so small and so far from the Sun really retain enough internal heat to support a vast, subsurface ocean similar to what we’ve found on Europa?

For the most part, the scientific literature has talked about a localized subsurface lake near the south pole or maybe just a tiny pocket of melt water. The kind of thing that might form periodically and then freeze solid again. This hardly sounds like a suitable environment for the evolution of life.

It was hard to believe in a vast subsurface ocean teeming with Enceladian microbes and Enceladian fish. Until now.

Just this month, an important new paper came out in the journal Icarus. It seems Enceladus rocks back and forth (“librates,” to use the technical term) a little too much to be solid all the way through. Something must be sloshing around inside, with the moon’s entire eggshell-like surface floating on top.

This discovery follows on the heels of another paper, published in July by Nature, which offered a global subsurface ocean as one of two possible explanations for an observed discrepancy in Enceladus’s cryovolcanic eruptions. The eruptions were occurring several hours after they should have according to previous models.

It’s interesting that not one by two scientific papers, each following different lines of research, came to almost the same conclusion. According to the paper in Nature, Enceladus might—just might—have a global subsurface ocean; and according to the Icarus paper, it totally does have an ocean, just like Europa.

None of this proves Enceladus has life, but that possibility seems a lot more credible in a global ocean than in tiny pockets of melt water.

So Enceladus, I’m sorry. I never should have doubted you.

P.S.: It’s still unclear how Enceladus maintains enough internal heat for its ocean. To quote the Icarus paper, “[…] a global ocean within Enceladus is problematic according to many thermal models […].” The best guess for now is that Saturn exerts more tidal forces on Enceladus than previously thought.

Links

Timing of Water Plume Eruptions on Enceladus Explained by Interior Viscosity Structure from Nature Geoscience.

Enceladus’s Measured Physical Libration Requires a Global Subsurface Ocean from Icarus.

What’s Inside Saturn Moon Enceladus? Geyser Timing Gives Hints from Space.com.

Enceladus: A Global Ocean from Centauri Dreams.

Sciency Words: Trojans

September 18, 2015 ~ J.S. Pailly ~ 2 Comments

$Sciency Words MATH$

Sciency Words is a special series here on Planet Pailly celebrating the rich and colorful world of science and science-related terminology. Today, we’re looking at the term:

TROJANS

Trojan asteroids are asteroids that share their orbits with a planet. This may not seem like a particularly safe arrangement for the asteroids (or the planet), but so long as the asteroids are positioned just right, their orbits will remain stable.

The asteroid must be located near something called a Lagrange point, specifically the L4 or L5 points. These are points in the orbital plane where the distance to the planet equals the distance to its host star. The combined gravitational pulls of the planet and star will cause the asteroid to circle round and round the Lagrange point in a bizarre, corkscrew-like orbital path.

The first known Trojans were discovered near Jupiter very early in the 20^th Century. The initial plan was to name them all after characters from the Trojan War, as told in Homer’s Iliad; however, it turned out that there were way, way more Trojan asteroids than named characters in that particular story.

We now know that Jupiter has over 6,000 Trojans, about 4,000 orbiting ahead of it and another 2,000 orbiting behind. Most of the other planets in the Solar System have Trojans too.

Neptune has a dozen confirmed Trojans, according to the IAU’s Minor Planet Center. Mars has four, which were probably captured from the asteroid belt. Earth and Uranus each have one. And Saturn… Saturn has none. No Trojans. Probably because Jupiter stole them all.

Aww, cheer up, Saturn! You have something way cooler than Trojan asteroids: Trojan moons!

Saturn is the only planet where moons are known to share orbits with each other. Tethys, Telesto, and Calypso orbit together, with Telesto near Tethys’s L4 point and Calypso near the L5 point. Dione, Helene, and Polydeuces make a similar set, with Helene and Polydeuces near Dione’s L4 and L5 points, respectively.

Trojan asteroids are interesting; Trojan moons moreso. But what would be really fascinating, should we ever discover them, are Trojan planets. Somewhere out there, could there be terrestrial worlds hovering near the L4 or L5 points of gas giants? Could these worlds support life? What sort of civilization might develop there, and what strange sights would they see in the night sky?

These are questions best answered by science fiction writers. At least for now.

Flying Through Saturn’s Rings

September 17, 2015 ~ J.S. Pailly ~ 4 Comments

Imagine you’re a hotshot space pilot on approach to Saturn. You know perfectly well you’re not supposed to fly through Saturn’s rings. The rings are protected by an intergalactic trust. You could get in a lot of trouble.

Okay, if we’re doing this, let’s do it the awesome way! The thickness and density of the rings varies somewhat, so let’s aim for one of the main rings (which astronomers call the A-ring, B-ring, and C-ring). In fact, aim for the middle band of the B-ring. That’s one of the thickest, densest parts.

Saturn’s rings are a mix of stuff, including rock and organic compounds, but most of the material is water ice. According to one source I found, the rings are composed of 90 to 95% ice. Most of this ice is in the form of teeny, tiny crystals, so basically we’re flying into a vast expanse of snowflakes.

Some of these snowflakes are floating free. Others have clumped together, forming larger objects. In 2005, the Cassini mission beamed radio waves at Saturn’s rings. By seeing which wavelengths bounced back, scientists got a rough estimate of the sizes of these tiny and sometimes not-so-tiny objects.

In the B-ring, most of the objects we’ll encounter will be at least 5 centimeters in diameter. Many will be larger than that. Perhaps much larger. Unfortunately, the ring particles in the middle of the B-ring are so close together that virtually all of Cassini’s radio waves bounced back. So it’s hard to say how large individual objects might be in there.

I guess we’re about to find out!

Don’t panic. It seems objects in Saturn’s rings are continuously coalescing and disintegrating due to collisions with each other and interactions with Saturn’s gravity. That suggests these objects are merely loose rubble piles of tiny ice crystals. Collide with one, and it should just burst apart like a lightly packed snowball.

Still, you should probably slow down a bit. At your current velocity, collisions with even the tiniest speck of dust could puncture your spaceship’s hull. Seriously. You need to slow down! Look out for the—!

Disclaimer: Today’s post is not intended as advice on whether or not you should attempt to fly through Saturn’s rings. If you decide to fly through Saturn’s rings, you do so at your own risk, and the author of this post cannot be held liable for any damages that may ensue.

Links

Cassini Radio Signals Decipher Saturn Ring Structure from NASA.

Particle Sizes in Saturn’s Rings from Astronomy Picture of the Day.

Saturn’s Rings from NASA Jet Propulsion Laboratory (great chart to help you identify each of Saturn’s rings).

Saturn Rapidly Creates and Destroys Its Moonlets from Discovery News.

Sciency Words: Cryovolcano

September 11, 2015 ~ J.S. Pailly ~ 3 Comments

Sciency Words is a special series here on Planet Pailly celebrating the rich and colorful world of science and science-related terminology. Today, we’re looking at the term:

VOLCANO

Okay, I guess this is a scientific term. It’s certainly an important concept in geology, but how about we do something a little more exotic for today’s Sciency Words post:

CRYOVOLCANO

Much better! Instead of a volcano spewing fire and lava and ash, picture a volcano that erupts with a mix of icy cold fluids and/or vapors which scientists call “cryomagma.”

How Do Cryovolcanoes Work?

When cryovolcanoes erupt, their cryomagma tends to include lots of liquid water, but at temperatures well below zero degrees Celsius. We all know that salt lowers the freezing point of water. Other substances, including ammonia and methane, can have the same effect.

Cold as they are, cryovolcanoes still require a heat source. This heat can be generated in several ways, including tidal forces, radioactive decay, or perhaps even a subsurface greenhouse effect whereby translucent surface ice allows light energy from the Sun to be trapped as heat energy deep underground.

Where Can We Find Cryovolcanoes?

Cryovolcanoes were first discovered on Triton, one of Neptune’s moons, in 1989. In 2005, the Cassini spacecraft observed cryovolcanic activity on Enceladus, a moon of Saturn, leading to rampant speculation about Enceladus’s possible subsurface oceans and possible organisms swimming in those oceans.

Enceladus remains on the shortlist of places astrobiologists want to check for alien life. And since cryovolcanoes often vent materials into space, we could easily go collect a sample.

Much of what we now know about cryovolcanoes is thanks to our ongoing observation and study of Enceladus.

How Rare are Cryovolcanoes?

So which are more common: volcanoes or cryovolcanoes? Thus far, regular volcanoes have been found on Earth and Io (one of Jupiter’s moons), and strong evidence of volcanic eruptions was just recently observed on Venus. Meanwhile, cryovolcanoes have only been confirmed on two worlds: Triton and Enceladus.

Based on that, it might seem like regular volcanoes are ahead, but hints of cryovolcanism have been found on a long, long list of moons in the outer Solar System (also Pluto).

At the beginning of this post, I insinuated that cryovolcanoes are “exotic,” but I’d guess that Earth-like or Io-like volcanic activity is far less common. Small, icy objects with their weird (to us) cryovolcanoes are probably scattered all across the cosmos.

Links

Active Volcanoes in Our Solar System from Geology.com.

Learning about Volcanic Activity on Triton from Bright Hub.

Ocean on Saturn Moon Enceladus May Have Potential Energy Source to Support Life from Space.com.

How Saturn Got Its Rings (And How Earth Can Too)

September 7, 2015September 7, 2015 ~ J.S. Pailly ~ 1 Comment

All the gas giants in our Solar System have rings. None of the terrestrial planets do. Based on that, you could be forgiven for assuming that only gas giants can have rings, but astronomers have discovered at least one asteroid has rings, and there’s no real reason why a planet like Earth couldn’t have rings too.

If Earth wants rings of its own, it should seek advise from Saturn. Saturn has the most beautiful rings of them all, but how did Saturn get its rings? That is a matter for ongoing scientific debate.

Here are four possible explanations:

A Former Moon: One of Saturn’s moons wandered too close to the planet. Once its orbit crossed the Roche limit, this poor unfortunate moon was torn apart by Saturn’s gravity.
A Failed Moon: Alternatively, the rings may consist of material left over from the formation of Saturn and its moons. Because this material was within the Roche limit, it never coalesced into a moon in the first place.
Meteorite Debris: Debris from meteorite impacts on Saturn’s various moons may have gradually accumulated inside the Roche limit, preventing it from re-coalescing as a new, rubble pile moon.
Outgassing: Volatiles like water vapor are constantly spewing from certain Saturnian moons. Perhaps these outgassed materials gradually accumulated around Saturn, either alone or in combination with meteorite debris.

Personally, I prefer the idea that Saturn destroyed one of its own moons to make its rings. Firstly, that would be awesome. Secondly, the exceptional size and brightness of Saturn’s rings seems to suggest, at least in my mind, that they formed suddenly and relatively recently.

However, compelling cases can be made for all of these ideas, especially outgassing. At least some of Saturn’s many rings clearly originate from nearby outgassing moons (but I can’t imagine outgassing accounting for all the rings).

So if Earth really wants rings of its own, the best bet is probably to get a moon inside the Roche limit and let gravity tear it apart.

Sp03 Destroying the Moon — Maybe this is why the Moon is slowly and cautiously moving away from the Earth.

* * *

Today’s post is part of Saturn month for the 2015 Mission to the Solar System. Click here for more about this series.

Sciency Words: Roche Limit

September 4, 2015 ~ J.S. Pailly ~ 3 Comments

Sciency Words is a special series here on Planet Pailly celebrating the rich and colorful world of science and science-related terminology. Today, we’re looking at the term:

ROCHE LIMIT

Our yearlong voyage through the Solar System now brings us to Saturn, arguably the Solar System’s most beautiful planet.

Where did Saturn’s rings come from? That’s a subject of ongoing scientific debate, but whatever the explanation, it probably has something to do with the Roche limit.

First calculated in 1848 by French astronomer and mathematician Edouard Roche, the Roche limit describes the distance at which an object orbiting a larger object will be torn apart by the larger object’s gravity.

Gravity becomes exponentially weaker the farther you get from the source of that gravity. This is known as the inverse square law. What it means for a moon, especially a large moon, is that the gravitational pull on one side of the moon is stronger than on the other. Move that moon closer to its planet, and the discrepancy gets worse. Exponentially worse.

If our hypothetical moon strayed too close, the planet’s gravity could start pulling one side of the moon away from the other, causing the moon to crumble. The resulting debris field would tend to spread out, eventually creating planetary rings.

Calculating Roche limits can get complicated. The relative densities of the planet and moon matter a lot, since lower density objects (remember the rubble pile asteroids?) will fall apart much more easily. Molecular composition can also be a factor, as some molecular bonds are stronger than others and can do a better job holding a moon together.

But for a planet and moon of roughly the same density, the Roche limit equals about 2.5 times the planet’s radius (measured from the planet’s center). And it just so happens that Saturn’s rings extend to about that distance.

So thanks to the Roche limit, we can predict where planetary rings are likely to form, but not necessarily how. On Monday, we’ll look at four different ways that Saturn might have gotten its glorious rings.

Links

The Roche Limit from Teach Astronomy.

Roche Limit Visualization from YouTube.