Sciency Words: Verona Rupes

Sciency Words PHYS copy

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

VERONA RUPES

In Wanderers, a short film by Erik Wernquist, we see ordinary humans of the future living, working, and having fun all across the Solar System. One of the fun parts is a cliff-jumping scene on Uranus’s moon Miranda, in a place called Verona Rupes.

The moons of Uranus are generally named after Shakespearean characters, or at least characters from classic literature. The Shakespeare theme also applies to features on those moons, so Verona Rupes is named after Verona, Italy, the setting of Romeo and Juliet. “Rupes” is the Latin word for cliff.

Estimated to be somewhere between 5 and 20 kilometers high (sources disagree wildly about the exact height), Verona Rupes is the tallest cliff in the Solar System, as far as we currently know. For comparison, commercial airliners here on Earth normally fly at an altitude of 9 kilometers.

That extreme height may sound crazy, but it makes sense in the context of Miranda’s landscape. Miranda is sometimes called the Frankenstein’s monster of moons because it has a bizarre, patchwork-like appearance. It looks as though someone took bits and pieces of different planets and moons and haphazardly stitched them together.

Only the southern hemisphere of Miranda has been photographed, so it’s entirely possible more Verona Rupes-like cliffs may be discovered one day in the northern hemisphere.

Jumping off Verona Rupes might not be as terrifying as it seems. Yes, it’s a long drop, but Miranda only has 0.8% of Earth’s surface gravity. So rather than plummeting to your death, you’d drift lazily to… actually, you’d still plummet to your death, or at least serious injury.

Acceleration due to gravity may be low, but after falling 5 to 20 kilometers, you’ll still smack the ground at a velocity of several hundred kilometers per hour. Fortunately, according to Erik Wernquist’s website, those thrill-seekers on Miranda have small rockets to brake their falls.

Links

Miranda High Resolution of Large Fault from JPL Photojournal.

Verona Rupes: Tallest Known Cliff in the Solar System from Astronomy Picture of the Day.

Bizarre Shape of Uranus’ “Frankenstein” Moon Explained from Space.com.

Uranus: How to Get There

We know next to nothing about Uranus. Telescopic observations can only tell us so much, and the only other data we have comes from a flyby mission (Voyager 2) back in the 80’s. To learn more about the 7th planet from the Sun, we need to put a spacecraft in orbit.

Oc06 Uranus Asks a Question

Setting Course for Uranus

First of all, you can’t just point your rocket at Uranus and go. You have to aim for where Uranus will be, not where it currently is.

Secondly, there are no straight lines in space. Your course will be a curved trajectory, heavily influenced by the Sun’s gravity and the gravities of any planets you happen to pass near. If you time things right, this can work to your advantage and help you conserve fuel.

Thirdly, once you reach Uranus, you’ll have to slow down enough to be captured by Uranus’s gravity. None of these issues are unique to Uranus, but this third point… this is where Uranus makes things extra challenging.

Slamming on the Brakes

The farther you want to travel into the Outer Solar System, the faster you need to go. Otherwise, the Sun’s gravity will start pulling you back. By the time you get into the general vicinity of Uranus, you’re approaching the kind of velocity needed to leave the Solar System entirely. Then at a critical moment, you have to decelerate rapidly in order to enter orbit.

It’s sort of like flooring it down the highway and then, just as you’re about to zoom right past your exit, slamming on the brakes. I won’t go into the role the rocket equation plays in a maneuver like that. Let’s just say your spacecraft will need a tremendous, stupendous amount of fuel to pull this off.

This is one of the reasons why Voyager 2 was a flyby mission. Even if NASA wanted to enter Uranian orbit, passing up the opportunity to flyby Neptune later, the spacecraft simply couldn’t do it.

Oc06 Uranus Flyby

A better option for a Uranus orbiter might be to accelerate at a slower pace, taking a much longer, more spirally course away from the Sun, like the MESSENGER mission in reverse. The only problem is that the journey would take many decades to complete, so most of the researchers involved would likely die of old age before the spacecraft reached its destination.

Could We Still Do It?

According to a JPL paper entitled “The Case for a Uranus Orbiter,” we could place a spacecraft in Uranian orbit within a reasonable time span and without breaking NASA’s budget. Such a mission would truly test the limits of current technology, but we could do it.

In some distant Sci-Fi future, full of anti-gravity and warp drive technology, a quick trip to Uranus or Neptune would sound a lot more feasible. But my guess is that even then, hotshot space pilots might find that rapid deceleration to be a bit of a challenge.

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

Sciency Words: Ice Giant

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

ICE GIANT

Depending on whom you ask, our Solar System has either four gas giants or only two. Uranus and Neptune are sometimes classified as ice giants instead.

Oc04 Vanilla Ice Giant

Why do we have to make this distinction? Because in the 1990’s (around the time that annoying Vanilla Ice song came out), astronomers began to realize that Uranus and Neptune are fundamentally different from Jupiter and Saturn.

While Jupiter and Saturn are composed of over 90% hydrogen, Uranus and Neptune have a more interesting mix of chemicals: methane, ammonia, water… They have hydrogen too, but the ratio of hydrogen to other stuff is much lower.

It’s believed that during the formation of the Solar System, Uranus and Neptune accumulated vast quantities of ice (hence the name ice giant). By ice, I mean any volatile substance in a solid state, not just water ice.

In describing modern Uranus and Neptune, astronomers continue to call substances like methane, ammonia, and water “ice” even though these substances aren’t necessarily in a solid form anymore. Also, don’t let any of this terminology mislead you into thinking these planets are cold. Their interiors are extremely hot, regardless of their so-called “icy” composition.

Perhaps the biggest difference between gas and ice giants relates to us humans. We don’t honestly know much about the gas giants, but we know even less about their icy cousins. Jupiter and Saturn have been visited by a handful of space probes. Uranus and Neptune have only been visited once each, and that was back in the 80’s.

Oc04 Uranus Spins Right Round

NASA is currently considering a flyby mission to Uranus or Neptune (or both) similar to the recent flyby of Pluto by New Horizons. Approval for that may come in the next year or so.

Of course, if we really want to understand what ice giants are like and why they’re so different, we should send an orbiter, not just a flyby mission. Unfortunately, entering orbit around Uranus or Neptune is much easier said than done. More on that next week.

Links

NASA’s Next Big Spacecraft Could Visit an Ice Giant from Astronomy Magazine.

The Atmospheres of the Ice Giants, Uranus and Neptune from NASA’s Jet Propulsion Laboratory.

Are There Oceans on Neptune? from Universe Today.

Uranus: Why’s It Sideways?

Something’s odd about Uranus. It spins sideways. In more technical lingo, the planet’s axis of rotation is titled approximately 98º in relation to the orbital plane of the Solar System. I feel like I say this a lot on this blog, but there are currently several competing theories to explain why.

One Big Collision: Maybe one large object, more massive than Earth, collided with Uranus, knocking Uranus sideways.

 

Oc02 Uranus Struck Once

Many Little Collisions: Or maybe a group of smaller objects collided with Uranus, knocking Uranus sideways.

Oc02 Uranus Struck Many Times

Computer simulations seem to favor this idea, mainly because it does a better job accounting for the sideways orientation of not only Uranus but also its rings and moons.

A Lost Moon: Or perhaps long ago, Uranus had an additional moon: an especially massive moon with a large gravitational pull, enough to cause Uranus to tip on its side. Later, this hypothetical moon would have been yanked out of orbit by gravitational interactions with one of the other gas giants.

I’m skeptical of this lost moon idea, mainly because Earth’s large moon supposedly prevents our own planet from wobbling or tipping over in its orbit.  I much prefer the collision or multiple collisions hypotheses.

Is Uranus really as odd as we think?

Consider the fact that Venus’s rotation is also out of whack with the rest of the Solar System. Venus rotates backwards (possibly because of a collision, by the way). That means two out of eight planets rotate out of alignment with the rest of the Solar System. That’s 25%!

We still don’t know much about planets in other star systems, but if this 25% statistic holds true (and given how common collisions are in space, I see no reason why it wouldn’t), then Uranus may not be all that unusual after all.

Links

Series of Bumps Sent Uranus into Its Sideways Spin from Europlanet.

A Collisionless Scenario for Uranus Tilting from arxiv.org.

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

Sciencey Words: Uranus

As we continue our voyage through the Solar System, we now reach a planet that has become the butt of far too many childish jokes.

Oc01 Presenting Uranus

I’ve sort of been dreading this. Uranus is the first planet discovered in modern times. It’s only been visited by a spacecraft once. It’s colder than it should be, the atmosphere is oddly featureless (at least in visible light), and some of its moons are pretty strange. Also, Uranus is spinning sideways for some reason.

But it’s hard to take any of that seriously because… well… you know why.

In fact, I rarely if ever hear about new discoveries on or concerning Uranus. Part of the reason is that Uranus is so far away and so difficult to observe; however, Neptune is even farther, and I do occasionally hear about new discoveries there.

I sometimes wonder if astronomers are deliberately avoiding this area of research. I mean, nobody wants to be the guy who probes Uranus for a living.

So how did the seventh planet from the Sun get this embarrassing name? The story, as it turns out, is really interesting.


So what do you think of Uranus’s name? Would you have preferred Herschel or Georgium Sidus or some other possibility?

Setting Foot on Titan

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

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.

Sp11 Tholins

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.

Sp11 Titan's Kraken

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.

Sp11 Titan's Microorganisms

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

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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

“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.

Sp09 Saturn's Hexagon

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

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.

Sp08 The Size of Enceladus

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.