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Sunset at Titan: The Problem of Haze

Given the high quality imagery returned by Cassini on an almost routine basis, it’s interesting to remember how little we knew about Saturn’s moon Titan back in November of 1980, when Voyager 1 made its closest approach to the planet. Think of the options the Voyager 1 team had in front of it. The craft could have been sent on to Uranus and Neptune, a trek Voyager 2 would later accomplish. It could have preempted New Horizons if, on a different trajectory, it had been sent to Pluto. But Titan had the allure of a thick atmosphere, making it an irresistible target.


Deflecting Voyager 1 past Titan meant taking it out of the plane of the ecliptic, canceling the other two options, and the frustration of the Titan images the spacecraft returned is summed up in the view we see at the right, a moon whose surface is completely obscured. The visually impenetrable atmosphere was also found to be topped by a thick layer of haze. Learning about that atmosphere was hugely important for planetary science — the spacecraft detected methane, ethane, nitrogen and numerous organic compounds — but I can recall the sense of letdown in the general public upon seeing a featureless orange ball instead of a detailed surface like those of other gas giant moons Voyager 1 had seen.

Image: Titan as seen by Voyager 1’s cameras, which could not penetrate the deep haze of organic aerosols. Credit: NASA.

Titan’s murk would eventually be penetrated by Cassini’s instruments and, of course, the Huygens lander that descended into the atmosphere for its long parachute drop to the surface. But the haze continues to be a major part of Titan’s story, and as this JPL news release points out, its effects can be useful even in terms of how we learn about exoplanets. For Cassini is in position to witness Titan’s sunsets, solar occultations that mimic what we observe when collecting spectra of an exoplanet’s atmosphere as its star’s light passes through it.

The technique is called transmission spectroscopy. As the star’s light passes through the atmosphere of an exoplanet in transit, some of that light is absorbed by the atmosphere, giving us a spectrum that can tell us about the atoms, molecules and grains found there. Knowing that clouds and high-altitude hazes like those on Titan are not uncommon in our own system, we can assume that many exoplanets will have them as well. That means that understanding their effects is key to describing the limits of this transit technique.

A team led by Tyler Robinson (NASA Ames) used four Cassini observations of Titan made between 2006 and 2011 using the spacecraft’s visual and infrared mapping spectrometer instrument (VIMS). The work, described in Proceedings of the National Academy of Sciences, then compared the complex effect of hazes to exoplanet models and observations. The result: Hazes like those on Titan provide a severe check on what we can learn from transmission spectroscopy, and may give us information only about the planet’s upper atmosphere. That’s a level that on Titan would be 150 to 300 kilometers above the surface.


Image: Using data collected by Cassini’s Visual and Infrared Mapping Spectrometer, or VIMS, while observing Titan’s sunsets, researchers created simulated spectra of Titan as if it were a planet transiting across the face of a distant star. The research helps scientists to better understand observations of exoplanets with hazy atmospheres. Credit: NASA/JPL.

We also learn that Titan’s hazes affect shorter, bluer wavelengths of light more strongly than other colors, a result not anticipated by previous studies of exoplanet spectra, which assumed that hazes affected all colors of light in more or less the same way.

“People had dreamed up rules for how planets would behave when seen in transit, but Titan didn’t get the memo,” said Mark Marley, a co-author of the study at NASA Ames. “It looks nothing like some of the previous suggestions, and it’s because of the haze.”

Using Titan as a close-up stand-in for a distant exoplanet helps us see how much an effect haze can have. In Titan’s case, we would be looking at layers far above the densest and most complex layers of its atmosphere. All of these complicated effects have to be worked out as we extract the signature of an exoplanet’s atmosphere, a challenge that is clearly formidable. The good news is that techniques like these can be applied to the atmospheres of planets in our own Solar System just as they were at Titan to help us develop more accurate, workable models.


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  • ljk May 29, 2014, 9:57

    Some more details on the Voyager 1 flyby of Titan from Andrew Lepage:


    Titan’s surface was detected by Voyager 1 at low resolution, it was later discovered:


    I still wish Voyager 1 had been aimed at Pluto.

  • ljk May 29, 2014, 12:37

    Speaking of the famous twin Voyager deep space probes:

    NASA’s Voyager Probes Still Healthy After Nearly 4 Decades in Space

    by Douglas Messier, Space.com Contributor | May 29, 2014 07:00am ET

    NASA’s Voyager 1 and Voyager 2 spacecraft are still going strong after nearly 37 years in space.

    “Both spacecraft are still operating, still very healthy. I guess as healthy as we are at the table right now,” Suzanne Dodd, the Voyager project manager at NASA’s Jet Propulsion Laboratory (JPL) said, drawing a big laugh from the audience at the SpaceFest VI conference in Pasadena, California, on May 11.

    Full article plus videos here:


    To quote:

    “Looking forward, we expect to get 10 more years of scientific data out of the Voyager spacecraft,” Dodd said. “We basically turned off everything we can turn off to save power. Backup heaters are off, backup systems are off. We’re having some serious discussions about how to move forward, because we’re almost down to the scientific instruments now.”

    After that, the spacecraft could continue on for another five to seven years sending engineering signals to Earth. Engineers are already in discussions with the Deep Space Network about what experiments could be conducted with those signals before the spacecraft fall silent.

  • william May 29, 2014, 19:19

    this just in:

    “Dutch Scientists Just Shattered Our Conception Of How Information Will Travel In The Future”

    Physicists at the Kavli Institute of Nanoscience at the Delft University of Technology in the Netherlands were able to successfully “teleport” information over a distance of 10 feet, reports the New York Times.

    There’s a lot going on in that idea, so let’s break it down.

    The rules for the subatomic world are totally unlike the rules for our macroscopic world. A particle can be in multiple places at the same time, and can even disappear on one side of a barrier and reappear on the other side without actually traveling through it. This comes from quantum theory, and while it sounds totally nonintuitive, it’s one of the most successful models physicists have for understanding our world.

    Many scientists around the world today are working to develop “quantum technology,” which is simply any technology that hinges upon these totally “abnormal” properties of the super-small stuff that makes up our world. The Mount Everest of quantum technology would be to build a quantum computer that could quickly solve problems that would leave our classical computers stumped. Instead of the standard bits we use in computers today — ones and zeroes — quantum bits, or “qubits,” can describe a one, a zero, or any value in between.

    If this all sounds crazy or hard to understand, you’re in good company with a lot of smart people. Hang in there. A legitimate, functional quantum computer (it’s debatable as to if one has actually been built yet) would be absolutely bursting with computational potential.

    Back to our Dutch scientists — they trapped qubits in diamonds and were able to establish a measurement of the qubits’ spin. This measurement is the acual information that was “teleported,” by way of a process called quantum entanglement. To simplify this idea a lot, entanglement is essentially what happens when one particle copycats another, even over a distance. Change the spin of one particle, the other instantly changes its spin to match.

    Einstein famously decried entanglement, calling it “spooky action at a distance.” But repeated variations of this experiment only lend more credence to it as a completely valid natural phenomena that we are slowly learning to manipulate.

    Forget Google Fiber. Once this stuff is perfected, a quantum internet that’s built upon it could mean instantaneous transmission and receipt of data around the world or even the universe! In 1964, an Irish physicist named John Bell predicted that this could be used to transmit data across light years of distance.

    While 10 feet is no light year, it’s certainly a step in the right direction.

  • william May 29, 2014, 19:30

    If transporting data by quantum entanglement is possible, then perhaps teleporting physical matter through space will also be possible.

  • FrankH May 30, 2014, 14:30

    quantum entanglement has nothing to to with instantaneous teleportation of information. The “key” to decode the entangled state has to be transmitted through normal, c (or slower) channels. It is not, will never be a way of transmitting information “instantaneously”.

  • ljk June 19, 2014, 11:37

    NASA wants to send a quadcopter drone to Titan

    Jesus Diaz

    Today 12:02 am

    NASA wants to search Saturn’s moon Titan for life but they’re having trouble coming up with a good way to cover a large territory and obtain samples. Now they think they may have a good solution: A 22-pound quadcopter that will work from a mothership. After reading about it, it’s a really cool idea.

    Larry Matthies—a Senior Research Scientist and the supervisor of the Computer Vision Group, in the Mobility and Robotic Systems Section of the JPL in Pasadena, California—thinks that this may be the only solution that can achieve mission objectives—the search for life or prebiotic chemistry in one of the places in the solar system more likely to have it—safely and at low cost and low risk.

    Full article here:


  • ljk September 15, 2014, 9:44

    Living On the Edge: The Mysterious Lakes of Titan (Part 4)

    By Leonidas Papadopoulos

    “On Titan, the molecules that have been raining down like manna from heaven for the last 4 billion years might still be there, largely unaltered, deep-frozen, awaiting the chemists from Earth.”

    — Carl Sagan, “Pale Blue Dot: A Vision of the Human Future in Space” (1997)

    You are standing on a shoreline peppered with small rounded rocks, watching the distant mountains on the horizon. Despite the dimly lit scenery and the thick smog that hangs in the air, you can detect clouds forming over those mountain tops that will soon develop into a raging rainstorm. Far from all this atmospheric fury, you enjoy the sight of the hundreds of small lakes around you which extend as far as the eye can see, unperturbed by the gentle breeze that blows through the landscape.

    You could be forgiven for mistaking the above as a description of a terrestrial sight; yet it’s one that describes a typical day on Titan, Saturn’s largest moon. With a diameter of 5,150 km, Titan is a planet-sized moon, which could be rightfully described as one of the most Earth-like worlds in the entire Solar System—replete with a thick, opaque atmosphere, a hydrologic cycle similar to Earth’s, seasons, clouds, small mountains, long rivers, sand dunes, rocks, lakes, and seas.

    Yet at the same time it is as alien as it is Earth-like. Its atmosphere is oxygen-free and mostly composed of nitrogen and methane, its sand dunes are made of nitrogen-rich organic compounds, its rocks are made of water ice as hard as granite, and its hydrologic cycle is based on hydrocarbons like methane and ethane. The latter are found in a gaseous state on Earth—better known as natural gas—but on Titan they are liquids due to the moon’s frigid surface conditions. Indeed, with a surface temperature of -179 degrees Celsius, Titan could hardly be described as “home.”

    Even so, this fascinating and mysterious moon is viewed by most scientists as an early Earth analog before life arose that is rich in the chemical elements that constitute the basic building blocks of life, making it one of the best places in the Solar System, alongside Europa and Enceladus, to search for potential habitable environments.

    Full article here: