≡ Menu

Atmospheric Changes Mark Triton Summer

A new instrument that lets us look deeper into things almost always changes the game. Such an instrument is CRIRES, the Cryogenic High-Resolution Infrared Echelle Spectrograph. Now operational at the Very Large Telescope, CRIRES has already done yeoman work on Pluto, and has now been used to study the atmosphere of Neptune’s large moon Triton in more detail than ever before. The result: A new understanding of Triton’s carbon monoxide, whose existence in its upper surface layer is now confirmed and shown to be an icy ‘film’ that, over time, adds to the atmosphere.

Image: Artist’s impression of how Triton, Neptune’s largest moon, might look from high above its surface. The distant Sun appears at the upper-left and the blue crescent of Neptune right of centre. Using the CRIRES instrument on ESO’s Very Large Telescope, a team of astronomers has been able to see that the summer is in full swing in Triton’s southern hemisphere. Credit: ESO/L. Calçada.

It should come as no surprise that astronomers have also identified seasonal variation in the atmosphere, given that we see similar changes on Pluto. The team, led by Emmanuel Lellouch, estimates that the atmospheric pressure on the distant moon may have risen by a factor of four compared to what Voyager found during its 1989 flyby. The spacecraft found a nitrogen and methane atmosphere at a pressure of 14 microbars, roughly 70,000 times less dense than the atmosphere of Earth. The pressure is now measured at between 40 and 65 microbars, or 20,000 times less than on Earth.

“We have found real evidence that the Sun still makes its presence felt on Triton, even from so far away,” says Lellouch. “This icy moon actually has seasons just as we do on Earth, but they change far more slowly.”

Slowly indeed. It’s hard to talk about summer on a place where the average surface temperature is minus 235 C, but Triton’s southern hemisphere is currently enjoying that season, causing a layer of frozen nitrogen, methane and carbon monoxide to sublimate into gas. It’s a long, slow process, with seasons on Triton lasting for forty years. The new findings will doubtless lead to a reassessment of atmospheric models on Triton.

You may remember a 2009 ESO study using CRIRES that revealed a temperature inversion on Pluto. The instrument helped scientists find more methane than anticipated in the atmosphere of the dwarf planet, a place where the thin envelope of nitrogen, methane and (most likely) carbon monoxide freezes out when Pluto moves away from the Sun during its 248-year orbit. Pluto’s atmospheric pressure is five times less than what is currently found on Triton. The Triton news means that the hunt for carbon monoxide on Pluto will now intensify.

The paper is Lellouch et al., “Detection of CO in Triton’s atmosphere and the nature of surface-atmosphere interactions,” Astronomy & Astrophysics Vol. 512, L8 (March/April 2010). Abstract available.


Comments on this entry are closed.

  • Adam April 9, 2010, 17:33

    Hi Paul

    Interesting time of year on Triton! According to JP Aerospace they can get a blimp to 200 kilo-feet altitude, which has an ambient pressure of just 17.76 Pa at 242 K (courtesy of the online Standard Atmosphere calculator ), thus 65 microbars (6.5 Pa) at 38 K is actually denser than that and would support blimps/balloons we can make today. Heated by an RTG and insulated by a double-layer design a probe could easily hot-air balloon around Triton. Would make quite a fascinating journey to follow remotely, particularly if an orbital relay satellite had enough signal strength to return live-video back to Earth.

  • Administrator April 9, 2010, 18:46

    A mind-blowing concept! Imagine the imagery…

  • Adam April 9, 2010, 19:45

    Triton is interesting for so many reasons – it’s practically zero-age surface means it has experience a LOT of cryovolcanism. If there’s enough van der Waals solids & clathrates coating its ammonia/water layers then the liquid cryo-mantle may only be a couple of kilometres down, at least in places. In theory there could be liquid nitrogen layers beneath the N2 ice too.

  • david lewis April 10, 2010, 13:58

    thus 65 microbars (6.5 Pa) at 38 K is actually denser than that and would support blimps/balloons we can make today.

    Here I was thinking with 1/20,000 of what we would have on earth that we might as well say the place has no atmosphere, or at least none that would be of any benefit other than scientifically. Yet that is enough to support a blimp? Wow!

    From wikipedia
    Triton’s eccentric post-capture orbit would have also resulted in tidal heating of the moon’s interior. This would have kept Triton liquid for a billion years, which is supported by evidence of differentiation in the moon’s interior.[7] This source of internal heat disappeared following circularization of the orbit.

    Might all be frozen now but I wonder what might have developed there during that time. What we might find frozen there now.

  • James M. Essig April 10, 2010, 16:45

    Hi Folks;

    With the stated objectives at least in spirit for NASA to develop new forms of rocket propulsion and robotic precursor missions to Mars, and the asteriods to study living off the land for bold manned space exploration programs to Mars and other destinations within the solar system, post cards such as might contain real images similar to that of artistic depiction of Triton above will likely become common place.

    I have always loved astrophotography and space art, and so I can imagine how such post card images could strike to the very core of the psyches of future recepients of postal service mail. We can imagine a real photograph of a Sunset or should I say, a starset on a planet or moon in orbit around any of the Proxima Centauri stars or perhaps Barnard”s star in a not too distant future if the signatures of biospheres are found to be common place within our local neck of the Galaxy.

    I have great hope that we will travel among the stars one day to extrasolar worlds, and I can imagine the wide variety of scenes, both real and of artistic rendition, that will become available on postcards and on other tourist attraction based printed media.

    My father who died about 4 1/3 years ago was an avid stamp collector and stamp dealer, as a new later in life career after he retired from active service as a U.S. Navy Officer and then as a DOE/DOD civil service employee. He did a lot a traveling on U.S. Navy ships earlier in His Navy carreer and so due to the numerous ports of call around the globe, he developed a great love of traveling and tourism.

    The point is that as we travel to other planets and extrasolar planets, art work in the form of post cards, etc., can be a very powerful tool to inspire future generations to travel even further abroad in our universe. Quite plain and simply, the Triton artistic image is just gorgeous.

  • Lionel W April 10, 2010, 21:12

    wow, a blimp probe on Triton is indeed a fascinating idea

    speaking of probes, i saw this video of Joel Levine from NASA talking about a plane he’s designed for Mars. makes me wonder what the pros and cons of it would be compared to a Mars blimp

    i presume a Mars blimp would last much longer… at about 14 minutes into the video Levine says that “in a 1 hour flight” the book on mars could be rewritten. i’m not sure if he’s saying that the plane’s flight would only last one hour, or whether it would fly for longer than that, and he meant that only 1 hour would be needed for major results

  • Adam April 11, 2010, 4:11

    Hi All

    Just working through the numbers for the balloon. Imagine it masses 75 kg (50 kg RTG/instruments & 25 kg envelope) – to displace that much Tritonian atmosphere at 38 K needs a volume of ~130,200 m^3 with a surface area of ~12,500 m^2, thus a 2 gr/sq.m envelope. Hmmm. Not easy to do. Might have to figure out just how big this sucker needs to be. BIG. But that’s a good thing ;-)

  • andy April 11, 2010, 4:30

    If I recall correctly, Triton is orientated nearly pole-on to the Sun, so a large proportion of its surface is in direct sunlight for many decades. The sunlight may be weak out there, but it has got a long time to do its work.

  • James M. Essig April 11, 2010, 19:48

    Hi Adam;

    I wonder if carbon naontube reinforced extremely thin Nylon, Polyester Teraphalate, or other common materials would work. I would imagine that such materials of thickness on the order 0f 0.05 mils to 0.02 mils might work although commercially available materials of these varieties are generally 0.5 mils or more thick.

    I do not know if carbon nanotubes are being used to reinforce polymeric thin films, but if they can be, then we might solve the beam sail problem soon as well.

    I like the balloon idea for several reasons but especially since it is whimsical. We can imagine such human made extraterrestrial balooons plying the atmosphere of Triton and Mars as well as those of the gas giant planets.

  • Adam April 11, 2010, 23:18

    Hi James

    I love JP Aerospace’s idea of flying an airship into orbit, though the details of the manoeuvring they’re planning to use for that purpose aren’t clear. If they can do it for Earth, then even more so for Titan, probably Triton, but I’m not too sure of Mars & Venus, since their mostly CO2 atmospheres have different thermodynamic properties. Might not be as easy to dissipate heat or do the drag reduction tricks JP is planning to use.

    But what goes up can come down even easier. The orbital velocity of Triton is so low that a large airship-shaped ‘drag ballute’ would easily ride down from orbit, though one has to get into orbit first. Aerobraking via ballute from a heliocentric approach orbit has a lot of plusses.

  • Eniac April 12, 2010, 10:23

    The whole airship to orbit thing makes no sense whatsoever to me. There is a certain airspeed above which an airfoil becomes superior to a balloon in terms of lift vs. drag. At ground level, that speed is around robust walking speed. At hypersonic speed an airfoil is always better than a balloon even in the most rarefied air.

    I have never seen a satisfying explanation from JPA on this, and I have to suppose there isn’t one.