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Remembering Voyager: Triton’s New Map

I’m glad to see Ralph McNutt quoted in a recent news release from the Johns Hopkins Applied Physics Laboratory. McNutt has been working on interstellar concepts for a long time, including the Innovative Interstellar Explorer mission that could become a follow-up to New Horizons. But he’s in the news in late August because of Voyager, and in particular Voyager 2, which made its flyby of Neptune on August 25, 1989, some 25 years ago. McNutt recalls those days, when he was a member of the Voyager plasma-analysis team:

“The feeling 25 years ago was that this was really cool, because we’re going to see Neptune and Triton up-close for the first time. The same is happening for New Horizons. Even this summer, when we’re still a year out and our cameras can only spot Pluto and its largest moon as dots, we know we’re in for something incredible ahead.”

I can only envy someone who was up close with the Voyager outer planet flybys and is now a key player on New Horizons, for which McNutt leads the energetic-particle investigation team. The image below is a long way from the much closer views Voyager gave us of Neptune, but it’s what New Horizons could make out with its Long-Range Reconnaissance Imager in mid-July. It’s what NASA’s Jim Green calls a ‘cosmic coincidence’ that New Horizons crossed the orbit of Neptune on the 25th anniversary of the Voyager flyby.


Image: The New Horizons spacecraft captured this view of the giant planet Neptune and its large moon Triton on July 10, 2014, from a distance of about 3.96 billion kilometers — more than 26 times the distance between the Earth and sun. The 967-millisecond exposure was taken with the New Horizons telescopic Long-Range Reconnaissance Imager (LORRI). New Horizons traversed the orbit of Neptune on Aug. 25, 2014 — its last planetary orbit crossing before beginning an encounter with Pluto in January 2015. In fact, at the time of the orbit crossing, New Horizons was much closer to its target planet — just about 440 million kilometers — than to Neptune.

I can remember staying up late the night of the Neptune encounter, being most curious not about Neptune itself but its moon Triton. We had already learned to expect surprises from Voyager — Io alone made that point — and Triton did not disappoint us with its unanticipated plumes, signs that the frozen world was active, and its odd ‘cantaloupe’ terrain. A bit larger than Pluto, Triton serves as a rough guide for what to expect at Pluto/Charon, but it’s also a point of departure, given its evident capture by Neptune and the resulting tidal heating.

Remember, this is a world that follows a retrograde orbit, moving opposite to Neptune’s rotation. The odds are strong that we’re looking at an object captured from the Kuiper Belt. Gravitational stresses would account for melting within this ice world, and explain the fractures and plume activity, evidently geysers of nitrogen, that Voyager saw. A newly restored Triton map, produced by Paul Schenk (Lunar and Planetary Institute) has a resolution of 600 meters per pixel and has been enhanced for contrast.


Image: The best-ever global color map of Neptune’s large moon Triton, produced by Paul Schenk. This map has a resolution of 600 meters per pixel. The colors have been enhanced to bring out the contrast but are a close approximation to Triton’s natural colors. Voyager’s “eyes” saw in colors slightly different from human eyes, and this map was produced using orange, green and blue filter images. Credit: Paul Shenk/LPI.

The video using the same data is a bit breathtaking. Have a look.

Keep in mind the limitations of the imagery. In 1989, the year of the Voyager flyby, Triton’s northern hemisphere was swathed in darkness, allowing the spacecraft to have a clear view of only one hemisphere during its closest approach. Now we wait to see what views New Horizons will generate of Pluto/Charon next summer. Given that Triton and Pluto are similar in density and composition, with carbon monoxide, carbon dioxide, nitrogen and methane ices on the surface, we may see some similar features. Will there be plumes on Pluto?


Comments on this entry are closed.

  • ljk August 29, 2014, 12:51

    Cosmic Quest: Who Really Discovered Neptune?

    By Geoff Gaherty, Starry Night Education | August 28, 2014 03:12 pm ET

    Neptune will appear directly opposite the sun in the sky tomorrow (Aug. 29), but despite the potentially clear view of the planet from Earth, the truth about the person who first discovered the distant world remains cloudy.

    Neptune was supposedly discovered in 1846 by Johann Gottfried Galle using calculations by Urbain Le Verrier and John Couch Adams, making it a joint British-French-German discovery.

    But these astronomers were not the first to observe Neptune. That honor goes to the famous Italian astronomer Galileo Galilei.

    Full article here:


  • steven rappolee August 29, 2014, 13:14

    plumes on triton most likely are caused by gravitational flexing from Neptune

    Chiron however is very close but a smaller world

    whats the math here?

  • James M Essig August 29, 2014, 14:34

    Could we actually send human explorers to Titan and Triton? I am thinking that if the radiation is not too intense, then sending landing parties using the NASA Space Launch System as a starting point might be great. The SLS will first fly in 2018, about as many years from now as the Kepler Probe has been operating. With all of the moons in our solar system, we’ve got a huge amount of territory for manned expeditions to practice readying our civilization for manned missions to other star systems.

    I would hazard a guess that Triton like moons are common around G, K, and M class stars. Lots of carbon, perhaps, to manufacture carbonaceous super-materials for starships and in-system infrastructure .

  • RX August 29, 2014, 17:19


    we are many decades away from sending manned missions to the outer solar system. With current technology, even manned missions to Mars are a challenge. That’s the best we can do until we have radically more powerfully propulsion methods.

  • Andrew Palfreyman August 30, 2014, 2:36

    Given the fact that we’ve squandered the past thirty years on an utterly unproductive zero-gee tin can called the ISS as far as manned presence in space is concerned, the prospect for a sudden advanced in space-based manufacturing technology is slight to slim. Ditto AI/robotics for building actual structures both in space and on planets or moons.

  • Michael August 30, 2014, 15:48

    What intrigues me most about Triton is its retrograde orbit around Neptune, most likely due to an binary interaction. Now given a few billion years would we start to see the formation of a thicker atmosphere and a new Titan?

  • ericSEct August 31, 2014, 4:59

    Andrew; I agree on the ISS …and instead of letting it burn up in our atmosphere in about 10 years and TOTALLY pissing that money away, how about we strap some boosters on it and send it into a high lunar orbit? Michael; I read somewher that Triton’s orbit will decay away in a couple hundred million years and it will crash into Neptune.

  • Dr. Ed Vivian August 31, 2014, 8:49

    Thank God someone else is concerned about our solar system and exploration. How can a president destroy the space shuttle with stroke of pen without intelligent debate,

  • Frank Smith August 31, 2014, 10:13

    The ISS is the biggest dead end of the Space Era. Thirty years of three guys making repairs and doing junior high school science experiments.

  • Andrew LePage August 31, 2014, 12:36

    I absolutely love Dr. Schenk’s new map of Triton. For a fuller discussion of the Voyager 2 encounter with Neptune and Triton, check out the following article:


  • Joëlle B. August 31, 2014, 20:22

    Some productive planning related to Neptune/Triton territory that has apparently been thrown to the way-side, as discussed in this pop description: http://www.technologyreview.com/view/424200/where-did-triton-come-from/

    The related papers:
    Odyssey 2 : A mission toward Neptune and Triton to test General Relativity http://arxiv.org/abs/1107.2316

    OSS (Outer Solar System): A fundamental and planetary physics mission to Neptune, Triton and the Kuiper Belt

    News article on the issues concerning the ISS: Save the ISS
    ‘Russia threatens the future of the space station, but so do U.S. budget cuts.’

    Exciting commercial endeavor involving whiskey and the ISS: Whiskey Particles Stored on International Space Station Headed for Earth http://abcnews.go.com/International/whiskey-made-board-international-space-station-headed-earth/story?id=25175451

  • Eniac September 1, 2014, 1:13

    Arguably, the permanent human presence in space afforded by the ISS is worth much more than short term excursions such as the moon landings. In any case, it being the only thing we have and pretty much the only thing technologically feasible at this time (although a moon base might be, too), it is not really becoming of a space enthusiast to dismiss it the way several commenters are, above. My opinion, of course.

  • Joëlle B. September 1, 2014, 22:05

    If we ever do decide to go ahead with the lunar base, it’d be called the Neil A. Armstong Lunar Outpost, as seen in Sec. 404 Lunar Outpost per the “National Aeronautics and Space Administration Authorization Act of 2008”: http://www.gpo.gov/fdsys/pkg/BILLS-110hr6063enr/pdf/BILLS-110hr6063enr.pdf

    My question is, what happened to the 1958 attitude the U.S. had with the Lunex Project? Back then they had planned a 21-airman Air Force base beneath the lunar surface. There were also Project Horizon & Project A119, which seemed to be much more macho thinking than anything we’ve ever conjured since:

    Orion in 2021/22 is sooooooo far away…. Luckily, we’ll have the chance for a new Presidential space policy before then. But that probably won’t be excuse enough to wait it out… there’s still ample time for privatized/commercial agencies to up the ante. The reality TV concept Mars One is hoping to milk may or not be feasable (only time will tell), but I think it’s the most innovative idea out there at the moment; taking advantage of the current sociological climate of those who have the munnies to consume such scientific advancement in the guise of entertainment. It’s genius.

    Titan and Triton may be a ways off, but aerostat habitats in Venus’ atmosphere, colonies on Mars, lunar bases, & mining on asteroids are well within our current powers–and would develop the necessary tools and data to enable those later manned endeavors of the outer solar system.

  • ljk September 2, 2014, 10:22

    Joëlle B. said on September 1, 2014 at 22:05:

    “My question is, what happened to the 1958 attitude the U.S. had with the Lunex Project? Back then they had planned a 21-airman Air Force base beneath the lunar surface. There were also Project Horizon & Project A119, which seemed to be much more macho thinking than anything we’ve ever conjured since.”

    There were many grand (and some crazy/dangerous) schemes for space in the 1950s. One of them was the thought that whoever controlled the Moon controlled Earth. Both sides in the Cold War considered building a lunar base housing nuclear missiles.

    The considered advantage of this plan was that if one nation’s nuclear defenses had been wiped out on Earth, they could still launch an attack on the enemy from the Moon – an extension of MAD, or Mutual Assured Destruction.

    The assumption here was that the Moon base would somehow avoid being destroyed because any missiles coming at it from Earth would take three days to get there and be seen well in advance to plan a counter strike.

    The down sides were if the other side also built a base with weapons, which meant that the enemy lunar base could be attacked in a matter of minutes to hours, not days. There were even plans for astronaut soldiers duking it out with cosmonaut soldiers fighting on the lunar regolith in hand-to-hand combat.

    And just as it would take three days for a rocket to reach the Moon from Earth, the same laws applied in the opposite direction; thus an enemy would also see the lunar missiles coming from afar and presumably take action against them, ruining the surprise revenge strike.

    In the end the “only” thing the Cold War superpowers did in terms of using the Moon was project Apollo and its Soviet counterpart. Technically the USA won that battle, but we are still waiting for a manned lunar base of any kind on that world, the logical extension of the initial explorations of Apollo.

    Now we will see what the Chinese and maybe the Russians will do with the Moon in the early 21st Century. Both are talking about lunar bases in the near future. China has already deposited a robotic rover on the Moon and will soon be sending a surface sample return mission there, Chang’e 5. Russia has made a lot of big talk about “conquering” first the Moon and then the Sol system, but we shall see if they walk the walk. India has also talked about their plans for the Moon but their space agency, while certainly impressive in its own right, has a ways to go in terms of manned missions.

    As for NASA, things might change tomorrow, but so far the agency’s administrator has said there are no manned plans for the Moon for the foreseeable future. I do not see much of anything happening from the Administration that canceled Constellation in 2009. We also have yet to see what the private sector will actually accomplish with our natural satellite.

    If spacefaring nations and companies are smart, they should be focusing their efforts and resources on “conquering” the Sol system in terms of claiming all the natural resources such as the planetoids to build communities in space. From there we can launch expeditions into the outer Sol system, specifically the moons, comets, and KBOs/TNOs to expand our plans from the inner system.

    We will then be well suited to prepare missions to the stars – first robotic, then colonization efforts assuming there are suitable places to colonize. Unless of course the interstellar travelers want to remain in space touring the galaxy and only stopping at a system to explore and resupply.

  • ljk December 15, 2014, 22:41

    DECEMBER 15, 2014

    NASA Voyager: ‘Tsunami Wave’ Still Flies Through Interstellar Space

    • The Voyager 1 spacecraft has experienced three shock waves

    • The most recent shock wave, first observed in February 2014, still appears to be going on

    • One wave, previously reported, helped researchers determine that Voyager 1 had entered interstellar space

    The “tsunami wave” that NASA’s Voyager 1 spacecraft began experiencing earlier this year is still propagating outward, according to new results. It is the longest-lasting shock wave that researchers have seen in interstellar space.

    “Most people would have thought the interstellar medium would have been smooth and quiet. But these shock waves seem to be more common than we thought,” said Don Gurnett, professor of physics at the University of Iowa in Iowa City. Gurnett presented the new data Monday, Dec. 15 at the American Geophysical Union meeting in San Francisco.

    A “tsunami wave” occurs when the sun emits a coronal mass ejection, throwing out a magnetic cloud of plasma from its surface. This generates a wave of pressure. When the wave runs into the interstellar plasma — the charged particles found in the space between the stars — a shock wave results that perturbs the plasma.

    “The tsunami causes the ionized gas that is out there to resonate — “sing” or vibrate like a bell,” said Ed Stone, project scientist for the Voyager mission based at California Institute of Technology in Pasadena.

    Full article here:


    To quote:

    “The density of the plasma is higher the farther Voyager goes,” Stone said. “Is that because the interstellar medium is denser as Voyager moves away from the heliosphere, or is it from the shock wave itself? We don’t know yet.”