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Headshot of Emily Lakdawalla

Looking back at Pluto

Posted By Emily Lakdawalla

24-07-2015 19:12 CDT

Topics: trans-neptunian objects, New Horizons, pretty pictures, Pluto, Cassini, Titan, Charon, explaining science, dwarf planets beyond Neptune, Pluto's small moons

I don't think anyone was prepared for the beauty -- or the instant scientific discoveries -- in this "lookback" image of Pluto, captured by New Horizons shortly after it flew by.

Pluto's hazes


Pluto's hazes
Just seven hours after closest approach, New Horizons looked back and captured this spectacular image of Pluto’s atmosphere, backlit by the sun. The image reveals layers of haze that are several times higher than scientists predicted. The image was taken at 19:06 on July 14, 2015, from a distance of about 370,000 kilometers. Three images have been deconvolved, stacked, and enlarged to make this photo.

The first time I saw it, I literally gasped. I know another scientist who cried. We knew, intellectually, that New Horizons would detect Pluto's atmosphere when it flew past. A large segment of the science being done after closest approach involved a stellar occultation, in which we were going to stare at our own star as it set behind Pluto to probe the structure of the atmosphere. But I certainly didn't expect that the atmosphere would shine so brilliantly to the camera. And I definitely didn't expect to see obvious layers.

As soon as I saw the photo today, I fired an email off to several people on the New Horizons team I knew had special reason to care about seeing Pluto's atmosphere, asking them for their reactions to the photo. All have published work on stellar occultations by Pluto, using much weaker stars to try to understand the atmosphere. Happily, two replied:

First reaction was esthetic. It is all so beautiful.

The second was evocative. We are moving away at 1000 Pluto radii a day.

The third was bafflement. It's a good thing we have such a complementary suite of instruments. Any single measurement would lead us astray.

- Leslie Young

My first reaction was that it was a stunning image.  It was beautiful and stark.

But then soon I started to think about it… how high is that haze?  Am I really seeing haze go up that high? And like so many other images from this encounter, it made me stop and think and reassess.

- Cathy Olkin

The New Horizons team "unwrapped" the image, taking out the curvature of Pluto, and squishing the result horizontally to emphasize subtle variatons in haze altitudes. You can clearly see a distinct haze layer as high as 83 kilometers above the surface; there are hints of more, even higher than that.

Pluto's hazes (annotated)

NASA / JHUAPL / SwRI / modified to metric by Emily Lakdawalla

Pluto's hazes (annotated)
Just seven hours after closest approach, New Horizons looked back and captured this spectacular image of Pluto’s atmosphere, backlit by the sun. The image reveals layers of haze that are several times higher than scientists predicted. Two distinct layers lie at 83 and 50 kilometers above Pluto's surface.

To my surprise, there were more lookback images. According to my "what to expect" post, the image at the top of this article was the only one I expected from the immediate post-flyby period. However, the mission added five more optical navigation photos into the downlink plan after the close-encounter period was over. Here is one of those opnavs (actually, it's two of them, stacked).

Looking back at Pluto


Looking back at Pluto
This photo was taken at 03:35 on July 16, 2015, UTC, about 39 hours after New Horizons' closest approach to Pluto, from a distance of about 2 million kilometers. It was made from two similar images that have been deconvolved, stacked, and enlarged, and rotated to place north at the top.

This image looked so, so familiar. Here, I've paired it with a photo of Titan from Cassini, taken with almost identical geometry, and scaled the same. Titan, on the left, is a bit more than twice the diameter of Pluto.

All Their Sunrises And Sunsets

NASA / JPL / JHUAPL / SwRI / Emily Lakdawalla

All Their Sunrises And Sunsets
Titan as seen by Cassini on June 22, 2010, and Pluto as seen by New Horizons on July 14, 2015. Both worlds are viewed from a phase angle of 165 degrees -- nearly from behind. Both have atmospheres; particles in the atmospheres scatter sunlight forward toward New Horizons, lighting them up. The observing spacecraft are seeing the skies in all the locations where the Sun is rising or setting on the surface. The Pluto image has been downsized to match the scale of the Titan image.

Kim Ennico told me the basic data for these post-flyby lookback opnavs:

Visit Name              Instrument      Target  N_image  Resn(km/IFOV) Phase(deg)       starttime(UTC)

NAV_C4_L1_NONCRIT_1_01  LORRI/1x1       Hydra   2       9.89    166.70  2015-07-16 03:35:01

NAV_C4_L1_NONCRIT_1_02  LORRI/1x1       Pluto   2       9.88    165.36  2015-07-16 03:39:41

NAV_C4_L1_NONCRIT_1_03  LORRI/1x1       Charon  1       9.95    165.53  2015-07-16 03:44:20

After today's press briefing, they released all the raw images that had been downlinked as of Tuesday. So I can finally complete my montage of the New Horizons Pluto encounter data set....except that now I know I am waiting for those five opnavs! They should be released next Friday.

The New Horizons Pluto flyby LORRI data set

NASA / JPL / JHUAPL / SwRI / Emily Lakdawalla

The New Horizons Pluto flyby LORRI data set
In the two weeks surrounding New Horizons' flyby of Pluto, only 1% of the science data that it acquired were downlinked to Earth.

Since the raw images were released so late in the day, I didn't want to rush to post about what amateurs are doing with them. I am going to give the amateur community all weekend to make terrific visualizations from the data released today, and I will do a roundup post on Monday. Stay tuned for that!

In the meantime, if you can't get enough Pluto, check out all the images from today's press briefing, and look around at all the top science news websites for people's writeups of what was said at the briefing today (I particularly recommend Alex Witze at Nature, Eric Hand at Science, Nadia Drake at National Geographic, and Mika McKinnon at io9; you may also enjoy Alex Parker's words on these images, and Sarah Horst's musings about haze. I need a little more time with these images before I'm ready to analyze!

See other posts from July 2015


Read more blog entries about: trans-neptunian objects, New Horizons, pretty pictures, Pluto, Cassini, Titan, Charon, explaining science, dwarf planets beyond Neptune, Pluto's small moons


Richard Adams: 07/24/2015 11:56 CDT

So, *so* very many thoughts about today's trove further filled to the brim with impossible excitement. First and foremost? The comparison image with Titan's atmosphere: This is why, even beyond being a strong supporter (and longtime member) of TPS, these blog entries have become my first destination for all things space - Emily is truly a credit to her entire field, and is simply amazing at presenting such things in exceptionally unique ways that shine ever greater insights into things already groundbreaking in nature. I simply *love* that Titan image by way of comparison to Pluto- so a thousand and one cheers for thinking of doing that! Pluto: My goodness, what a world (and a planetary one, at that!). What. A. World!! Pluto has always held a special place in my heart; why I was such a strong advocate and supporter for a mission there, then following NH quite closely ever since. It's singularly what sparked my passion for astronomy: At age 9 (in 1993) I, armed with the Internet (the only one I knew at the time who was), did a presentation on the solar system. My 4th grade teacher? Failed me. Why? "Because that is ridiculous - and wrong! Pluto is *not* the eighth planet from the Sun, dummy, it is the ninth!" "Oh, no," says child I, "It indeed is the eighth this very moment - switching places with Neptune for but a few years over one orbit of centuries." The day after, armed further with a dot-matrix printout, I make said teacher eat their words in front of the entire class. So, bottom line, I have always loved this planet - still would've, even had it been a dead icy sphere. But... this?!? Move over Titan, Europa and Io - this solar system has a brand new King! "New Horizons will rewrite textbooks?" Wrong! Try, "New Horizons will mean Pluto will need an *entire* textbook, all to itself!" The dynamic and amazing processes on Pluto? Insane! But the sheer number of them, so very many, each one of which finding some of the most extreme examples known in all of...

Richard Adams: 07/25/2015 12:20 CDT

… space itself? Really and truly, words cannot describe it. I think we all need to wake up every day for the rest of the year thanking all those who saved a mission to Pluto, and are responsible for our ever knowing Pluto as anything more than some tiny dot, an abused & neglected "world that's not a world" as the IAU's very own whipping post. Without NH, the odds Pluto would've had a mission in any of our lifetimes? I'd not have held my breath. This, this *right* here, is why we must *all* be tireless and unstoppable in our efforts advocating for space, astronomy and all such things: Imagine if this mission didn't fly. Then, consider all those missions that never did leave the drawing board; all that discovery and amazement that we won't know, simply because we never properly tried to discover. Look at Kepler - then, imagine how we could (and should) have a fleet of Keplers unlocking exoplanetary wonders. Think about those 2 "super Hubble" lenses sitting in cold storage, gifted to NASA by some spy agency who wasted hundreds of millions, only to never use them. Then, NASA can't even scrape up the funds to retrofit and launch them. Each mission lost to such insanities, and this right here is a prime example of what we might lose out on; this right here is why we must all do all that we can do to aid the effort of mankind's ongoing exploration. Look at these images, these discoveries, then envision what lurks beneath Europa's frozen crust. What organic, even biological, impossibilities,.might Titan's haze yet obscure? Or what more has Enceladus? Neptune or Uranus, planets whose surfaces haven't even been scratched? Beyond the Sun, further into the reaches of space? This universe holds things we cannot even begin to imagine - lucky for us, we don't need to! Our inquisitive nature means we can investigate and explore firsthand! And yet... today, NASA is little more than a pitiable husk. Humanity must never stop exploring: Because this is what happens when we do

Jean-Luc: 07/25/2015 02:56 CDT

fantastic images, so beautifull ! and thank you, Emily, for these comments and analysis. A vocabulary question (I am french) : why everybody says "haze" and just sometimes "atmosphere" ? Do you know if the VBSDC had worked during flyby so to detect dust ?

David Frankis: 07/25/2015 05:31 CDT

Jean-Luc, haze means solid particles in the atmosphere, usually produced by a chemical reaction (see the link to Sarah Hörst's tweets). A clear atmosphere can indeed scatter light, as you see when you look up at the blue sky, but there are layers here so there's more than just atmosphere (I take the NH team's word for it that they are not compression artefacts). I don't know how they know they are not clouds (condensed gas that can re-evaporate); presumably the pressure is just too low for that.

sepiae: 07/25/2015 10:15 CDT

Gasping - yes, exactly what I did as well...! I expected something today according to the outlaid time-map, but I didn't expect THIS! Incredibly beautiful... From invisible to faint dots to 1st features to what's now an increasingly *known system of worlds*... What a wonderful solar system we're living in :)

sepiae: 07/25/2015 10:33 CDT

... this seriously impedes all my other planned activity today, I keep staring at these images. Would *anyone* have expected all this only several weeks ago...?

Plutoresque: 07/25/2015 11:07 CDT

Aphelion is at 49.31 AU, Perihelion at 28.6 AU. Flyby was at around 32.8AU What kind of surface and atmosphere, and pressure, and surface temperatures would Pluto have showed us at 49.AU iso 32.8AU? I wonder.

Messy: 07/25/2015 11:25 CDT

Hydra looks like an animal cracker. Weird. So that's it until the fall, eh?

Richard Adams: 07/25/2015 03:22 CDT

@Plutoresque: I'd suspect changes to the atmosphere would likely be the only dramatic observable difference in store for us... all of which hinging, but of course, on just how much said atmosphere might change nearing aphelion + thusly might refreeze/cover the surface. Of course, our anticipation for a drastically altered Pluto system due to its distance from the Sun (and the reason why a mission to Pluto was desired so very badly a decade ago in the first place) was all based on our expectations prior to this past week's many startling discoveries. In other words, what we've learned this month has blown those assumptions to kingdom come. No one anticipated *this* - and all of "this" is because Pluto is somehow generating or drawing energy/heat at levels we could never have dreamt to have been possible for so distant & frozen of a "dead world." (Also recall how NH was largely pursued in order to investigate a KBO Pluto to glean info about the solar system's origins - a world frozen in time for billions of years, far more so than almost any other celestial body we'd ever explored. Instead, the total opposite: One of the very 'newest' surfaces we've ever seen!) All of that extra (and unanticipated) energy must come from somewhere, however, and it now seems most unlikely that it all comes solely from the Sun. Should the ongoing process of radioactive decay from an abundance of such elements below Pluto's crust be the source (as many now expect), then any such dramatic differences arising from Pluto reaching perihelion/aphelion would also be considerably muted as a result. Instead, Pluto might rather enjoy much more continuous activity and dynamism, in place of a polarized/binary existence centered around its orbit.

Jonathan Torres: 07/26/2015 05:31 CDT

Just out of curiosity I calculated the distance of 370,000 kilometers 7 hours after the closest approach and 2 million kilometers 39 hours after the closest approach to see if after 32 hours from the last taken picture it really reached 2 millions kilometers of distance, with the New Horizons' relative speed to Pluto of 13.8 kilometers per seconds, the final number I got was 1.959.760 kilometers after 39 hours, pretty much 2 millions kilometers. Yeah, I really had nothing to do at that time... hahahaha Congratulation New Horizons team, you guys are my heros!!!! S2

Jim Shirey: 07/26/2015 07:46 CDT

You have a comparison picture with Titan, how about showing how large the sun would have been behind Pluto? I assume much smaller but it totally depends on how far New Horizons was from the "planet". If it was barely smaller, couldn't some of the "haze" be of the sun itself? I assume not, but I read no mention of the apparent solar size.

Plutoresque: 07/27/2015 05:03 CDT

@ Richard Adams Yes Richard, everything is exciting about Pluto! Thank you for taking the time to reply to my post. and @ anyone who has some time to waste on my post:) As just a recent space enthusiast - not a scientist, not even an amateur-astronomer - I'm stuck with so many questions, that it has become fun trying to understand, to "investigate" what's going on. Inside Pluto: Yes, that Pluto is at aphelion or at perihelion won't make a difference if energy/heat is generated inside Pluto. And this heat has to come from inside, hasn't? It couldn't be from the sun, it's too far away. It couldn't be from the negligible tidal forces either. My questions would be; if there is internal radioactive decay, what would it amount for? Which amount of heat is generated by radioactive decay? Which amount of heat is coming from the formation of Pluto, at the accretion time? A big source of radiogenic heat is Potassium-40. Could it be that? In this case, wouldn't we find traces of Argon 40 in the atmosphere? Could we have a natural nuclear fission reactor inside Pluto? Also, shouldn't the three elements, Nitrogen, Methane and Carbon Monoxide present in the atmosphere, reflect the process of accretion of Pluto and the material differentiated in its interior? And there is also....

Plutoresque: 07/27/2015 05:18 CDT

...the Atmosphere. As for the atmosphere, being further away from the sun would indeed bring dramatic changes. The atmosphere would freeze out. No more haze?? The NH team has mentioned that the atmosphere has started to collapse (to be confirmed as they said). But actually, what do they mean by "collapsing"? Thinning out? Could it be the result of having been recently the closest to the sun? Yet, another question: Nitrogen makes for 90% of the atmosphere on Pluto. We know that it's a very volatile element, unreactive with many other elements, but also very stable when in presence of solar radiation. Could we infer that the Nitrogen abundance at the time of NH Flyby was due to the "proximity" to the sun? Could we infer, as Pluto goes further away from the sun, from solar radiation, that Nitrogen will start to dwindle as it becomes unstable with no solar radiation, and eventually "vanish" from the atmosphere? Or is Nitrogen on Pluto like on Earth? Being stable, it has built up overtime and has become the main element in the atmosphere, regardless of its position to the sun? Or, has the atmosphere changed overtime due to the fact that Pluto's North Pole was exposed to the sun for the first time in over 100 years? Ice sublimating, releasing more Nitrogen? What about....

Plutoresque: 07/27/2015 05:28 CDT

....The Haze: The particles of haze are scattered way up to roughly 100 miles, higher than expected (expected closer to the cold surface, but actually found starting at 50 miles up where it is warmer). Due to lack or weak gravity??? It was also said a few years ago that plumes might exist on Pluto. The NH team, from what I understood, has yet to confirm, waiting for more feedback from the spacecraft. In case of cryo-volcanism, plumes can be in form of vapor, right? Could the "haze" be a manifestation of plume? The problem is that we would have to have tidal forces to have cryo-volcanism, right? Or could we have frozen materials creating a subsurface greenhouse effect, building up heat, leading to the "haze"?? And the final....

Plutoresque: 07/27/2015 05:36 CDT

..questions: Could we find organic life on Pluto? 90% of Nitrogen on Pluto. Maybe a subsurface ocean, water ice sustaining mountains. Potential life...? And at this stage, is it crazy to think that Pluto, instead of being a distant relative, might be a foreigner to our solar system? A protoplanet being booted out from a solar system in formation nearby? I have so much more questions, but by now, you must have enough:))

ScienceNotFiction: 07/28/2015 10:20 CDT

The existence of microbes(extremophiles) on Pluto is very possible if we compare the great impact event of Earth's early formation. The warm surface temperature near the equator during perihelion may free up some of the microbes from the frozen plain. They flow toward the basin areas where they feed on tholins as a food source. They can breakdown the tholins and release nitrogen into the atmosphere, thus Pluto's atmosphere is at its thickiest before and after its perihelion. The darken patches/basins (including the whale) of the equator belt may also contain a lot of dead microbes, their waste products and sticky methane liquid. The equatorial temperature at perihelion may reached above 80K. Precipitation of liquid nitrogen may redistribute some of the microbe back on the plain. At aphelion, Pluto surface will be frozen up and its microbial migration cycle will be stopped until the next perihelion. Perhaps this family of microbes exists in huge amount on Titan. They can survive at temperature between 80K to 90K, feeding off tholins and other hydrocarbons while giving off nitrogen as a byproduct, similar to plants on Earth which they absorb CO2 and release oxygen into the atmosphere. This could explain why Pluto has an abundance of nitrogen in its atmosphere.

Eagha50: 08/08/2015 02:43 CDT

Hi Emily, New Horizons, besides taking an eclipse shot of Pluto, was supposed to do the same thing with Caron. Did that not happen? I can not find those results anywhere. Thanks, Eddie

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