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Plutonian views

Life on Pluto? (with thanks to Chris McKay)

8/23/2015

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The first fictional Plutonians were spindly underground dwellers (below), closely modelled on the Selenites in H. G. Wells' 1905 novel First Men in the Moon. Invented by Stanton H Cobblentz for his 1931 novella "Into Plutonian Depths", their most noticeable difference was the multi-coloured lamps that grew from their heads, providing both illumination for the tunnels in which they lived and an emotional outlet too.
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Many later stories featured living creatures on Pluto, sometimes equipped with super-conductive nervous systems and/or superfluid "blood", suggested by Pluto's low temperatures (which is much too high for superfluidity in reality).
Unlike the far more popular Martians that have been imagined by countless writers and film makers for almost two centuries, Plutonians were not based on any scientific theory or observation, and, unlike Mars (and to a lesser extent Venus), the exploration of Pluto and Charon was not prompted by any expectation of finding life, or its remnants, there. Everything we knew about the Pluto system before New Horizons could be explained without invoking living processes as an explanation for its presence. Has New Horizons changed anything in this regard?

To answer that question, let's remind ourselves of what (as far as we know) is required for living things to develop from non-living materials: liquid water, a suitable source of energy, organic chemicals, and an environment sheltered from such hazards as hard radiation.

Just one of these was known definitely to be present, pre-New Horizons, at least on Pluto: both methane and ethane, two of the simplest of all organic chemicals, exist there in both solid and gaseous form.

Water is present in abundance on Pluto though on the surface is it frozen hard as steel. And Charon's possible underground sea must be (or have been) a water-based one. This was known before New Horizons, but the discovery clear evidence of current, or very recent, geological activity on Pluto and similar possibilities on Charon, mean there should surely be enough energy to produce pockets of liquid water, at the very least.

That geological activity means we can now tick the "a suitable source of energy" box too: as is well known, life flourishes in the depths of our own oceans, and some of that life draws energy and nutrition from geothermal sources, like black smokers (below). Another source of energy might be solar ultraviolet radiation, the driver for processing atmospheric methane on Pluto to tholins, though it might be that such radiation would be inimical to surface life.
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Finally, underground seas would certainly provide complete protection from hard radiation.

Of course, it's one thing to show that life could survive in a particular setting, another that it could evolve there - but the theory that life on Earth first evolved near alkaline hydrothermal vents is at least as likely to be true as any other*.

So, if good evidence of a (water-based) sub-surface sea is found on either Pluto or Charon, that would make either world as likely a home for life as Europa or Enceladus.

  NASA astrobiologist Dr Chris McKay is the foremost expert on the possibility of life on such moons, and has developed models which show that the methane (and nitrogen) detected in plumes on Enceladus (below) could have their origins in living processes.**
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Could any of the methane on Pluto have been produced by living things, either recently or long ago? To quote Dr McKay : "A characteristic of biologically produced methane is that it is not accompanied by very much non-methane-hydrocarbons (NMH). However, methane produced by abiotic methods such as thermal decay or Fischer-Tropf type [Fischer-Tropf synthesis was developed in the 1920s as a method of producing a range of hydrocarbons from carbon monoxide and hydrogen. Methane is produced as a by-product - MJG] synthesis usually has ethane and other non-methane-hydrocarbons. This is why we suggested a high ratio of methane to NMH could be a biosignature on Enceladus and presumably Pluto as well."

Prior to New Horizons, information on the quantities of different chemicals present on, in and around Pluto was scanty and rough, and modelling of the photochemistry there was also approximate, largely because there is hardly any laboratory data about the properties of complex molecules at Plutonian surface conditions. At present, relatively little data from New Horizons has been downlinked to Earth, and what has is still being analysed. So, whether the makeup of Pluto's surface and atmosphere can be better explained by atmospheric and surface photo-chemistry and some kind of geological processing, or whether it makes more sense to invoke a role for the processes of life, is still an open question. Watch this space!


* http://www.astrobio.net/topic/origins/extreme-life/hydrothermal-vents-explain-chemical-precursors-life/

** C P McKay, C Porco, T Altheide, W L Davis & T A Kral, "The Possible Origin and Persistence of Life on Enceladus and Detection of Biomarkers in the Plume", Astrobiology, Vol. 8, 5, 2008. & C P McKay, A D Anbar, C Porco & P Tso, "Follow the Plume: The Habitability of Enceladus", Astrobiology Vol. 14, 4, 2014.

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Mission with a difference

8/4/2015

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For the major planetary encounters of the 1970s and 1980s, anyone not directly connected with the launch teams had to rely on the schedules and selections of newspaper editors and news broadcasters for information. But New Horizons was the agent of an interconnected world, so anyone with an internet connection could follow many of the encounter events and discoveries almost in real-time (once, of course, the signals from the probe had spent four hours and twenty-five minutes travelling through the Solar System).

Perhaps nothing sums up more how the world had changed since the Voyager missions than NASA's method of releasing the first sharp image of Pluto : via Instagram, owned by FaceBook. NASA's own site only showed the image one hour later, at about 8 AM ET. This was undoubtedly a shrewd move, drawing in audiences which might be less likely either to go searching for news online or to pay much attention to regular news broadcasts.

It was of course no surprise that US President Obama sent a message of congratulation regarding an event which was both of worldwide significance and very much an American triumph; and his chosen medium was just as 21st-century as NASA's' he sent a tweet :

"Pluto just had its first visitor! Thanks ‪@NASA — it's a great day for discovery and American leadership,"

The teams involved in other recent and ongoing missions would be justified in feeling just a little hurt that the Pluto encounter received so much more public interest than their own missions, each just as groundbreaking in its own way : Dawn (NASA) went to Vesta and Ceres, the two largest objects in the asteroid belt; The Rosetta orbiter and Philae lander(ESA) made up the first robot-landing mission to a comet; Cassini (NASA/ESA/ASI) has been orbiting Saturn and beaming home information about it since 2004; The Mars Orbiter Mission (ISRO) is the first successful Indian mission to Mars, and Venus Express (ESA) entered Venusian orbit in 2004 and is still sending back new data.

Maybe there are several reasons for the way New Horizons have captured the imaginations of so many. Almost everyone on the (our!) planet, of whatever age, has heard of Pluto. The debate about Pluto's "demotion" from planet to dwarf planet made international headlines. The struggle for funding was harder, longer and more painful than - probably - any other space mission (the first serious plans were drawn up back in 1989). But perhaps above all it was that everyone knew that what they were going to see had never been seen before. The maps that had been deduced from Earth- and HST-based observations had whetted appetites far more than they had satisfied them: what were those dark and changing shapes and stark contrasting patterns? And perhaps there was one other reason: the knowledge that, in a real sense, this was the last big encounter. There will be discoveries aplenty ahead, but this dramatic reveal of a new world, with all its beautiful colours and mysterious landscapes, will not likely be repeated in our time.

After all the anticipation, Pluto and Charon might just have been a let-down; just a couple of desolate chunks of ice and rock, deader than dinosaurs, their cratered surfaces unchanged for a billion years. But of course, as we all know now, Pluto is as full of surprises as anyone could have hoped, with its dynamic atmosphere, its system of crazily spinning moons, its weird landscapes and its active interior. New Horizons will have fallen silent long before all its secrets are unlocked.

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    Mike Goldsmith, one-time astronomer, full-time science writer.

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