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.
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.
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.
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.**
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.**
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.
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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