July 8, 2015, by Brigitte Nerlich

Joining the dots: Pluto, Kant and the nature of scientific knowledge

15-011a-NewHorizons-PlutoFlyby-ArtistConcept-14July2015-20150115In his Critique of Practical Reason (1788) Immanuel Kant wrote these most beautiful words: “Two things fill the mind with ever new and increasing admiration and reverence, the more often and steadily one reflects on them: the starry heavens above me and the moral law within me. I do not need to search for them and merely conjecture them as though they were veiled in obscurity […]; I see them before me and connect them immediately with the consciousness of my existence.” (CPrR5: 161-2; transl. Gregory) If only everybody thought that!

What does Kant have to do with Pluto you might ask? In his Critique of Pure Reason (1781) Kant asked: What can we know and how do we know? I think the NASA New Horizons mission to Pluto provides us with some visible insights into the workings of human reason and scientific knowledge acquisition. But most of all, watching this voyage and the gradual homing in on more and more detailed features of an unknown world connects the starry heavens above us with the consciousness of our existence.


We are relentlessly bombarded with sensory input. In order to think and live in this chaotic sea of information, we have to bring some order to it. If I remember correctly, and that is probably not the case, according to Kant, concepts and categories help us sort through this mess and bring order to it. In a sense they help us frame reality and make it amenable to knowing and acting. For example, where ordinarily we just see starry dots in the sky, categories and concepts help us frame these, connect them up and see them as, for example “Orion, the Great Hunter”. Once a frame is in place, this act of recognition happens instantly. We ‘know’ stuff. This knowledge emerges in a sort of give and take between us and the universe (and technology). [I bet Kant is turning in his grave now!]

In the case of Pluto we are, in as sense, witnessing a very slow process of knowledge formation, organization and reorganization, which I find quite fascinating. We have at present a rather fragile concept of ‘Pluto’ but we are now on a voyage of discovery that provides us with ever better and closer images of Pluto and the extremely distant cosmic context in which it ‘lives’ (and this again will provide insights into how we live here on earth). We are also reframing steadily what we know about Pluto. As Jim Green, Director of NASA’s Planetary Science division said, “As New Horizons closes in on Pluto, it’s transforming from a point of light to a planetary object of intense interest.” Other researchers call it ” a pretty dinky little spot” (Will Grundy, a New Horizons team member) (see article in National Geographic by Nadia Drake)


Pluto is really interesting as an object of knowledge and knowledge acquisition. It was discovered in 1930 by Clyde Tombaugh and became one of our ‘planets’ – actually one that almost everybody knew because it was new. In the olden times, when I was young, and when we had to enumerate the planets, Pluto was one of them – a sort of bonus planet. Then in 2006, as everybody knows, things changed. So now instead of being allowed to point to a dot in the sky (ok, you need a pretty good telescope and a lot of patience) and say: “That’s Pluto, one of our planets” (“I know that”), we have to say things like: “That’s Pluto, a quasi-planet, minor planet, a planetoid, a dwarf planet of some sort”… This reframing influenced not only how we understand planets but also how we understand ourselves, at least for a short time: in “2006 in its 17th annual words of the year vote, the American Dialect Society voted plutoed as the word of the year. To ‘pluto’ is to ‘demote or devalue someone or something’”. (wikipedia)

For children the whole thing is quite confusing, but a nice lesson in the fragility, humility, contestability and openness of scientific knowledge. As Alan Stern, New Horizons’ principal investigator said; “The Pluto we imagined will just go away like smoke“.

New Horizons

Just as Pluto was downgraded from planet to dwarf planet, a NASA space probe called New Horizons was launched to study ‘it’. New Horizonslaunched on Jan. 19, 2006; it swung past Jupiter for a gravity boost and scientific studies in February 2007″. It is now conducting a five-month-long reconnaissance flyby study of Pluto and its moons. “Pluto closest approach is scheduled for July 14, 2015. As part of an extended mission, the spacecraft is expected to head farther into the Kuiper Belt to examine one or two of the ancient, icy mini-worlds in that vast region, at least a billion miles beyond Neptune’s orbit.”

As NASA explains: “New Horizons seeks to understand where Pluto and its moons ‘fit in’ with the other objects in the solar system, such as the inner rocky planets (Earth, Mars, Venus and Mercury) and the outer gas giants (Jupiter, Saturn, Uranus and Neptune).” As you will have seen, the word ‘moons’ was used above. Pluto has moons! “Using Hubble Space Telescope images, New Horizons team members have discovered four previously unknown moons of Pluto: Nix, Hydra, Styx and Kerberos” and there might be more. The known moon (discovered in 1978) is called Charon and New Horizons is just beginning to beam down intriguing images of this moon. “Wow”, somebody said when I told them this factoid about the moons, “if that doesn’t mean Pluto is a planet – how many more moons do you need!”

Zooming in

What fascinates me in all this is the fact that the closer we get to Pluto and the more we can see, the more complex and intriguing things become. Not only are we beginning to see the real and varied surface of this planetary object, which is changing from a point of light to a ball, to a ball with spots, we also see it surrounded by a whole new world of moons, rocks, debris and dust. This is like a parable of scientific discovery more generally. The more we zoom in, the more complex things become. As one mission statement said on 22 June: “Increasing Variety on Pluto’s Close Approach Hemisphere, and a ‘Dark Pole’ on Charon”; or as Alan Boyle from NBC news wrote on Twitter on 2 July: “OMG: Black spots on Pluto“! (See also here and follow New Horizons on Twitter for updates)

In 1930 there was a dot in the sky that became Pluto and fascinated people. In 2006 that dot was demoted to a minor dot. Now in 2015 that dot has become a whole little planetary system of dots that fascinates people. The point of light has been promoted to a whole new world of interest, something we are beginning to see in a whole new light. It is becoming an object of admiration and reverence that points to our place in the cosmos.

Kant and Cosmology

When I started to write this post I had this vague/mad idea of putting a bit of Kant into the Pluto story, metaphorically trying to build a bridge between Kant’s voyage of discovery into human reason and New Horizons’ voyage of discovery to Pluto. I had forgotten how important Kant actually is to cosmology, especially his Universal Natural History and Theory of Heaven (1755) in which he proposed something later called the (Kant-Laplace) ‘nebular hypothesis’. This hypothesis grew, as Martin Schönfeld points out “into the knowledge of what happens in the solar system”. More interestingly still: “In 1949 G. P. Kuiper found a remote ring orbiting the Sun behind Pluto, the Kuiper belt of gas, dust, asteroids, and planetoids. He used the Kant-Born-Weizsäcker ideas for tracing the belt’s origin inside the solar system. The sight of an additional far-flung shell, the Oort cloud of comets, clinched the case for the nebular turbulence theory. Before this outer ‘cloud bank’ was observed, it had been formally demonstrated by J. H. Oort (1927). Bank and belt behave as Kant had said. In this way, his […] Universal Natural History wound up informing twentieth-century astrophysics.”

To find out more about all that, you have to read Schönfeld’s 2009 chapter on the topic in A Companion to Kant, where he also makes the even more intriguing point: “We can expect data that clarify Kant’s celestial metaphysics further from the 2006 New Horizons probe (NASA), which will provide information on the Kuiper belt and Oort cloud after its Pluto flyby in 2015.” So let’s see how things go in a week’s time – or in one Pluto day!


This essay was supposed to be a Kant inspired reflection on scientific wonder and scientific discovery. During the process of writing it has turned serendipitously into a discovery of Kantian science and its relevance for modern cosmology, astronomy, astrophysics and so on. Knowledge is weird – and wonderful!

(This is a post in a series on ‘space exploration‘ – if you like, making space public)


Image: New Horizons approaching Pluto and Charon (artist concept).




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