If Pluto Has Clouds Can It Still Be A "Dwarf Planet"?

A sequence of images taken by the Long Range Reconnaissance Imager and Multispectral Visible Imaging Camera from the New Horizons spacecraft Pluto flyby  in July, 2015. The images show possible evidence for clouds on Pluto but altitude data are needed to confirm this.

Alan Stern, New Horizons principal investigator,  gave a terrific analogy to the demotion of Pluto to a 'dwarf planet' in the NOVA special  'Chasing Pluto'.  He compared the ridiculous IAU vote (to decide Pluto was a "dwarf" as opposed to "real" planet)  to a similar vote by canine specialists to vote all small dogs, i.e. pugs, Chihuahuas etc. to 'dwarf dogs' while all larger dogs are 'real dogs'.   

Stern has been consistent in his position that Pluto is emphatically a genuine planet , never mind the contrived definition offered by some (e.g. Michael Brown).  Stern maintains Pluto is a planet simply because it is massive enough that gravity has forced it into a spherical shape.

Now it appears there is even further physical evidence -  from the New Horizons mission - that this dwarf planet nonsense might finally be put to rest. And who might we thank other than the same Alan Stern who has described several lines of evidence that Pluto may exhibit partly cloudy skies.  Can such clouds be an attribute of a dwarf planet? I doubt it, for the same reason that it is unlikely a genuine dwarf world would have adequate gravity to force it into a spherical shape.  Bottom line:  a dwarf world wouldn't have the gravity to retain any kind of atmosphere, it would be outgassed.  We can use:

v =  Ö( (3 k T/m)

where k is Boltzmann's constant (1.38 x 10 ^-23   J/K), T is the absolute temperature applicable in degrees K, and m is the mass of the most prominent, constituent single gas  molecule . We then compare this value to the escape velocity of the object.

Anyway, Stern's new findings were presented on October 18 last year to a joint meeting of the American Astronomical Society Division for Planetary Sciences and European Planetary Sciences Congress.  This took place in Pasadena, California and interested readers can find more details at:   

http://bit.ly/aas-dps

Let's note that previous observations have shown that Pluto does have a hazy atmosphere. This arises as a result of a process involving sunlight (even at that great distance) and hydrocarbons present. In particular, when sunlight strikes the planet it triggers formation of the haze composed of hydrocarbons like acetylene and ethane.  These chemicals then coagulate into small particles that scatter sunlight - visible as a blue mist captured in the images captured by the instruments aboard the New Horizon.

This haze, to be sure, is extremely thin whereas the particles of vapor that meteorologists would classify as clouds must be discrete, optically thick objects that block the surface.. So again, we have to deal with some scientific semantics here.

How to reconcile the Earth meteorologists' definition with what Stern's New Horizons team found? Well, the latter actually spotted - using the instruments cited- several bright smudges at apparently low altitudes that blocked Pluto's surface. (Refer to the last two images on the right of the top panel). These appeared at Pluto's dawn and dusk when lower temperatures would allow condensed clouds to form.

Moreover, the Stern team spotted these features at low altitudes which totally conforms with what a planetary atmospheric model of cloud formation would expect to yield.

The bugbear or the primary obstacle preventing a definite confirmation?  Because the Stern team lacks altitude data they can't yet confirm whether the features detected optically hang above Pluto's surface  or lie atop it. Once we get that resolved then a more unambiguous conclusion is possible.

For my part - and Stern's (who's articulated this before) we don't need the cloud confirmation to ascertain Pluto is definitely a planet - and not a mere "dwarf" planet.

In Stern's Wall Street Journal interview (July 18-19, 2015 p. A9) he addressed the admission of one IAU voter to vote for Pluto being a dwarf planet. To wit,  "We're not so keen to have Pluto and all his friends in the club because it gets crowded. By the end of the decade we would have had 100 planets.."

Hmmm...can't have too many planets, eh?, Otherwise they'd all have to be named and the poor little school kids wouldn't be able to remember them all.  Stern's response (ibid.):

"That's a very 20th century view. Our technology used to be very limited, so we could only see a few planets, and we could memorize the list because we thought we knew them all. Arbitrarily limiting the number of planets to a familiar few is like deciding to name only seven mountains on Earth,"

Of course, one response of the pro-dwarfers would be that gazillions of people are more interested in space and the planets rather than all the terrestrial mountains. But in fact that planet -space prejudice is immaterial to Stern's basic point. In another parallel universe, many more might be interested in mountains... but planets -  not so much.

Another type of objector who might brainlessly ask: "Why does it matter if we call Pluto a planet?  Only a bean counter might care"

However, we do care because scientific terminology has consequences. It's not a mere casual parlor game of semantics. It matters because scientific methods and processes are important, not because "a name by any other name" means anything....to anyone.  If people (laymen) perceive that planetary status (which ought to be an OBJECTIVE finding) is accomplished by subjective vote, then you really can't blame them for buying into the agnotology message- i.e. hat consensus, i.e. in the anthropogenic warming setting, means science is decided by popularity.

And more importantly, if scientific words and terms meaning nothing and are all relative, that opens the door to direct exploitation by ideology and  authoritarians who'd like to play upon the fake news idiom. This we cannot afford.   As one blog commenter Laurel  Kornfield put it:

"Clearly, more than "a few bean counters" care about what we call Pluto, and this is a good thing. It means they are paying attention to astronomy and have the discretion to distinguish a poor definition from a good one. "


Would it be nice and seal the deal to learn Pluto has a bona fide atmosphere? Sure, but in the end it is not necessary for regarding Pluto as a bona fide planet - as opposed to a dwarf planet.

See also Laurel's blog at:

http://laurele.livejournal.com