What the dust ring around Venus means for our understanding of science

We all remember the debate about whether Pluto was a planet. The IAU came up with some rules that defined what we call a planet or not. According to these rules, Pluto is a "dwarf planet", or possibly a Kuiper Belt Object (KBO) Object.

My recollection of these rules was that one stated that for an object to be a planet, it must have cleared out its orbit, dragging them into its gravity well. Pluto failed this definition due to other KBOs such as Orcus and Albion.

But Venus has a dust ring - not a ring around the planet like Saturn and Uranus have, but an agglomeration of dust all along its orbit - it looks like a donut around the Sun.

We've known about this ring for a little while - it has been observed by a couple of other instruments in orbit, but it's now been photographed by the Parker Solar Probe.

The photo puzzled me.

"a planet clears out its orbit"

Does it?

How could Venus have a dust ring and not violate this definition?

I went back and had a look. NASA says that the planet: "must be big enough that its gravity cleared away any other objects of a similar size near its orbit around the Sun".

"...of a similar size."

It seems to me that the definition of a planet rests on our fudging what "a similar size" is.

For something that will keep you interested for the rest of your life, look up the works of Karl Popper and Thomas Kuhn, and how their theories of scientific behaviour are at work here. Popper would argue that we need an entirely new theory of what a planet is how we define it. On the other hand, Kuhn would argue that this is not a crisis, but our shifting understanding is part of the same paradigm, just altered a little for new observations.

Retrofitting our definition of what a planet is seems, to me, at least, typical of a Kuhnian scientific methodology. With my Popperian hat on, I'd call it wimping out.



Image source: https://www.nasa.gov/feature/goddard/2021/nasa-s-parker-solar-probe-sees-venus-orbital-dust-ring-in-first-complete-view


  • Karl Popper, Conjectures and Refutations, the Growth of Scientific Knowledge, 1962
  • Thomas Kuhn, The Structure of Scientific Revolutions, 1962
  • Arthur Koestler, The Sleepwalkers: A History of Man's Changing Vision of the Universe, 1959