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Episode 159 - A Proposal for the Geologic Definition of "Planet," Interview with Kirby Runyon

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Recap: In 2006, the International Astronomical Union sparked an uproar and furious debate among scientists and non-scientists alike when they voted for a definition of the word, planet. Numerous proposals since that time have been made for the definition of that term. Eleven years later, a new proposal has gotten a lot of media attention and in this episode, we discuss that new proposed definition. This is closer to a friendly debate style because the host of this podcast and the guest have different points of view on this issue.

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Episode Summary

Bio of Guest, Kirby Runyon: Kirby Runyon is a graduating PhD candidate in planetary geology at Johns Hopkins University where he researches wind-blown geology on Mars and impact cratering on planets such as the Moon. He is a science team affiliate on the New Horizons mission to the double planet Pluto-Charon and the Kuiper Belt and is passionate about engaging the general public in the passion, beauty, and joy of space exploration and promoting scientific literacy among non-scientists.

As this was a live recording with a guest, there is no specific transcript. Topics discussed include:

  • You've been in the news a lot due to an abstract you wrote for the upcoming Lunar and Planetary Science Conference. What's going on?
  • There's been a lot of news coverage of this. Do you think it's fairly represented your position?
  • What is your position on the issue, and why?
  • The bulk of the episode was a free-flowing discussion about the implications of the definition and how useful or unuseful it may be. The host (Robbins) is on the side that this is not that useful, but the IAU definition is not useful either. The guest (Runyon) is advocating for his new definition.

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Comments to date: 3. Page 1 of 1. Average Rating:

Jeffrey Wolynski   Cocoa, FL

12:32pm on Wednesday, June 7th, 2017 

Planets are evolved/evolving/dead stars. The theory that explains this is stellar metamorphosis. Best of luck!

Raviv   Haifa

3:53am on Sunday, March 26th, 2017 

To Jason.
Continuing with your example of exoplanets, how sure are you that those planets cleared their orbit?
that means that we already do NOT use that condition (clearing the orbit) when we describe exoplanets.
So dropping that condition and adding the term moon plant is the logical way to continue.
I would describe that system as having 5 planets and 3 moon planets.
on top of that we have moons that are not in hydro-static equilibrium, this will help differentiate them.

Jason Goemaat   Iowa

8:19am on Thursday, March 23rd, 2017 

So frustrating... Why go against 2,000 years of history to redefine a word because you prefer to define a planet by its intrinsic properties? The term has been used since 1630 from where I read to refer to orbitting a star. I would rather call every asteroid and comet in the solar system a planet before calling the largest moon one. Following his logic you need to start calling anything smaller than a planet either an asteroid or a comet depending on its composition too.

After redefining the word planet, how would you describe an object in hydrostatic equilibrium that orbits a star? Let's say kepler discovers a**tem with five traditional planets, one of them being a gas giant large enough to have 3 moons it can detect. How do you describe that system? There are eight planets in 5 orbits with three of the planets orbitting another planet in the second orbit? Isn't it easier to say there are five planets and the second one has three moons?

Removing "orbitting a star" fr... read more »

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