RSS Feed
iTunes Link

Episode 89: Remaining Issues with Lunar Formation, Interview with Robin Canup

Download the Episode

Recap: Dr. Robin Canup is the Associate Vice President of the Planetary Science Directorate at the Southwest Research Institute in Boulder, CO. She received her BS in physics from Duke University and her PhD in planetary sciences from the University of Colorado, and Robin has been at the forefront for over a decade in simulating how the moon may have formed. In this interview, we discuss some of the remaining issues with how the moon may have formed and what the current state of the research is.

Puzzler for Episode 89: There is no puzzler in episode 89.

Answer to Puzzler from Episode 88: There was no puzzler in episode 88.

Q&A: There was no Q&A in episode 89.

Additional Materials:

  • Logical Fallacies / Critical Thinking Terms addressed in this episode: Special Pleading.
  • Relevant Posts on my "Exposing PseudoAstronomy" Blog


Since this was an interview, there is no transcript. The topics discussed included:

  • Overview of different lunar formation models.
  • Why a giant impact isn't improbable or special pleading.
  • Numerous tweaks to the impact model that can explain observations today that are incongruous with the current versions of the impact model.
  • Where the field is going today and outstanding issues the community hopes to answer in the next several years.

Provide Your Comments:

Comments to date: 7. Page 1 of 1. Average Rating:

Stuart R.   Lyons, CO, USA

11:47pm on Tuesday, October 29th, 2013

Jason: I suggest looking over . I think it explains stuff well, and differently than I did. Basically you have 18O, 17O, 16O, and they will be the SAME RATIO amongst each other for all rocks from one parent object. They will be the same ratio again, relative to each other, for all rocks of a different parent, but that ratio may be different from the ratio of the other parent. I would think that if 19O were stable, it would show the same thing. So, it's 18:17:16 will be one value for Earth, and 18:17:16 will be another value for Mars. But, it will always be that value for any rock from Mars.

David: What you stated in the first paragraph does not follow from the simulations of where material ends up that I have seen. And could you point to a paper that discusses the oxygen isotope ratio from Icelandic volcanoes?

David Lippert   Cleveland Ohio

9:56pm on Monday, October 28th, 2013 

If the Moon formed primarily from the Mars-sized object and therefore the oxygen isotope ratio of the Moon matches the oxygen isotope ratio of the continents and upper mantle of the Earth, it follows that the continents and upper mantle of the Earth also originated from the Mars-sized object.
Samples from the lower mantle from Iceland volcanoes have a different oxygen isotope ratio.

Jason Goemaat   Des Moines, IA

3:03pm on Friday, October 25th, 2013 

Thanks for explaining more about the Oxygen isotope ratios, but I still don't get one thing. Why exactly does the O17/O16 ratio track the O18/O16 ratio? Is there some process we know of that makes that happen? If O19 was stable, would the O19/O16 ratios follow the same pattern?

I could understand why the O18/O16 ratios of say Earth and Mars could be different, but why would rocks from the two planets with the same O18/O16 ratio always have the same different O17/O16 ratio?

Stuart R.   Lyons, CO, USA

3:30pm on Friday, October 18th, 2013

Jorik -- The audio sounded okay when it was being recorded, I'm not sure what happened as it was actually recorded. When I was editing, I tried several versions of pop filters and what came out was the best one. It was unfortunate, but it was still bearable and I thought good enough to put out.

Jason - Search for "oxygen isotope earth moon" and see what you find. There are a lot of places that talk about this, though most are professional papers. Here's one more lay explanation that briefly discusses it: . I'll try to explain better during Feedback in the next episode.

Jason Goemaat   Des Moines, IA

12:10am on Thursday, October 17th, 2013 

Thanks for another great podcast, I'm always happy when a new episode shows up. I have a hard time understanding why the ratios of 17/18 matter and why they can change together at all. Is it known and can you provide a link to an explanation? If the proportion of O18 to O16 can change, why can't the proportion of O18 to O17? I've seen where O18/O16 ratios can change due to elevation and temperature, why does O17 perfectly track O18?

If that weren't the case it could be that Mar's over-abundance of O17 compared to O18 might be because the rich atmosphere of Earth was disproportionately bled of it's lighter oxygen isotype.

I also have a hard time understanding why that causes a problem for the giant impact model of lunar formation. I would picture much of the material from the collision falling back to the Earth instead of orbiting in a disc of debris that formed the moon meaning that no matter what each body started with, the end result would be well mixed at least near the s... read more »

Russ   Phoenix, AZ

3:27pm on Wednesday, October 16th, 2013 

Great interview, very enlightening. Now I'm going to youtube and search for video of the impact hypothesis.
Best Regards

Jorik   Location unknown

5:38am on Sunday, October 13th, 2013

Hey Stuart,

I'm sure you already know this, but the sound quality was pretty bad in this episode. All those cracks and pops from her microphone are almost painful when you listen to this with a headset.

Other than that, it's good as always. I know you can't change her microphone. It's just not up to the usual quality level.

Keep up the great work!

Your Name:

Your Location:


Your Comment:

Security check *

security image