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Met Name

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127.2 grams.   CM2

TKW 100 kg. Observed fall 28 September 1969, near Near Murchison, Victoria, Australia.



Steve writes:

Photos:

1: Murchison Individual (top)
2: Murchison Individual (reverse)
3: Murchison Individual (side)
4: Murchison Individual (back)
5: Murchison Individual (in display case)
6: Murchison Rollover Lip
7: Murchison Empty Chondrule
8: Murchison Incluson X-Ray (animated GIF)

Past MPOD submissions have already presented some outstanding examples of Murchison, including the recent one by Pierre-Marie that posted just as I was finishing this write-up. But I thought I’d go ahead and still offer mine, partly because I’d already put the work in, but mostly in hopes of benefitting from the knowledge of MPOD’s viewers regarding a couple of characteristics I know very little about.

Murchison is arguably the best-studied meteorite of all time and, because of its contributions to our understanding of the universe around us, it’s one of my personal favorites. Most readers already know of its organic compounds, extraterrestrial amino acids with biased handedness similar to that caused by biological processes on Earth¹, and even nucleobases². Its pre-solar grains predate our solar system by as much as a billion years³, and isotopic signatures of some of its organics point to a possible extra-solar origin that if true suggests the presence of life’s building blocks outside of our own solar system⁴.

This 127.2 gram oriented individual was acquired many years ago through a Smithsonian trade for some d’Orbigny (hence the USNM/NMNH catalog number seen in some of the photos). Photos 1 through 4 were taken under very strong lighting and the contrast and color balance were adjusted to better show its features; alternately Photo 5 was not manipulated and shows a truer representation of its actual color (for reference, the round case displaying a separate Murchison fragment has a diameter of 1”). Photo 6 presents a collage of different areas of the rollover lip that displays its frothy fusion crust, molten splatters, and an unaltered portion of the trailing side that offers a window into the meteorite’s interior. And the enlarged view in Photo 7 shows a spherical depression that apparently once held an approximately 1 mm diameter chondrule.

My first question has to do with the tan-colored streaking most evident in Photos 1 and 2. Only some of the pieces of Murchison I’ve seen exhibit this coloration, and I’ve been told it’s either from ablated minerals in parts of the original meteoroid or from interactions with something encountered in Earth’s atmosphere as pieces of the meteor fell. I’m not sure which (if either) explanation is correct and would value feedback from those with knowledge about what it actually is.

My second question is in regards to some x-ray scans I took of the meteorite. Photo 8 is an animated gif overlaying pictures at two different x-ray intensities to show some extremely dense inclusions that were effectively opaque to all energy levels I tried. Though I was (probably naively) unaware that metal in CM meteorites could appear as blebs, I’m guessing from their opacity to x-rays that those in the photo are indeed that. Some of the orange-colored areas on the back side of the meteorite (Photo 4) do appear that they might be from metal oxidation, though I understand staining from Fe-rich silicates and other mineral inclusions is a more likely explanation for many – if not all – of them. But I’m a real amateur when it comes to the science of meteorites, so I would greatly appreciate others’ thoughts regarding what these opaque blebs might be.

Thanks for reading, and Happy Holidays!


¹ There is some work suggesting that aqueous alteration could explain Murchison’s abundance of L- compared to D-enantiomers (refer to www.psrd.hawaii.edu/April11/amino_acids.html).

² arxiv.org/ftp/arxiv/papers/0806/0806.2286.pdf

³ iopscience.iop.org/article/10.1088/0004-637X/694/1/359http

⁴ www.britannica.com/topic/Murchison-meteorite