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Astonishingly old Antarctic space rock could explain mystery of life's weird asymmetry

An image of a piece of the Antarctic meteorite Asuka 12236 as seen through a microscope; the sample is about 0.3 inches (1 centimeter) across.
An image of a piece of the Antarctic meteorite Asuka 12236 as seen through a microscope; the sample is about 0.3 inches (1 centimeter) across.
(Image: © Carnegie Institution for Science/Conel M. O'D. Alexander)

A time capsule of the earliest days of the solar system may be the first clue in explaining a long-standing puzzle for those who study life: It appears to be stubbornly asymmetrical.

The story begins in 2012, when scientists discovered a golf-ball-sized hunk of rock now known as Asuka 12236 on the icy expanses of Antarctica. Asuka 12236 wasn't just any rock, it was a space rock — and not just any space rock either. Researchers think it's a particularly old meteorite, perhaps containing material even older than our solar system, and that makes it the stuff of scientists' dreams.

"It's fun to think about how these things fall to Earth and happen to be full of all this different information about how the solar system formed, what it formed from, and how the elements built up in the galaxy," Conel M. O'D. Alexander, a meteorite scientist at the Carnegie Institution for Science in Washington, D.C., and co-author on the new research, said in a NASA statement.

Related: Want to learn how to survive on Mars? Look to Antarctica.

And when scientists ground up a tiny chunk of Asuka 12236 and compared the results with other meteorite samples, they realized this particular space rock stood out. In fact, it could hold the key to a longstanding mystery about life. Life, it turns out, is asymmetrical at a very tiny level. Amino acids — the building blocks of proteins, the large molecules that run our bodies and everyone else's — each come in two mirror-image forms, which scientists have dubbed left- and right-handed. But all the life that scientists have studied uses exclusively left-handed amino acids; right-handed versions of these molecules exist but don't make it into proteins. No one knows why.

Asuka 12236, the scientists realized, was particularly rich in amino acids, and just like life, the amino acids in the meteorite favored left-handedness. But unless the sample was contaminated by terrestrial life — always a possibility scientists must consider — there must be some other reason for the imbalance in the meteorite.

An artist's depiction of a meteorite entering Earth's atmosphere.

An artist's depiction of a meteorite entering Earth's atmosphere. (Image credit: NASA's Goddard Space Flight Center/Declan McKenna)

"The meteorites are telling us that there was an inherent bias toward left-handed amino acids before life even started," Daniel Glavin, lead author on the new research and an astrobiologist at NASA's Goddard Space Flight Center in Maryland, said in the same statement. "The big mystery is why?"

Glavin and his colleagues suspect that the key may lie in what happened to the meteorite back when it was a part of an asteroid whizzing through space. Inside asteroids, forces like water and heat can affect the chemistry of the space rock, including producing — but also destroying — amino acids.

Some particular balance of such effects is likely responsible for the unusually high levels of amino acids in Asuka 12236 and may also explain the asymmetry between left- and right-handed varieties, as compared with other meteorites.

"It is pretty unusual to have these large left-handed excesses in primitive meteorites," Glavin said. "How they formed is a mystery. That's why it's good to look at a variety of meteorites, so we can build a timeline of how these organics evolve over time and the different alteration scenarios."

An artist's depiction of the processes an asteroid undergoes.

An artist's depiction of the processes an asteroid undergoes. (Image credit: NASA's Goddard Space Flight Center/Declan McKenna)

And if the imbalance in the meteorite isn't the result of terrestrial contamination, the same process responsible may also address the mystery of life's asymmetry, the researchers hope. Glavin and his colleagues are going to keep looking at meteorites in hopes of better understanding how amino acids manifest in space rocks.

But the researchers have another tactic up their sleeve as well: sample-return missions, the spacecraft-enabled equivalent of meteorite deliveries. Unlike meteorites, spacecraft-carried samples can be protected from the harsh journey through Earth's atmosphere, keeping the rock more pristine than even the best-preserved meteorite.

Two asteroid missions are currently working on just such deliveries: NASA's OSIRIS-REx, which is preparing to grab a sample of an asteroid called Bennu, and Japan's Hayabusa2, which is trekking back to Earth with pieces of an asteroid called Ryugu to deliver home in December. Conducting similar analysis on these samples may help scientists better understand how amino acids form and change in space rocks, the researchers hope.

The research is described in a paper published on Aug. 20 in the journal Meteoritics & Planetary Science.

Email Meghan Bartels at mbartels@space.com or follow her on Twitter @meghanbartels. Follow us on Twitter @Spacedotcom and on Facebook.

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  • Catastrophe
    Really very interesting, but does it tell us anything about why the LH preference (allegedly) pre-dates the BB?
    Reply
  • TheMatrixDNA
    Well,.. the Matrix/DNA Theory has different suggestions:
    1) Left handed amino acids are related to birth and grow, while right handed are related to the second phase of any natural system, entropy and death. Below is the universal formula of all natural systems. F1 is the initial source, then the systemic circuit goes clock-wise through left side till reaching F4. Since the circuit is built by the vital cycle process, when applied to a human body which is a system, F1 is the mother, F2 is the baby, F3 the teenage and F4 the young adult. From here, F4, begins entropy, the level of energy decreases, going to F6 ( old adult), to F7 (seniors) and the decomposed cadaver goes back to the source ( it is a closed system), or to other place ( if it is a opened system). At F4 begins the reproductive process and here life demonstrates its wisdom: i the first living system was complete with the two sides, never the first would to reproduce before dying. Pick up the phase of life growing and you will have life forever.
    2) Information for left-handed ( F1 to F4) are delivered by planets nucleus reactions reaching the surface and right-handed are delivered by stars like the Sun. So, this meteorite must be from some destroyed planet.
    Reply
  • Torbjorn Larsson
    I know this is a fashionable research area, but a smidgen of cellular biology implies that this or similar pre-biotic scenarios did not happen.

    Despite that modern cells have enzymes that keep the amino acid metabolism dominantly left chiral (and the sugar metabolism dominantly right handed), there is a frozen series of two chiral filters in the genetic core machinery. Each filter - one for charging tRNA with a specific amino acid, another for inserting the charged tRNA into the rRNA protein factory - has about 70 % selectivity for left handed amino acids being selected and incorporated into proteins, a total 90 % selectivity.

    This points to that early life evolved with achiral environmentally produced amino acids and that chiral selection evolved later as more ordered proteins were produced. The outcome is no more mysterious than the exact triplet genetic code then used.
    Reply
  • Torbjorn Larsson
    Catastrophe said:

    Really very interesting, but does it tell us anything about why the LH preference (allegedly) pre-dates the BB?

    That was a funny take on a terrible paper, I suspect. I can't find it now - and I would appreciate if you can dig it up, since you referred to it - but a similar naive extrapolation of genome length puts life evolving before Earth existed https://phys.org/news/2013-04-law-life-began-earth.html ].

    But of course no stars and planets existed until way after the hot big bang.

    As for why the chiral choices (left for amino acids, right for sugars and B-DNA helix), as my earlier comment implies it looks like a random outcome. Compare the 50 % likelihood for each choice with the one-in-a-million likelihood for the rather optimized genetic code result.
    Reply
  • Torbjorn Larsson
    TheMatrixDNA said:
    the Matrix/DNA Theory

    Nothing with that name seems to have been published in peer review literature, and you give no reference, so that isn't a theory. It is no more a theory than there is a formula you claim, then fail, to produce.

    Did they not teach science and math were you studied? You can start contact some local educational resource to catch up on these things if you are so fascinated with them (and most people find them useful after learning them).
    Reply
  • Catastrophe
    Torbjorn Larsson said:
    That was a funny take on a terrible paper, I suspect. I can't find it now - and I would appreciate if you can dig it up, since you referred to it - but a similar naive extrapolation of genome length puts life evolving before Earth existed https://phys.org/news/2013-04-law-life-began-earth.html ].

    But of course no stars and planets existed until way after the hot big bang.

    As for why the chiral choices (left for amino acids, right for sugars and B-DNA helix), as my earlier comment implies it looks like a random outcome. Compare the 50 % likelihood for each choice with the one-in-a-million likelihood for the rather optimized genetic code result.
    Since my post was #2, I can only assume that the paper was:


    Astonishingly old Antarctic space rock could explain mystery of life's weird asymmetry : Read more
    Cat :)
    Reply