DNA Can Survive Reentry from Space | Hacker News Reader

DNA Can Survive Reentry from Space

scientificamerican.com

73 pointssoftdev1237 comments

Just note that DNA itself is code and completely useless without an interpreter/compiler. The DNA is just a storage mechanism, the true complexity relies on the cell.

See: http://ds9a.nl/amazing-dna/

If we lost all cells but had DNA, we could not do anything with it. The same way that source code is useless if you don't have a compiler.

Too bad they didn't test RNA... self replicating RNA doesn't need a compiler. ;)

https://en.wikipedia.org/wiki/Viroid (possible relics from the theoretical RNA world still around today)

RNA is highly unstable.

Temperatures on the exterior of the rocket reached as high as 115.4 degrees Celsius during liftoff and 128.3 degrees Celsius during atmospheric reentry

Doesn't that re-entry temperature seem way too low? I get that its probably a rear-facing surface, but still...

Yes, it's extremely low - even a "rear-facing surface" would get hot enough to melt metals such as aluminium during a typical reentry. That's why the space shuttle has all those insulating tiles.

Maybe not?

Aluminium melts at 660.32 °C / 1220.58 °F [1]. I guess aluminium alloys probably melt at slightly higher temperatures. Unless, of course, there's an aluminium alloy eutectic - I don't know.

"Felt reusable surface insulation (FRSI). White Nomex felt blankets on the upper payload bay doors, portions of the midfuselage and aft fuselage sides, portions of the upper wing surface and a portion of the OMS/RCS pods. Used where temperatures stayed below 371 °C (700 °F)."[2]

"The Space Shuttle thermal protection system (TPS) is the barrier that protected the Space Shuttle Orbiter during the searing 1,650 °C (3,000 °F) heat of atmospheric reentry."[2]

1. http://en.wikipedia.org/wiki/Aluminium

2. http://en.wikipedia.org/wiki/Space_Shuttle_thermal_protectio...

(Edit: added bit about eutectic)

The rockets used were sounding rockets—not orbital. I'm not sure just how much slower they are than orbital rockets, but if my hours of playing KSP are any guide, the answer is "quite a bit slower".

The recent Cosmos remake has a good episode that touches on this. I think it's http://en.wikipedia.org/wiki/The_Immortals_%28Cosmos:_A_Spac...

One theory set forth is that earlier in Earth's history, while bacteria were first evolving meteors would periodically strike and extinguish life, but cast rocks with dormant bacteria into space that would later re-enter and re-seed the planet after the dust settled. First time I heard the idea but it's intriguing, and segues into the whole idea of panspermia.

That's fine and dandy, but it doesn't solve how the first lifeform sparked into existence.

Very gradually.

RNA can autonomously assemble with the right mix of raw materials and minerals.

Miller Urey expt.

http://en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment#...

I've wondered this for many years: could the idea that life originated here on Earth be the final geocentrism?

This is really quite interesting too:

http://www.technologyreview.com/view/513781/moores-law-and-t...

All this is pure hypothesis and speculation until we can find some life out there and engage in some comparative analysis. If we found life elsewhere and it appeared to trace back to a common ancestor, then this would suggest that life originated far back in the history of the cosmos rather than independently in many places. Perhaps life -- if interpreted as a phase of matter -- arose along with all the other phases of matter during the early cooling of the universe?

"The final geocentricism.". Duh. You could be in a mixed state of |life had originated on earth| + |life had originated elsewhere| + |physics doesn't actually exists, and you are just a bitstring|.

edit: downvoter ;) you are an unfriendly and uneducated bitstring ;)

The problem with life evolving this early is that life absolutely requires the higher-mass elements from the supernovae arising from the first few stellar generations. The early universe was an inhospitable desert of Hydrogen.

This could make more plausible the theory that life on Earth is coming from space and then it evolved from there, rather than being born from scratch on Earth.

By Occams Razor, however, it’s probably better to assume that it formed spontaneously on Earth: "Just turning on the spark in a basic pre-biotic experiment will yield 11 out of 20 amino acids." [1]

[1]: https://en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment

This is conjecture. We don't really know how many billions of years it takes to spontaneously evolve life. Panspermia may well be a much simpler vector.

Hmm, I wonder if Occam's razor is really applicable. Is it simpler for life to form on multiple planets, or one and spread? I would guess your interpretation is more likely, but I suppose we don't know

It’s applicable if one hypothesis is simpler than the other. Panspermia simply defers the origin of life elsewhere and now you have to explain how seeds survived travelling through the hostile environment of space and impacting on Earth, which complicates it quite a bit.

Ockham's razor is either useless, or a special case of Bayes' Rule. People argue endlessly about it because they fail to recognize they are assuming different priors.

If the Urey experiment is reasonably representative of conditions on primordial Earth, no further work is required to get amino acids. So for some people P(terrestrial primordial amino acids) is ~1

If the Murchison meteor and other evidence is correct, amino acids are common in the universe. Data from the Philae lander may tell us more about this. So for some people P(extra-terrestrial primordial amino acids) is ~1

Nor are these exclusive groups. It appears amino acids aren't all that hard to make, so they may have both fallen from the sky and been created on Earth.

But... amino acids are not life. There is a further step that is required for the actual pan-spermia hypothesis: the synthesis of more complex molecules, like RNA and DNA. If you think P(RNA|amino acids) ~ 1 then pan-spermia becomes at best irrelevant: not impossible, but not very interesting.

If you think P(R/DNA|amino acids) ~ ε then pan-spermia becomes very important, because it is far more likely than not that life on Earth is due to RNA or DNA that descend from an original synthesis that happened elsewhere.

Evidence suggests RNA synthesis given amino acids is not very probable. I don't believe it has ever been observed to happen spontaneously the way amino acids are spontaneously synthesized in the Urey experiment. So pan-spermia cannot be dismissed on the basis that it is uninteresting.

DNA propogating itself across the universe is also not very probable, so the two hypotheses remain in competition, and it isn't obvious which is more plausible. Pan-spermia requires things like "DNA can survive re-entry." So the OP is correct: discovering that DNA can survive re-entry makes "Life originated elsewhere" more plausible.

You'll notice I never used the word "simplicity" in any of this. There is no simplicity: only probability and plausibility. Evidence is more or less probable. Propositions are more or less plausible. Bayes' rule is the only way to update our beliefs consistently, such that no matter what order we get the evidence we come to the conclusion.

From the same article: "The Murchison meteorite that fell near Murchison, Victoria, Australia in 1969 was found to contain over 90 different amino acids, nineteen of which are found in Earth life."

There's Occam's Razor but then there's also things like Gravity. Gravity happens on all planets/masses. It could be that life formed on Earth and also forms other places. It could be that the life on Earth has been interbred on a genetic level (think virus insertion of bacteria-based epigenetics) Perhaps for life to really thrive we need very specific planetary conditions (such as Earth-like but for different life with different chemistries they may thrive under different planetary conditions) but the more basic modules of life could be quite plentiful in comparison to what we think of as full-fledged organisms. There is some evidence of bacteria on other planets and in space even. (although scientists are being careful not to rule out contamination from Earth)

Occam's razor is only useful if it removes complexity. Since amino acids can form just as easily on comets, for instance, how is it any more plausible to form on earth? All our water comes from comets; it would be ludicrous to think it's not also a source of organic material. Indeed, Philae confirmed that organic molecules were abundant on the comet on which it landed.

Now whether RNA came from a comet is another story, and one that will probably be very difficult to answer, given the lack of archeological evidence.

And finally, what does it matter where our RNA came from? Our roots are in these tiny, self-assembling structures. That's the miracle. It's not like we're surrounded by other solar systems that may be candidates for precursors to our life: either life sat around in a very primitive form for probably billions of years before coming to rest at earth, or it formed somewhere in the vicinity of our solar system.

It's still quite unlikely. The original biochemistry needed a liquid aqueous environment to form and replicate, and you won't find that condition outside of a reasonably deep gravity well in a solar habitable zone. Only Venus, Earth, and Mars would be plausible candidates inside the Solar System for an early incubator of life, and relatively speaking, there wasn't all that much matter transferred between these bodies. Early life probably wasn't as tough as modern bacteria, and likely used something less robust than DNA. The problem with the idea that life could have originated from outside the solar system is that Earth has a laughably small "absorption cross-section" with respect to matter ejected from another solar system, plus the fact that it's very unlikely any information-bearing polymer could survive the integrated radiation flux over its long subrelativistic journey between the stars.

The other interesting theory is smashing comet ice onto a barren Earth gives you amino acids.

http://www.bbc.co.uk/programmes/b04pkvpq 28mins30secs

http://www.newscientist.com/article/dn24199-crack-a-comet-to...

I have an outside bet with myself that we will find basic life on comets that are using the tail as a dispersion mechanism.

edit - if smashing comets into earth makes amino acids, presumably so might smashing small rocks into comets.

Serious question: why is it so necessary for life to have evolved off world? What is the obsession here? Popular science type publications seem single mindedly fixated on the panspmeria hypothesis. What is it about geogenic emergence of life that is so unsatisfying?

Maybe because we haven't been able to conceive a single how life originated from constituent elements.

To me, one fact about geogenic emergence of life is very suspicious. The fact that life arose so very quickly here. Certainly within 1 billion of Earth's 4.5 billion years' history. Perhaps sooner. When you consider that in ancient times Earth was molten rock at the surface it seems that, in geological terms, life arose almost as soon as it possibly could. That being the case, we can suppose that getting life going ab initio is trivial in nature (or Earth is a many-sigma anomaly). Life certainly should have arisen many times in this galaxy of 10^11 stars - many of which have planetary systems.

So we presumably have life all over this galaxy, let alone the others. Whether life spontaneously arose many times independently or it got spread through panspermia is difficult to get a handle on but, given the age of the Universe (13 billion years), and the fact that distances used to be shorter, the latter hypothesis seems more intuitive to me.

Either way, given the precocity of life here on Earth we may reasonably suppose the galaxy to be teeming with the stuff.

Good, now let's rebuild Cmdr. Shepard

Proof we possibly originated from extraterrestrial life!

edit oh, grow up, downvoters. panspermia is a real concept http://www.livescience.com/13363-7-theories-origin-life.html

I guess you are being downvoted, because the fact "DNA can survive (re?)entry from space" is not a proof.

I think "Proof (that we) Possibly" kinda sums it up. This is "Proof" that there is a possibility (does not rule it out). He's being down voted because people are splitting hairs about the wording. What he said was generally correct however the word "proof" has a strong pull in one direction.

"Proof we possibly" is an oxymoron, like "60% of the time it works every time." It's not so much splitting hairs as it is attempting vainly to understand phrasing that inherently makes no sense.

I agree it was bad phrasing, that was not my point. I was simply pointing out that even though his wording was bad what he was trying to get across (Proof that is's still a viable hypothesis) was technically correct. Here i'll fix it for you "This is proof that that DNA can survive re-entry from space, due to this finding there is still a possibility that life came from somewhere else"

Harsh! Yes, it’s an oxymoron. It doesn’t “make no sense;” it was an attempt at humor (which clearly failed).

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