Exoplanets identified with enough light to activate life chemistry and with liquid water

A group of exoplanets have the same chemical conditions that may have led to life on Earth.

The star give off sufficient ultraviolet (UV) light could kick-start life on their orbiting planets in the same way it likely developed on Earth, where the UV light powers a series of chemical reactions that produce the building blocks of life.

The researchers have identified a range of planets where the UV light from their host star is sufficient to allow these chemical reactions to take place, and that lie within the habitable range where liquid water can exist on the planet’s surface.

“This work allows us to narrow down the best places to search for life,” said Dr Paul Rimmer, a postdoctoral researcher with a joint affiliation at Cambridge’s Cavendish Laboratory and the MRC LMB, and the paper’s first author. “It brings us just a little bit closer to addressing the question of whether we are alone in the universe.”

In the lab UV lamps were used to generate the precursors to lipids, amino acids and nucleotides. These are all essential components of living cells.

Among the known exoplanets which reside in the abiogenesis zone are several planets detected by the Kepler telescope, including Kepler 452b, a planet that has been nicknamed Earth’s ‘cousin’, although it is too far away to probe with current technology. Next-generation telescopes, such as NASA’s TESS and James Webb Telescopes, will hopefully be able to identify and potentially characterize many more planets that lie within the abiogenesis zone.

Using a known reliable pathway for photochemically building up the prebiotic inventory in large yields, we show that hotter stars serve as better engines for prebiotic chemistry. Investigating the race between light and dark bisulfite chemistry, we find, based on our requirement for >50%. yields, that, even for early Earth, the prebiotic inventory would need to be built up in places where the surface temperature is below ~ 20∘C.

Because of the efficiency of the bisulfite photochemistry, rocky planets within the liquid water habitable zones of K dwarfs can also lie within the abiogenesis zone, so long as the temperature is very close to 0∘C. We applied our results to a catalog of potentially rocky exoplanets within the liquid water habitable zones of their host stars. For gas giants within the liquid water habitable zone, there is a tantalizing possibility that some of their larger moons may be primed for life (20).

The abiogenesis zone we define need not overlap the liquid water habitable zone. The liquid water habitable zone identifies those planets that are a sufficient distance from their host star for liquid water to exist stably over a large fraction of their surfaces. In the scenario we consider, the building blocks of life could have been accumulated very rapidly compared to geological time scales, in a local transient environment, for which liquid water could be present outside the liquid water habitable zone. The local and transient occurrences of these building blocks would almost certainly be undetectable. The liquid water habitable zone helpfully identifies where life could be sufficiently abundant to be detectable.

For main sequence stars cooler than K5 dwarfs, the quiescent stellar flux is too low for the planets within their habitable zones to also lie within their abiogenesis zones. Planets within the habitable zones of quiet ultracool dwarfs may be able to house life, but life could not presently originate as a result of photochemistry on these worlds, although it possibly could have done in the past, if these stars emitted much more strongly in the UV before they entered into the main sequence or if they had been much more active in the past. Our results are only valid for the stars as they are now.

Scientific Advances – The origin of RNA precursors on exoplanets


Given that the macromolecular building blocks of life were likely produced photochemically in the presence of ultraviolet (UV) light, we identify some general constraints on which stars produce sufficient UV for this photochemistry. We estimate how much light is needed for the UV photochemistry by experimentally measuring the rate constant for the UV chemistry (“light chemistry”, needed for prebiotic synthesis) versus the rate constants for the bimolecular reactions that happen in the absence of the UV light (“dark chemistry”). We make these measurements for representative photochemical reactions involving Embedded Image and HS−. By balancing the rates for the light and dark chemistry, we delineate the “abiogenesis zones” around stars of different stellar types based on whether their UV fluxes are sufficient for building up this macromolecular prebiotic inventory. We find that the Embedded Image light chemistry is rapid enough to build up the prebiotic inventory for stars hotter than K5 (4400 K). We show how the abiogenesis zone overlaps with the liquid water habitable zone. Stars cooler than K5 may also drive the formation of these building blocks if they are very active. The HS− light chemistry is too slow to work even for early Earth.

17 thoughts on “Exoplanets identified with enough light to activate life chemistry and with liquid water”

  1. It is ENTIRELY beside the point. What you’re debating is whether the presence of precursors is a sensible starting point for investigation of life, not whether the complexity of the precursors implies guided process. You’re hopping topics.

  2. He apparently didn’t ask Lane. As well, even if it is a complete mystery, complete mystery and “guided process” are a very wide logical step apart.

  3. There is a notion in biochemistry of the “non replicating life” step; that is, the possibility that for a while in Earth’s history, living organisms that didn’t contain a mechanism for self replication were predominant in alklaline submarine vents – some form of life that’s barely a step above non-living organics – and that some quirk had to take place after an indeterminate period of time to give rise to self replication. The idea that life keeps going once it forms once requires us to assume that life and self replication are inseparable, though we have no evidence for that. It is entirely possible that half a billion years of non replicating life popped in and out of existence in untold variation and gradually increasing or fluctuating design and complexity before self replication appeared and became the dominant form of life.

  4. The paper is not behind a paywall and explains why this premise is in the abstract. They address the differences between UV photochemistry and non-UV photochemistry.

  5. Hello superstitious moron. We already know that over time exactly that happened.

    There is no gap, for crying out loud amino acids occur spontaneously from raw materials and energy input.

    It scarcely matters how rare an event is, when once it happens all sequelae follow absent active intervention to the contrary, and every cubic centimeter within 1 meter of the ocean surface gets a few million dice rolls per second for the initiating event.

  6. That’s besides the point, which is that these are the basic building blocks, and not just raw material. I do think that lipids, amino acids, and nucleotides can arise through a not-too-complex sequence of unguided reactions, though I admit I don’t know the specific sequence(s). Like I said, these aren’t very complex molecules. They’re not macromolecules either.

  7. When you build molecular machines & nanotech as Tour does, you understand how hard it is to synthesize macromolecules. Which is Tour’s point. He’s asked plenty of other top scientists, including Nobel Laureates, about this, and they admit to not understanding how it is possible via unguided processes. However, they will only say this in private. The ferocious blowback for a public comment casting doubt on Right Thinking is more than they wish to take on.

  8. Tour hasn’t demonstrated any such thing. He’s expressed his professional scepticism of the concept, but that’s a rather different thing entirely.

  9. Lipids, amino acids, and nucleotides are fairly simple molecules. Not as simple as water or methane, but far from requiring any sort of long sequences (and information contained therein) that may be statistically improbable. These aren’t proteins, DNA, and RNA (nor even peptides – the shorter cousins of proteins).

    A nucleotide is simply a nitrogenous base connected to a sugar connected to a phosphate group – just 2-3 rings and a few other atoms. An amino acid is just an amine group (NH2), a carboxyl group (COOH), and some small side group attached to the same central carbon atom. A lipid is a long chain of carbons and hydrogens (or two or three such chains) connected to a polar group such as a phosphate. Sometimes there is a sugar or other polar group attached to other side of the phosphate.

    So a better analogy would be “if it has transistors, resistors, and capacitors, maybe it has computers” (note that “maybe” isn’t the same as “likely”).

  10. “Hotter than K5 (4400 K)” excludes all red dwarf stars (as well as the cold end of orange dwarfs), which is where many of the habitable-zone planets have been discovered so far (due to detection bias). But as GoatGuy notes, colder stars still emit UV. Given that light energy is quantized, a smaller flux of UV simply means less chemistry. In other words, it would take longer to accumulate the same stock, but if it doesn’t degrade, it’ll still accumulate. So we may expect life to start later on planets orbiting such stars. But on the other hand, these stars burn longer.

    For red dwarfs, we also must consider their tendency for flares. It’s generally considered that flares are detrimental to life’s survival. But ironically, they may promote similar prebiotic photochemistry.

  11. Quoting (paraphrased correctly…)

    A star producing sufficient ultraviolet (UV) could kick-start life on orbiting planets within their speculative Goldilocks Zone in the same way life may have developed on Earth, where it is thought that UV light powered a series of interlocked chemical reactions making the building blocks of life, and providing both potential photochemical energy, and actual physics-energy (of distillation, evaporation, heating, cooling, introduction of chemical and mixing gradients), which again — quite speculatively — were tantamount in giving rise to “life” as we are coming to know it.

    Now … With VUUKLE not providing the usual indenting, quotation, block quotes and italics aside, I think that reads rather well.

    Thing is — if you would look at that phase diagram above — thing is, that the diagonal red-orange cutoff line for what might be necessary from a UV-infusion perspective is HIGHLY speculative. For instance: although the amount of UV definitely falls off when a star’s temperature declines below 5000 K (our lovely star is presently gurgling along at 5777 K), it ALSO is true that the amount of UV doesn’t entirely disappear.

    Consider: tho’ no longer much used, in my youth one could buy “black lights” … incandescent bulbs having special borosilicate glass envelopes (they transmit UV better than ordinary flint or crown glass), and that were literally “painted” (dipped) in a dark dark purple-blue colored plastic varnish that was tuned to maximally let thru UV, and block nearly all visible light.

    The temperature of the filaments … was only 3000 K.

    And a single 100 watt bulb could pretty merrily light up a corner of the Rock’n’Roll party. The point isn’t parties, or bulbs, but that 3000 K definitely exhibits UV emissions.

    Here’s the speculative part: WHAT quantity of UV is really necessary to catalyze the QUANTITY OF chemical reactions in order that life might arise? Well… in a nutshell, no one has the slightest hard clue. The ANTHROPOCENTRIC principle would say “well, it happened here, it apparently happened in the first 0.5 billion years (or perhaps even much shorter), old Sol once young was once also somewhat hotter (or cooler … take your pick), so that ought to have been the winning equation”.

    OK, maybe that’s so. And maybe that’s right.

    But I’m not sure.
    I think life is a statistically improbable phenomenon, but ONCE it starts, it takes off.
    And goes, and goes, and goes.

    Like a single living yeast cell in a petri dish.
    Not many days later, it covers the whole dish with billions of cells.

    Life is like that.
    Just needs to start.


  12. “In the lab UV lamps were used to generate the precursors to lipids, amino acids and nucleotides. These are all essential components of living cells.”

    And, as top chemist James Tour has demonstrated, there is a VAST gap between “precursors” and actual working lipids, amino acids, and nucleotides. And we haven’t even begun to explain the enormous amount of information necessary to create living cells, even if the lipids, amino acids, and nucleotides are assumed to begin with.

    Honestly, the lab results are rather like saying that an exoplanet has silicon, a necessary precursor for computers, so it likely has computers. Nonsense.

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