Life around cool stars may be different than us

By Phil Plait | April 7, 2009 11:28 am
Artist’s concept of a planet forming around a cool star
Artist’s view of a planet forming around a cool star. Note the dark disk partially covering the star.

It’s amazing to think that just a few years ago we had no clue about planets around other stars. Now we know of over 300, and we’re getting an idea of how they form, where they form, how they behave, and whether there’s a chance of any being like home, our home. Not only that, we’re learning whether they can form around stars that are different than the Sun: more massive, less massive, hotter, cooler, whatever.

And new Spitzer Space Telescope results show that when conditions to form planets are different, the chemistry is different as well.

Spitzer spectrum showing no HCN around cool stars

Planets form from disks of rock, metal, and ice surrounding young stars, accreting material much like a snowball rolling down a hill. When they get big enough from random collisions, their gravity takes over, pulling in far more material, and a proper planet can form.

During this process, we can point telescopes at the disk, and by breaking the light up into a spectrum — think of it like a rainbow with thousands of colors instead of just seven — we get all sorts of diagnostic info about the material, including its composition.

Spitzer does this in the infrared, where lots of interesting molecules give off light. And when astronomers observed the disks of material surrounding 44 young stars about as massive of the Sun, and compared them to 17 disks around smaller, cooler stars (all aged between 1 – 3 million years), they found a surprise: cooler star disks showed no indication of the presence of hydrogen cyanide (HCN) around them.

Given that HCN is a deadly poison to humans — not to Godwin myself, but Nazis used it in WWII, and it’s on a list of potential chemical weapons — you might be relieved. However, if you take five of these little guys and let them dance for a while, they’ll combine to form adenine, a nucleobase amino acid that is a basic component to life as we know it.

That’s interesting — planets that form around such cooler stars will have a different mix of prebiotic chemicals brewing in them. This might make life more difficult to get an initial toehold (or tentacle hold or pseudopod hold), or it may just mean life will take a different path than it did here on Earth 4 billion years ago. We don’t know enough to say yet. But what this does mean is that we have to be careful about generalizing our knowledge to different environments.

Spitzer observations like this one tell us more and more about these prebiotic materials in cosmic environments, opening the door to understanding how life originates yet another crack. And in a few years the giant James Webb Space Telescope may kick that door wide open: equipped with a mirror 8 times wider than Spitzer’s, it will give us vast amounts of data about such organic materials. It may be a long, long time before we know if life exists Out There, but in the meantime there’s still much to be learned.

Image credits: NASA/JPL-Caltech and NASA/JPL-Caltech/JHU

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Comments (49)

  1. Bill

    Mr. Astronomy say hello to Mr Chemistry. And both of you shake hands with Mr. Biology.

  2. The Other David M.

    Time to face facts Phil. Life around cool stars is way different than ours. We’re nerds, and even if we get to hang out with those cool kids, it’s simply so they can laugh at us.

    And don’t forget the swirleys.

  3. So ethyne (aka acetylene) is their baseline molecule? I assume that means it forms in all stars. Why is that? Why not a more saturated aliphatic compound? Same question for HCN, why the triple-bond and not a saturated compound?

  4. Cheyenne

    “It may be a long, long time before we know if life exists Out There”-

    I don’t know, maybe not. I’d say it’s probably a long shot but if we could launch some sample return missions to Mars and some other moons in our Solar System we might get a nice surprise of returning life that didn’t originate here. And we could do those missions relatively soon if we geared up and geeked out for them.

    @Bill- Nice one! :)

  5. Azathot

    Unfortunately he forgot about Mr. Biochemistry.
    Adenine isn’t a amino acid, its a purine derived nucleobase, mainly used in our DNA, as a energy source (ATP) and used in different cofactors as FAD or NAD.
    But nice finding indeed.

  6. Gary Ansorge

    So timely: I just read this article about the thermodynamic constraints on the formation of amino acids:

    http://www.technologyreview.com/blog/arxiv/23309/?nlid=1918

    Here’s a sample of the article:

    “We know that amino acids are common in our solar system and beyond. Various first experiments to recreate the conditions in the Earth’s early atmosphere have produced 10 of the amino acids found in proteins. Curiously, analyses of meteorite samples have found exactly these same 10 amino acids. Various researchers have noted this link but none have explained it.

    Now we know why, say Higgs and Pudritz. They have ranked the amino acids found in proteins according to the thermodynamic likelihood of them forming. This turns out to match the observed abundances in meteorites and in early Earth simulations, more or less exactly.”

    This is WAY cool!

    GAry 7

  7. Quiet Desperation

    Who was the “artist”, and why are they still using Bryce 1.0? 😉

    It’s amazing to think that just a few years ago we had no clue about planets around other stars. Now we know of over 300,

    Is it? We found a way to detect them, and started detecting them. That’s how science rolls. Eh, maybe I’m just jaded.

  8. @BA “That’s interesting — planets that form around such cooler stars will have a different mix of prebiotic chemicals brewing in them. This might make life more difficult to get an initial toehold (or tentacle hold or pseudopod hold), or it may just mean life will take a different path than it did here on Earth 4 billion years ago. We don’t know enough to say yet. But what this does mean is that we have to be careful about generalizing our knowledge to different environments.”

    I’d like to propose a different explanation if I may. I’m assuming that Spitzer is detecting IR absorbtion of these materials (acetylene and hydrogen cyanide) in the gaseous state, right? Then the following comes into play:

    Hydrogen cyanide (HCN): boiling point = 26 deg C

    Acetylene (H2C2): boiling point = -84 deg C

    My explanation is this. The cooler stars have the same amount of HCN in the stellar disk, only it’s in liquid or solid form and thus Spitzer can’t detect it. So at some position in the circumstellar disk (say 1.0 A.U.) the cooler stars don’t have enough energy to raise HCN over the boiling point of 26 deg C but they do have enough energy to raise H2C2 over its boiling point of -84 deg C. For the sun-like stars they have more than enough energy to boil both compounds.

    Thus, the implications for any future life evolving are negligible because the HCN is still there in the cool stellar disks, only it’s in liquid form.

  9. Is the amount of ultraviolet radiation put out by such cool stars significantly less than that put out by solar-type stars (as you would expect from Planck spectra), or do the flares more than compensate?

  10. Eh, maybe I’m just jaded.

    Indeed you are! But that’s okay when your handle is “Quiet Desperation”.

  11. Gary Ansorge

    Hah! No comments on the thermodynamic constraints? Well, poo on all you non-physicists. (,,,bunch a dad-gummed astronomers,,,)

    Gary 7
    If the constraints indicated are valid, I expect most(carbon based) life in the universe will be very similar to our own,,,

    Did anyone catch Colbert last night? I note he commented on one of his employees having 12 fingers and that they had a tough time converting his paycheck to base 12,,,

  12. Ethanol

    Tom Marking:
    are those boiling points at vacuum? Interesting theory. Another question: If the elemental composition of large and small systems is the same, where’s the nitrogen? Ammonia? If so, would the the heat and electrical discharge on a forming planet be sufficient to create HCN even if it didn’t predominate in the disk?

  13. Isn’t it cool that we have the intellectual integirty to say, “I don’t know.” And then we use that as a springboard to figurte cool stuff out!

  14. @Ethanol “are those boiling points at vacuum?”

    Those boiling points are for 1 atm pressure (sea level), but since the circumstellar disk is embedded in gas there must be some kind of vapor pressure existing in the system. So the numbers may not be the same, but acetylene should boil at a lower temperature than hydrogen cyanide.

    “Interesting theory. Another question: If the elemental composition of large and small systems is the same, where’s the nitrogen? Ammonia?”

    It may be in the form of HCN in the case of cooler stars only the HCN is in liquid or solid form. Or it may be in a variety of other nitrogenous compounds including ammonia. Either way, this evidence is way too weak to rule out the possibility of life on planets orbiting cooler stars.

    “If so, would the the heat and electrical discharge on a forming planet be sufficient to create HCN even if it didn’t predominate in the disk?”

    It’s not entirely clear if HCN is a required pathway. For example, the simplest amino acid, glycine, has been found directly in interstellar clouds. If you get glycine directly deposited on a planetary surface maybe you don’t need HCN.

    http://physicsworld.com/cws/article/news/18059

  15. T_U_T

    If so, would the the heat and electrical discharge on a forming planet be sufficient to create HCN even if it didn’t predominate in the disk?

    I personally think that much of the prebiotic chemistry happened around geothermal systems on the ocean floor, so the chemistry of the protostellar disk is pretty much irrelevant.

  16. Didac

    Well. May be red dwarf systems are not a good place to HCN -> adenine (the so-called Oró’s pathway). However, red dwarf stars are far more stable and have longer fusion time spans than “orange” stars such ours. So, when Earth’s biosphere will begin to crumble in, say, 1 or 2 billion years, all your biological descendants will pray for having been born around a red dwarf star.

  17. @ Tom Marking:
    I was gonna go one step beyond what Ethanol said — boiling points given with no temperature or volume? What the heck are you talking about? If you grabbed those off some chart of standard BPs, then it was set for standard conditions (20 centigrade, 1 atm). The BPs near vacuum are ridiculously low, because there’s no pressure to keep the molecules in solid or liquid phase. Water, for instance, supposedly freezes, boils, and sublimates simultaneously (at the triple point) when the crust of Europa cracks and exposes the underlying ocean to the raw vacuum of space. The pressure drops hard enough, and bam, it becomes vapor for Spitzer to detect 😉

    pV=nRT (as the pressure drops to zero so does temperature, unless volume drops too)
    http://en.wikipedia.org/wiki/Ideal_gas
    http://en.wikipedia.org/wiki/Triple_point

  18. T_U_T

    So, when Earth’s biosphere will begin to crumble in, say, 1 or 2 billion years, all your biological descendants will pray for having been born around a red dwarf star.

    What about our descendants living around a red dwarf star ?

  19. JB o Brisbane

    Sorry to be a grammar Nazi, but my dear departed mother taught me this –

    It’s “different from”, not “different than” or “different to”.

  20. Torbjörn Larsson, OM

    Hey, that’s cool! (No, really.) I missed that.

    I personally think that much of the prebiotic chemistry happened around geothermal systems on the ocean floor, so the chemistry of the protostellar disk is pretty much irrelevant.

    Well, I’m not sure about the opinion in the astrobiology area, but it sure seems to be the dominant position among molecular biologists as well.

    [See for example Martin or Koonin. Btw, I like their poetical picture of the primordial metabolic electro potential driven cells percolating from acidic primordial ocean through rocks to alkaline warm vents to start off with dimensions of kilometers, to subsequently shrink to within vent deposited inorganic iron sulfide membrane compartments of dimensions of tenths of millimeters, to end up in mobile organic lipid membrane compartments of tenths of micrometers. It’s not just the internet that gets the goods out of miniaturization and mobility!]

    Though, if HCN is rare, perhaps nitrogen is too, and that would presumably be influential on the easiness to form various amino acids and nucleobases.

    Now we know of over 300,

    Careful, it’s 344 today, according to The Extrasolar Planets Encyclopedia, so with our own we are closer to 400 planets and counting.

    But, bother, I can’t find any convenient browser gadget that keeps track of them, and their properties such as closeness to Earth mass or the habitable zone. Does anyone know of one?

    [Btw, wouldn’t that, or similar astronomical info gadgets, be a splendid combination of income and public education for a Badass Astronomer? Or at least a good astronomical blog service?]

  21. @T_U_T “I personally think that much of the prebiotic chemistry happened around geothermal systems on the ocean floor, so the chemistry of the protostellar disk is pretty much irrelevant.”

    Where did the atoms in the ocean floor and ocean originally come from? :)

  22. jimmy

    Hey Dr. Phil.

    Your blog is a nice place to go for some astronomy news. So thanks for that. But you know what would be great? If you would stop talking down to us. For example:

    “During this process, we can point telescopes at the disk, and by breaking the light up into a spectrum — think of it like a rainbow with thousands of colors instead of just seven — we get all sorts of diagnostic info about the material, including its composition.”

    Really? Do you really think we need to define “spectrum” for us? Is that how little you think of your readers?

    I picked this example somewhat at random, but I see this all the time in your posts, and it is jarring. I think you underestimate your audience – hell I bet half your readers know what an FFT is – and it is insulting, and frankly makes it hard to your blog.

  23. Ethanol

    Tom Marking:

    Without a doubt the elemental composition of the protostellar disk matters, but a lack of HCN doesn’t necessarily imply a lack of nitrogen. If all the chemistry happens on the planet surface, then the chemistry of the protosteller disk is not important, only the elemental composition. Unless the chemical form of elements in the disk could influence their distribution in the disk before planets formed. hmmm…..

  24. Let’s time travel back to the 1970’s… Imagine a planet where the only life-form are “Fonzie’s”. Now, that would be cool! Ayyyyyyyyyy!!

  25. jimmy: I’m glad you’re so smart and educated and everything. But not everyone knows what a spectrum is, and this blog has a lot of readers, including kids and people who have an interest but not devotion to astronomy. I like to be inclusive rather than restrictive.

    If you’re insulted by the level of this blog, then please avail yourself of the professional journals. I’m sure they make fun of any astronomer who feels they have to define what isentropic layers are.

  26. HCN

    Phil spoke of HCN thus: “However, if you take five of these little guys and let them dance for a while, they’ll combine to form adenine, a nucleobase amino acid that is a basic component to life as we know it.”

    Woo Hoo! I’m useful!

  27. “This might make life more difficult to get an initial toehold (or tentacle hold…”

    So THAT’S where PZ’s from! And here we were thinking he evolved with us on EARTH!

  28. Flying sardines

    Awesome artwork.
    Who was the artist?

    Can we get that cool star painting as a screensaver / wallpaper from somewhere?

    I always thought aliens would be *VERY* different -not just peopel with different coloured skin and knobbly foreheads. Science as always shows up much the science fiction as less strange than likely reality.

  29. Rob P.

    Jo – that’s not a real rule of English. See, Columbia Guide to Standard American English, for example.

    http://www.bartleby.com/68/37/1837.html

  30. Brasidas

    Hi Phil

    You did indeed Godwin yourself, and you could have easily avoided it by replacing “Nazis used it in WWII” with “Americans used it up until at least 1999” (on a German on that occasion, ironically).

    HCN is the lethal gas used in American gas chambers, with effects so horrific that on occasion the press has been forced to leave while the prisoner is still struggling to breathe after some 10 minutes of agony.

    Darn those evil Nazis and their horrible methods of killing people.

  31. Joe Meils

    Hey, Jimmy… my grandmother reads this blog, and she appreciates the fact that it’s written in a way that she can understand. So shut it!

  32. @ JB o Brisbane – your mother’s opinion is valid, but it’s just her opinion of style. “Different than” has been around as long as “different from”, and there’s no good reason to ban it. It’s hardly “different against”, say. English isn’t a collection of single-form phrases. You’re free to hate “different than” but don’t claim it’s ungrammatical. It’s not.

    And Phil? Please don’t stop explaining things. I read you, not a journal, for a reason.

  33. Google Images
    miller urey 8440 hits
    http://en.wikipedia.org/wiki/Miller-Urey_experiment
    Tetrahedron 59 2749 (2003)

    HCN chemistry through diaminomaleonitrile to adenine and other heterocycles, formaldehyde polymers to sugars, amino acids from Strecker synthesis, plus other pathways summing to the star tar called life, is planetary not nebular. Lightning in a reducing atmosphere is entirely adequate to scum a whole planet with life’s precursors. Terrestrial photosynthesis is spectrally and metabolically optimized for a cool red sun and an anoxic environment.

  34. @Brock “I was gonna go one step beyond what Ethanol said — boiling points given with no temperature or volume? What the heck are you talking about?”

    The boiling and melting points assume a standard pressure of 1 atmosphere.

    “The BPs near vacuum are ridiculously low, because there’s no pressure to keep the molecules in solid or liquid phase.”

    The assumption of very low pressure in the protostellar disk may not be realistic. We have comparatively little information concerning what the gas pressure is in the inner parts of the protostellar disk.

    “Water, for instance, supposedly freezes, boils, and sublimates simultaneously (at the triple point) when the crust of Europa cracks and exposes the underlying ocean to the raw vacuum of space. The pressure drops hard enough, and bam, it becomes vapor for Spitzer to detect”

    This begs the question of why the entire crust of Europa (frozen H2O) doesn’t spontaneously sublimate into water vapor. Why hasn’t Europa turned into a gas if the BP is so ridiculously low?

  35. Here is a good research paper concerning the formation of benzene in protostellar disks:

    http://planetquest.jpl.nasa.gov/TPFDarwinConf3/documents/posters/woodsPoster.pdf

    Benzene is one of the key building blocks for PAH’s (polyaromatic hydrocarbons) which are in turn basic building blocks of biological systems.

  36. Ethanol

    “Why hasn’t europa turned into a gas if the BP is so ridiculously low?”

    I think that only the heated sub layer, exposed through cracks, is warm enough to sublimate at any significant rate. I am also skeptical about whether a protoplanetary disk would have enough material to sustain any significant pressure before collapsing down into individual planets, so i don’t think the 26 degrees is particularly relevant, but I am having trouble finding a B.P at vacuum for HCN.

  37. BTW, I’m surprised Phil didn’t post this recent example of pareidolia from the Chandra X-ray observatory:

    http://chandra.harvard.edu/photo/2009/b1509

    This is one of the cooler astro pics I’ve seen in a long while. It does look like some type of cosmic hand. Enjoy!

  38. Flying sardines

    Given that HCN is a deadly poison to humans — not to Godwin myself, but Nazis used it in WWII, and it’s on a list of potential chemical weapons — you might be relieved.

    Godwin’s law strikes me as just dumb. I don’t think refences or comparisons with nazi’s as a benchmark of evil should be outside discussion or see why they should end any debate. Can we perhaps apply the the law of FAQIL to Godwin now please?

    As for the gas chamber bit, the most humane way of conducting executions has to be the guillotine for my money. Not that I’ve tried or witnessed either! 😉

  39. Flying sardines

    That’s the law of FAIL as in “Godwin’s law” just Fails natch.

  40. Flying sardines

    @ Quiet Desperation Says:

    Who was the “artist”, and why are they still using Bryce 1.0?

    Yes, Phil Plait, please tell us. If you’re still reading this I’d like to know too – not so much about Bryce 1.0 (a computer art prorgame I presume?) but the identity of the artist – awesome illustration. 8)

    BA : It’s amazing to think that just a few years ago we had no clue about planets around other stars. Now we know of over 300,

    QD : Is it? We found a way to detect them, and started detecting them. That’s how science rolls. Eh, maybe I’m just jaded.

    Maybe you are. The exoplanet discoveries still sne da shiver down my spine. Oh & we’ve actually found way*S* – plural – not just one way of detecting exoplanets :

    1. radial velocity wobbles,
    2. transits
    3. microlensing

    & now we can add photographing them directly to that list with Fomalhaut b, HR8799 & maybe a couple of others. I still think that’s just an absolutely magnificnet acheivement.

    @ jimmy :
    (April 7th, 2009 at 6:20 pm)

    Hey Dr. Phil.

    Your blog is a nice place to go for some astronomy news. So thanks for that. But you know what would be great? If you would stop talking down to us. … I bet half your readers know what an FFT is – and it is insulting, and frankly makes it hard to your blog.

    What is “insulting and makes it hard to your blog” Jimmy, an FFT? 😉

    I’llbe honest, Idon’t know what an FFT is. (I know what aspectrum is though not what what “isentropic layers” are.)

    This isnt a professional specialist niche blog, Jimmy, this is for the public – its hard to find a balance between talking down & confusing the public with jargon and technospeak. Byanfd large ithink the BA gets the balance right.

    Science is complicated, its often esoteric and hard for ordinary people to comprehend – do you really want to make it more hostile and less welcoming to beginners that may come here with just their curiousity and very little knowledge? I say make it easier for people to understand and they’ll become more interested – and fund it better and live better, richer, saner lives.

    Which I think Phil is helping to accomplish. THX BA. :-)

  41. Asimov Fan

    @ Flying sardines Says:
    (April 8th, 2009 at 1:45 am)

    I always thought aliens would be *VERY* different – not just people with different coloured skin and knobbly foreheads. Science as always shows up much of the science fiction as less strange than likely reality.

    Well, yes some but NOT all. The strangest aliens I ever read were in Isaac Asimov’s ‘The Gods Themselves’* ; multi-dimensional, three gendered beings that were ingeniously done – & Asimov also created several other really exotic and strange aliens species. He didn’t do them often but when he did he did them very well. (Complete with different biochemistry and biologies. Yes, I’m afan so I’m biased but still .. its true.)

    Other’s to have done SF aliens really well – IMHO naturally – include Stephen Baxter’s neutron star people and his cleverly imagined maammoths, Orson Scott Card’s alien hive queens and Pequinino’s plus others and the “Shadows” in Babylon-5.
    Yes, a lot of “aliens” haven’t been done so well or creatively; esp. in TV series like ‘Star Trek’ and to a lesser extent ‘B-5’ where budgetary constraints no doubt provide a limiting factor – and the standard “funny forehead” approach was applied. (Incidentally, surely I’m not the first to observe that if Spock can be born as half-Vulcan, half human it means Vulcans are biologically the same species as us!)

    Yes, reality is likely to prove stranger than fiction when we finally discover alien life.

    But, come on, a lot of SF still is very imaginative and good too -give it a chance and you may be surprised!

    If its great -and very alien – aliens you want, then I’d recommend ‘The Gods themselves’ by Isaac Asimov, ‘Speaker for the Dead’ & ‘Xenocide’ by Orson scott Card & ‘Flux’ by Stephen Baxter for starters .. :-)

    (Assuming of course you haven’t read them already.)

  42. Asimov Fan

    * The title of which was a quote from Shakespeares King Lear done in three parts for each section :

    Against Stupidity …
    The Gods Themsleves …
    Contend in Vain?

    (The question mark being Asimov’s saving hopeful note addition.)

    I thibk that quote suits this BA blog to a T & could make a good slogan here .. Or even a good tattoo for the BA himself! 😉

  43. Spectroscope

    Artist’s view of a planet forming around a cool star. Note the dark disk partially covering the star.

    I presume that covering disk depicted there is meant to represent the still forming planets and asteroid belt(s?) aroudn the cool star right?

    Oh & BTW/ How cool is the cool star -spectral type K like Epsilon Eridaniand Epsilon Indi? Or cooler still spectral type M or even L like Proxima centauri, Barnard’s Star or Wolf 359? How coool is “cool” here?

    I second those asking to know who the artist is.

  44. Flying sardines

    THX Asimov Fan – point taken.

    I read and loved the whole, ‘Enders Game’ series as a kid. I’llhave tosee if I can track the other two down.

    As for strange aliens on TV Dr Who has had some beauties – the Daleks and many other others.

  45. Ken Croswell, anotherastronomer-author-populariser has awhole series of interetsing artciles onred dwarfs online incl. one written ages ago about their prospects of life .. with a neat twist at the end.

    Click on my name above for the link & then scroll down a fair way through the subjects menu to find it. Its the one titled “Red, Willing & Able.”

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