You Need Just the Right Amount of Killer Asteroids to Promote Complex Life

An artist’s impression of the different configurations of asteroid belts that could occur. Image credit: NASA/ESA/A. Feild, STScI

Sure, asteroids can be planetary annihilators, scouring the surface of a world with fire and molten rock. But asteroids might also help seed a planet with the right ingredients to set up the conditions for life, and give that life encouragement to evolve more complex survival strategies.

As with all things, it’s just about balance. Too many asteroids, and you’ve got an unrelenting cosmic shooting gallery, raining fiery death from above. Too few asteroids, and complex life might not get the raw material it needs to get rolling. Life never gets that opportunity to really shake things up and evolve into more complex forms.

This conclusion comes from Rebecca Martin, a NASA Sagan Fellow from the University of Colorado in Boulder and Mario Livio of the Space Telescope Science Institute in Baltimore, Md. The researchers created a series of theoretical models based on observations of debris disks around other stars, as well as the Jupiter-sized planets discovered so far.

They found that only a fraction of the planetary systems out there have giant planets at the right locations to help create an asteroid belt of the right size. In fact, it looks like the Solar System might be rare and special when it comes to perfectly-sized asteroid belts.

“Our study shows that only a tiny fraction of planetary systems observed to date seem to have giant planets in the right location to produce an asteroid belt of the appropriate size, offering the potential for life on a nearby rocky planet,” said Martin, the study’s lead author. “Our study suggests that our solar system may be rather special.”

There are three potential models for asteroid belt formation in other star systems.

  1. A Jupiter-sized world migrates slowly inward, disrupting the asteroid belt before it can really form. All the potential asteroids are consumed or flung out into deep space. A potential Earthlike world is deprived of the chemicals (and catastrophic incentive) to evolve complex lifeforms. That’s bad
  2. No large Jupiter-sized world forms at all, allowing the solar system to create a massive asteroid belt. Material from this enormous asteroid belt would be too punishing to Earthlike worlds for complex life to stand a chance. Also bad.
  3. A Jupiter-sized world forms in the outer solar system, and only moves in a little, preventing an overly large asteroid belt from forming. There are still enough asteroids out there to seed an Earthlike world with chemicals and evolutionary encouragement, but not enough to set its progress back. That’s us!

To come to this conclusion, Martin and Livio created models of protoplanetary disks around various stars, and then watched what would happen with various Jupiter-sized planets. They compared their models to 90 protoplanetary disks that have been discovered so far by NASA’s Spitzer Space Telescope, and 520 giant planets found orbiting other stars.

So far, only 4% of the systems they’ve observed have the right combination of a compact asteroid belt with a Jupiter-sized planet nearby. This gives researchers a very specific configuration of asteroid belt and planetary arrangement to look for when searching for worlds that could contain complex life.

Original Source: NASA News Release

33 Replies to “You Need Just the Right Amount of Killer Asteroids to Promote Complex Life”

  1. I think it is also important that a Jovian planet not be too close to the star. If it is close this perturbs the orbit of any terrestrial planet that might be in the ~ 1AU orbital range.


    1. Well if a Jovian planet is too close then therefore it wouid have migrated in, thus there would already be a disrupted belt, correct?

  2. Reformed killer asteroids promote life. Read all about it! Thanks, excellent article I really need to study and learn in detail. Retweeting for tomorrow for breakfast

  3. Reminds… We might be thankful for the ‘astronomical’ number of circumstances that led to life on this planet? Should we ever find highly evolved life elsewhere, it will no doubt be accompanied by a similar number of near miraculous circumstances? No wonder many have turned to religious or divine interpretation for our existence… Evolved lifeforms elsewhere might feel similarly so? I hope so.. it would breed benevolence and a respect for life. That would be better than the alternative…

    1. Religion breeds benevolence and respect for life?!?! What planet do you live on? One quick look at any time in human history and it’s hard not to see a great deal of egotisim, ignorance, bigotry and violence caused directly by religion.

      1. My intent was not to tout religion, but to recognize instead how the realization that the incredible set of happenstance that lead to life on this planet, might lead to worship or at least be respected… here and elsewhere. Respect for life is not a religious tenant. Religion has been and is and will be, as you state, the source of much of mankind’s misery.

      2. Life is rare and precious, agreed, but you don’t need a god to explain it’s existance and certianly not to respect that fact. If human history is anything to go by and one day we do meet an E.T. brandishing a belief in god may well start an interstellar holy war. Before we even consider moving out into the universe we need to shed ourselves of the superstitious nonsense that is religion and take responsibility for our own actions. besides, any “highly evolved life elsewhere” most likely won’t consider us to be highly evolved.

    2. I find “Rare Earth” models based on bayesian reasoning daft.

      You can pick any number of factors specific for Earth and conclude Earth is unique. Similarly you can pick any number of factors specific for you and conclude you are unique. Say, very few children had your father and mother in common, and I’m sure you can think of dissimilarities to your siblings.

      That is not what astrobiology is based on. It looks at life and its constraints everywhere. We know humans, or species in general, are not uncommon. Similarly we can look for factors that are relevant for life and conclude that it is likely not uncommon.

      For example, to get life started we need energy, water and CHNOPS, the most common elements in the universe. And we find plenty of planets with those.

      If you want to look at complex multicellularity and intelligence (to compare with us), it becames more of an open field. Would bayesian or asteroid disk models close it? Not likely.

      For example, we have had 2-3 mass extinctions since land life arose, with a complete recovery of diversity between – independent diversified worlds. In one of those language competent intelligent life arose. Then maybe at least 1 out of 4 oxygenated worlds (depending on number of mass extinctions) will have such life.

      And yes, it is a wonder people willingly turn away from knowledge and a possible answer, for any reason whatsoever. It has nothing to do with science though, so it doesn’t place on these blogs.

      1. “…2-3 mass extinctions…”? More like 5 or possibly 6 mass extinctions, making our existence even more precarious and rare…. and that an evolved alien culture might reach the same conclusion.

      2. I did a Bayesian analysis of the possible orbital stability of an Earth mass planet at 1AU around other stars. I used known extrasolar system data and computed the Lyapunov exponents for the chaotic drift of these planets. Only one other planetary system produced a Lyapunov for a putative 1AU terrestrial mass planet comparable to Earth. Earth’s orbit is perturbed mostly by Jupiter, and the occurrence of Jovian planets is the critical factor.This was used as a Bayesian prior and I estimate there are only about 1000 planets in our galaxy comparable to Earth,

        This of course does not preclude other biologically active planets. For all we know Mars may have subsurface life in the liquid water at glacier surfaces and Enceladus may be spewing out microbes in its geyser vents. Life may be relatively common in the universe. Conditions for complex life and ecological systems may be far less prevalent.

        A close in Jovian planet in a stellar system would perturb the motion of a terrestrial planet. From this article it appears that it will also rob the planet of some resources needed to promote biology, or at least complex biology.


      3. This shows how it isn’t relevant. We have already observed habitable planets at a larger frequency. Trying to specify characteristics for “an Earth analog” is open ended, while measures are unequivocal.

      4. Most of these planets are around M-class stars which means they are likely tidally locked. I might be wrong, but I think this reduces the chances for those planets to be comparable to Earth. Also M-class stars do a fair amount of flaring. Also if there is a Jovian planet within a couple of AU of this planet the orbit of this planet is likely perturbed heavily. This means it is highly probable the orbit is rattled around and conditions are not terribly stable.

        While the Earth has exhibited a wide range of changes in its geological past these are actually fairly stable. Temperature variations are estimated to be within 15C, the content of the atmosphere has remained relatively constant, 21%O_2 now and this was up to 27% in the Permian to Jurassic, the oceans have been chemically pretty stable. This might be contrasted to some planet with that has a 25C variation in temperature, with much larger shifts in chemistry and so forth. This planet might bear life, but I suspect such biology is more rudimentary.


  4. Might I point out that Vesta and Ceres had its history, but not a destructive one.
    An Earth like planet residing in a massive belt might actualy be more benificial towards evolving space travel than our Earthly enviroment, from an economical point of view.

  5. I agree (I think) with Ivanman, we need an accompanying explanation of why and how an asteroid belt helps to encourage (initiate) life. That is definitely not part of my world view. Why is it we can form from the same protoplanetary disc but still need asteroidal content? Is that because our heavier elements have sunk into our molten earth before a crust is formed that can absorb an asteroidal impact and keep the new elements on the surface where they can mix with our atmosphere and atmospherics?

  6. Nice prediction of persistent asteroid belts.

    The rest is less likely. Other models predicts the necessary scarceness of water and carbon on inner planets naturally from disk models. That model has been tested by the recent find of Mars initially having the same amount of water in its mantle.

    It is difficult to predict this same amount from an asteroid belt hammering Earth and Mars differentially due to the different distances and planetary sizes.

    And generally there is way too much of water and carbon in ordinary asteroids (~ 10 % average in the most common carbonecaous chondrites) for a planet with land and oceans and rocks (~ 0.05 % for Earth). A terrrestrial outside the snow line could instead have a 100s of km thick ocean with correspondingly thick diamond shell that would cap the metal minerals that life would need.

    And no plausible amount of asteroids impact rates can sterilize a planet with prokaryote life on it, according to Mojzsis et al models. At least with an asteroid belt from our density and an unknown density upwards. Mars sized planetesimals of original disk impactors suffice to sterilize yes (e.g. the Earth-Moon impactor), later asteroids after planet accretion has finished no.

    Mainly, Jupiter seems to gain us more asteroids and low velocity (IIRC) comets than it protects us from. So it is a nuisance.

    1. What’s wrong if there are too few asteroid impacts (as would happen with a gas giant-disrupted asteroid belt?

      They cause mass extinctions. The less asteroids, the better (or I am missing something?).

      And in the model that explain why the Earth is so dry, the few water that actually is on Earth is mainly from accretion (and posterior degassing from mantle) or from later asteroid and comet impacts?

  7. ~ “But asteroids might also help seed a planet with the right ingredients to set up the conditions for life, and give that life encouragement to evolve more complex survival strategies.” ___________________________

    I hope I bend the line of that subject question by asking: Does the rubble belt (leftover material of Nebular Hypothesis), swarming fragments, and rogue objects, through violent impacts and crashing bombardments, play any role in explaining today’s superbly arranged World-System wrapping Earth in Life—one set-up for it (whether by endless chance, or no): chemical, mineral properties, Moon and oceans, continental masses and crustal mechanisms, life-enclosing-supporting spheres, above and below; ….?

    Break down the concept, like a grinding stream of asteroids hurtling around the Sun (the unconsolidated remains, or unused material on a construction site?), and what you have is a violent hail-storm episode(s?) raining down random destruction (while supplying essential elements, according to concept), or by later single hammer-blows, pounding a star-orbiting body’s surface (or/and atmosphere), setting the stage for the emergence of self-organizing, super complex life-arrangements (one CELL is no tinker-toy assembly)—and their supporting, symbiotically-tied environments, preset to promote and sustain its overall matrix. From explosive, fiery chaos—“Time, TIME stirs the endless sea”—highly ordered self-assembly, cascading outward like expanding fractuals of scale: living soil to small seed; root plant to branching ecology; weave of forest to pattern of continental-fabric (all seamlessly tailored with, and fitted to the aquatic world below)—one “grand design” planetary Biosphere. (Fast forward version.) The world-supporting ground, and its “Tree of Life”.

    So, could say, it too, started with a Bang?

    Destruction of one form or another falling from the sky, brings about a life-breathed, environment-clothed creation. And one not just localized, like the imagined subterranean Martian colony, but spinning a Planet-turning Web of Life—infinitely more complex than any “ingenious” silky work of spider’s spinneret.

    – Expansive disks of dust, and belts of icy-rock debris (if hard-facts do indeed agree), equals youthful Planet Systems in formation. Could they possibly be aged world-systems in deterioration? Slow-motion build-up, or time-frozen break-down? (I use the conceptual word “debris”, another will use “building blocks”—with its own train of MODEL-enclosed thought.) Well, if the star is young, the disks must be stages of early planet formation, or stillborn remains thereof.

    – In reading subject and comments: Just posing non-conformist questions—that have nothing to do with the straw man of “religion”. It relates to ORIGINS—cause and effect. The genesis of things: whether they be a living cell, a planet, a star, or a Universe. Is that not Scientific? _________________________________

    > “In fact, if one considers the possible constants and laws that could have emerged, the odds against a universe that produced life like ours are immense. …. The remarkable fact is that the values of these numbers [cosmic expansion rate] seem to have been very finely adjusted to make possible the development of life …” [he later speaks of] “Spontaneous creation” – “It is not necessary to invoke God to light the blue touch paper and set the universe going.” (Pg 180)
    – Stephen Hawkings, (A Brief History of Time), “British theoretical physicist and author.”

    > “There is for me powerful evidence that there is something going on behind it all. It seems as though somebody has fine-tuned nature’s numbers [30+ set?] to make the Universe. The impression of design is overwhelming.”
    – Paul Davies, English physicist, writer and broadcaster, currently a professor at Arizona State University.

    1. The speed with which life was established on Earth shows that it is an easy enough process on habitable planets (which we have many of).

      Since it is a process, there is no question about cause and effect. Cosmology shows that the universe started out from elementary particles after inflation ended. Abiotic chemistry caused biotic chemistry.

      1. You label Mr. Davies a “deist”, and promptly dismiss an observation by an accomplished physicist as unscientific (by inference), and imply its a statement of “religious” belief: “Deists believe in the existence of God without any reliance on revealed religion, religious authority or holy books.” That eliminates the “religion” label.

        ~ Mr. Davies ” is affiliated with the Institute for Quantum Studies.
        ~ “He is also an adviser to the Microbes Mind Forum.” [has nothing to do with deism or “religion” that I can read]
        ~ *His “inquiries have included theoretical physics, cosmology, and astrobiology; his research has been mainly in the area of quantum field theory in curved spacetime.” [Sounds like high-
        SCIENCE to me. I do not read “Creation Science” anywhere here.]
        ~ Among other things, as a “communicator of science”, the man has been awarded several prizes [from NON-religious organizations]: Eureka Prizes, and in the UK; Kelvin Medal and Prize by the Institute of Physics; Faraday Prize by The Royal Society; and the Templeton Prize [“The Templeton Prize honors a living person who has made an exceptional contribution to affirming life’s spiritual dimension, whether through insight, discovery, or practical works. ….—outstanding individuals who have devoted their talents to expanding our vision of human purpose and ultimate reality. The Prize celebrates no particular faith tradition or notion of God, but rather the quest for progress in humanity’s efforts to comprehend the many and diverse manifestations of the Divine.”]
        ~ He has an Asteroid named after him.
        ~ He has done BBC programs on SCIENCE, ….
        ~ He has been affiliated with several Universities: Chapman University in California; with “academic appointments at the University of Cambridge, University of London, University of Newcastle upon Tyne, University of Adelaide and Macquarie University.”

        An “opinion piece published in the New York Times, generated controversy over its exploration of the role of faith in scientific inquiry. [perhaps where you got your notion]…. a response by Davies… ‘I was dismayed at how many of my detractors completely misunderstood what I had written. Indeed, their responses bore the hallmarks of a superficial knee-jerk reaction to the sight of the words “science” and “faith” juxtaposed.’ While atheists [of course, completely unbiased] Richard Dawkins and Victor J. Stenger have criticised Davies’ public stance on science.” _______________________________________________________

        In effect, what I think you are saying is, even suggest the possibility of something other than naturalistic explanation for life, or the Universe, and you—your work, accomplishments and credentials, (perhaps your sanity!) must be discounted, dismissed as invalid—unscientific—discredited.

        – Wikipedia

      2. – The observation of Davies religion was to predict his religious claim. (As much as you can predict individual behavior from individual’s behavior, so to speak.)

        – Obviously Davies claim is religious, it says nature is not enough: “bheind it all”, “somebody”, “design”.

        – Obviously deism is a religious position, it invokes superstition to predict nature. You are trying to equivocate between personal religious belief and organized belief. There are no deist churches is all, but there could be.

        If you don’t get the two last points, which isn’t an opinion but a description of religion as it is usually defined, we can’t have a discussion.

      3. The close minded will draw their automatic conclusions (based on bias?). The open-minded can judge for themselves.

  8. Do not the planets themselves derive from gravity upon the contents of the original belt? If so why the importance of asteroid hits later from the same belt contents.

    1. During the initial stages of the Earth’s formation, it was molten and the heavy elements sank to the core of the Earth due to its gravity; consequently, this left the crust depleted of the essential elements needed for life, such as iron. However, these essential elements eventually came in from asteroids (and also water from comets) in the later stages of the Earth’s formation to enrich its crust.

      1. Iron is siderophilic but it is also rock forming and was always retained in the crust as I understand it. It is many of the other transition elements that are depleted.

        We now know the mantle contained enough hydrogen and oxygen to reconstitute today’s oceans when degassing and volcanism created the initial CO2 atmosphere.

        We also know from hydrogen isotope ratios that comets could have supplied a minor part of water.

        The participation of asteroids is an open question, I believe. In some core formation models they resupply all the depleted elements, in some others there was incomplete mixing in the first place.

      2. Well, what I said also says so in the introduction of the paper (linked above):

        […]. Heavy elements, including some that are essential for life, were also probably delivered to the Earth’s crust through collisions. During the early times of formation the Earth was molten and its gravity pulled heavy elements to its core leaving the crust depleted of elements such as iron, gold and platinum. […].

      3. Yes, the crust is relatively depleted of iron compared to the (iron!) core. But the question is if impactors delivered appreciable amounts.

      4. Furthermore, referring to your link, it states there:

        […]. Manganese, iron and molybdenum do form strong bonds with oxygen but in the free state (as they existed on the primitive earth when free oxygen did not exist) can mix so easily with iron that they do not concentrate in the siliceous crust as do true lithophile elements. […].

  9. Laughs, chokes and makes a sheep-like bleating sound… We live and learn? Have we been down this path before? Recently I (re)read a Sci-Fi story by Ross Rocklynne entitled, ‘Time Wants a Skeleton’. It was written way back in 1941. In this story an astronaut, one Tony Crow, crash lands on a remote asteroid while chasing two criminals he hopes to capture. The asteroid he lands on is a remnant of an earlier collision between two much larger proto planets. The story follows a convoluted series of circumstances wherein Tony finds a skeleton in a cave with an emerald ring on it’s finger… ergo the title. Included in the story is time travel, cops and robbers, a genius scientist with a newly developed warp drive/propulsion system which bends time and space as part of its function. And of course, there is a beautiful girl, the daughter of the genius scientist. There are many typical artifacts of that genre included in this story. In retrospect… it’s a hoot!

    What stood out for me in this story was the idea that our asteroid belt was created by a collision and breakup of two earlier evolved planets. We know now there is not enough mass in the asteroid belt for this to have been the case.. or was there? True, if you add up all the matter in the asteroid belt today, there simply is not enough to make a planet, much less two colliding bodies… or is there?

    Were we to include the estimated mass of all the crater forming impacts on the solid planets and moons, then included an estimate of a similar number ingested by the gas giants… then maybe… ‘Tony’ was on to something? Just saying…. What we THINK we know, often later turns out to be only part of the whole story…. Live and learn! Tvist and turn!

    1. We know from observing other systems, and from modeling our own, that disks are formed and then asteroids et cetera. It is also obvious from all available samples that they were never planets.

      Hoofbeats, horses, zebras.

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