Comets Not So Likely to Smash Into Earth and Kill Us All

By Eliza Strickland | July 30, 2009 5:42 pm

cometA comet from the deep space far beyond Pluto probably won’t smash into the Earth and obliterate all life, reassuring researchers said today. New calculations have determined that most extinction events that have occurred over our planet’s history probably weren’t caused by killer comet showers, which bodes well for the future, too. The findings are both welcome and well-timed since only last week an object dramatically smashed into Jupiter; many researchers believe the culprit was a comet.

In the new study, published in Science, researchers focused on long-period comets, which are among the wild cards in a thick deck of cosmic threats. In contrast with short-period comets, such as Comet Halley and Comet Tempel-Tuttle, long-period comets trace insanely eccentric orbits that range out beyond Neptune, Pluto and the Kuiper Belt to a little-understood region on the solar system’s edge known as the Oort Cloud [MSNBC]. The Oort cloud, which contains billions of small, icy objects, may extend from about 93 billion miles from the sun to as far as 9 trillion miles away.

Scientists have long thought that visible comets came mostly from the outer ring of the Oort cloud, because Saturn and Jupiter have enough gravity to eject from the solar system any comet that creeps in from the inner portion.  Sometimes, those inner comets actually slam into the giant planets, which happened to Jupiter last week [Discovery News]. However, the researchers’ computer models showed that the solar system’s structure does allow some comets from the Oort cloud’s inner ring to slip past our guardian gas giants. That region may even be the dominant source of long-period comets, the researchers found.

But when the computer models were run for half a billion years, they found that the most powerful comet showers from the inner Oort cloud produced only two or three impacts with the Earth over that time. Lead author Nathan Kaib explains that the most powerful comet impact identified, 40 million years ago, did not cause mass extinction…. “That tells you that the most powerful comet showers caused minor extinctions and other showers should have been less severe, so comet showers are probably not likely causes of mass extinction events,” he said [Telegraph].

However, Kaib notes that asteroids, which unlike comets are made of rock not ice and tend not to have a “tail”, could still pose a major “threat to life.” … Many scientists believe that a collision from an asteroid was responsible for the extinction of dinosaurs from the earth 65 million years ago [Telegraph].

Related Content:
80beats: Mysterious Smash on Jupiter Leaves an Earth-Sized Scar
80beats: Space Shuttle Exhaust Provides Clues to the Mysterious Tunguska Event
80beats: Nano-Diamond Discovery Suggests a Comet Impact Killed the Mammoths
DISCOVER: NASA Takes a Wild Comet Ride
DISCOVER: Comets: Powdery Puffballs in Space?
DISCOVER: Hail, Bopp!

Image: Mike Solontoi / University of Washington

  • Albert Bakker

    I get the impression that those who do still believe in the Chicxulub – KT boundary – dinosaur extinction connection as something of a given are far more likely to be astronomers and geologists, than paleontologists, or in other words those who know what they are talking about on this subject. Even though it is often repeated, because it is so clean cut and easy to understand, I’m afraid it is another beautiful hypothesis slayed by ugly facts. (Quite a while ago.)

    So maybe we are even safer than we thought and then again maybe we are under severe threat of something we don’t even have the faintest clue of. In any case as humans we can put comfort in the fact that we are able to and probably will wipe ourselves off this planet far more quickly than nature would.

  • Gozza

    What the hell are you talking about Bakker?

    “the Chicxulub – KT boundary – dinosaur extinction connection”
    No idea what that means…

  • YouRang

    It seems to me if paleontologists paleontologists are less likely to accept the C-K-D extinction connection then it must because C-K-D gives them less to do. If something other than the meteor obliterated the dinosaurs, then there is something to research (paleoecology e.g.). If there is a good deal of doubt, there is also something for which for them to get grants (relative contribution). If it’s merely tying up loose ends, grants are harder to get.

  • YouRang

    But comets aren’t particularly in the ecliptic. E.G. it seems highly likely that the planet that captured Halley’s comet is TERRA. Hailey crosses the ecliptic right near earth’s 93 million miles; so Jupiter may have modified the orbit, but earth captured it. And if earth captured it, earth could have been blasted by it. Maybe the posited comet extinction event of the Younger Dryas was from Hailey.

  • Albert Bakker

    Happy to explain what the hell I was saying.

    Please read the last sentence of the article: “Many scientists believe that a collision from an asteroid was responsible for the extinction of dinosaurs from the earth 65 million years ago. ”

    The Chicxulub krater (Yucatan, Mexico) is generally believed to be where the asteroid impacted that is the cause of the KT boundary, which is a certain layer between the Cretaceous and Tertairy deposits. The hypothesis, originally proposed by Alvarez in the 1980’s was that this impact would then have thrown up enough dust in the atmosphere to cause somekind of nuclear winter scenario, which would then explain why the dinosaurs died out.

    As far as I know, there is no serious disagreement about the impact. The disagreement rises over whether the coincidence (the impact and the extinction happening at roughly the same time – also by the way, the Deccan Traps in India went beserk at this time.. most likely shortly before the asteroid impact) also suggests a causal relation between these events. But while this remains very difficult to prove or disprove, the evidence is stacking up against it.

    And that is where I said I get the impression that oftentimes different types of scientists tell a different kind of story. Because of their expertise and/or affinities they look at this very difficult subject from a different angle, so that (overly generalized) astronomers and physicists take one side, the paleontologists the other and geologists are collectively sitting on the fence.

  • Franklin J Tyler

    A few comments to add:

    a) Early in the article it states “a little-understood region on the solar system’s edge known as the Oort Cloud” but then goes on to say that based on computer models of this region, we should have 2 to 3 comet impacts in half a billion years. I wouldn’t suggest ‘comets are less likely to smash into Earth’ based on this new study alone;

    b) Regarding the ‘and kill us all’ part – In the half a billion years it takes to have 2 or 3 comet impacts from the inner Oort cloud, I’m sure the human race would have successfully achieved mass extinction all on its own;

    c) I’m pretty sure that, at our current capacity, we can view a mere 3% of space from earth leaving a 97% guessing game; and

    d) Though I find ‘YouRang’ hypothesis of a Halley Comet/Younger Dryas event intriguing, the current scientific evidence points to the introduction (and thus mass imbalance) of cold freshwater into the Atlantic (which in turn, shut down the Gulf Stream) as the likely culprit…. And Halley’s comet is expected to return in 2061.

  • Albert Bakker

    #6d – I’ll ignore the Halley angle, because I fail to see any relevance. Ideas proposed on the connection between an impact event 12900 yrs ago (christened the “Clovis Comet”) and the (partial?) shutting down of the thermohaline circulation via the North Atlantic conveyor belt is addressed in this presentation of the theory: (and goes on in part 6.)

    The third link under the related content section addresses the nano-daimonds that were edited out in the above.


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!


80beats is DISCOVER's news aggregator, weaving together the choicest tidbits from the best articles covering the day's most compelling topics.

See More

Collapse bottom bar