From White Dwarfs to Dark Matter Clouds, the Universe May Have Many Homes for Habitable Planets

By Patrick Morgan | March 31, 2011 3:06 pm

What’s the News: While the Kepler spacecraft is busy finding solar system-loads of new planets, other astronomers are expanding our idea where planets could potentially be found. One astronomer wants to look for habitable planets around white dwarfs, arguing that any water-bearing exoplanets orbiting these tiny, dim stars would be much easier to find than those around main-sequence stars like our Sun. Another team dispenses with stars altogether and speculates that dark matter explosions inside a planet could hypothetically make it warm enough to be habitable, even without a star. “This is a fascinating, and highly original idea,” MIT exoplanet expert Sara Seager told Wired, referring to the dark matter hypothesis. “Original ideas are becoming more and more rare in exoplanet theory.”

How the Heck:

  • Because white dwarfs are much smaller than our Sun, an Earth-sized planet that crossed in front of it would block more of its light, which should make these planets easier to spot. So astronomer Eric Agol suggests survey the 20,000 white dwarfs closest to Earth with relatively meager 1-meter ground telescopes.
  • And because white dwarfs are so cool, a planet in a white dwarfs habitable zone would be very close, meaning its transit would happen very fast. Agol says we’d only need to watch a star for 32 hours to pick up on any transiting, habitable planets.
  • One leading theory about dark matter is that it’s made of theoretical particles called WIMPS (weakly interacting massive particles). It’s thought that when WIMPs collide (if, of course, they exist), they would explode. Astronomers think that these WIMP explosions could possibly heat a planet enough to make it habitable.
  • There are no immediate plans to test the dark matter hypothesis, which is quite theoretical, and any plan to find dark matter-fueled planets would need to look far from here: our part of the universe doesn’t have nearly enough dark matter to bring a planet to habitability.

What’s the Context:

Not So Fast:

  • It’s not at all clear if white dwarfs have any planets, and if so, whether any of them could possibly support water or life as we know it. For one thing, planets in the habitable zone would be tidally locked with the star—permanent scalding daylight on one side; permanent frozen nighttime on the other.
  • Taking 32 hours to find a planet orbiting a white dwarf may seem like a short time, but when you’re looking at tens of thousands of stars, it adds up. Agol told UW Today, “This could take a huge amount of time, even with [a network of telescopes].”
  • And just like star-orbiting planets have their Goldilocks zones (not to hot or too cold), dark matter-containing planets would need the right amount of dark matter to be habitable. “It’s not something that’s likely to produce a lot of habitable planets,” Fermilab researcher Dan Hooper told Wired. “But in very special places and in very special models, it could do the trick.” 

References: Eric Agol. “TRANSIT SURVEYS FOR EARTHS IN THE HABITABLE ZONES OF WHITE DWARFS.” doi: 10.1088/2041-8205/731/2/L31

Dan Hooper and Jason H. Steffen. “Dark Matter And The Habitability of Planets.” arXiv:1103.5086v1

Image: NASA/European Space Agency

  • Jonathan

    None of the 80s beats links are working

  • Georg

    Because white dwarfs are small, the angle of observation of a passage is small.

    White dwarfs are the final stadium of main sequence stars, aren’t they?
    This means they have been red giants before and some very violent
    things happened between the red giant and white dwarf situaton.
    Any chance for a planet to survive in the habitable zone of the white dwarf?

  • Jeff

    The link to information about a planet that’s been observed with visible light is not working. I really wanted to read about that!
    Sorry, folks—minoks chewin’ on the power cables. Links all fixed now.
    —Amos Zeeberg, Discover busted-links-factory foreman

  • Aaron

    Here is a link to Phil Plait’s Bad Astronomy post “Gallery of exoplanets.” Astronomers have seen quite a few of these things!

  • dave chamberlin

    The definition of a habitable planet for complex life has to be very strict and therefore very very rare. I refer to the Rare Earth Hypothesis by Peter Ward. Requirements include 1) stable temperature within a narrow range, (liquid water not too hot and not too cold.) 2) a freak collision between two planets very early in the formation of the solar system where a large moon is created and the vast majority of the dense elements remain in the earth like planet. The earth is 3.4 times as dense as the moon, we wouldn’t have the carbon cycle without the movement of tectonic plates which depends on a hot core of heavy metals. The moon is the reason we are not gravitationally locked with one side of the earth facing the sun at all times. 3) A powerful magnetic field that protects complex life from death by sun radiation. 4) An atmosphere with enough oxygen to feed the higher energy requirements of complex life, a recent development that only happened after the last time ice covered the entire earth. 5) lots of water from comets early in the planets history and nothing too significant later on. 6)The list goes on, but you get the point.

    The Fermi Paradox is the apparent contradiction between the high estimates of the probability of extraterrestrial civilizations and the lack of evidence or contact with them. The earth has had primitive life for at least 3.5 billion years and an atmosphere rich enough in oxygen for 550 million years. Sorry UFO fans, but we are very alone. If intelligent was out there and they found another planet they could inhabit it makes sense they would have.

    Simple life will probably be very common and it wouldn’t surprise me at all if it is found in our own solar system maybe below ground on Mars or in the liquid water expected below the frozen surface on some moons in our own solar system.

  • Torbjörn Larsson, OM

    Fascinating. (ò o)

    @ dc:

    The definition of a habitable planet for complex life has to be very strict

    For biologists there is no such list, and specifically much of Rare Earth hypothesis has been rejected. Essentially it is a laundry lists of what ifs, and not good science. (To poison the well to boot: IIRC it was religiously motivated!? That would explain the essentially non-testable idea.)

    [I don’t know if your claim on oxygen atmosphere places on it, it is a consequence of life and we now know that photosynthesizers were early @ ~ 3.5 Ga.]

    What is required biologically is a habitable planet, apparently a common occurrence, enough time and a great deal of contingency. Multicellularity in itself is common, today we know of bacteria that diversify as they build spore complexes AFAIU.

    But in the energy hypothesis of eukaryotes, it is the mitochondria that provides 4-6 order of magnitude more energy for the genes and gene products. Endosymbiosis is now known to happen between bacteria, but have only once resulted in energy providers (what we know of). So it may be a rare occurence at an average delay of ~ 2-3 Gy.

    With given data, it may be that not every habitable planet is inhabited @ ~ 3 Gy (but almost certainly @ 4-5 Gy, using a Poisson model for prediction). Of those fewer still will have energy non-constrained multicellulars. If a simplest possible stochastic model of Poisson process is used for prediction, the relative likelihood for the later would be on the order of tens of percent.

    Given the number of habitable planets, multicellularity is likely a common enough occurence. It is, again, the contingency of intelligence that is the question. Noting other intelligent animals and so permitted to go through the same machinery of modeling stochastic contingent attempts, and assuming worst case of independent contingency, we would land in the order of percents or less of 5 Gy old or older suns having planets in the ETI set.

    If intelligent was out there and they found another planet they could inhabit it makes sense they would have.

    That doesn’t follow. If for example “they” expand naturally to inhabit the Oort cloud, they could colonize the Milky Way in some Gy but would have no sensible reason to go down the gravity well to visit planets, if they even had the technology to find them. Redeveloping landing and launching technology would be difficult, the return small and the venture risky.

  • Chris the Canadian

    So another dark matter theory without proof of it actually existing. Fascinating that nearly the ENTIRE scientific community hails Dark Matter & Dark Energy as fact when there is no tangible proof of existence.

    “…our part of the universe doesn’t have nearly enough dark matter to bring a planet to habitability” How about NONE??? No Dark Matter, and the theory of it’s existence is also WRONG!!! Oh but, that can’t be because people in our past tell us it must exist or else fundamental physics and astronomical mathematics wouldn’t be able to make any sense. Hogwash. As a child I learned that if the hypothesis had no proof to support it then the hypothesis was itself wrong and you came up with a new hypothesis, not new fangled ways to explain why the original premise was correct.

    Dark Matter and Dark Energy, the science communitys greatest witch hunt. By the way, I’m not a crazy theologin raging against Science. On the contrary, I would like to see science get back to it’s origins and PROVE theories to be correct before it becomes a religion unto itself, where we are told by our science gods (Einstein, Keppler, Newton etc) how the Universe and life itself came to be, where their theories are taken as truths even when they are unproven, where current scientists preach the gospil and try to explain that something is a truth when there is no proof, and where these same people call on our FAITH to believe in these truths even though there is little evidence to support them as being real.

  • dave chamberlin

    I agree that the rare earth hypothesis is a laundry lists of ifs and not good science. What we have is a sample size of one and that is the number it will stay for a long long time. But to out of hand reject the rare earth hypothesis is also bad science.

    We don’t know.

    It is a fun thought exercise, that is all. It is fun to lob an idea out there devil’s advocate style and let the good folks here shred it. It isn’t known what kick started the Cambrian Explosion, probably a number of factors. As a gambler I would put my money on intelligent life being very very rare. But then again, I’m as bad at gambling as I am at convincing folks of oddball science theories.

  • dave chamberlin

    Torborn Larsson

    If you think the rare earth hypothesis was religiously motivated than you don’t know a thing about it. Peter Ward is a serious scientist, a Paleontologist at the University of Washington specializing in the earth’s extinction events. The book “Rare Earth, Why Complex Life is Uncommon in the Universe” and co-authored by astronomer Donald Brownlee received excellent reviews from The New York Times, Science, and Discover Magazine. You can go to Blogging Heads and watch a one hour discussion between Carl Zimmer and Peter Ward regarding the Rare Earth Hypothesis. It is a laundry list of ifs, no doubt about it. What we have is a sample size of one when it comes to earth like planets so you are correct to call it highly speculative. But the book isn’t one of those sloppy sales jobs where the reader is deceived by bad science, the author admits what he doesn’t know. Perhaps I poorly represented The Rare Earth Hypothesis, but at least I read the book, which I am quite certain you have not.


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