ADVERTISEMENT
  About the SA Blog Network













Observations

Observations


Opinion, arguments & analyses from the editors of Scientific American
Observations HomeAboutContact

Earth-Like Planets Fill the Galaxy

The views expressed are those of the author and are not necessarily those of Scientific American.


Email   PrintPrint



Kepler telescope's field of view

This is Kepler's field of view superimposed on the night sky. Credit: Carter Roberts

LONG BEACH, Calif.—Look up on a starry night. Almost every one of those tiny pricks of light is home to an unseen world. Our Milky Way galaxy is full of planets—100 billion or more—and many of those planets are Earth-like rocks (although our solar system still appears to be an oddball). Such are the major findings that astronomers are announcing here at the semi-annual meeting of the American Astronomical Society, where the halls are crackling with excitement as we all bear witness to a hidden, rocky universe beginning to coalesce out of the darkness.

The great explosion of planetary information is coming courtesy of the Kepler telescope, which has been peering at one small slice of the night sky to search for momentary dips in brightness that happen when a planet passes in front of its host star. Kepler scientists announced that they have found an additional 461 planet candidates, bringing the total number of such Kepler-found candidates to 2,740. (These objects all look like planets, but could potentially turn out to be something else like a double-star system upon further examination. “It’s likely that 90 percent or more of these candidates are going to be bona fide planets,” according to astrophysicist Natalie M. Batalha of NASA Ames Research Center.)

Most of Kepler’s new planet candidates aren’t the big Jupiter-like planets that early planet scans were sensitive to—they’re Earth-like planets or so-called “super-Earths,” planets about twice the diameter of Earth.

Of course, Kepler can only find planets that are aligned just so—the planet must pass directly between its host star and us. There’s no reason to think that most planets are lined up this way. “For every transiting planet that we identify there are 10 to 100 more that aren’t transiting,” said Batalha. The question becomes: how many planets are out there that we don’t see? The answer: lots.

“Almost all sun-like stars have a planetary system,” said Francois Fressin, an astronomer at the Harvard-Smithsonian Center for Astrophysics who has been exploring statistical models of Kepler data. “If you travel to a sun-like star it will have a planet. We can’t say if it will be welcoming, but it will have a planet.” What would an unwelcoming planet be? Something very close to its star, and therefore very hot. Those close-up planets whip around their stars in a matter of days or weeks, which means that Kepler has seen them cross in front of their stars many times by now. Fressin’s recent work has shown that about one in six stars is home to a rocky, Earth-like planet that orbits its star within 85 days or less. For longer-period planets, we just have to wait for more observations.

What about Earth-like planets with Earth-like orbits? Of the 461 new planet candidates, 51 of them are in the so-called “habitable zone,” the Goldilocks region around the star that’s at just the right temperature for liquid water to exist. And one of these new planet candidates has all three of the qualities we’re looking for in a twin Earth: it’s in the habitable zone, it’s only 1.5 times the size of Earth, and it’s orbiting a sun-like main sequence star.

This last attribute is important, because most stars are not, in fact, like our sun. Most stars in the galaxy are so-called red dwarfs­­–small, dim, cool stars that are our galaxy’s “silent majority,” according to John Johnson of the California Institute of Technology. Red dwarfs make up 70 percent of all stars in the galaxy, and these are absolutely full of planets, says Johnson–on average, about one per star. Summing up all the red dwarfs in the galaxy and all the planets that they host, we can estimate that the Milky Way is home to at least 100 billion planets. “Our solar system is rare among the galaxy’s population of planetary systems,” says Johnson, “because our star is not a red dwarf.” But with 100 billion possibilities to choose from, who would bet that there’s one not like us peering back through that darkness?

 

About the Author: Michael Moyer is the editor in charge of space and physics coverage at Scientific American. Follow on Twitter @mmoyr.

The views expressed are those of the author and are not necessarily those of Scientific American.





Rights & Permissions

Comments 39 Comments

Add Comment
  1. 1. cy_starkman 6:55 pm 01/8/2013

    70% of stars in the milky way are red dwarf. Okay.

    But

    1) What is the percentage of sun-like stars in this galaxy?
    2) What is the percentage of red dwarves in other galaxies?

    Link to this
  2. 2. lostjohn 6:57 pm 01/8/2013

    It’s time to rethink our religious views, we are not all that special.

    Link to this
  3. 3. chrisrus 7:25 pm 01/8/2013

    Michio Kaku predicted this would happen last year. He said that we would all be confronted with an exestentialist crisis once we learned that everywhere you look in the sky, you will find earth twins. Earth twins are common and the sky is full of them. What does that mean for philosophy? I agree with the comment by lostjohn that religions are going to have to wrestle with the significance of this fact, but are we atheists immune to the need to ruminate on this for a while?

    Link to this
  4. 4. chrisrus 7:29 pm 01/8/2013

    What would life on earth be like if it were twice as large? The atmosphere would be much thicker, making flying easier. Wouldn’t the oceans be much deeper? Or maybe the water would be spread more thinly across the surface. Would it be harder or more difficult for life to form on a planet twice as large?

    Link to this
  5. 5. rloldershaw 9:00 pm 01/8/2013

    Answers for cy starkman

    1. Very low; maybe < 1%

    2. 70% to 80%, roughly (depends on star formation rates, etc.)

    The 70% is by mass. For abundances in terms of numbers of stars:

    Red dwarfs ~ 90%
    White dwarfs ~ 9%
    More massive stars ~ 1%

    These are just rough approxmations for overall universal averages.

    Robert L. Oldershaw
    Discrete Fractal Cosmology

    Link to this
  6. 6. rloldershaw 9:27 pm 01/8/2013

    Note also that the 90%, 9% and 1% equally well characterizes atomic abundances (by numbers)

    hydrogen ~ 90%
    helium ~ 9%
    heavier atoms ~ 1%

    Coincidence? I don’t think so!

    Robert L. Oldershaw
    Discrete Scale Relativity
    http://www3.amherst.edu/~rloldershaw

    Link to this
  7. 7. NormWolfe 10:00 pm 01/8/2013

    If you think Joel`s story is great,, one week ago my boy frends sister basically brought home $6296 working eighteen hours a week an their house and their friend’s mother`s neighbour has done this for four months and earnt more than $6296 in there spare time at their labtop. the advice from this address…. http://www.youtube.com.bit40.ℂom/watch?v=QZEpDqP3IrQ/

    Link to this
  8. 8. RSchmidt 11:11 pm 01/8/2013

    @chrisrus, religions have been lying to themselves for thousands of years. A few more fact for them to ignore will not change anything.

    “Would it be harder or more difficult for life to form on a planet twice as large?” as long as there is liquid water the formation of life would be just as probable. But if you are talking about megafauna evolution you would likely have big differences. In fact, if you reran evolution on the earth you would likely have very different megafauna than we have now with no guarantees there would be intelligent life or even vertebrates for that matter. Evolution is a complex phenomenon and so it is hard to predict how things would turn out.

    Link to this
  9. 9. littleredtop 11:44 pm 01/8/2013

    Even if only 1% of the planets in the “habitable zone” of stars in our Milky Way are actually hospitable hosts for human life, we are left with possibly millions of potential earth-like environments. With that fact in mind, its difficult to understand why we aren’t more aggressively developing programs to explore those potential host planets.

    Link to this
  10. 10. vinodkumarsehgal 8:20 am 01/9/2013

    rloldershaw (5)

    Red dwarfs and white dwarfs are the later evolved stages of a main sequence stars when its main fuel of H is exhausted by burning. If 99 % of stars are red dwarfs and white dwarfs, it implies, sometime in past share of main sequence stars or massive one was higher than present 1%. Over the period, percentage of steadily decreased to 1%.

    In post 6, you have indicated percentage of abundance of H (99%), He (9%) and heavy elements (1%) and compared the same with abundance of stars implicitly pointing towards principle of Cosmic self scale similarity. But there is one basic difference in this analogy. Heavy elements are the later evolved stages of lighter elements ( H and He) but this may not be true for stars.

    Link to this
  11. 11. vinodkumarsehgal 8:44 am 01/9/2013

    rloldershaw and others

    If during the past 13.72 billion years since BB, 99 % of main sequence stars (MSS) have changed to red dwarfs and white dwarfs this implies that balance 1% MSS ( including our Sun) shall also become red dwarfs and white dwarfs soon in a few billion years. A stage may come when there may not be even a single MSS. Astronomers consider presence of a MSS as one of the three prerequisites, as stated in the article, for the habitable zone. In the absence of any MSS, there shall be no habitable planet in universe ( at least observable universe) and hence absence of life at all in the entire universe . This situation may continue fir billion or even trillion of years till universe dissolves thru crunch or freeze or bounce.

    Does this scenario appeals a rational and logical mind where life may exist in universe only for a few billion years and for bulk of life of universe, which may run into even trillion of years, there may be no life in universe? At least, this scenario does not appeals me.
    Either there is some fault in my line of thinking or indicated percentage of abundance of different stars are wrong

    Link to this
  12. 12. Torbjörn Larsson, OM 9:12 am 01/9/2013

    @ chrisrus: Kaku predicted something that hasn’t happened yet, and we don’t know if it will happen. He is a futurist, which is basically your pseudoscience nut working out of confirmation bias. (Eg only the ideas that are lucky will be noted.) Everyone predicted that this would be the year for Earth analogs, if not before, due to Kepler’s trends.

    Heavier planets will likely have less winged flyers, because it takes more energy to get off the ground (slightly larger surface gravity, a lot more viscosity from high atmosphere density). Inner terrestrials seems to have the same water content by mass, which would mean thicker oceans. Combined with a slightly larger surface gravity so lower mountain ranges, land would be a scarcity.

    @ rloldershaw: A coincidence, of course. When you hear hoof beats, think horses not zebras. Eager pattern search will turn up patterns, so is the generic pseudoscience used by crackpots.

    @ RSchmidt: We don’t even know if complex multicellulars will arise. The necessary eukaryote type endosymbiosis, mitochondria for energy, only arose once here.

    Link to this
  13. 13. rloldershaw 11:20 am 01/9/2013

    Vino: Your assessment of the origin of Red Dwarf stars is completely wrong- they are not the remnants of aged main sequence stars.

    Torb: You seem to have a very intimate knowledge of crackpots. Well, self-knowledge is an important goal.

    Link to this
  14. 14. rloldershaw 1:26 pm 01/9/2013

    Yo Torb,

    I forgot to mention this additional “coincidence”

    The H/He mass ratio is 1:4.

    The peak of the red dwarf mass function is 0.15 solar mass.
    The peak of the white dwarf mass function is 0.6 solar mass.

    Can you still do math, Oh Great OM?

    Link to this
  15. 15. Lenedwin 2:55 pm 01/9/2013

    It’s all very interesting and humbling. But the prospect of ever journeying to one of these ‘new earths’ is dim.
    The nearest star (other than the Sun) is 4.5 light years away. If we could travel at 1 million miles per hour it would take over 3000 years to reach it. And at that speed colliding with a spec of debris would probably destroy the ship. So by all means marvel at the Universe but lets concentrate on preserving this haven in the vastness of the cosmos.

    Link to this
  16. 16. dwbd 8:28 pm 01/9/2013

    Lenedwin, you don’t even have the remotest idea as to how travel to these planets could be achieved. Not something we are doing any time soon. So? And making a statement like “..lets concentrate on preserving this haven in the vastness of the cosmos..” which is ENTIRELY irrelevant to the entire discussion is idiotic. You could make the same worthless statement on any tech or science or arts subject, and it would be just as stupid.

    So for the time being, lets focus on finding these new worlds and determining their properties including if any have life on them – which is quite feasible with instruments based in our neighborhood. And maybe someday we might want to send a probe to one of these worlds. Oh, and yeah, while we our doing that, any idiot will tell you we have to look after our home planet too – brilliant.

    Link to this
  17. 17. CharlieinNeedham 10:26 pm 01/9/2013

    “many of those planets are Earth-like rocks (although our solar system still appears to be an oddball)” – Michael Morer in the article above.

    Really???!!!

    Where is the proof?

    The earth ([and the "oddball" inner planets of our solar system] is made of remnants of an exploded supernova. Only inside a massive star could the large amount of heavy elements be made from fusion of lighter elements.

    Thus the earth has large amounts of carbon, oxygen, nitrogen and iron.

    And we really are a “rocky” planet – at least our very thin tectonic plates.

    But no where in this story, or its references, is there any proof that there are indeed “many earth-like rocks”.

    So what are the odds that all those planets out there have the carbon, oxygen and nitrogen to make life possible?

    How many planets out there have the complex array of elements that result from coalescing fragments from an exploded supernova?

    Where is the proof that ANY of those billions of planets have water?

    What are the odds of having an iron core to give a planet a magnetic field to shield against solar winds?

    This author, and the many who write such simplistic articles, ignore the unknowns that would make a reasonable estimation of the chances for life out there.

    Garbage in means garbage out in any probability predictions of truly earth-like planets, let alone estimations of the probability of life.

    Link to this
  18. 18. Schroedercurt 11:02 pm 01/9/2013

    I highly suspect that SETI quality life forms are not peering back at Earth. Just because we may find planets in the Goldilocks zone, does not mean life as we know will be present. The conditions for life here on Earth go far beyond the three qualities mentioned in this article.

    Link to this
  19. 19. david123 7:23 am 01/10/2013

    With all those planets, and all those candidates for earth-like planets (which I do believe are out there, I’m not doubting that), I have to ask the Fermi Question: Where are they?

    And I don’t mean “where are they?” as in “why aren’t there ships landing on the DC Mall?” I mean:

    Where are their I-Love-Lucy early TV broadcasts (or equivalents)? Where are their FDR early radio speeches (or equivalents)?

    Ours are out there, 50-60 light years out there by now… but theirs should have been traveling for millions of years and should have been picked up by SETI. But they are not? Why not? Where are they?

    The sun is a young star. Stars capable of spawning earths have been around for billions of years longer. Some of them must have intelligent life, with TV and radio broadcasts.

    Where are they?

    Link to this
  20. 20. vinodkumarsehgal 9:12 am 01/10/2013

    david123 (19) Present civilization on earth has a history of e.m. transmission and reception of about 100 years only. If some alien civilization located some 1000 years light years away from earth had transmitted some radio signal, it may take 1000 years to reach earth

    Link to this
  21. 21. David Marjanović 1:08 pm 01/10/2013

    Does this scenario appeals a rational and logical mind where life may exist in universe only for a few billion years and for bulk of life of universe, which may run into even trillion of years, there may be no life in universe? At least, this scenario does not appeals me.
    Either there is some fault in my line of thinking or indicated percentage of abundance of different stars are wrong

    …Did you just seriously imply that only what appeals to you can be real? Or what have I missed?

    And we really are a “rocky” planet – at least our very thin tectonic plates.

    And, you know, all the rest between the even thinner hydrosphere and the metallic core.

    So what are the odds that all those planets out there have the carbon, oxygen and nitrogen to make life possible?

    Very high. Those are among the most common elements other than hydrogen and helium.

    How many planets out there have the complex array of elements that result from coalescing fragments from an exploded supernova?

    Probably all of them. After all, all elements other than hydrogen, helium, and a tiny bit of lithium result from supernovae.

    Where is the proof that ANY of those billions of planets have water?

    Oxygen being common and hydrogen being nearly ubiquitous, water is common, too. The question is if there’s the right amount on any given planet, and whether the temperatures and pressures are such that the right amount of it is liquid.

    (“The right amount” is of course a range of values, but we don’t really know what that range is.)

    What are the odds of having an iron core to give a planet a magnetic field to shield against solar winds?

    Very high. Supernovae working the way they do, it’s very difficult to get a rocky planet without a pretty big iron core.

    The sun is a young star. Stars capable of spawning earths have been around for billions of years longer. Some of them must have intelligent life, with TV and radio broadcasts.

    Some of them must have life; many perhaps. A tiny fraction of those may have complex multicellular-or-similar organisms with several different organs and stuff. A tiny fraction of those may have intelligent life.

    http://en.wikipedia.org/wiki/Rare_Earth_hypothesis

    Link to this
  22. 22. europamoon100 4:53 pm 01/10/2013

    “Earth-Like Planets Fill the Galaxy”

    So? We have known this for a long time.

    It has been shown by computer simulations and lots of other ways, for many decades, dating all the way back to the 1950s and 60s.

    See the book “Inhabitable Planets for Man”,
    by Stephen H. Dole, and other books and technical articles in astrophysics.

    See also “Planets for Man”, by Isaac Asimov, based on the above book, but written for a less-technical audience.

    Why can’t the articles say, “Just as we have known all along?”
    Dale

    Link to this
  23. 23. Postman1 4:57 pm 01/10/2013

    david123 We have no idea how long we will be using radio and TV for communications, or at what distance our signals will be undetectable from the background radiation. Perhaps we will use radio waves for most communications for 500 years and the signal can be read up to 1000 light years (only a guess). that would mean that any signal we pick up would have to have been sent from within 1000 ly radius globe (Earth at the center) and sometime within the last 1500 years.
    That will eliminate most of the galaxy and of those stars not eliminated, most of the possible civilizations would be well past the time of radio wave use. I don’t have the numbers, but I would bet Torbjorn can pull them up quickly and they will not be in favor of our picking up a signal without a lot of luck.

    Link to this
  24. 24. Pilar 5:46 pm 01/10/2013

    It is sad that Carl Sagan is not here to witness it… At least Frank Drake can readjust his formula using the data from these discoveries …

    Link to this
  25. 25. Quark333 6:08 pm 01/10/2013

    Frank Drake’s equation is based on evolution and evolution has never been seen to occur so the equation calculates to zero. The fossil record supports creationism. There should be billions of fossils between the dog or cow and whale and it should be happening now. Planets around stars simply means God created it this way, maybe for his remnant of believers to explore after the Great White Throne judgment of humanity and fallen angels, the one who duped humanity into thinking there are outer space evolved aliens on other planets.

    Link to this
  26. 26. Benjowo 9:52 pm 01/10/2013

    Quark333 (no25) If you have nothing to contribute but religious babble, stay out of it and get educated, but first open your mind to knowledge not fantasy drivel.

    Link to this
  27. 27. Quark333 10:16 pm 01/10/2013

    @Benjowo…..Christianity is a philosophy. Evolutionary humanism is the fake religion constantly speaking religious babble. You are a hypocrite and will be vacuumed into the new age occult movement which also has you half-way in with science-fiction and fantasy. I have degrees in Chemical Engineering and computer programming. You will be judged someday, even for this comment of drivel. Guaranteed, it will come back to haunt you.

    Link to this
  28. 28. david123 6:07 am 01/11/2013

    vinodkumarsehgal, Postman1, our sun is a young star in this galaxy. There has been time for civilizations to grow and flourish not in the past thousands of years, but the past billions of years. With all the planets in the galaxy, how unlikely is a billion-year-old civilization? In my opinion (and the opinion of many), very likely indeed. In fact, there should be many such civilizations, beaming broadcasts steadily for far longer than we’ve been around. Why don’t we hear them?

    Perhaps they are all part of a mighty Coalition of the Willing, participating in some kind of Galactic Non-Intervention Policy and have silenced their broadcasts so as to not influence the youngsters in their midst, such as ourselves.

    Or perhaps they aren’t there, which doesn’t seem likely at all.

    Whatever the answer, the question isn’t mine. It’s known as the Fermi Paradox, asked by the great Fermi himself.

    The galaxy has been habitable for about 10 billion years. That’s 6 billion years longer than the age of the earth. There has been more than enough time for not just the spread of radio/TV broadcasts but the spread of actual civilizations, even at very low fractions of the speed of light.

    Where are they? (asked Fermi)

    Where are they? (echo I)

    Link to this
  29. 29. vinodkumarsehgal 6:50 am 01/11/2013

    david123 (28)

    There could be many possibilities :

    i) When signal sent by civilizations reached earth in past, we did not had the technology to detect the signals. Now either those civilizations might have become extinct or stopped sending signals.

    ii) The earth did not lie on the route along which civilizations had transmitted signals. but those signals might be present some where else in MW galaxy

    iii) There might be a deliberate design by civilizations to not to interfere with other civilizations.

    iv) Our civilization during current period uses radio signals for communication purpose which was not known to us some 150 years ago. May be civilizations be using some technology for communication with which we may be totally unfamiliar.

    v) E.m signals sent by civilizations might be around us but at frequencies but our present technology incapable of detecting.

    Link to this
  30. 30. dwbd 9:47 am 01/11/2013

    “..mighty Coalition of the Willing…deliberate design by civilizations to not to interfere with other civilizations…”

    Pretty hard to do that when communication takes 100,000 years from one edge of the Galaxy to the other, two-way would be 200,000 yrs. Nope, any technological civilization that lasts for a significant time will be able to send, powerful signals, life-bombs (directed panspermia), robot probes by the millions, nano-self-assembling robotic life forms, self reproducing robotic lifeforms, and even starships and quickly propagate throughout the entire galaxy via geometric progression. A few million years tops to completely inundate the entire galaxy in one way or another. And stars move about coming close to other systems and galaxies collide over millions of years.

    Nope, intelligent life should be ubiquitous throughout the Galaxy. Only explanations I can come up with are

    1) we live within a simulation that limits life to a select few planets, to conserve computational? resources
    2) anthropic principle – if the probable had happened we wouldn’t be here discussing this, alien life would long ago have settled the Earth. We live in a freak galactic cluster, one in a billion.

    Link to this
  31. 31. David Marjanović 12:10 pm 01/11/2013

    So, nobody has any comments on the Rare Earth hypothesis?

    Frank Drake’s equation is based on evolution and evolution has never been seen to occur so the equation calculates to zero.

    I’ve seen evolution happen with my own eyes, overnight, in a petri dish. It’s part of a compulsory introductory lab course for students of molecular biology where I come from: I put bacteria on a dish, waited till they had grown to cover it with a visible “lawn”, put a virus on, and the next morning there were three colonies – descended from one cell each – growing on the dish while all the other bacteria were dead. Those three cells had mutations that happened to make them resistant against the virus, so the population ended up consisting only of their descendants.

    It really is that simple.

    The fossil record supports creationism.

    I’m a postdoc in paleontology. Evolution just leaps at you if you look at the fossil record.

    There should be billions of fossils

    Of what, vertebrates? You have no idea of fossilization, do you?

    between the dog or cow and whale

    Cows and whales are pretty close relatives (not as close as hippos and whales, though); they’re both artiodactyls. Their ancestors and other relatives have left a pretty good fossil record. Have you never heard of Gujaratia, Diacodexis, the entelodonts, Indohyus, Pakicetus, Ambulocetus, Maiacetus, Rodhocetus, Georgiacetus, Dorudon, Basilosaurus and a long list of others? I guess you haven’t… because you haven’t bothered to look.

    and it should be happening now.

    It is. Just watch. And not just in labs: Google will find you a heap of examples that are going on in the wild.

    Planets around stars simply means God created it this way, maybe for his remnant of believers to explore after the Great White Throne judgment of humanity and fallen angels

    Religion: the oh so humble belief that everything was made specifically for you.

    Evolutionary humanism

    There is no such thing.

    I have degrees in Chemical Engineering and computer programming.

    That’s kind of a random thing to mention. Well, except for the Salem hypothesis.

    The galaxy has been habitable for about 10 billion years.

    Were there enough heavy elements 10 billion years ago??? Our sun is a 3rd-generation star: born from the ashes of not just 1, but 2 supernovae in a (looooong) row.

    Link to this
  32. 32. CharlieinNeedham 1:35 pm 01/11/2013

    David,

    What is the probability that a star gains just the right amount of elements in the right proportion from an exploded supernova to form an earth like planet and have it orbit at just the right distance to be neither too hot or too cold?

    [Space is a big place. Accretions of supernova remnants to coalesce to form a rocky earth-like planet of the right size and with the right combination of elements can not be common. This is my main complaint with the author's contention that "Earth-Like Planets Fill the Galaxy".]

    This is just one of the variables in the Rare Earth Hypothesis.

    Have you taken a statistics course yet?

    Link to this
  33. 33. dwbd 7:36 pm 01/11/2013

    “..What is the probability that a star gains just the right amount of elements in the right proportion from an exploded supernova to form an earth like planet and have it orbit at just the right distance to be neither too hot or too cold?..”

    The odds are pretty good actually, so far statistical analysis considering the likelihood of finding Earth like planets using present methods, indicates they are indeed common.

    Link to this
  34. 34. david123 7:52 pm 01/11/2013

    Interesting discussion. A lot of good ideas here.

    I have a question for any physicists, radio engineers or just anyone informed enough to answer:

    How far out is one of our radio broadcasts still viable? Take any Clear Channel 50,000 Watt broadcasts… how many light years can it travel and still be picked up by a civilization at our level of technology.

    5 light years? 50? 500?

    I have no idea. I’d love to read an educated guess at the answer.

    Link to this
  35. 35. David Marjanović 8:40 am 01/12/2013

    What is the probability that a star gains just the right amount of elements in the right proportion from an exploded supernova to form an earth like planet

    High. All second- and third-generation stars form from supernova remnants, AFAIK.

    and have it orbit at just the right distance to be neither too hot or too cold?

    No idea. The odds of a planet staying there further depend on what the outer planets do, and apparently they move inward in many solar systems.

    This is just one of the variables in the Rare Earth Hypothesis.

    Uh, yeah, and I defend that hypothesis. So I’m not sure what your point is.

    Link to this
  36. 36. David Marjanović 8:43 am 01/12/2013

    I should explain that I count both Venus and Mars as “earth-like”. Mars, however, is so small that asteroid impacts have eroded its atmosphere, and Venus (being clearly outside the habitable zone) had that runaway greenhouse effect that put all the water into the atmosphere where UV from the sun has been splitting it, so that the hydrogen gets lost.

    Link to this
  37. 37. dwbd 12:07 pm 01/12/2013

    “..Mars, however, is so small that asteroid impacts have eroded its atmosphere..”

    No, it was the Solar Wind that eroded the atmosphere, since Mars lacks a protective magnetic field.

    Statistical analysis of recent planet discoveries indicates their will be billions of Earth-like worlds in the habitable zone, approx one in six stars. Most stars are red dwarfs where the planet may be tidally locked. However, Earth-like planets will certainly be common in our galaxy and others, that is pretty certain as of now.

    Link to this
  38. 38. lfweigel88 7:44 pm 01/15/2013

    Do these planets have cores that sustain a magnetic field that protects their atmosphere from being stripped away? Do they even have an atmosphere? Are they protected from impacts like Earth is? Earth is such a mass of EXTREMELY lucky qualities that I think saying the sky is “full” of Earth twins and we need to rethink our theology is a little hasty. Haha.

    Link to this
  39. 39. katesisco 8:38 pm 06/10/2013

    Rare Earth p 42 “the sun is peculiar in that it contains 25% more heavy elements than typical nearby stars of similar mass.” Every time I read some info that says ‘stars heavier than our sun, I think how many could there be when our Sol is in the 90 percentile?
    So maybe we have it wrong? That Sol is a planetary nova, that Proxima is our binary gone wrong, and the Oort shell is the remains of our exploded event. O Manuel and M Molina offer choices.

    Link to this

Add a Comment
You must sign in or register as a ScientificAmerican.com member to submit a comment.

More from Scientific American

Scientific American Dinosaurs

Get Total Access to our Digital Anthology

1,200 Articles

Order Now - Just $39! >

X

Email this Article

X