Solar Systems Without a Jupiter Can Have up to Seven Earth-like Planets

58 thoughts on “Solar Systems Without a Jupiter Can Have up to Seven Earth-like Planets”

1. Or maybe we don’t see them because we can’t see them. What evidence could we possibly observe even as close as 10 – 20 LY?

   If you don’t discard it all as QED impossible, there is also plenty of what could be considered evidence of visitation here on Earth. Catherine Wheel, Quetzalcoatl, hundreds of other stories from the past. https://en.wikipedia.org/wiki/List_of_reported_UFO_sightings

2. As long as they don’t stay is close contact they will culturally and genetically drift apart. That happened to the hominids on the earth where we evolved into different homo sapiens species like denisova and neanderthal and sapiens.

3. Over a stretch of billions of years a few hundred years is extremely unlikely. Take us for instances homo sapiens sapiens, a species about 300,000 years old. Almost nothing for most of our history, and then everything in about 10,000 years. Same with evolving intelligent species. Brains have been around for a few hundred million years. Why the big jump in the last ten million? People have this crazy idea that evolution is incremental slow changes but it isn’t. Large changes can occur thru a simple mutation or thru the duplication of a single gene. There isn’t much genetic differences between us and the other large apes. A raptor could have hatched one day with a larger brain, and from him an intelligent dinosaur species would have evolved.

4. I’ve read it, thoroughly. If anything it doesn’t go far enough, as it is now several years old and, for each new discovery that might give us a bit more hope of meeting “someone like us” or “someone that used to be something like us,” there seem to be multiple discoveries that further reduce the overall probability of such a meeting, even if we don’t know precisely what that probability was in the first place (other than that it seems to be extremely low).

   I’ve also come to suspect that if you are not a member (or progenitor) of the first intelligent species in your galaxy that will ever emerge from it’s home system and spread to others, then you will never even come into existence to wonder why there does not seem to be anyone out there. This being because all those people are unlikely to behave exactly the same and some will probably always seek to expand, regardless of how many may decide not to.

   In short, the first intelligent star travelling species in a galaxy precludes the existence of any others.

5. For the purposes of SETI, “technological civilization” means one which we have a hope of detecting from where we are now, which basically means “is broadcasting lots of radio or shining a laser at us”, or maybe “has altered the atmosphere of their planet in a way which we can detect and rule out the possibility of it occurring naturally”.

6. That’s a bit harsh. I think we are technological since we learned to use fire. Oh, and culture transfer by language.

   Tool making isn’t enough. Several animals make tools and teach their young how to make and use them.

   But all are instinctively afraid of fire and avoid it. Well, except for some Australian hawks (there is always an exception to everything)!

7. Even with human, we have not been what could be classified as a “technological” civilization until the past 100 to 200 years or so.

8. Concur. Where are all those other extraterrestrial civilizations? The galaxy should be filled with them. That we don’t see them could be indicative that they don’t exist. We may well be alone in the Milky Way.

9. Rare-earth hypothesis. You can look it up for counter-arguments.

10. You’re overestimating the size of the shadow. Taking Jupiter as an example, its closest moon is 1.8 Jupiter radii away. That may be close enough, but even there, the shadow would only cover approximately D/(1.8*pi*D) = 20% of the orbit.

    But this is much too close to the giant for a habitable moon. Too much radiation. The closest moon to Jupiter where surface radiation is just barely tolerable is Ganymede, at 15 Jupiter radii. At that distance, the shadow will only cover about 1/(15pi) = 2% of the orbit, and even that only if it’s on the same plane as the giant’s orbit around the star (that’s not guaranteed!). Any closer than this, and you can only have subsurface life.

11. I think you have it backwards. Intelligence leads to tool use, not the other way. And intelligence is a very wide spectrum. More intelligence = more sophisticated tool use, among other things.

    edit: Btw, chimps don’t just use whatever stick or stone they happen to find. They modify it specifically for the task. IIRC, some lesser monkeys and crows do that too.

12. You may be over-estimating the ‘sweet spot’ value of finding planets, solar systems, or even systems groups/ clusters (in the sense of star-centred collections of planets, not galaxies) that will even support lichens (or other composite organisms). Research and supported-theory-driven speculation indicates that there are many areas of the galaxy (i.e. older, overly dense or overly sparse, too close to high-grav core, interfering with other galaxies, etc.) that may further reduce likelihood of safe/ productive planetary conditions for anything but the most simple life (read: without photosynthesis or potential for more complex life) based on: life expectancy of stars in that galactic region, chance of negative-destructive impact or unsympathetic galactic fields/ exposures/ gravity wells, sparsity of more complex elements or even metals, rarity of positive/pre-cursor organic/bases impacts (comets, etc), and just the lack of conditions for a planet-forming matter-disk. I.e: the number of good neighbourhoods within a galaxy is likely rare on its own – so, millions out 300+ billion stars (for Milky Way – dumb name, who thought of that?) may be high, especially when it is also about not just sweet spot; but sweet timing and sweet window of opportunity. My thoughts are that there are currently hundreds of complex-potential solar systems with a window of a few billion years for complex life. I think more likely that an existing intelligence is searching, finding, and seeding those

13. I’m not convinced that true tool use/ or the pre-cursor to intelligence is simply the obvious using of easily found items to do the same activity as one would do without tools such as bashing your enemies with a big stick instead of arm, or poking/pulling with a twig instead of using beak/ finger/ claw – even if using a hand/foot configuration only partly suited. Further, it is a bit too simple to assign pre-cursor to intelligence from the ability to see quick patterns or retain certain short-term results to activities- such as crow with many pebbles raising the height of water by adding stones, or pushing various buttons to get food or other such experiments. I like the idea of long-term strategy, group dynamics (different individuals with complementary skills acting together), and passing on skills as being the minimal level of abstraction required for ‘early intelligence’ and thus a ‘competitive advantage’.

14. The terms “habitable” and “terrestrial” are so abused as to be useless without a definition attached every time they are used.

    When I bake a cake, an edible cake, I have to use all the ingredients, and in the right proportions. It’s not just about throwing the right amount of mass into the oven, at the correct heat, for a designated period of time.

    The Earth has 92 elements on it (only six of which might be so rare as not to matter at all). What are the odds of getting the proportions close enough on all of these that matter? And a bunch of them do seem to matter.

    Then of course, how likely is it to get them to the right heat (little more, little less) without something smacking into the planet and liquefying the surface (except, for the initial big strike that produced the Moon, a tremendous cosmic fluke responsible for a large number of factors that made Earth suitable for life and have helped keep it that way)?

    Our planet, our solar system, our star, our place in the galaxy (and likely even our galaxy itself) have properties that, were they much different, would preclude us from being here to go a little overboard on the Copernican “we are not special in any way” theme.

    We are not necessarily unique in the cosmos, or even the galaxy, but the odds that had to be beaten to get us here, even at their most optimistic, even when multiplied by many times the number of stars in the Milky Way, support a figure of less than one. I still look at the news, hoping I am wrong.

15. It may also be possible “inside” of the habitable zone. If the moon orbits the gas giant once per day, it will be in the shadow of the gas giant half the time and thus reduce the average heating by a factor of two. Meaning that it could be a factor sqrt(2) closer to the star than what would otherwise be possible.

    So this moon would then have a “global” night (when it is behind the gas giant) followed by a normal day/night cycle due to its own rotation. Pretty facinating. All animals would have to cope with periodic complete darkness, as being in the shadow of the gas giant results in a “perfect” shadow with zero light unless there is another moon to provide som illumination.

16. Well, Saturns moon Titan is almost half the diameter of Earth, so there is that..

17. But there is a more probably story that is almost as intriguing. The first sentient race colonizes the other planets in the solar system, but encounters fascinating wild life and struggles to survive. 

    After a while, say, some thousands of years, the people of different planets will have radically different cultures. Wait long enough, and there will be biological differences as well to add some spice to the drama..

18. YouTube Isaac Arthur Fermi Paradox series.

19. That’s a good point. Though it’s not exactly a random walk, but just the difference in orbits will affect the evolutionary pathways. Then there are geological and other factors. Planet size, composition, amount of water and land, moons, and so on. It’s very likely that one of the planets will produce a technological species well before the others. Just one million years could make a huge difference, but it’s more likely to be many tens, if not a few hundred million years apart.

    Even if two technological species arise on two neighboring planets at about the same time, climate, biosphere, and mineralogical differences will affect their civilization development. So one of them will have at least a few hundred years technological advantage, and very likely much longer than that.

20. Once you have an error prone mechanism for copying DNA you will have evolution. And once you have evolution you will have more complex forms of life. Its “inevitable”.

21. After a random walk of 4.5 billions years they all reach the same place at the same time. I think that is doubtful.

22. Basic tool use evolved independently in several animals. Crows are an example of tool use without dextrous hands, nor even a dedicated limb. One could argue that all of these things can evolve separately, since they each have their own use. Good vision is useful to avoid predators; depth perception to catch prey; opposable thumbs to climb trees; dextrous hands to manipulate fruit etc to separate the edible parts.

    Strategy is also useful without tools, to plan for food shortages, outsmart prey or predators, etc. And it may be a side-effect of a complex social structure.

    OTOH, oxygenesis did take a while to evolve, and only evolved once that I know of. (Note: oxygenesis = generation of oxygen, not its consumption)
    But that too took only about twice as long as the appearance of first life after there was liquid water, or first Eukaryotes after there was oxygen around.

23. That’s exactly what I was going to argue; most of those steps (abiogenesis, multicellularity, and even oxygenation) seem to happen early and often. I expect that the _real_ difficult step is the appearance of a species with a tool-using strategy, since it requires lots of previous adaptations to co-occur on the same organism (good vision, dexterous manipulation, a free set of limbs to turn into manipulators for that matter, and living on land, at least) before actual evolutionary advantage will be conferred. It’s much easier to develop big teeth or a fast reproductory model.

24. Some more thoughts:

    According to https://en.wikipedia.org/wiki/Symbiogenesis , plant plastids have also evolved from captured bacteria, similar to mitochondria, but derived from a different bacteria phylum. So this capture process occurred at least twice.

    This captured bacteria then enabled – and encouraged – the development of the nuclear membrane and other eukaryotic cell structures. But for mitochondria to function the way they do, their progenitor bacteria had to be oxygen breathing. It couldn’t evolve until there was oxygen around.

    Oxygenic photosynthesis started ~3000-3500 Ma ago. But initially, most of that oxygen was consumed by dissolved iron in the oceans. The Great Oxidation Event is dated to 2500 Ma. At that point, the oxygen levels were still low, but were starting to have an effect on other species. Eukaryotes appeared by 1850 Ma, just ~600 Ma after the GOE. And once the oxygen level crossed a certain threshold, the Cambrian Explosion occurred almost immediately after.

    These points suggest that the limiting factor isn’t even Eukaryote evolution. It’s not multicellularity or complex life, either. The limiting factor may be evolution of oxygenesis.

    Another thing that took a while was evolution of protozoa. IOW, evolving the enzymes to digest organic matter. That one may also be hard, and it’s necessary for higher animals. But such enzymes are needed for internal recycling, so they seem likely to evolve given enough time.

25. Among our own population, I think there are at least as many people (possibly more) siding with preservation, as with sterilization. In our case, since most people don’t spend much thought on ET threats, the equivalent of “sterilization” is blind exploitation of natural resources. Or maybe the complete elimination of enemies, to the point of genocide.

    The tendency for preservation seems to increase with cultural development. If you consider the vastness of space, the fact that most useful resources are outside of habitable planets, and the huge technological advantage that even a few hundred years can make (let alone millions of years), primitive species aren’t really a threat to earlier ones. Consider the difference in energy scale between different Kardashev levels, for example.

    So I think the sterilization approach may be similarly rare among advanced ET, and a zoo hypothesis situation is more likely.

26. Life as we know it, basically does one thing. It multiplies, expands and consumes all energy and resources possible. If needed, it evolves intelligence to solve these problems. Evolution is a very powerful mechanism.
    Other intelligent life will most likely have observed this in action. If they want to survive long term, they have little choice but disinfecting all worlds where life starts.
    The big filter probably looks a bit like in A.C. Clarkes Time Odyssey.

27. We do know (or at least suspect) that some of the planets formed in different orbits than they are now. It’s the part about the Sumerians that is suspect.
    (edit: In my understanding though, the orbital migration ended pretty early.)

28. Earth/Moon may be an outlier, but Pluto/Charon are much closer in size still.

29. That said, it does suggest that complex life requires high-energy chemistry such as oxygen, which would indeed act as a filter for where and when it can evolve. In our own solar system, we’ve found lots of bodies with water (at least suspected, some confirmed), but only one with free oxygen.

    Oxygen is the most likely form, since it’s much more common than the alternatives.

30. Formation of eukaryotes may be the rate-limiting step, but that just means it’s slow, not necessary that it’s rare. It may still be quite common if given enough time. And it might not be a requirement for complex life (though probably makes it easier).

    According to https://en.wikipedia.org/wiki/Multicellular_organism#Evolutionary_history multicellularity evolved independently at least 25 times in eukaryotes, and also in some prokaryotes. Complex multicellular organisms evolved in six eukaryotic groups.

    Timing-wise, the earliest life appeared on Earth between ~100 to 600 Ma after first liquid water. It took another ~2000 Ma for eukaryotes to appear. The earliest multicellular prokaryotes predate (single-cellular) eukaryotes by ~1000-1500 Ma. They appear about the same time as the split between archaea and bacteria, ~300-1300 Ma after first life.

    From the first eukaryotes, it’s another 1100 Ma to first protozoa, and then only another ~200 Ma to the Cambrian explosion.

    The Cambrian explosion occurred shortly after large amounts of oxygen finally accumulated in the atmosphere. The oxygen accumulation started much earlier, but was held back a long time by ocean and land oxidation processes. So formation of complex animals was largely limited by geological factors, rather than evolution.

    https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_history_of_life
    https://en.wikipedia.org/wiki/Earliest_known_life_forms
    https://en.wikipedia.org/wiki/Great_Oxidation_Event

31. “The various planets are thought to have formed from the solar nebula, the disc-shaped cloud of gas and dust left over from the Sun’s formation. ”
    Not sure that this is a contradiction per se. May a short cut or a different view if it is true. Maybe they did not have enough vocabulary to talk about the solar nebula? especialy in the context that they were telling the story?

32. That probably has to do with statistics and power laws. The vast majority of our gas giants’ moons are pretty small.

    For an Earth-sized moon, you need first to have an Earth-sized body, and then for it to get captured into a stable orbit. There aren’t many such bodies to start from, and the likelihood of being captured is small. Larger bodies have higher momentum, so should be harder to capture. But you’re probably right that a bigger planet will have a better chance of capturing a larger moon.

    edit: Specifically re upper limits to size, IIRC there are binary asteroids of nearly identical size, so it’s not unreasonable to occasionally have binary planets of nearly the same size. But it’s probably rare, maybe very rare.

33. One of the pleasant surprises of examining our own solar system is that water is more plentiful than previously believed. It is even on multiple moons in the outer solar system, albeit often below ice covers that block out the (dim) sun.
    This means we ought to start factoring in the probability of life on moon(s) as well. Given that there are on average over a dozen moons per planet in our own solar system, which is probably fairly normal, the odds of life overall might be double, or more, whatever the probability of life is just by planet odds alone, even if the odds for life on individual moons is much smaller than for planets.
    Another thing: the odds for a space-faring civilization go up astronomically (pun intended) if there is even one more inhabitable solar body. Look how hard we are trying to get to Mars, and Mars isn’t remotely Earth like; it doesn’t have a breathable atmosphere, nor free water. If Mars had the mass of Earth, we’d be there by now, or, Martians would be here by now. A War of the Worlds impetus to spur inter-planetary development cannot be over-estimated. All of that has implications for getting through the “funnel” of civilization-ending sentient being induced catastrophes, probably to the positive side.

34. “Planets formed from the sun” ??? Not according to the current accepted view of how the solar system formed. That current view is that a large cloud of gas gravitationally collapsed, the central portion becoming the sun and the outer portion becoming the planets, comets, etc. The planets, etc. never were part of the sun, in the current view. If the initial step is wrong, the rest couldn’t ever have happened.

35. It’s been postulated that the planet that collided with Earth, ejecting the Moon, could have formed in the same orbit as Earth, but 120 degrees ahead or behind it. Trojan asteroids gather at the same interval in Jupiter’s orbit, and orbiting habitats are proposed for the Lagrangian points L4 and L5 around Earth. It’s possible Earth-sized planets could form sharing the same orbit, and so the same climate zone, in a system with no Jupiter-sized planet to disrupt them.

36. Planets formed from the sun. Planet X. We have recognized its traces in the solar system. A lot of parallels with this creation myth. Nothing in the video is not explained in Astrophysical terms. Pluto odd orbit. We think that we have acquired the moon as a consequence of a planetary collision but not sure about the details which is another parallel. The only big difference is that the current understanding is that Kupiter belt is a planet that hsas never been formed, but time will tell if it is true or not. Besides, how did the Sumerians knew about the outer planets and the Kupiter belt?

37. In general and in natural sciences, by assuming that the natural laws are parsimonious and don’t make exceptions or crazy unexpected changes on certain periods of time. Allowing us to predict the future and reconstruct the past state of a system.

    Any strong planetary orbit disruption, like changes of orbit or ejected bodies in recent geological times, let alone historical times (making the Sumerians aware of them, for example) would be perceptible in the other planetary orbits and in the geological record. It isn’t.

    If you assume that natural laws suspend from time to time leaving the place to magic and Annunaki gods’ frolicking that leave no trace afterwards, then you aren’t respecting the assumption of parsimoniousness of natural laws.

    That is fine for religious beliefs, which assume some very special moments of time when gods do frolic, exist. But that ain’t science.

38. Well, but I took a quick look, we have several gas giants in the Solar system, and not one of their moons are remotely big enough to hold an atmosphere if they were in the habitable zone. (Such atmospheres as they do have are because they’re so cold.)

    Earth’s moon is a serious outlier in being even remotely near as large as its primary. Perhaps there’s some upper limit on the ratio between the size of a planet and its moons, so that only a super-Jupiter could have a moon large enough to be habitable?

39. Contradict how? You can say at most that there isn’t sufficient evidence to corroborate what is brought here.

40. A rogue Neptune entered the Sol system per the novel. There may well be more ejected planetary bodies than those in orbit. Pluto didn’t go free flight—still makes a periodic close approach.

41. I think it’s more likely someone forgot to take his pills.

42. I have modestly postulated in many comments for many years that a solar system with lower metallicity, and hence without a greedy giant, could have a whole series of smaller terrestrial planets. The question is how many of those could be in the HZ. More than 2 or 3 seems unlikely to me.

43. Physics, planetology, geology and a long etc.

44. It is nowadays scientifically assumed that Jupiter absorbs about as many objects as it casts into the inner solar system.

45. I love chicken tikka masala.

46. Umm have you read any science fiction written from the 1920s-1950s?

47. That’s the theory at least. I still have to say though, thanks a lot Jupiter [said sarcastically] could have had more earths if it weren’t for you.

48. According to…

49. No.

50. Either they got this information from aliens, or those ancient people were a whole lot smarter than we are.

    You see a pyramid and think, I don’t know how it was done so aliens must have built this!
    I see a pyramid and think, Wow those Egyptians were smart.

51. When Worlds Collide-book 1933, movie 1951. Reduces habitility, zone or not. Increased collisions/ disruptions with large number of smaller forming planets.
    – collisions are commonplace in the late stages of planet formation, as many researchers believe that Earth’s Moon was the result of the collision of our planet with a Mars-sized planet about 4.5 billion years
    ago. Various planet configuration simulations tracking atmosphere loss during such collisions using the COSMA supercomputer – uses smoothed particle hydrodynamics (SPH) to model giant impacts. Higher-speed and/or head-on impacts create the greatest atmospheric loss, sometimes completely destroying not just the atmosphere but parts of the planet’s mantle layer beneath the crust.  Atmospheric survival is not assured in the early planet-forming environment, a time when planetary embryos collide after
    their accretion from a proto-planetary disk. To acquire an atmosphere, planets accrete gases from surrounding materials as well as from impacting volatiles.  Less likely to be habitable, this configuration is.

52. Out solar system used to be arranged differently. They Sumerians knew about it. They received this information from the alien race that they used to worship. It is all in their tablets. But our diggers bound by the scientific dogma of what the Sumerians and others were supposed to know are ignoring it. Yet there are others that have learned to read this tablets, free of of misconceptions, have created another reading.

    https://www.youtube.com/watch?v=E8sCVl2IUuM&t=544s

53. My thought too. Possibly one gas giant could have more than seven earth-sized moons in the habitable zone. I wonder what their calculations for that are.

54. Yep, there is no dearth of terrestrial planets. And every star system has a Goldilocks zone. By mere statistics, planets with temperatures, liquid water, magnetic field, day length and atmospheric conditions very close to Earth’s must be in the millions in this Galaxy alone.

    The big filter is somewhere else. My hunch is the probability of life starting, or of it becoming complex.

    I think we will eventually find several bacteria-inhabited planets (not soon, but in the long course of human history), but probably nothing with anything more complex than lichens.

55. Kind of how the early 20th century sci/fi writers imagined the Solar System to be.

56. Jupiter has janitorial duties in our system. It’s a comet cleaner. Which is better than them slamming into us with regularity.

57. What a great science fiction scenario! Having several intelligent species evolve on separate planets would create great drama!

58. Even further out is looking for habitable moons of gas giants. They’ll be fairly hard to detect, given proximity to their planet, but they’re distinctly possible if a gas giant is inside the habitable zone.

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