Earth Is Among the Lucky 1%: The Solar System Follows the Galactic Standard – But It Is a Rare Breed

The Single Star Nature of TRAPPIST-1

Researchers at the Niels Bohr Institute, University of Copenhagen, have investigated more than 1000 planetary systems orbiting stars in our own galaxy, the Milky Way, and have discovered a series of connections between planetary orbits, number of planets, occurrence, and the distance to their stars. It turns out that our own solar system in some ways is very rare, and in others very ordinary.

It is rare to have 8 planets, but the study shows that the Solar system follows exactly the same, very basic rules for the formation of planets around a star that they all do. The question about what exactly makes it so special that it harbors life is still a good question. The study is now published in the Monthly Notices of the Royal Astronomical Society.

Eccentric planet orbits are the key to determining the number of planets

There is a very clear correlation between the eccentricity of the orbits and the number of planets in any given solar system. When the planets form, they begin in circular orbits in a cloud of gas and dust. But they are still relatively small in size, up to sizes comparable to the Moon. On a slightly longer time scale they interact via gravitation and acquire more and more eccentric or elliptic orbits. This means they start colliding because elliptical orbits cross one another – and so the planets grow in size due to the collisions. If the end result of the collisions is that all the pieces become just one or a few planets, then they stay in elliptical orbits. But if they end up becoming many planets, the gravitational pull between them makes them lose energy – and so they form more and more circular orbits.

Study Reveals TRAPPIST-1 is Older Than Our Solar System

Illustration showing an artist’s interpretation of what the TRAPPIST-1 solar system could look like. The seven planets of TRAPPIST-1 are all Earth-sized and terrestrial, and could potentially harbor liquid water, depending on their compositions. Credit: NASA/JPL-Caltech

The researchers have found a very clear correlation between the number of planets and how circular the orbits are. “Actually, this is not really a surprise”, professor Uffe Gråe Jørgensen explains. “But our solar system is unique in the sense that no other solar systems with as many planets as ours are known. So perhaps it could be expected that our solar system doesn’t fit into the correlation. But it does! As a matter of fact it is right on!”

The only solar systems that don’t fit into this “rule” are systems with only one planet. In some cases the reason is that in these single-planet systems the planet is orbiting the star in very close proximity, but in others, the reason is that the systems may actually hold more planets that initially assumed. “In these cases we believe that the deviation from the rule can help us reveal more planets that were hidden up until now” Nanna Bach-Møller, first author of the scientific article explains. If we are able to see the extent of eccentricity of the planet orbit, then we know how many other planets must be in the system – and vice versa, if we have the number of planets, we now know their orbits. “This would be a very important tool for detecting planetary systems like our own solar system, because many exoplanets similar to the planets in our solar system would be difficult to detect directly, if we don’t know where to look for them”.

The Earth is among the lucky 1 percent

No matter which method is used in the search for exoplanets, one reaches the same result. So, there is basic, universal physics at play. The researchers can use this to say: How many systems possess the same eccentricity as our solar system? – which we can then use to assess how many systems have the same number of planets as our solar system. The answer is that there are only 1 % of all solar systems with the same number of planets as our solar system or more. If there are approximately 100 billion stars in the Milky Way, this is, however, still no less than one billion solar systems. There are approximately 10 billion Earth-like planets in the habitable zone, i.e. in a distance from their star allowing for the existence of liquid water. But there is a huge difference between being in the habitable zone and being habitable or having developed a technological civilization, Uffe Gråe Jørgensen stresses. “Something is the cause of the fact that there aren’t a huge amount of UFOs out there. When the conquest of the planets in a solar system has begun, it goes pretty quickly. We can see that in our own civilization. We have been to the Moon and on Mars we have several robots already. But there aren’t a whole lot of UFOs from the billions of Earth-like exo-planets in the habitable zones of the stars, so life and technological civilizations in particular are probably still fairly scarce”.

The Earth is not particularly special – the number of planets in the system is what it is all about

What more than being an Earth-size planet in the habitable zone does it take to harbor life? What is really so special here at our Earth and in our solar system? As planet considered, Earth is not special – there are plenty of Earth like planets out there.  But perhaps it could be the number of planets and the nature of them. There are many large gas planets in our solar system, half of all of them. Could it be that the existence of the large gas planets are the cause of our existence here on Earth? A part of that debate entails the question whether the large gas planets, Saturn and Jupiter, “directed” the comets to Earth carrying water when Earth was half a billion years old, enabling the forming of life here.

This is the first time a study has shown how unique it is for a solar system to be home to 8 planets, but at the same time showing that our solar system is not entirely unique. Our solar system follows the same physical rules for forming planets as any other solar system, we just happen to be in the unusual end of the scale. And we are still left with the question of why exactly we are here to be able to wonder about it.

Reference: “Orbital eccentricity–multiplicity correlation for planetary systems and comparison to the Solar system” by Nanna Bach-Møller and Uffe G Jørgensen, 30 October 2020, Monthly Notices of the Royal Astronomical Society.
DOI: 10.1093/mnras/staa3321

42 Comments on "Earth Is Among the Lucky 1%: The Solar System Follows the Galactic Standard – But It Is a Rare Breed"

  1. If there was a mirror civilization on a planet orbiting Tau Ceti some 12 light years away at the same level of technological development as we are currently on Earth, they could detect Jupiter (after a few years of study), probably Venus, maybe Earth, and possibly Saturn but only after a long period of time. So we’d say Sol has between 1 and 4 planets. Maybe we shouldn’t be saying 8 planets are atypical when we should be saying, we aren’t capable of resolving the population of planets in our own solar system from any other star system so we are for sure missing many planets out there.

  2. Our planet is also unique that it has a moon that is the perfect size and distance to stabilize our orbit and a powerful magnetic field.
    How many planets are in the habitable zone with those traits?

    • Torbjörn Larsson | December 1, 2020 at 10:30 am | Reply

      Rare Earth models seems daft to me, you can add or remove factors to get the result you want. Is it even testable?

      Specifically in your variant:

      – Why is the Moon stabilizing the orbit, according to the paper persented here moons ahev nothing to do with “the standard configuration” orbit behavior?

      I think you mean an earlier hypothesis that Moon stabilizes Earth tilt, but then again all terrestrial planets have small tilts with and without moons. (Especially if Venus, as it is believed, is retrograde spin because of spin braking towards tidal lock with Sun.)

      – From my own home turf more or less, I present to you:

      “On 13 November Moa Persson, Swedish Institute of Space Physics (IRF) and Umeå University, will defend her doctoral thesis. Her thesis shows that only a small part of the historical water content on Venus has been lost to space over the past 4 billion years. This is much less than researchers previously thought.”

      “The results of the thesis can be compared to similar studies of Mars and Earth. The comparisons between the three sibling planets give a more comprehensive picture of the solar wind effects on planetary atmospheres. For example Earth, with its strong magnetic field, has a larger loss of atmosphere to space than both Venus and Mars.”

      [“Surprisingly Little Water Has Escaped from Venus” @ Astrobiology]

      The magnetic field concentrates the solar wind atmosphere loss to the poles. Apparently experts can claim that the loss is larger than if you had no field.

      If you want to conclude that humans are unique, why not embrace Weinberg’s “anthropic” multiverse selection on the observed vacuum energy density? Planck collaboration 2018 cosmological survey observed the necessary slow roll inflation that produces it naturally (i.e. else you need to somehow prevent it) and eBOSS collaboration 2020 cosmological survey agreed on the cosmology parameters and shortlisted precisely Weinberg’s proposal.

    • Torbjörn Larsson | December 1, 2020 at 10:36 am | Reply

      I forgot: A middle position is to have Milky Way rare. It may be, it developed early but mildly (small mergers). “Family tree of the Milky Way deciphered” @ Phys Org; the paper makes the claim. (But only day after another group added a putative merger that show up in the core, which is larger – and made the opposite claim of a violent history. YMMV, this isn’t a settled area.)

  3. DAVID KYNASTON | December 1, 2020 at 5:56 am | Reply

    I remain unconvinced.

  4. Ceriah McDowell | December 1, 2020 at 6:25 am | Reply

    Interesting.f there was a mirror civilization on a planet orbiting Tau Ceti some 12 light years away at the same level of technological development as we are currently on Earth, they could detect Jupiter (after a few years of study), probably Venus, maybe Earth, and possibly Saturn but only after a long period of time.
    p.s im 12

  5. Torbjörn Larsson | December 1, 2020 at 10:13 am | Reply

    Very interesting discovery, if it stands up to scrutiny!

    The paper looks superficially good. It has a lot of data, they use both transit and radial method data which should eliminate line-of-sight bias (it seems to be there as an offset, but the transit trend, the radial trend and the sum trend is the same, see their figure 4), and they test the significance of the eccentricity factor. The power law fit looks nice, could be expected (most systems have few planets), and accords with earlier papers – my only nitpick is that they didn’t explicitly test if that was the best distribution to describe data (but simply says “Our best fit …”).

    The article discussion is sketchy. From the cited frequencies they make it sound like our system can be seen as one in 10, not one in 100, as in “habitable Earth-like planet in a 8 planet system”. And the UFO discussion makes no sense at all, we don’t yet know if interstellar travel is doable.

  6. This is an interesting article. Our planets configuration to me is yet another wonderful indication of just how beautifully special our miraculous planet is and how perfect it is for life. Our abundant fresh and salt water constantly moving to refresh itself, temperature controlling 24 hour spin, our season & tide controlling moon, our solar flare resistent magnetic field and even our peaceful milky way position persaud me that earth is a one in a billion planet at least. I am further convinced that earth is extremely special by the lack of radio signals detectable here here from space. It would be wonderful to make alien contact but even if we don’t because of articles like yours my mind will be filled with awe and wonder concerning our own home.

    JM

    • Torbjörn Larsson | December 2, 2020 at 6:43 pm | Reply

      I don’t want to rehash the entire comment I made in response to Theopilus with a similar “Rare Earth” model, but I note specifically that experts still question that a geodynamo field is protective:

      “The results of the thesis can be compared to similar studies of Mars and Earth. The comparisons between the three sibling planets give a more comprehensive picture of the solar wind effects on planetary atmospheres. For example Earth, with its strong magnetic field, has a larger loss of atmosphere to space than both Venus and Mars.”

      [“Surprisingly Little Water Has Escaped from Venus” @ Astrobiology]

      I also gave better reasons why the galaxy or the universe may have been suitable for us than the 1 % (or 10 % among habitable Earth massed planets) likelihood of Earth suggests.

      Or you can go the biology route and note that while life evolved early and diverse – so is an easy process – language capable species evolved one and late – so is “once in a blue moon” result.

  7. Abhira Fashaukahn | December 1, 2020 at 11:18 am | Reply

    The relativity of life? Is it typically???was something ’habitually’ underscored to a historical value for which
    when such answers are derivative to recognizing as ‘key’?
    Or are we to overcome destiny, with revelation towards meeting compulsory long awaited ‘belief’, of “ we are not alone”!!!

  8. Jesus died for you all,your loved
    Get a closer relationship with him
    GOD sees you

    • Torbjörn Larsson | December 2, 2020 at 6:45 pm | Reply

      Superstition.

      That the universe is observed to be flat gives us now a constraint for naturalness – average flat space over cosmological volumes means energy and work must sum to zero according to general relativity – and we can now see there are no ‘gods’ of ancient myths and current suoperstitions.

      • Dallas Morrison | January 24, 2021 at 10:32 am | Reply

        Don’t condemn as superstition something you do not understand or care to investigate.
        That is very condescending.
        God is beyond your comprehension. That does not mean He does not exist.
        I’ll pray for you. Maybe someday you will acquire faith and ask God to reveal Himself to you.

    • Dallas Morrison | January 24, 2021 at 10:37 am | Reply

      Amen!

  9. Dr. Daniel R. Thomas. Ph.D.. Math/Comp. Sci. , D.D. Counseling | December 2, 2020 at 3:51 am | Reply

    I am beginning to think that if indeed we are so unique and the odds of our existence are so greatly stacked against us, then our even being here cannot be an “accident.”

    I am lead to believe then that if life like ours is common throughout the Universe, it certainly should be detectable. But reality forces me to deal with the great “time machine” of the night sky. Those febal, flickering lights have taken millions (billions?) of years to travel from there to here. Perhaps when they started on their journey there was no “life like ours” behind it. But now, with so much time having passed, life like ours may be abundant – or may be extinct. Either way there is nothing we can really do about it. Perhaps our time is better spent caring for our neighbor right here? You know, feeding them, sheltering them, helping to provide a safe place to sleep … respectable work …
    You know? All those “little things” we just seem to take for granted?

    Just a thought.

    • An intellectual Greek mind | December 19, 2020 at 4:15 pm | Reply

      Excellent! Enjoyed your one and a million comment purposley directed to the only thing that should matter in this tumultuous time that everyone who has lived or died is responsible for the way human life is enduring its presence on this beautiful pale blue dot we are all responsible for the way it is Ghandi and Carl Sagan hit it out of the park when relaying their messages. Enjoyed reading your comment DDT phd

  10. Hello How are you

  11. “Something is the cause of the fact that there aren’t a huge amount of UFOs out there. When the conquest of the planets in a solar system has begun, it goes pretty quickly. We can see that in our own civilization. We have been to the Moon and on Mars we have several robots already. But there aren’t a whole lot of UFOs from the billions of Earth-like exo-planets in the habitable zones of the stars, so life and technological civilizations in particular are probably still fairly scarce”

    Well, one of the main arguments against UFO sightings being alien, is that it is too far for them to come here. Yet the above statement is implying alien civilisations are rare because we do not see UFOs everywhere. I don’t think you can have it both ways?

  12. Jon A Martinez | December 5, 2020 at 9:50 am | Reply

    As each solar system exists in its own relative place in the space time continuum, there will be infinite times and places where everything lines up for intelligent life to exist on different planets.
    When the infinitesimal numb of planets and space are taken into consideration, although the occurrences of diverse life on a given planet are unquestionably high, the possibility of them coming across our relative existence in the same space time continuum is basically 0%

  13. Sentient life is a cosmic once in 15 billion year-give or take-event. It takes that long for all the unlikely events to all line up even in the vastness of the number of galaxies and stars and planets for just the right conditions. Does this mean there was a “maker” No. we had better start looking after this place called Earth if we wish to survive as a species, because there is likely not another one like it, anywhere.

  14. Nice down play when there or over 40 billion Earths

  15. The writer of this article is apparently an idiot who doesn’t know there is only one solar system. Sol is the name of our star. You can refer to our system in several ways; The Solar System, our planetary system, our stellar system, or our star system. You can refer to systems other than ours in any of those ways EXCEPT as solar systems. None of the stars in those systems are named Sol! There is only one solar system!

  16. You mean the Enterprise isn’t real…???

  17. Robert Specht | January 9, 2021 at 7:45 pm | Reply

    Lucky 1%, What. The heavens and earth were. Reated by God for our benefit. Look to the heavens at his creation but live here and praise him what he is. The only one true God.

  18. The author is speaking in terms of today it seems. The strength of the sun’s varies with time, so we are the lucky ones now, but other planets ca be the lucky ones in our system let’s say a million years from now. Who knows?

  19. Sharon Belisle | February 2, 2021 at 2:14 pm | Reply

    I think that all there is an abundance of life in the Universe. I believe that life is part and part and parcel of an unimaginable large system that is all connected. I believe that consciousness resides over the whole system and we, humans are just a part of it. We are the “Great Creation” knowing and enjoying itself. Our task should we care to accept it is to enjoy the creation. On the way, we should help and take care of our fellows and all things as best as we can. I also believe that this Great Creation responds to you. Think positively and the Great Creation will respond positively. Think Negatively and the Great Creation will respond Negatively.

  20. Do to the betterment of earth before trumpeting hypothetical things about the universe.There a Supreme authority who revealed himself through his son Jesus Christ. Pride of all I know takes you nowhere. Thanks!

  21. Vickie L Gardner | February 16, 2021 at 12:20 pm | Reply

    I lean towards Zecharia Sitchin on the formation of our solar system. Sumerians obviously weren’t stupid.
    As for origins of life, the elemental makeup of the universe appears to be a self-assembling kit. Dust motes in outer space are coated with a brownish layer rich in organics. Clays on Earth tend to make amino acid precursors. The Urey/Miller experiment… nothing added but energy. The finding that certain lipid structures may replicate. Our life form, perhaps tuning to conditions specific to Earth, selected 20 amino acids out of several dozen possibilities to work with. There is plenty of room for diversity. The universe should be full of lifeforms.
    And, I happen to KNOW that others exist. In about 1951-53, at age 5-7, I was taken aboard an alien craft where a “tall gray” put a “bead” behind my left ear. It stayed there for many years. Scoff if you must, but this is my memory.

  22. Something is the cause of the fact that there aren’t a huge amount of UFOs out there. When the conquest of the planets in a solar system has begun, it goes pretty quickly. We can see that in our own civilization. We have been to the Moon and on Mars we have several robots already. But there aren’t a whole lot of UFOs from the billions of Earth-like exo-planets in the habitable zones of the stars, so life and technological civilizations in particular are probably still fairly scarce”.

    No offence but how would you or anyone know that? We can barely see other galaxies let alone very tiny spacecraft from billions of lightyears away. Our tech isn’t advanced enough to look at anything in detail. We only know somethings there when there’s a dip in the light.

    • Absolutely. Aliens are not a great example either since one, we don’t know their makeup. We assume they breath and drink water but the truth is they could be made of silicone and not breath or need water. Secondly we assume they are from another planetary system when they may have been earthlings all along. When we think about another systems distance it becomes apparent that the light travels slower than the human lifetime allows not to mention sustaining life there or back. Unless the UFO can travel much faster than light and or they live many hundreds of years, don’t need food, water, oxygen or fuel I just don’t fathom a journey so far. My guess and belief is they are a companion solar humanoid just a bit older and wiser than us.

  23. Regarding the lack of evidence of the existence of superior civilisations from other planets, it would seem logical that if the universe began with one event, the big bang, at one time, then no one part of it has a developmental advantage over another (no head start) and as we have such a long way to go still in developing the capability of detecting them, it looks like neither should any of the others have it yet.

  24. I have pondered the question many times and yes we being in the goldie locks zone is a primary in the equation but there are many variables, star type and size, moon, etc. Too many to list. Bringing UFOs or aliens into it really says little since we don’t really understand their biological make-up. They could be made of silicone and not need water or oxygen. Either way we are special in our own right but we need to preserve our planet or we won’t be around much longer.

  25. John Trowbridge | February 28, 2021 at 6:57 am | Reply

    Without advanced detection equipment or a means to travel fast enough to see or visit other solar systems we may never know if we are alone. In respects to the universe light is reletively slow compared to our lifespan and distance needed to get to any star outside our solar system. We don’t know what or who aliens are and for sale of any argument they may have been earthlings all along. Unless they found a way to travel through worm holes or black holes they would have spent most of their life just to travel from the nearest star (one way) at light speed.

  26. Porque es especial nuestro planeta tierra y todo el sistema solar? porque fue creado para nosotros el hombre,el ser humano, por nuestro creador Dios.no se desgasten dando vueltas y vueltas que de todas maneras caen dónde mismo.todo el universo se mueve por voluntad de Dios nuestro creador

  27. The answer to the statement, rather a question as to why we are here to wonder about it…is in short simply to acknowledge the fact that there is a Creator and to worship Him.
    “The Qur’an is different places states, such as: “Verily in the heavens and the earth are signs for those who believe. And in the creation of yourselves, and the fact that animals are scattered (through the earth), are signs for those of assured faith. And in the alternation of night and day, and that fact that Allah sends down sustenance from the sky, and revives therewith the earth after its death, and in the change of the winds, are signs for those who are wise.” (45:3-5).
    The Qur’an says that “the heavens and the earth were joined together as one unit, before We clove them asunder” (21:30). Following this big explosion, Allah “turned to the sky, and it had been (as) smoke. He said to it and to the earth: ‘Come together, willingly or unwillingly.’ They said: ‘We come (together) in willing obedience'” (41:11). Thus the elements and what was to become the planets and stars began to cool, come together, and form into shape, following the natural laws that Allah established in the universe.

    The Qur’an further states that Allah created the sun, the moon, and the planets, each with their own individual courses or orbits. “It is He Who created the night and the day, and the sun and the moon; all (the celestial bodies) swim along, each in its rounded course” (21:33).
    He it is Who created the heavens and the earth in six days, then established Himself on the Throne. He knows what enters within the heart of the earth, and what comes forth out of it, what comes down from heaven, and what mounts up to it. And He is with you wherever you may be. And Allah sees well all that you do” (57:4).

    The Qur’anic account of creation is in line with modern scientific thought about the development of the universe and life on earth.

  28. How do we know that Venus isn’t a proto-planet that has yet to develop? Didn’t early Earth in Archean times look similar?

  29. Seeing that scientists have calculated if you take every grain on sand on earth as comparison, there would be roughly 10000 stars per grain – so obviously even if our solar system was one in a million, the odds are still overwhelmingly in favor of life on other planets, and considering the mind blowing time perspective on top of that it seems near impossible that there are or have never been, or will never be other intelligent life out there. As others commented, there are many reasons why we haven’t found evidence, size of space, and time being the main ones.

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