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At Science Daily: Early planetary migration can explain missing planets

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Computer simulations by Rice University scientists and their collaborators are the first to integrate a model of planet formation and evolution that explains two puzzling observations of exoplanets orbiting distant stars: the rarity of worlds about 1.8 times larger than Earth and the near-identical size of adjacent planets in hundreds of planetary systems.

A new model that accounts for the interplay of forces acting on newborn planets can explain two puzzling observations that have cropped up repeatedly among the more than 3,800 planetary systems cataloged to date.

Plot of distribution of confirmed exoplanet masses. Note that Earth’s mass is about 0.003 Jupiter masses, or just to the left of the left-most column in the histogram.

One puzzle known as the “radius valley” refers to the rarity of exoplanets with a radius about 1.8 times that of Earth. NASA’s Kepler spacecraft observed planets of this size about 2-3 times less frequently than it observed super-Earths with radii about 1.4 times that of Earth and mini-Neptunes with radii about 2.5 times Earth’s. The second mystery, known as “peas in a pod,” refers to neighboring planets of similar size that have been found in hundreds of planetary systems. Those include TRAPPIST-1 and Kepler-223, which also feature planetary orbits of near-musical harmony.

“I believe we are the first to explain the radius valley using a model of planet formation and dynamical evolution that self-consistently accounts for multiple constraints of observations,” said Rice University’s André Izidoro, corresponding author of a study published this week in Astrophysical Journal Letters. “We’re also able to show that a planet-formation model incorporating giant impacts is consistent with the peas-in-a-pod feature of exoplanets.”

Izidoro, a Welch Postdoctoral Fellow at Rice’s NASA-fundedCLEVER Planets project, and co-authors used a supercomputer to simulate the first 50 million years of the development of planetary systems using a planetary migration model. In the model, protoplanetary disks of gas and dust that give rise to young planets also interact with them, pulling them closer to their parent stars and locking them in resonant orbital chains. The chains are broken within a few million years, when the disappearance of the protoplanetary disk causes orbital instabilities that lead two or more planets to slam into one another.

“The migration of young planets towards their host stars creates overcrowding and frequently results in cataclysmic collisions that strip planets of their hydrogen-rich atmospheres,” Izidoro said. “That means giant impacts, like the one that formed our moon, are probably a generic outcome of planet formation.”

The research suggests planets come in two “flavors,” super-Earths that are dry, rocky and 50% larger than Earth, and mini-Neptunes that are rich in water ice and about 2.5 times larger than Earth. Izidoro said new observations seem to support the results, which conflict with the traditional view that both super-Earths and mini-Neptunes are exclusively dry and rocky worlds.

Based on their findings, the researchers made predictions that can be tested by NASA’s James Webb Space Telescope. They suggest, for instance, that a fraction of planets about twice Earth’s size will both retain their primordial hydrogen-rich atmosphere and be rich in water.

Full article at Science Daily.

Planetary sizes, masses, and orbital distances from their host stars are found to not be uniformly distributed. Most exoplanets discovered so far are much more massive than Earth, larger in radius than Earth, and orbit much closer to their host star than Earth. None of these deviations from Earth-likeness would be advantageous for advanced life.

4 Replies to “At Science Daily: Early planetary migration can explain missing planets

  1. 1
    bornagain77 says:

    As to: “Planetary sizes, masses, and orbital distances from their host stars are found to not be uniformly distributed.”

    In regards to those findings, it is also interesting to note that these findings of planetary sizes, masses, and orbital distances not being ‘uniformly distributed’ blew up our old ‘frost line’ model of planetary formation.

    As the following 2013 article stated, “Before we ever discovered any [planets outside the solar system] we thought we understood the formation of planetary systems pretty deeply.” We had our frost line. We knew how solar systems formed. “It was a really beautiful theory,” he says. “And, clearly, thoroughly wrong.”,,,

    Our Very Normal Solar System Isn’t Normal Anymore by Robert Krulwich – May 07, 2013
    Excerpt: In astronomy class (for any of us who took astronomy) they talked about a “frost line.” That’s a line, some distance from the sun, where it gets too cold to make rocky planets.
    They said when a planetary system forms, the dust that’s closer in, on the hot side of that line, melts into rocky minerals, forming solid balls, like Earth and Mars.
    But farther out, on the frosty side, the dust stays gassy, mostly hydrogen compounds, swelling to gigantic size, like Jupiter, Saturn and Neptune.
    Distance from the sun sculpts the neighborhood. That’s why most planetary systems in the universe were supposed to look like us. Rocky planets in, gassy planets farther out.
    Then we looked. And what did we discover?
    Big gassy planets not where they should be. Instead of keeping their distance, and staying past the frost line, there are dozens and dozens of Jupiter-sized balls (big! really big!) tucked incredibly close to their star, squeezing so close, their “year,” their orbit, lasts only a few Earth days. They are in tighter than Mercury.
    Which means these once-cold planets are now, puzzlingly, hot. Astronomers call them “hot Jupiters,” because temperatures at their cloud tops can sizzle at 1,000 degrees Celsius.
    Or — and here’s a pattern that shows up very often — you’ll get not one, but two biggish Neptune-sized planets, like hungry twins, nuzzling together near their star. Very near.
    Or we find a bunch of rocky planets — larger than Earth, but definitely rocky — gathered in tight formation around a star (with orbits that last 3.7 days! 10.9 days! Would you feel the whip, like a roller coaster?) and they come in alternating sizes — large, then small, then large again, then small, then large … How odd.
    As of this month, we’ve discovered 884 planets, 692 planetary systems, 132 of them with more than one planet and, strange to tell, almost none of them look like us.,,,
    “Before we ever discovered any [planets outside the solar system] we thought we understood the formation of planetary systems pretty deeply.” We had our frost line. We knew how solar systems formed. “It was a really beautiful theory,” he says. “And, clearly, thoroughly wrong.”,,,
    “It really is something that I find deeply weird,” he (an astronomer) writes. “What does it all mean? I don’t know. I am certain that this single-minded emphasis on planets-in-habitable-zones is making people forget that there is still a lot of weird stuff happening out there and that we still don’t even understand the basics of how we ourselves got here.”

    And as this 2018 article noted, “as the menagerie of young planetary systems grows, researchers are struggling to square their observations with current theories on how our Solar System and others formed.”

    (2018) “But as the menagerie of young planetary systems grows, researchers are struggling to square their observations with current theories on how our Solar System and others formed. Such ideas have been in turmoil ever since astronomers started discovering planets around distant stars — a list that now numbers in the thousands. The Solar System has rocky planets near the Sun and giant gas balls farther out, but the panoply of exoplanets obeys no tidy patterns. And the rule book for world-building is getting more complicated as researchers find evidence of planets in the process of being born. Still, astronomers hope that witnessing such birth pangs will shed light on how all planetary systems, including our own, came to be. “We see all kinds of structure in these disks, even at very young ages,” says Follette. “Even younger than we classically thought planets should form.”
    – Rebecca Boyle, “These dusty young stars are changing the rules of planet-building” at Nature
    – per uncommon descent

    And as the following 2022 article stated, “Planetary scientists, forced to abandon decades-old models, now realize there may not be a grand unified theory of world-making — no single story that explains every planet around every star, or even the wildly divergent orbs orbiting our sun.”

    At Quanta: Astronomers Reimagine The Making Of The Planets – June 13, 2022
    Excerpt: Most of the stars harbor planets of their own. Astronomers have spotted thousands of these distant star-and-planet systems. But strangely, they have so far found none that remotely resemble ours. So the puzzle has grown harder: Why these, and why those?
    The swelling catalog of extrasolar planets, along with observations of distant, dusty planet nurseries and even new data from our own solar system, no longer matches classic theories about how planets are made. Planetary scientists, forced to abandon decades-old models, now realize there may not be a grand unified theory of world-making — no single story that explains every planet around every star, or even the wildly divergent orbs orbiting our sun.

    Even planet formation itself is now found to be have “non-traditional implications”,

    New study sheds new light on planet formation – July 4, 2012
    Excerpt: The study,, began with a curious and unexpected finding: Within three years, the cloud of dust circling a young star in the Scorpius-Centaurus stellar nursery simply disappeared.”The most commonly accepted time scale for the removal of this much dust is in the hundreds of thousands of years, sometimes millions,” said study co-author Inseok Song,,, “What we saw was far more rapid and has never been observed or even predicted. It tells us that we have a lot more to learn about planet formation.”,,, “Many astronomers may feel uncomfortable with the suggested explanations for the disappearance of the dust because each of them has non-traditional implications,” Song said, “but my hope that this line of research can bring us closer to a true understanding of how planets form.”

    As to, “That means giant impacts, like the one that formed our moon, are probably a generic outcome of planet formation.”

    Yet, even the ‘impact theory’ for how our moon supposedly formed is also found to be, by no means, ‘settled science’,

    Textbook theory of moon’s origin is challenged – Aug. 4, 2017
    Excerpt: In the past five years, a bombardment of studies has exposed a problem: The canonical giant impact hypothesis rests on assumptions that do not match the evidence. If Theia hit Earth and later formed the moon, the moon should be made of Theia-type material. But the moon does not look like Theia — or like Mars, for that matter. Down to its atoms, it looks almost exactly like Earth.

    How the Moon Supports the Privileged Planet Hypothesis – December 5, 2013
    Excerpt: Planetary scientists were optimistic that the Apollo missions would help decide among three leading hypotheses: capture, fission, and accretion. After Apollo, all three were rejected, leaving theorists without a theory until the “giant impact” hypothesis came along in the 1980s. Till recently, the scenario of a Mars-sized object striking the Earth at a glancing blow was hailed as accepted truth. TV documentaries animated the event handsomely, in vivid color. However, new observations have cast doubt on the (impact) idea.

    Thus, as we learn more, we find that we lack any coherent theories for how solar systems form, how planets themselves form, and we even lack a coherent theory for how our moon formed.

    Yet, despite having no coherent theories for how any of them formed, we find that our solar system, our planet, and even our moon, have to be almost exactly as they are or we would not even be here to talk about the fact that we have no coherent theories for how any of them came to be.

    “You might also think that these disparate bodies are scattered across the solar system without rhyme or reason. But move any piece of the solar system today, or try to add anything more, and the whole construction would be thrown fatally out of kilter. So how exactly did this delicate architecture come to be?”
    R. Webb – Unknown solar system 1: How was the solar system built? – New Scientist – 2009

    Is the Solar System Stable? By Scott Tremaine – 2011
    Excerpt: So what are the results? Most of the calculations agree that eight billion years from now, just before the Sun swallows the inner planets and incinerates the outer ones, all of the planets will still be in orbits very similar to their present ones. In this limited sense, the solar system is stable. However, a closer look at the orbit histories reveals that the story is more nuanced. After a few tens of millions of years, calculations using slightly different parameters (e.g., different planetary masses or initial positions within the small ranges allowed by current observations) or different numerical algorithms begin to diverge at an alarming rate. More precisely, the growth of small differences changes from linear to exponential:,,,
    As an example, shifting your pencil from one side of your desk to the other today could change the gravitational forces on Jupiter enough to shift its position from one side of the Sun to the other a billion years from now. The unpredictability of the solar system over very long times is of course ironic since this was the prototypical system that inspired Laplacian determinism.
    Fortunately, most of this unpredictability is in the orbital phases of the planets, not the shapes and sizes of their orbits, so the chaotic nature of the solar system does not normally lead to collisions between planets. However, the presence of chaos implies that we can only study the long-term fate of the solar system in a statistical sense, by launching in our computers an armada of solar systems with slightly different parameters at the present time—typically, each planet is shifted by a random amount of about a millimeter—and following their evolution. When this is done, it turns out that in about 1 percent of these systems, Mercury’s orbit becomes sufficiently eccentric so that it collides with Venus before the death of the Sun. Thus, the answer to the question of the stability of the solar system—more precisely, will all the planets survive until the death of the Sun—is neither “yes” nor “no” but “yes, with 99 percent probability.”

    Linked from Appendix C from Dr. Ross’s book, ‘Why the Universe Is the Way It Is’:
    Probability Estimates for the Features Required by Various Life Forms:
    Excerpt: Requirements to sustain intelligent physical life:
    Probability for occurrence of all 816 parameters approx. 10^-1333
    dependency factors estimate approx. 10^-324
    longevity requirements estimate approx. 10^45
    Probability for occurrence of all 816 parameters approx. 10^-1054
    Maximum possible number of life support bodies in observable universe approx. 10^22
    Thus, less than 1 chance in 10^1032 exists that even one such life-support body would occur anywhere in the universe without invoking divine miracle

    “If some god-like being could be given the opportunity to plan a sequence of events with the expressed goal of duplicating our ‘Garden of Eden’, that power would face a formidable task. With the best of intentions but limited by natural laws and materials it is unlikely that Earth could ever be truly replicated. Too many processes in its formation involve sheer luck. Earth-like planets could certainly be made, but each would differ in critical ways. This is well illustrated by the fantastic variety of planets and satellites (moons) that formed in our solar system. They all started with similar building materials, but the final products are vastly different from each other . . . . The physical events that led to the formation and evolution of the physical Earth required an intricate set of nearly irreproducible circumstances.”
    – Peter B. Ward and Donald Brownlee, Rare Earth: Why Complex Life is Uncommon in the Universe (New York: Copernicus, 2000)

    “Earth is a precious jewel possessing a rare combination of qualities that happen to make it almost perfect for sustaining life. Lucky Planet investigates the idea that good fortune, infrequently repeated elsewhere in the Universe, played a significant role in allowing the long-term life-friendliness of our home and that it is unlikely we will succeed in finding similarly complex life elsewhere in the Universe.”
    London astrobiologist – David Waltham, Lucky Planet: Why Earth is Exceptional — and What That Means for Life in the Universe (Basic Books, 2014), p. 1.)

    No Moon, no magnetic field, no life on Earth: study – April 2016
    Excerpt: Without the Moon, there would be no life on Earth, French scientists claim.
    The gravitational push-pull of the Moon on iron deep inside Earth keeps it hot and molten. And a liquid core is needed to generate a magnetic field, which forms a protective shield against blasts of particles from the Sun.
    Denis Andrault from Blaise Pascal University in Clermont-Ferrand, France, and colleagues propose the Earth’s heated interior should have dropped by about 3,000 ºC over the past four billion years or so, but has instead remained almost constant – all because of the Moon.

    etc.. etc..

  2. 2
    bornagain77 says:

    Of related note, ‘anomalies’ have recently been found in the Cosmic Microwave Background Radiation (CMBR), (anomalies that were recently discovered by the WMAP and Planck telescopes). Moreover, these ‘anomalies’ are found to ‘strangely’ line up with the earth and solar system,

    Here is an excellent clip from “The Principle” that explains these ‘anomalies’ in the CMBR, that ‘unexpectedly’ line up with the earth and solar system, in an easy to understand manner.

    Cosmic Microwave Background Proves Intelligent Design (disproves Copernican principle) (clip of “The Principle”) – video

    Moreover, as the following paper highlights, we find that Radio Astronomy now reveals a surprising rotational coincidence for Earth in relation to the quasar and radio galaxy distributions in the universe, “implying an apparent breakdown of the Copernican principle or its more generalization, cosmological principle, upon which the standard cosmological model is based upon”,,,

    A large anisotropy in the sky distribution of 3CRR quasars and other radio galaxies
    – Ashok K. Singal
    Astrophysics and Space Science volume 357, Article number: 152 (2015)
    We report the presence of large anisotropies in the sky distributions of powerful extended quasars as well as some other sub-classes of radio galaxies in the 3CRR survey, the most reliable and most intensively studied complete sample of strong steep-spectrum radio sources. The anisotropies lie about a plane passing through the equinoxes and the north celestial pole. Out of a total of 48 quasars in the sample, 33 of them lie in one half of the observed sky and the remaining 15 in the other half. The probability that in a random distribution of 3CRR quasars in the sky, statistical fluctuations could give rise to an asymmetry in observed numbers up to this level is only ?1 %. Also only about 1/4th of Fanaroff-Riley 1 (FR1) type of radio galaxies lie in the first half of the observed sky and the remainder in the second half. If we include all the observed asymmetries in the sky distributions of quasars and radio galaxies in the 3CRR sample, the probability of their occurrence by a chance combination reduces to ?2×10?5. Two pertinent but disturbing questions that could be raised here are—firstly why should there be such large anisotropies present in the sky distribution of some of the strongest and most distant discrete sources, implying inhomogeneities in the universe at very large scales (covering a fraction of the universe)? Secondly why should such anisotropies lie about a great circle decided purely by the orientation of earth’s rotation axis and/or the axis of its revolution around the sun? It seems yet more curious when we consider the other anisotropies, e.g., an alignment of the four normals to the quadrupole and octopole planes in the CMBR with the cosmological dipole and the equinoxes. Then there is the other recently reported large dipole anisotropy in the NVSS radio source distribution differing in magnitude from the CMBR dipole by a factor of four, and therefore not explained as due to the peculiar motion of the Solar system, yet aligned with the CMBR dipole which itself lies close to the line joining the equinoxes. Are these alignments a mere coincidence or do they imply that these axes have a preferential placement in the larger scheme of things, implying an apparent breakdown of the Copernican principle or its more generalization, cosmological principle, upon which the standard cosmological model is based upon?

    And it is these large scale structures of the universe, combined on top of the CMBR ‘anomalies’, which, amazingly, overturn the Copernican principle and strongly support the archaic ‘medieval’ Christian belief that the earth should be considered to have a ‘central’ position in the universe.

    As the following article, (with a illustration) explains,

    “Of course to have an exact position, (or what we would call an ‘exact center’ in the universe), we would need an X axis, a Y axis, and a Z axis, since that will give us three dimensions in Euclidean space. The CMB dipole and quadrupole gives us the X axis and Y axis but not a Z axis. Hence, the X and Y axis of the CMB provide a direction, but only an approximate position. That is why we have continually said that the CMB puts Earth “at or near the center of the universe.”
    For the Z-axis we depend on other information, such as quasars and galaxy alignment that the CMB cannot provide. For example, it has been discovered that the anisotropies of extended quasars and radio galaxies are aligned with the Earth’s equator and the North celestial pole (NCP)4.,,, Ashok K. Singal describes his shocking discovery in those terms:
    “What is intriguing even further is why such anisotropies should lie about a great circle decided purely by the orientation of earth’s rotation axis and/or the axis of its revolution around the sun? It looks as if these axes have a preferential placement in the larger scheme of things, implying an apparent breakdown of the Copernican principle or its more generalization, cosmological principle, upon which all modern cosmological theories are based upon.”
    – Ashok K. Singal4 “Is there a violation of the Copernican principle in radio sky,” Ashok K. Singal, Astronomy and Astrophysics Division, Navrangpura, Ahmedabad, India, May 17, 2103,..
    Signal states: “We can rule out at a 99.995% confidence level the hypothesis that these asymmetries are merely due to statistical fluctuations.”
    – illustration
    – article

    Thus, contrary to the presumption of atheistic materialists, (i.e. reductive materialists), far from the small temperature variations in the CMBR being a product of random quantum fluctuations, (as they presuppose within their inflation model), the small temperature variations in the CMBR combine with the ‘largest scale structures of the observable universe’ to reveal teleology, (i.e. a goal directed purpose, a plan, a reason), that specifically included the earth and solar system from the creation of the universe itself.,,, The earth and solar system, (from what our best science can now tell us), is not just the result of some random quantum fluctuation as atheists had erroneously presupposed within their inflation model.

    Genesis 1: 1-3
    In the beginning God created the heaven and the earth.
    And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters.
    And God said, Let there be light: and there was light.

    Proverbs 8:26-27
    While as yet He had not made the earth or the fields, or the primeval dust of the world. When He prepared the heavens, I was there, when He drew a circle on the face of the deep,

    Job 26:10
    He has inscribed a circle on the face of the waters at the boundary between light and darkness.

    i.e. From what our best science can now tell us, we are NOT merely ‘chemical scum’ as the late Stephen Hawking, (via the Copernican Principle), had once erroneously claimed,,,

    “The human race is just a chemical scum on a moderate-sized planet, orbiting around a very average star in the outer suburb of one among a hundred billion galaxies. We are so insignificant that I can’t believe the whole universe exists for our benefit.,,,”
    – Stephen Hawking – 1995 TV show, Reality on the Rocks: Beyond Our Ken,

    Supplemental note:

    Moreover, the Copernican Principle and/or the Principle of Mediocrity has now been overturned by both General Relativity and Quantum Mechanics, our two most powerful theories in science: (as well as by several other lines of scientific evidence)
    March 2022

  3. 3
    bornagain77 says:

    Of supplemental note:

    Rare Planetary System by Hugh Ross – June 12, 2017
    Excerpt: Thanks in large part to research on extrasolar planets, astronomers also know that every planet in the solar system fulfills a key role in making advanced life possible on Earth. Two Brazilian astronomers showed that even tiny adjustments in the orbits of Jupiter, Saturn, Uranus, and Neptune would prove catastrophic for life in our solar system.5 Regions beyond the precise orbital positions of Jupiter, Saturn, Uranus, and Neptune abound in destructive mean motion resonances. As it is, Uranus is close to a 7:1 resonance with Jupiter (where Jupiter would make exactly 7 orbits around the Sun for every single orbit of Uranus), a 2:1 resonance with Neptune, and a 3:1 resonance with Saturn. Meanwhile, Jupiter and Saturn are very close to 5:2 resonance. If any of the solar system gas giant planets’ orbital positions were to shift ever so slightly, that shift would destabilize the orbit of one or more of the eight planets in the solar system with catastrophic consequences for a long history of life on Earth.
    Three Canadian astronomers further demonstrated that the orbital positions of Venus, Earth, and Mars must be fine-tuned so as to break up mean motion resonances that could be damaging for life on Earth. They showed that even the orbital features of the Earth-Moon system must be fine-tuned for this purpose.6 The Earth-Moon system suppresses a resonance in Venus’ orbit that is generated from the orbital patterns of Jupiter, Saturn, Uranus, and Neptune. Unless the Earth-Moon system is configured the way it is, both Venus’ and Mercury’s orbits would destabilize and generate destructive chaos throughout the inner solar system.
    Every planet in our solar system and Earth’s Moon contribute to making advanced life possible on Earth. The solar system’s array of eight planets must be exactly the way it is. Have you thanked God today for Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune?

  4. 4
    relatd says:


    More disappointment. Planetary formation. Dust coalesces and becomes a planet? That’s it? Where did the dust come from? Especially enough to form a ball the size of a planet? And what held the dust in place? Gravity? I doubt it.

    In the early days, Earth’s moon was depicted as being flung away – hurled – into space from the molten ball of the early earth. Why would that happen? I doubt anyone knows. Why didn’t the Earth split in two instead?

    Maybe scientists should get a copy of Worlds in Collision by Immanuel Velikovsky (1950).

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