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Five-planet Nice model
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Five-planet Nice model
The five-planet Nice model is a numerical model of the early Solar System that is a revised variation of the Nice model. It begins with five giant planets, the four that exist today plus an additional ice giant between Saturn and Uranus in a chain of mean-motion resonances.
After the resonance chain is broken, the five giant planets undergo a period of planetesimal-driven migration, followed by a period of orbital instability with gravitational encounters between planets similar to that in the original Nice model. During the instability the additional giant planet is scattered inward onto a Jupiter-crossing orbit and is ejected from the Solar System following an encounter with Jupiter. The model was first formally proposed in 2011 after simulations indicated that it was more likely to reproduce the current Solar System than a four-planet Nice model.
The following is a version of the five-planet Nice model that results in an early instability and reproduces a number of aspects of the current Solar System. Although in the past the giant planet instability has been linked to the Late Heavy Bombardment, a number of recent studies indicate that the giant planet instability occurred early. The Solar System may have begun with the giant planets in another resonance chain.
The Solar System ends its nebula phase with Jupiter, Saturn, and the three ice giants in a 3:2, 3:2, 2:1, 3:2 resonance chain with semi-major axes ranging from 5.5 – 20 AU. A dense disk of planetesimals orbits beyond these planets, extending from 24 AU to 30 AU. The planetesimals in this disk are stirred due to gravitational interactions between them, increasing the eccentricities and inclinations of their orbits. The disk spreads as this occurs, pushing its inner edge toward the orbits of the giant planets. Collisions between planetesimals in the outer disk also produce debris that is ground to dust in a cascade of collisions. The dust spirals inward toward the planets due to Poynting-Robertson drag and eventually reaches Neptune's orbit. Gravitational interactions with the dust or with the inward scattered planetesimals allow the giant planets to escape from the resonance chain roughly ten million years after the dissipation of the gas disk.
The planets then undergo a planetesimal-driven migration as they encounter and exchange angular momentum with an increasing number of planetesimals. A net inward transfer of planetesimals and outward migration of Neptune occurs during these encounters as most of those scattered outward return to be encountered again while some of those scattered inward are prevented from returning after encountering Uranus. A similar process occurs for Uranus, the extra ice giant, and Saturn, resulting in their outward migration and a transfer of planetesimals inward from the outer belt to Jupiter. Jupiter, in contrast, ejects most of the planetesimals from the Solar System, and as a result migrates inward. After 10 million years the divergent migration of the planets leads to resonance crossings, exciting the eccentricities of the giant planets and destabilizing the planetary system when Neptune is near 28 AU.
The extra ice giant is ejected during this instability. The extra ice giant enters a Saturn-crossing orbit after its eccentricity increases and is scattered inward by Saturn onto a Jupiter-crossing orbit. Repeated gravitational encounters with the ice giant cause jumps in Jupiter's and Saturn's semi-major axes, driving a step-wise separation of their orbits, and leading to a rapid increase of the ratio of their periods until it is greater than 2.3. The ice giant also encounters Uranus and Neptune and crosses parts of the asteroid belt as these encounters increase the eccentricity and semi-major axis of its orbit. After 10,000–100,000 years, the ice giant is ejected from the Solar System following an encounter with Jupiter, becoming a rogue planet. The remaining planets then continue to migrate at a declining rate and slowly approach their final orbits as most of the remaining planetesimal disk is removed.
The migrations of the giant planets and encounters between them have many effects in the outer Solar System. The gravitational encounters between the giant planets excite the eccentricities and inclinations of their orbits. The planetesimals scattered inward by Neptune enter planet-crossing orbits where they may impact the planets or their satellites The impacts of these planetesimals leave craters and impact basins on the moons of the outer planets, and may result in the disruption of their inner moons. Some of the planetesimals are jump-captured as Jupiter trojans when Jupiter's semi-major axis jumps during encounters with the ejected ice giant. One group of Jupiter trojans can be depleted relative to the other if the ice giant passes through it following the ice giant's last encounter with Jupiter. Later, when Jupiter and Saturn are near mean-motion resonances, other Jupiter trojans can be captured via the mechanism described in the original Nice model. Other planetesimals are captured as irregular satellites of the giant planets via three-body interactions during encounters between the ejected ice giant and the other planets. The irregular satellites begin with wide range of inclinations including prograde, retrograde, and perpendicular orbits. The population is later reduced as those in perpendicular orbits are lost due to the Kozai mechanism, and others are broken up by collisions among them. The encounters between planets can also perturb the orbits of the regular satellites and may be responsible for the inclination of Iapetus's orbit. Saturn's rotational axis may have been tilted when it slowly crossed a spin-orbit resonance with Neptune.
Many of the planetesimals are also implanted in various orbits beyond Neptune's orbit during its migration. While Neptune migrates outward several AU, the hot classical Kuiper belt and the scattered disk are formed as some planetesimals scattered outward by Neptune are captured in resonances, undergo an exchange of eccentricity vs inclination via the Kozai mechanism, and are released onto higher perihelion, stable orbits. Planetesimals captured in Neptune's sweeping 2:1 resonance during this early migration are released when an encounter with the ice giant causes its semi-major axis to jump outward, leaving behind a group of low-inclination, low-eccentricity objects in the cold classical Kuiper belt with semi-major axes near 44 AU. This process avoids close encounters with Neptune allowing loosely bound binaries, including 'blue' binaries, to survive. An excess of low-inclination plutinos is avoided due to a similar release of objects from Neptune's 3:2 resonance during this encounter. Neptune's modest eccentricity following the encounter, or the rapid precession of its orbit, allows the primordial disk of cold classical Kuiper belt objects to survive. If Neptune's migration is slow enough following this encounter the eccentricity distribution of these objects can be truncated by a sweeping mean-motion resonances, leaving it with a step near Neptune's 7:4 resonance. As Neptune slowly approaches its current orbit, objects are left in fossilized high-perihelion orbits in the scattered disk. Others with perihelia beyond Neptune's orbit but not high enough to avoid interactions with Neptune remain as a scattering objects, and those that remain in resonance at the end of Neptune's migration form the various resonant populations beyond Neptune's orbit. Objects that are scattered to very large semi-major axis orbits can have their perihelia lifted beyond the influences of the giant planets by the galactic tide or perturbations from passing stars, depositing them in the Oort cloud. If the hypothetical Planet Nine was in its proposed orbit at the time of the instability a roughly spherical cloud of objects would be captured with semi-major axes ranging from a few hundred to a few thousand AU.
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Five-planet Nice model
The five-planet Nice model is a numerical model of the early Solar System that is a revised variation of the Nice model. It begins with five giant planets, the four that exist today plus an additional ice giant between Saturn and Uranus in a chain of mean-motion resonances.
After the resonance chain is broken, the five giant planets undergo a period of planetesimal-driven migration, followed by a period of orbital instability with gravitational encounters between planets similar to that in the original Nice model. During the instability the additional giant planet is scattered inward onto a Jupiter-crossing orbit and is ejected from the Solar System following an encounter with Jupiter. The model was first formally proposed in 2011 after simulations indicated that it was more likely to reproduce the current Solar System than a four-planet Nice model.
The following is a version of the five-planet Nice model that results in an early instability and reproduces a number of aspects of the current Solar System. Although in the past the giant planet instability has been linked to the Late Heavy Bombardment, a number of recent studies indicate that the giant planet instability occurred early. The Solar System may have begun with the giant planets in another resonance chain.
The Solar System ends its nebula phase with Jupiter, Saturn, and the three ice giants in a 3:2, 3:2, 2:1, 3:2 resonance chain with semi-major axes ranging from 5.5 – 20 AU. A dense disk of planetesimals orbits beyond these planets, extending from 24 AU to 30 AU. The planetesimals in this disk are stirred due to gravitational interactions between them, increasing the eccentricities and inclinations of their orbits. The disk spreads as this occurs, pushing its inner edge toward the orbits of the giant planets. Collisions between planetesimals in the outer disk also produce debris that is ground to dust in a cascade of collisions. The dust spirals inward toward the planets due to Poynting-Robertson drag and eventually reaches Neptune's orbit. Gravitational interactions with the dust or with the inward scattered planetesimals allow the giant planets to escape from the resonance chain roughly ten million years after the dissipation of the gas disk.
The planets then undergo a planetesimal-driven migration as they encounter and exchange angular momentum with an increasing number of planetesimals. A net inward transfer of planetesimals and outward migration of Neptune occurs during these encounters as most of those scattered outward return to be encountered again while some of those scattered inward are prevented from returning after encountering Uranus. A similar process occurs for Uranus, the extra ice giant, and Saturn, resulting in their outward migration and a transfer of planetesimals inward from the outer belt to Jupiter. Jupiter, in contrast, ejects most of the planetesimals from the Solar System, and as a result migrates inward. After 10 million years the divergent migration of the planets leads to resonance crossings, exciting the eccentricities of the giant planets and destabilizing the planetary system when Neptune is near 28 AU.
The extra ice giant is ejected during this instability. The extra ice giant enters a Saturn-crossing orbit after its eccentricity increases and is scattered inward by Saturn onto a Jupiter-crossing orbit. Repeated gravitational encounters with the ice giant cause jumps in Jupiter's and Saturn's semi-major axes, driving a step-wise separation of their orbits, and leading to a rapid increase of the ratio of their periods until it is greater than 2.3. The ice giant also encounters Uranus and Neptune and crosses parts of the asteroid belt as these encounters increase the eccentricity and semi-major axis of its orbit. After 10,000–100,000 years, the ice giant is ejected from the Solar System following an encounter with Jupiter, becoming a rogue planet. The remaining planets then continue to migrate at a declining rate and slowly approach their final orbits as most of the remaining planetesimal disk is removed.
The migrations of the giant planets and encounters between them have many effects in the outer Solar System. The gravitational encounters between the giant planets excite the eccentricities and inclinations of their orbits. The planetesimals scattered inward by Neptune enter planet-crossing orbits where they may impact the planets or their satellites The impacts of these planetesimals leave craters and impact basins on the moons of the outer planets, and may result in the disruption of their inner moons. Some of the planetesimals are jump-captured as Jupiter trojans when Jupiter's semi-major axis jumps during encounters with the ejected ice giant. One group of Jupiter trojans can be depleted relative to the other if the ice giant passes through it following the ice giant's last encounter with Jupiter. Later, when Jupiter and Saturn are near mean-motion resonances, other Jupiter trojans can be captured via the mechanism described in the original Nice model. Other planetesimals are captured as irregular satellites of the giant planets via three-body interactions during encounters between the ejected ice giant and the other planets. The irregular satellites begin with wide range of inclinations including prograde, retrograde, and perpendicular orbits. The population is later reduced as those in perpendicular orbits are lost due to the Kozai mechanism, and others are broken up by collisions among them. The encounters between planets can also perturb the orbits of the regular satellites and may be responsible for the inclination of Iapetus's orbit. Saturn's rotational axis may have been tilted when it slowly crossed a spin-orbit resonance with Neptune.
Many of the planetesimals are also implanted in various orbits beyond Neptune's orbit during its migration. While Neptune migrates outward several AU, the hot classical Kuiper belt and the scattered disk are formed as some planetesimals scattered outward by Neptune are captured in resonances, undergo an exchange of eccentricity vs inclination via the Kozai mechanism, and are released onto higher perihelion, stable orbits. Planetesimals captured in Neptune's sweeping 2:1 resonance during this early migration are released when an encounter with the ice giant causes its semi-major axis to jump outward, leaving behind a group of low-inclination, low-eccentricity objects in the cold classical Kuiper belt with semi-major axes near 44 AU. This process avoids close encounters with Neptune allowing loosely bound binaries, including 'blue' binaries, to survive. An excess of low-inclination plutinos is avoided due to a similar release of objects from Neptune's 3:2 resonance during this encounter. Neptune's modest eccentricity following the encounter, or the rapid precession of its orbit, allows the primordial disk of cold classical Kuiper belt objects to survive. If Neptune's migration is slow enough following this encounter the eccentricity distribution of these objects can be truncated by a sweeping mean-motion resonances, leaving it with a step near Neptune's 7:4 resonance. As Neptune slowly approaches its current orbit, objects are left in fossilized high-perihelion orbits in the scattered disk. Others with perihelia beyond Neptune's orbit but not high enough to avoid interactions with Neptune remain as a scattering objects, and those that remain in resonance at the end of Neptune's migration form the various resonant populations beyond Neptune's orbit. Objects that are scattered to very large semi-major axis orbits can have their perihelia lifted beyond the influences of the giant planets by the galactic tide or perturbations from passing stars, depositing them in the Oort cloud. If the hypothetical Planet Nine was in its proposed orbit at the time of the instability a roughly spherical cloud of objects would be captured with semi-major axes ranging from a few hundred to a few thousand AU.