Properties Of Mercury, Venus, Earth And Mars Explained By Cosmic History

Eddie Gonzales Jr. – MessageToEagle.com – Astronomers have managed to link the properties of the inner planets of our solar system with our cosmic history: with the emergence of ring structures in the swirling disk of gas and dust in which these planets were formed.

The rings are associated with basic physical properties such as the transition from an outer region where ice can form where water can only exist as water vapor. The astronomers made use of a spread of simulation to explore different possibilities of inner planet evolution.

26 16 Share Email Home Astronomy & Space Planetary Sciences DECEMBER 30, 2021 Cosmic history can explain the properties of Mercury, Venus, Earth and Mars by Max Planck Society This is the sharpest image ever taken by ALMA — sharper than is routinely achieved in visible light with the NASA/ESA Hubble Space Telescope. It shows the protoplanetary disc surrounding the young star HL Tauri. These new ALMA observations reveal substructures within the disc that have never been seen before and even show the possible positions of planets forming in the dark patches within the system. Credit: ALMA (ESO/NAOJ/NRAO) Astronomers have managed to link the properties of the inner planets of our solar system with our cosmic history: with the emergence of ring structures in the swirling disk of gas and dust in which these planets were formed. The rings are associated with basic physical properties such as the transition from an outer region where ice can form where water can only exist as water vapor. The astronomers made use of a spread of simulation to explore different possibilities of inner planet evolution. Our solar system's inner regions are a rare, but possible outcome of that evolution. The results have been published in Nature Astronomy. The broad-stroke picture of planet formation around stars has been unchanged for decades. But many of the specifics are still unexplained—and the search for explanations an important part of current research. Now, a group of astronomers led by Rice University's Andre Izidoro, which includes Bertram Bitsch from the Max Planck Institute for Astronomy, has found an explanation for why the inner planets in our solar system have the properties we observe. A swirling disk and rings that change everything The broad-stroke picture in question is as follows: Around a young star, a "protoplanetary disk" of gas and dust forms, and inside that disk grow ever-larger small bodies, eventually reaching diameters of thousands of kilometers, that is: becoming planets. But in recent years, thanks to modern observational methods, the modern picture of planet formation has been refined and changed in very specific directions. The most striking change was triggered by a literal picture: The first image taken by the ALMA observation after its completion in 2014. The image showed the protoplanetary disk around the young star HL Tauri in unprecedented detail, and the most stunning details amounted to a nested structure of clearly visible rings and gaps in that disk. As the researchers involved in simulating protoplanetary disk structures took in these new observations, it became clear that such rings and gaps are commonly associated with "pressure bumps," where the local pressure is somewhat lower than in the surrounding regions. Those localized changes are typically associated with changes in disk composition, mostly in the size of dust grains. Three key transitions that produce three rings In particular, there are pressure bumps associated with particularly important transitions in the disk that can be linked directly to fundamental physics. Very close to the star, at temperatures higher than 1400 Kelvin, silicate compounds (think "sand grains") are gaseous—it is simply too hot for them to exist in any other state. Of course, that means that planets cannot form in such a hot region. Below that temperature, silicate compounds "sublimate," that is, any silicate gases directly transition to a solid state. This pressure bump defines an overall inner border for planet formation. Farther out, at 170 Kelvin (-100 degrees Celsius), there is a transition between water vapor on the one hand and water ice on the other hand, known as the water snowline. (The reason that temperature is so much lower than the standard 0 degrees Celsius where water freezes on Earth is the much lower pressure, compared to Earth's atmosphere.) At even lower temperatures, 30 Kelvin (-240 degrees Celsius), is the CO snowline; below that temperature, carbon monoxide forms a solid ice. Pressure bumps as pebble traps What does this mean for the formation of planetary systems? Numerous earlier simulations had already shown how such pressure bumps facilitate the formation of planetesimals—the small objects, between 10 and 100 kilometers in diameter, that are believed to be the building blocks for planets. After all, the formation process starts much, much smaller, namely with dust grains. Those dust grains tend to collect in the low-pressure region of a pressure bump, as grains of a certain size drift inwards (that is, towards the star) until they are stopped by the higher pressure at the inner boundary of the bump. As the grain concentration at the pressure bump increases, and in particular the ratio of solid material (which tends to aggregate) to gas (which tends to push grains apart) increases, it becomes easier for those grains to form pebbles, and for those pebbles to aggregate into larger objects. Pebbles are what astronomers call solid aggregates with sizes between a few millimeters and a few centimeters. The role of pressure bumps for the (inner) solar system But what had still be an open question was the role of those sub-structures in the overall shape of planetary systems, like our own Solar system, with its characteristic distribution of rocky, terrestrial inner planets and outer gaseous planets. This is the question that Andre Izidoro (Rice University), Bertram Bitsch of the Max Planck Institute for Astronomy and their colleagues took on. In their search for answers, they combined several simulations covering different aspects and different phases of planet formation. Specifically, the astronomers constructed a model of a gas disk, with three pressure bumps at the silicates-become-gaseous boundary and the water and CO snow lines. They then simulated the way that dust grains grow and fragment in the gas disk, the formation of planetesimals, the growth from planetesimals to planetary embryos (from 100 km in diameter to 2000 km) near the location of our Earth ("1 astronomical unit" distance from the sun), the growth of planetary embryos to planets for the terrestrial planets, and the accumulation of planetesimals in a newly-formed asteroid belt. In our own solar system, the asteroid belt between the orbits of Mars and Jupiter is home to hundreds of smaller bodies, which are believed to be remnants or collision fragments of planetesimals in that region that never grew to form planetary embryos, let alone planets. Variations on a planetary theme An interesting question for simulations is this: If the initial setup were just a little bit different, would the end result still be somewhat similar? Understanding these kinds of variations is important for understanding which of the ingredients are the key to the outcome of the simulation. That is why Bitsch and his colleagues analyzed a number of different scenarios with varying properties for the composition and for the temperature profile of the disk. In some of the simulations, they only the silicate and water ice pressure bumps, in others all three. The results suggest a direct link between the appearance of our solar system and the ring structure of its protoplanetary disk. Bertram Bitsch of the Max Planck Institute for Astronomy, who was involved both in planning this research program and in developing some of the methods that were used, says: "For me, it was a complete surprise how well our models were able to capture the development of a planetary system like our own—right down to the slightly different masses and chemical compositions of Venus, Earth and Mars." As expected, in those models, planetesimals in those simulations formed naturally near the pressure bumps, as a "cosmic traffic jam" for pebbles drifting inwards, which would then be stopped by the higher pressure at the inner boundary of the pressure bump. Recipe for our (inner) solar system For the inner parts of the simulated systems, the researchers identified the right conditions for the formation of something like our own solar system: If the region right outside the innermost (silicate) pressure bump contains around 2.5 Earth masses' worth of planetesimals, these grow to form roughly Mars-sized bodies—consistent with the inner planets within the solar system. A more massive disk, or else a higher efficiency of forming planetesimals, would instead lead to the formation of "super-Earths," that is, considerably more massive rocky planets. Those super-Earths would be in close orbit around the host star, right up against that innermost pressure bump boundary. The existence of that boundary can also explain why there is no planet closer to the sun than Mercury—the necessary material would simply have evaporated that close to the star. The simulations even go so far as to explain the slightly different chemical compositions of Mars on the one hand, Earth and Venus on the other: In the models, Earth and Venus indeed collect most of the material that will form their bulk from regions closer to the sun than the Earth's current orbit (one astronomical unit). The Mars-analogs in the simulations, in contrast, were built mostly from material from regions a bit farther away from the sun. How to build an asteroid belt Beyond the orbit of Mars, the simulations yielded a region that started out as sparsely populated with or, in some cases, even completely empty of planetesimals—the precursor of the present-day asteroid belt of our solar systems. However, some planetesimals from the zones inside of or directly beyond would later stray into the asteroid belt region and become trapped. As those planetesimals collided, the resulting smaller pieces would form what we today observe as asteroids. The simulations are even able to explain the different asteroid populations: What astronomers call S-types asteroids, bodies that are made mostly of silica, would be the remnants of stray objects originating in the region around Mars, while C-type asteroids, which predominantly contain Carbon, would be the remnants of stray objects from the region directly outside the asteroid belt. Outer planets and Kuiper belt In that outer region, just outside the pressure bump that marks the inner limit for the presence of water ice, the simulations show the beginning of the formations of giant planets—the planetesimals near that boundary typically have a total mass of between 40 and 100 times the mass of the Earth, consistent with estimates of the total mass of the cores of the giant planets in our solar system: Jupiter, Saturn, Uranus and Neptune. In that situation, the most massive planetesimals would quickly gather more mass. The present simulations did not follow up on the (already well-studied) later evolution of those giant planets, which involves an initially rather tight group, from which Uranus and Neptune later migrated outwards to their present positions. Last but not least, the simulations can explain the final class of objects, and its properties: so-called Kuiper-belt objects, which formed outside the outermost pressure bump, which marks the inner boundary for the existence of carbon monoxide ice. It even can explain the slight differences in composition between known Kuiper-belt objects: again as the difference between planetesimals that formed originally outside the CO snowline pressure bump and stayed there, and planetesimals that strayed into the Kuiper belt from the adjacent inner region of the giant planets. Two basic outcomes and our rare solar system Overall, the spread of simulations led to two basic outcomes: Either a pressure bump at the water-ice snowline formed very early; in that case, the inner and outer regions of the planetary system went their separate ways rather early on within the first hundred thousand years. This led to the formation of low-mass terrestrial planets in the inner parts of the system, similar to what happened in our own solar system. Alternatively, if the water-ice pressure bump forms later than that or is not as pronounced, more mass can drift into the inner region, leading instead to the formation of super-Earths or mini-Neptunes in the inner planetary systems. Evidence from the observations of those exoplanetary systems astronomers have found so far shows that case is by far the more probable—and our own Solar system a comparatively rare outcome of planet formation. Outlook In this research, the focus of the astronomers was on the inner solar system and the terrestrial planets. Next, they want to run simulations that include details of the outer regions, with Jupiter, Saturn, Uranus and Neptune. The eventual aim is to arrive at a complete explanation for the properties of ours and other solar systems. For the inner solar system, at least, we now know that key properties of Earth and its nearest neighboring planet can be traced to some rather basic physics: the boundary between frozen water and water vapor and its associated pressure bump in the swirling disk of gas and dust that surrounded the young sun. The results described here have been published as A. Izidoro et al., "Planetesimal rings as the cause of the Solar System's planetary architecture" in the journal Nature Astronomy. Explore further The orbital flatness of planetary systems Journal information: Nature Astronomy Provided by Max Planck Society Facebook Twitter Email Feedback to editors Featured Last Comments Popular Early humans gained energy budget by increasing rate of energy acquisition, not energy-saving adaptation 3 HOURS AGO 1 Ultraluminous X-ray sources in NGC 891 investigated by researchers 5 HOURS AGO 0 Skeleton of young man killed by ancient tsunami found on Turkish coast DEC 29, 2021 0 Distant quasar J0439+1634 explored in X-rays DEC 29, 2021 5 Experiments suggests archerfish can differentiate between numbers DEC 28, 2021 0 Possible chemical leftovers from early Earth sit near the core 17 MINUTES AGO Plasma lensing discovered in black widow pulsar 2 HOURS AGO Scientists design and construct minimized synthetic carbon fixation cycle 3 HOURS AGO Early humans gained energy budget by increasing rate of energy acquisition, not energy-saving adaptation 3 HOURS AGO Ultraluminous X-ray sources in NGC 891 investigated by researchers 5 HOURS AGO 2021: A year of space tourism, flights on Mars, China's rise 9 HOURS AGO Secrets of regulatory T cell development reveal clinical possibilities 21 HOURS AGO Relevant PhysicsForums posts How does the Poynting vector factor into a normal circuit? DEC 28, 2021 Getting a sauna to a certain temperature - faster with more rocks? DEC 28, 2021 Usage of First Order Elastic Constants in Soft Body Equations DEC 27, 2021 Can a static force do work? DEC 25, 2021 Why does a DC motor have a restricted speed? DEC 24, 2021 Work and friction DEC 21, 2021 More from Other Physics Topics 1 2 More news stories Possible chemical leftovers from early Earth sit near the core Let's take a journey into the depths of the Earth, down through the crust and mantle nearly to the core. We'll use seismic waves to show the way, since they echo through the planet following an earthquake and reveal its internal ... EARTH SCIENCES 18 MINUTES AGO 0 2 Early humans gained energy budget by increasing rate of energy acquisition, not energy-saving adaptation A team of researchers affiliated with multiple institutions in the U.S., the Institute for Advanced Study in Toulouse, France and the Max Planck Institute for Evolutionary Anthropology in Germany has found evidence that suggests ... EVOLUTION 3 HOURS AGO 1 265 Cosmic history can explain the properties of Mercury, Venus, Earth and Mars Astronomers have managed to link the properties of the inner planets of our solar system with our cosmic history: with the emergence of ring structures in the swirling disk of gas and dust in which these planets were formed. ... PLANETARY SCIENCES 2 HOURS AGO 0 42 Ultraluminous X-ray sources in NGC 891 investigated by researchers Researchers from the University of Chicago and Fordham University have conducted a long-term monitoring of three ultraluminous X-ray sources (ULXs) in the spiral galaxy NGC 891. Results of the research, presented in a paper ... ASTRONOMY 5 HOURS AGO 0 80 Plasma lensing discovered in black widow pulsar Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), a research team led by Dr. Wang Shuangqiang from the Xinjiang Astronomical Observatory (XAO) of the Chinese Academy of Sciences discovered plasma lensing ... ASTRONOMY 2 HOURS AGO 0 35 Scientists design and construct minimized synthetic carbon fixation cycle Scientists from the Institute of Microbiology of the Chinese Academy of Sciences (IMCAS) recently reported a minimized synthetic carbon fixation cycle. The cycle only contains four biochemical reactions and is capable of ... BIOCHEMISTRY 3 HOURS AGO 0 77 2021: A year of space tourism, flights on Mars, China's rise From the Mars Ingenuity helicopter's first powered flight on another world to the launch of the James Webb telescope that will peer into the earliest epoch of the Universe, 2021 was a huge year for humanity's space endeavors. PLANETARY SCIENCES 9 HOURS AGO 1 120 Secrets of regulatory T cell development reveal clinical possibilities Immunologists at St. Jude Children's Research Hospital have identified biochemical "switches" that control development of regulatory T cells and offer a novel strategy for treatment of autoimmune diseases and cancer. The ... CELL & MICROBIOLOGY 21 HOURS AGO 0 218 Distant quasar J0439+1634 explored in X-rays Using ESA's XMM-Newton spacecraft, an international team of astronomers has conducted X-ray observations of the most distant known gravitationally lensed quasar—J0439+1634. Results of the study, published December 20 on ... ASTRONOMY DEC 29, 2021 5 162 Skeleton of young man killed by ancient tsunami found on Turkish coast An international team of researchers has found and excavated the remains of a young man killed approximately 3,600 years ago by a tsunami created by the eruption of Thera—a volcano located on what is now the island of Santorini. ... ARCHAEOLOGY DEC 29, 2021 0 686 Nits on ancient mummies shed light on South American ancestry Human DNA can be extracted from the 'cement' head lice used to glue their eggs to hairs thousands of years ago, scientists have found, which could provide an important new window into the past. ARCHAEOLOGY DEC 29, 2021 0 239 Researchers capture high-frequency oscillations in the gigantic eruption of a neutron star An international scientific group with outstanding Valencian participation has managed to measure for the first time oscillations in the brightness of a magnetar during its most violent moments. In just a 10th of a second, ... ASTRONOMY DEC 28, 2021 26 1367 Drunken solution to the chaotic three-body problem The three-body problem is one of the oldest problems in physics: It concerns the motions of systems of three bodies—like the sun, Earth, and the moon—and how their orbits change and evolve due to their mutual gravity. ... ASTRONOMY DEC 28, 2021 5 1098 Research inspects very high energy emission from Messier 87 An international team of astronomers has investigated a very high energy (VHE) emission from the radio galaxy Messier 87. Results of the study, published December 16 on arXiv.org, could help us better understand the nature ... ASTRONOMY DEC 28, 2021 0 471 Experiments suggests archerfish can differentiate between numbers A trio of researchers at the University of Trento, in Italy, has found via experimentation that archerfish can distinguish between numbers. Davide Potrich, Mirko Zanon and Giorgio Vallortigara have published their study on ... ECOLOGY DEC 28, 2021 0 200 New data-decoding approach could lead to faster, smaller digital tech Most scientists would blanch at being labeled a spin doctor. But when it comes to Evgeny Tsymbal, Ding-Fu Shao and their colleagues, the lab coat fits. QUANTUM PHYSICS DEC 28, 2021 0 200 Medical Xpress Medical research advances and health news Tech Xplore The latest engineering, electronics and technology advances Science X The most comprehensive sci-tech news coverage on the web Newsletters Email Science X Daily and the Weekly Email Newsletter are free features that allow you to receive your favorite sci-tech news updates in your email inbox Follow us Top Home Search Mobile version Help FAQ About Contact Science X Account Sponsored Account Archive News wire Android app iOS app RSS feeds Push notification © Phys.org 2003 - 2021 powered by Science X Network Privacy policy Terms of use 1 / 1This is the sharpest image ever taken by ALMA — sharper than is routinely achieved in visible light with the NASA/ESA Hubble Space Telescope. It shows the protoplanetary disc surrounding the young star HL Tauri. These new ALMA observations reveal substructures within the disc that have never been seen before and even show the possible positions of planets forming in the dark patches within the system. Credit: ALMA (ESO/NAOJ/NRAO)

This is the sharpest image ever taken by ALMA — sharper than is routinely achieved in visible light with the NASA/ESA Hubble Space Telescope. It shows the protoplanetary disc surrounding the young star HL Tauri. These new ALMA observations reveal substructures within the disc that have never been seen before and even show the possible positions of planets forming in the dark patches within the system. Credit: ALMA (ESO/NAOJ/NRAO)

Our solar system’s inner regions are a rare, but possible outcome of that evolution.

The broad-stroke picture of planet formation around stars has been unchanged for decades. But many of the specifics are still unexplained—and the search for explanations an important part of current research. Now, a group of astronomers led by Rice University’s Andre Izidoro, which includes Bertram Bitsch from the Max Planck Institute for Astronomy, has found an explanation for why the inner planets in our solar system have the properties we observe.

A swirling disk and rings that change everything

The broad-stroke picture in question is as follows: Around a young star, a “protoplanetary disk” of gas and dust forms, and inside that disk grow ever-larger small bodies, eventually reaching diameters of thousands of kilometers, that is: becoming planets. But in recent years, thanks to modern observational methods, the modern picture of planet formation has been refined and changed in very specific directions.

The most striking change was triggered by a literal picture: The first image taken by the ALMA observation after its completion in 2014. The image showed the protoplanetary disk around the young star HL Tauri in unprecedented detail, and the most stunning details amounted to a nested structure of clearly visible rings and gaps in that disk.

As the researchers involved in simulating protoplanetary disk structures took in these new observations, it became clear that such rings and gaps are commonly associated with “pressure bumps,” where the local pressure is somewhat lower than in the surrounding regions. Those localized changes are typically associated with changes in disk composition, mostly in the size of dust grains.

Three key transitions that produce three rings

In particular, there are pressure bumps associated with particularly important transitions in the disk that can be linked directly to fundamental physics. Very close to the star, at temperatures higher than 1400 Kelvin, silicate compounds (think “sand grains”) are gaseous—it is simply too hot for them to exist in any other state. Of course, that means that planets cannot form in such a hot region. Below that temperature, silicate compounds “sublimate,” that is, any silicate gases directly transition to a solid state. This pressure bump defines an overall inner border for planet formation.

Farther out, at 170 Kelvin (-100 degrees Celsius), there is a transition between water vapor on the one hand and water ice on the other hand, known as the water snowline. (The reason that temperature is so much lower than the standard 0 degrees Celsius where water freezes on Earth is the much lower pressure, compared to Earth’s atmosphere.) At even lower temperatures, 30 Kelvin (-240 degrees Celsius), is the CO snowline; below that temperature, carbon monoxide forms a solid ice.

Pressure bumps as pebble traps

What does this mean for the formation of planetary systems? Numerous earlier simulations had already shown how such pressure bumps facilitate the formation of planetesimals—the small objects, between 10 and 100 kilometers in diameter, that are believed to be the building blocks for planets. After all, the formation process starts much, much smaller, namely with dust grains. Those dust grains tend to collect in the low-pressure region of a pressure bump, as grains of a certain size drift inwards (that is, towards the star) until they are stopped by the higher pressure at the inner boundary of the bump.

As the grain concentration at the pressure bump increases, and in particular the ratio of solid material (which tends to aggregate) to gas (which tends to push grains apart) increases, it becomes easier for those grains to form pebbles, and for those pebbles to aggregate into larger objects. Pebbles are what astronomers call solid aggregates with sizes between a few millimeters and a few centimeters.

The role of pressure bumps for the (inner) solar system

But what had still be an open question was the role of those sub-structures in the overall shape of planetary systems, like our own Solar system, with its characteristic distribution of rocky, terrestrial inner planets and outer gaseous planets. This is the question that Andre Izidoro (Rice University), Bertram Bitsch of the Max Planck Institute for Astronomy and their colleagues took on. In their search for answers, they combined several simulations covering different aspects and different phases of planet formation.

Specifically, the astronomers constructed a model of a gas disk, with three pressure bumps at the silicates-become-gaseous boundary and the water and CO snow lines. They then simulated the way that dust grains grow and fragment in the gas disk, the formation of planetesimals, the growth from planetesimals to planetary embryos (from 100 km in diameter to 2000 km) near the location of our Earth (“1 astronomical unit” distance from the sun), the growth of planetary embryos to planets for the terrestrial planets, and the accumulation of planetesimals in a newly-formed asteroid belt.

In our own solar system, the asteroid belt between the orbits of Mars and Jupiter is home to hundreds of smaller bodies, which are believed to be remnants or collision fragments of planetesimals in that region that never grew to form planetary embryos, let alone planets.

Variations on a planetary theme

An interesting question for simulations is this: If the initial setup were just a little bit different, would the end result still be somewhat similar? Understanding these kinds of variations is important for understanding which of the ingredients are the key to the outcome of the simulation. That is why Bitsch and his colleagues analyzed a number of different scenarios with varying properties for the composition and for the temperature profile of the disk. In some of the simulations, they only the silicate and water ice pressure bumps, in others all three.

The results suggest a direct link between the appearance of our solar system and the ring structure of its protoplanetary disk. Bertram Bitsch of the Max Planck Institute for Astronomy, who was involved both in planning this research program and in developing some of the methods that were used, says: “For me, it was a complete surprise how well our models were able to capture the development of a planetary system like our own—right down to the slightly different masses and chemical compositions of Venus, Earth and Mars.”

As expected, in those models, planetesimals in those simulations formed naturally near the pressure bumps, as a “cosmic traffic jam” for pebbles drifting inwards, which would then be stopped by the higher pressure at the inner boundary of the pressure bump.

Recipe for our (inner) solar system

For the inner parts of the simulated systems, the researchers identified the right conditions for the formation of something like our own solar system: If the region right outside the innermost (silicate) pressure bump contains around 2.5 Earth masses’ worth of planetesimals, these grow to form roughly Mars-sized bodies—consistent with the inner planets within the solar system.

A more massive disk, or else a higher efficiency of forming planetesimals, would instead lead to the formation of “super-Earths,” that is, considerably more massive rocky planets. Those super-Earths would be in close orbit around the host star, right up against that innermost pressure bump boundary. The existence of that boundary can also explain why there is no planet closer to the sun than Mercury—the necessary material would simply have evaporated that close to the star.

The simulations even go so far as to explain the slightly different chemical compositions of Mars on the one hand, Earth and Venus on the other: In the models, Earth and Venus indeed collect most of the material that will form their bulk from regions closer to the sun than the Earth’s current orbit (one astronomical unit). The Mars-analogs in the simulations, in contrast, were built mostly from material from regions a bit farther away from the sun.

How to build an asteroid belt

Beyond the orbit of Mars, the simulations yielded a region that started out as sparsely populated with or, in some cases, even completely empty of planetesimals—the precursor of the present-day asteroid belt of our solar systems. However, some planetesimals from the zones inside of or directly beyond would later stray into the asteroid belt region and become trapped.

As those planetesimals collided, the resulting smaller pieces would form what we today observe as asteroids. The simulations are even able to explain the different asteroid populations: What astronomers call S-types asteroids, bodies that are made mostly of silica, would be the remnants of stray objects originating in the region around Mars, while C-type asteroids, which predominantly contain Carbon, would be the remnants of stray objects from the region directly outside the asteroid belt.

Outer planets and Kuiper belt

In that outer region, just outside the pressure bump that marks the inner limit for the presence of water ice, the simulations show the beginning of the formations of giant planets—the planetesimals near that boundary typically have a total mass of between 40 and 100 times the mass of the Earth, consistent with estimates of the total mass of the cores of the giant planets in our solar system: Jupiter, Saturn, Uranus and Neptune.

In that situation, the most massive planetesimals would quickly gather more mass. The present simulations did not follow up on the (already well-studied) later evolution of those giant planets, which involves an initially rather tight group, from which Uranus and Neptune later migrated outwards to their present positions.

Last but not least, the simulations can explain the final class of objects, and its properties: so-called Kuiper-belt objects, which formed outside the outermost pressure bump, which marks the inner boundary for the existence of carbon monoxide ice. It even can explain the slight differences in composition between known Kuiper-belt objects: again as the difference between planetesimals that formed originally outside the CO snowline pressure bump and stayed there, and planetesimals that strayed into the Kuiper belt from the adjacent inner region of the giant planets.

Two basic outcomes and our rare solar system

Overall, the spread of simulations led to two basic outcomes: Either a pressure bump at the water-ice snowline formed very early; in that case, the inner and outer regions of the planetary system went their separate ways rather early on within the first hundred thousand years. This led to the formation of low-mass terrestrial planets in the inner parts of the system, similar to what happened in our own solar system.

Alternatively, if the water-ice pressure bump forms later than that or is not as pronounced, more mass can drift into the inner region, leading instead to the formation of super-Earths or mini-Neptunes in the inner planetary systems. Evidence from the observations of those exoplanetary systems astronomers have found so far shows that case is by far the more probable—and our own Solar system a comparatively rare outcome of planet formation.

Outlook

In this research, the focus of the astronomers was on the inner solar system and the terrestrial planets. Next, they want to run simulations that include details of the outer regions, with Jupiter, Saturn, Uranus and Neptune. The eventual aim is to arrive at a complete explanation for the properties of ours and other solar systems.

For the inner solar system, at least, we now know that key properties of Earth and its nearest neighboring planet can be traced to some rather basic physics: the boundary between frozen water and water vapor and its associated pressure bump in the swirling disk of gas and dust that surrounded the young sun.

Paper

A. Izidoro et al., “Planetesimal rings as the cause of the Solar System’s planetary architecture” in the journal Nature Astronomy.

Written by Eddie Gonzales Jr. – MessageToEagle.com Staf