Can rocky worlds exist between alien gas giants?

The article reports: "Because of the sheer amount of computational resources needed to fully simulate the planet-formation process in these hundreds of scenarios, the researchers adopted a statistical approach: They began their simulations with a protoplanetary disk (a rotating disk of gas and dust surrounding a newly formed star) composed of 500 Mars-mass embryonic protoplanets, and allowed them to collide, merge and splinter. The researchers found that even though the giant planets gobbled up most of the inventory of raw materials for planet making, there was still plenty of material left to make an Earth-size world. What's more, the gravitational influence of those massive worlds did not disrupt the planet-making process in between them, the team wrote in a paper recently published to the preprint database arXiv."

It is good to run simulations and then look for observations that may support the simulation in exoplanet studies. However, I note many of the computer models performing planet formation scenarios from the spinning, accretion disk model start out with larger bodies in the simulation vs. tiny dust grains that encounter the meter barrier problem. The meter barrier problem I find in my studies is not commonly reported to the public. Here is an example. Streaming instability on different scales - I. Planetesimal mass distribution variability, https://ui.adsabs.harvard.edu/abs/2021MNRAS.500..520R/abstract, January 2021.

My note. The meter barrier in protoplanetary disks models is still difficult to show growth from the very small to planetesimal size and planet size objects in the accretion disks models. The starting amount of dust and gas used in the spinning, protoplanetary disk in the simulations is a critical input parameter too. New observations of Elias 2-27 suggest the total disk mass could be 17% of the host star mass, https://skyandtelescope.org/astrono...y-unstable-disk-may-collapse-to-form-planets/

Applying 17% of the Sun's mass to a protoplanetary disk could change everything in the models. The Sun disk mass then could be greater than 57,000 earth masses initially. The prepint link provided in the article is good and helpful. https://arxiv.org/abs/2105.10105 "On the formation of terrestrial planets between two massive planets: The case of 55 Cancri,,,Considering the huge computational resources required by smoothed particle hydrodynamics (SPH) simulations and the overestimation of post-collision materials from perfect merging, we develop a statistical method to deal with collisions during the formation of planetary systems by introducing random material loss. In this method the mass and water content lost by the sole outcome from every merger vary randomly within a range dependent on the total mass and water content of colliding bodies. The application of the random loss method to the planet formation in the solar system shows a good consistency with existing SPH results. We also apply this method to the extrasolar planetary system 55 Cancri which hosts (at least) five planets and study the formation of terrestrial planets between the outermost two planets. A disk with 500 Mars mass embryos in dynamically cold orbits before the late-stage accretion phase is assumed. Scenarios with different amounts of planetary embryos and different loss parameters are adopted in our simulations. The statistical result from hundreds of simulations shows that an Earth-like planet with water inventory of roughly 6 Earth ocean could form between 55 Cnc f and d. It may reside between 1.0 and 2.6 AU but the most likely region extends from 1.5 to 2.1 AU. Thus the probability of this planet being in the potentially habitable zone (0.59--1.43 AU) is relatively low, only around 10\%. Planets 55 Cnc f and d could also be shaped and gain some water from giant impacts and consequently the orbits of them may also change accordingly."

Very interesting. 500 Mars mass embryos is about 54 earth masses in the disk used in the simulations.
 
Last edited:
  • Like
Reactions: sam85geo
Using our solar system as a model, it seems that when our Sun "turned on" the solar wind swept lighter gas and dust farther away than the rocky/heavy material that was close in. Hence, Mercury, Venus, Earth, Mars are the rocky planets that formed closest the Sun while the gas giants formed more distantly. Such might be usual operation for a dwarf main sequence star and contribute to long lasting rocky planets like Earth.
 
  • Like
Reactions: Catastrophe and rod
FYI, simulating the formation of the inner solar system planets, i.e. Mars, Earth, Venus, and Mercury is fraught with issues :)

The Effect of a Strong Pressure Bump in the Sun's Natal Disk: Terrestrial Planet Formation via Planetesimal Accretion Rather than Pebble Accretion, https://ui.adsabs.harvard.edu/abs/2021ApJ...915...62I/abstract, July 2021.

A very interesting 28 page report to study. "...The planetesimal formation efficiency in our model is treated as a free parameter. If planetesimal formation efficiency is sufficiently high near 0.5 au, terrestrial planetary embryos grow to large masses and should migrate to the disk inner edge becoming hot planets/super-Earths. All our simulations form planetesimals inside 0.4-0.5 AU, which is probably inconsistent with the current Solar System. We envision two potential solutions for this issue: i) the Solar System natal disk was hotter compared to our nominal disk model such that dust grains sublimated inside ∼0.5 au; ii) our assumed conditions for planetesimal formation to occur via gravitational collapse of over-dense clumps – created via zonal flows, vortices and streaming instability – are too generous and in fact it never took place inside ∼0.5 au because of local low Stokes number and/or dust-to-gas ratio."

Isotopically distinct terrestrial planets via local accretion, https://ui.adsabs.harvard.edu/abs/2021Icar..35414052M/abstract, January 2021. arXiv paper, https://arxiv.org/pdf/2008.08850.pdf, 20-August-2020, 18 pages. "3. Results and discussion...Most of the terrestrial planets produced in the simulations are generally less massive than the Earth and Venus, albeit with a few exceptions. Planet masses are also smaller when the depletion radius is closer to the Sun because the amount of mass available in the disc to form planets is smaller..."

If you dig into the computer models used to simulate the evolution of our solar system based upon the solar nebula and protoplanetary accretion disk, there is much to chew on, especially contemplating how we avoided complete destruction at the start :)
 

Latest posts