The “pressure bumps” in the sun’s protoplanetary disk explain many features of the solar system – ScienceDaily


Before the solar system had planets, the sun had rings – bands of dust and gas similar to Saturn’s rings – that likely played a role in the formation of the Earth, according to a new study.

“In the solar system, something happened to prevent Earth from becoming a much larger type of terrestrial planet called a super-Earth,” Rice University astrophysicist André Izidoro said, referring to the Massive rocky planets seen around at least 30% of sun-like stars in our galaxy.

Izidoro and his colleagues have used a supercomputer to simulate the formation of the solar system hundreds of times. Their model, which is described in a study published online in Nature Astronomy, produced rings like those seen around many distant young stars. It also faithfully reproduced several features of the solar system missed by many previous models, including:

  • An asteroid belt between Mars and Jupiter containing objects from the inner and outer solar system.
  • The stable and almost circular locations and orbits of Earth, Mars, Venus, and Mercury.
  • The masses of the inner planets, including Mars, that many models of the solar system overestimate.
  • The dichotomy between the chemical composition of objects in the inner and outer solar system.
  • A region of the Kuiper Belt made up of comets, asteroids, and small bodies beyond Neptune’s orbit.

The study by astronomers, astrophysicists and planetologists at Rice, the University of Bordeaux, the Southwest Research Institute in Boulder, Colorado and the Max Planck Institute for Astronomy in Heidelberg, Germany, builds on the latest astronomical research on infantile star systems.

Their model assumes that three bands of high pressure appeared in the young sun’s gas and dust disk. Such “pressure bumps” have been observed in stellar discs ringed around distant stars, and the study explains how the pressure bumps and rings might explain the architecture of the solar system, senior author Izidoro said. , a postdoctoral researcher from Rice who obtained his doctorate. training at the State University of Sao Paulo in Brazil.

“If super-Earths are super-common, why don’t we have any in the solar system?” Izidoro said. “We propose that the pressure bumps produce disconnected reservoirs of disk material in the inner and outer solar system and regulate the amount of material available to grow planets in the inner solar system.”

Pressure surges

For decades, scientists believed that the gas and dust in protoplanetary disks gradually became less dense, falling smoothly with distance from the star. But computer simulations show that planets are unlikely to form in smooth disk scenarios.

“In a smooth disc, all solid particles – dust grains or rocks – should be drawn inward very quickly and lost in the star,” said astronomer and study co-author Andrea Isella, associate professor of physics and astronomy at Rice. “Something is needed to stop them in order to give them time to become planets. “

When the particles move faster than the gas around them, they “sense a headwind and drift towards the star very quickly,” Izidoro explained. At pressure bumps, gas pressure increases, gas molecules move faster, and solid particles stop feeling a headwind. “This is what allows dust particles to build up at the pressure bumps,” he said.

Isella said astronomers observed pressure bumps and protoplanetary disc rings with the Atacama Large Millimeter / submillimeter Array, or ALMA, a massive 66-antenna radio telescope commissioned in Chile in 2013.

“ALMA is able to take very sharp images of young planetary systems that are still forming, and we have found that many protoplanetary disks of these systems are characterized by rings,” Isella said. “The effect of the pressure bump is that it collects dust particles, and that’s why we see rings. These rings are areas where you have more dust particles than in the spaces between the rings.

Ring formation

Izidoro and his colleagues’ model speculated that pressure bumps formed early in the solar system at three locations where particles falling toward the sun would have released large amounts of vaporized gas.

“It’s just a function of the distance from the star, because the temperature rises as you get closer to the star,” said geochemist and study co-author Rajdeep Dasgupta, Professor Maurice Ewing of earth systems science at Rice. “The point where the temperature is high enough for the ice to vaporize, for example, is a line of sublimation that we call the snow line. “

In the Rice simulations, pressure bumps at the silicate, water, and carbon monoxide sublimation lines produced three distinct rings. At the silicate line, the basic ingredient in sand and glass, silicon dioxide, became vapor. This produced the ring closest to the sun, where Mercury, Venus, Earth, and Mars will later form. The middle ring appeared at the snow line and the farthest ring at the carbon monoxide line.

Planetesimals and planets birth rings

Protoplanetary discs cool with age, so the lines of sublimation would have migrated towards the sun. The study showed that this process could allow dust to accumulate in asteroid-sized objects called planetesimals, which could then come together to form planets. Izidoro said previous studies assumed that planetesimals could form if the dust was concentrated enough, but no model offered a convincing theoretical explanation for how dust could accumulate.

“Our model shows that pressure bumps can concentrate dust, and moving pressure bumps can act like planetesimal factories,” Izidoro said. “We simulate the formation of planets by starting with grains of dust and spanning many different stages, from small grains the size of a millimeter to planetesimals and then to planets.”

Taking into account cosmochemical signatures, the mass of Mars and the asteroid belt

Many previous simulations of the solar system have produced versions of Mars up to 10 times more massive than Earth. The model correctly predicts that Mars has about 10% of Earth’s mass because “Mars was born in a low-mass region of the disk,” Izidoro said.

Dasgupta said the model also provides a compelling explanation for two of the solar system’s cosmochemical mysteries: the marked difference between the chemical compositions of objects in the inner and outer solar system, and the presence of each of these objects in the asteroid belt. between Mars and Jupiter.

Izidoro’s simulations showed that the central ring could explain the chemical dichotomy by preventing material from the external system from entering the internal system. The simulations also produced the asteroid belt in its correct location and showed that it was being fueled by objects from the inner and outer regions.

“The most common type of meteorite that we get from the asteroid belt is isotopically similar to Mars,” Dasgupta said. “André explains why Mars and these ordinary meteorites should have a similar composition. He provided a nuanced answer to this question.

Pressure and super-earth synchronization

Izidoro said that the delayed appearance of the sun’s central ring in some simulations led to the formation of super-Earths, which underscores the importance of the moment of pressure.

“By the time the pressure bump formed in these cases, a lot of mass had already invaded the internal system and was available to make super-Earths,” he said. “So, when this medium pressure bump formed could be a key aspect of the solar system.”

Izidoro is a postdoctoral associate researcher in the Department of Earth, Environmental and Planetary Sciences at Rice. Additional co-authors include Sean Raymond from the University of Bordeaux, Rogerio Deienno from the Southwest Research Institute and Bertram Bitsch from the Max Planck Institute of Astronomy. The research was supported by NASA (80NSSC18K0828, 80NSSC21K0387), the European Research Council (757448-PAMDORA), the Brazilian Federal Agency for the Support and Evaluation of Higher Education (88887.310463 / 2018-00) , the Welch Foundation (C-2035) and the National Planetology Program of the National Center for Scientific Research.


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