Strange things happened in the outer Solar System when it was first born. Tea ice giants, Uranus and Neptune are the two main outermost planets of the family of our Sun, and in size, volume, composition and great distance from our Star, they are very similar. Both distant worlds are distinctly different from the quartet of small rocky inner planets (Mercury, Venus, Earth, and Mars), as well as from the duo of gas giant planets, Jupiter and Saturn. Ithese giants They are planets that contain elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur. Although the two planets should be nearly identical twins, they are not. In February 2020, a team of planetary scientists at the University of Zurich in Bern, Switzerland, told reporters that they believe they have discovered why.
“There are … notable differences between the two planets that require explanation,” commented Dr. Christian Reinhardt in February 2020. PlanetS Press Release. Dr. Reinhardt studied Uranus and Neptune with Dr. Alice Chau, Dr. Joachim Stadel, and Dr. Ravit Helled, who are all Planets members working at the University of Zurich, Institute of Computational Sciences.
Dr. Stadel commented in the same PlanetS press release that one of the notable differences between the two planets is that “Uranus and its main satellites are tilted about 97 degrees in the solar plane and the planet is effectively rotating retrograde with respect to the Sun”.
Also, the distant duo’s satellite systems are different. The main satellites of Uranus are in regular, inclined orbits with the planet, suggesting that they formed from a disk, similar to Earth’s Moon. By contrast, Triton, Neptune’s largest moon, is heavily tilted and is therefore considered a captured object. Triton also shows important similarities to the distant ice dwarf planet, Pluto, suggesting that the two may have been born in the same region: the Kuiper Belt which lies beyond the orbit of Neptune, and is the icy, dimly lit home to a myriad of comet nuclei, small minor planets, and other frozen bodies. Planetary scientists predict that in the future Triton’s orbit will break down to the point of colliding with its adoptive parent planet.
In addition to other differences, Uranus and Neptune can also differ with respect to heat fluxes and internal structure.
Ice giants
In astrophysics and planetary science, the term “ice” refers to volatile chemical compounds that have freezing points above 100 K. These compounds include water, ammonia, and methane, with freezing points of 273 K, 195 K, and 91 K, respectively. In the 1990s, scientists first realized that Uranus and Neptune are a different kind of giant planet, very different from the other two giant inhabitants of our Sun’s family, Jupiter and Saturn. The constituent compounds of the duo of ice giants they were solid when they were primarily incorporated into the two planets during their ancient formation, either directly as ice or encased in water ice. Currently, very little water on Uranus and Neptune remains in the form of ice. Instead, water exists primarily as a supercritical fluid at the temperatures and pressures within them.
The overall composition of the duo of ice giants it is only about 20% hydrogen and helium by mass. This differs significantly from the composition of the two gas giants in our Solar System. Jupiter and Saturn are more than 90% hydrogen and helium by mass.
Modeling the history of the formation of the terrestrial planets and gas giants that inhabit our Solar System is relatively straightforward. It is generally believed that the quartet of terrestrial planets was born as a result of collisions and mergers of planetesimals within protoplanetary accretion disk. Tea accretion disk that surrounded our newborn Sun was composed of gas and dust, and the extremely fine specks of dust possessed a natural “stickiness.” The tiny dust particles collided with each other and merged to form bodies that gradually grew in size, from the size of a pebble to the size of a rock, the size of the moon, and ultimately the size of the planet. The rocky and metallic planetesimals of the primordial Solar System served as the “seeds” from which the terrestrial planets grew. Asteroids are the lingering relics of this once abundant population of rocks and metals. planetsimals which eventually became Mercury, Venus, Earth, and Mars.
In contrast, the two gas giant planets in our own Solar System, as well as the extrasolar gas giants that surround the stars beyond our Sun, are believed to have evolved after the formation of solid nuclei that weighed about 10 times more mass than the other. Land. Therefore, the cores of gas giants, such as Jupiter and Saturn, formed as a result of the same process that produced the terrestrial planets:as they accumulate heavy gaseous envelopes of the ambient solar nebula over the course of a few to several million years. However, there are alternative models of nucleation based on the accumulation of pebbles that have been proposed more recently. Alternatively, some of the giant exoplanets may have arisen as a result of gravity. accretion disk instabilities.
The birth of Uranus and Neptune through a similar nucleus accretion process is much more complicated and troublesome. Escape velocity for the little primordial protoplanets (baby planets still in formation) located about 20 astronomical units (AU) from the center of our own Solar System it would have been comparable to their relative speeds. Those bodies crossing the orbits of Jupiter or Saturn could well have been sent on hyperbolic trajectories that shot them howling out of our Sun family entirely, and into the icy darkness of interstellar space. Alternatively, such bodies, trapped by the duo of gas giants, would likely have been augmented on Jupiter or Saturn, or thrown into distant cometary orbits beyond Neptune. One FOR it is equal to the average distance between the Earth and the Sun, which is approximately 93,000,000 miles.
Since 2004, despite the problematic modeling of their formation, many aliens ice giant Candidates have been observed orbiting distant stars. This suggests that they may be common inhabitants of our Milky Way.
Considering the orbital challenges of protoplanets located 20 FOR or more from the center of our Solar System, it is likely that Uranus and Neptune were born between the orbits of Jupiter and Saturn, before being gravitationally dispersed in the more distant, dark and frigid domains of the family of our Sun.
Two different worlds
“It is often assumed that both planets formed similarly,” noted Dr. Alice Chau in February 2020. PlanetS press release. This would likely explain their similar compositions, our Sun’s mean orbital distances, and its cognate masses.
But how do you explain their differences?
Our primordial Solar System was a “cosmic shooting gallery”, where impacts from colliding objects were frequent, and so are alien planetary systems beyond our Sun. For this reason, a catastrophic giant impact was previously proposed as the source of the mysterious differences between Uranus and Neptune. However, previous work only studied impacts on Uranus or was limited due to strong simplifications regarding impact calculations.
For the first time, the team of planetary scientists at the University of Zurich studied a range of different collisions in both of them Uranus and Neptune using high resolution computer simulations. Starting with a very similar pre-impact ice giants showed that the impact of a body with 1-3 times the mass of the Earth in both of them Uranus and Neptune can explain the differences.
In the case of Uranus, a grazing collision would tilt the planet but would not affect its interior. In dramatic contrast, a head-on collision in Neptune’s past would affect its interior, but would not form a disk. This is consistent with the absence of large moons in regular orbits as seen on Neptune. Such a catastrophic crash, which shook the deep interior of the traumatized planet, is also suggested by the increased heat flux observed from Neptune.
Future NASA and European Space Agency (ESA) missions to Uranus and Neptune may provide significant new limitations in these scenarios, improve our understanding of the formation of the Solar System, and also provide astronomers with a better understanding of exoplanets in this particular mass range.
“We clearly demonstrate that an initially similar formation pathway to Uranus and Neptune can result in the observed dichotomy in the properties of these fascinating outer planets,” Dr. Ravit Helled commented to the press in February 2020.
This research was published in the November 22, 2019 issue of the Monthly Notices from the Royal Astronomical Society (MNRAS) under the title “Fork in the history of Uranus and Neptune: the role of the giant planets”.
