The orbits of the planets around the Sun have been the subject of much scientific debate. Their current orbital characteristics are well understood, but planetary orbits have evolved and changed since the formation of the solar system. Planetary migrations have been the most prominent idea in recent decades, suggesting that planetary interactions caused the young planets to migrate inward or outward from their original positions. Now a new theory suggests that an object with a mass of 2-50 Jupiters passing through the solar system could be the cause.
The evolution of planetary orbits is a complex process. The planets originally formed from a rotating disk of gas and dust around the young, hot sun. The phenomenon of conservation of angular momentum caused the material to form a plane, resulting in circular orbits in the same plane.
The latest image of Saturn from NASA's Hubble Space Telescope captures exquisite details of the ring system – which looks like a vinyl record with grooves representing the detailed structure within the rings – and atmospheric details that could previously only be captured by spacecraft exploring the distant visited the world. Hubble's Wide Field Camera 3 observed Saturn on June 20, 2019, when the planet came closest to Earth at a distance of about 845 million miles. This image is the second in an annual series of snapshots taken as part of the Outer Planets Atmospheres Legacy (OPAL) project. OPAL helps scientists understand the atmospheric dynamics and evolution of our solar system's gas giant planets. In the case of Saturn, astronomers can track changing weather patterns and other changes to identify trends. Image credits: NASA, ESA, A. Simon (GSFC), MH Wong (University of California, Berkeley) and the OPAL team
As the planets grew, interactions within the protoplanetary disk resulted in orbital migrations, in which the planets moved inward or outward. There were also gravitational interactions that caused significant changes in eccentricity and inclination, sometimes causing protoplanets to be ejected from the solar system. Tidal forces from the sun could also have changed the orbits.
While protoplanet ejections are thought to have been fairly common during the formation of the solar system, celestial objects have also occasionally visited us. These objects appear to have been rare and provide valuable insights into distant planetary systems. Oumuamua was discovered in 2017 and was the first confirmed interstellar visitor. It had an elongated shape and unusual acceleration, likely caused by outgassing or other non-gravitational forces. A recent paper suggests that such an interstellar visitor may have caused changes in the orbits of our cousins, planets.
An artist's impression of the interstellar comet 'Oumuamua as it heated up as it approached the Sun and outgassed hydrogen (white nebula), slightly changing its orbit. The most likely pancake-shaped comet is, other than dust grains, the first known object to visit our solar system from another star. (Image credit: NASA, ESA and STScI's Joseph Olmsted and Frank Summers)
The article was written by a team of scientists led by Garett Brown University of Toronto. They explore the nature of the gas giants' eccentricity and suggest that current theories are unlikely to explain the observations. Instead, they show that an object with 2 to 50 times the mass of Jupiter traveling through the solar system was a more likely cause. Their paper explains that a passing object with a perihelion distance (closest distance to the Sun) of less than 20 astronomical units and a hyperbolic excess velocity of less than 6 km/s-1 could explain the observations.
Their calculations suggest that the chance that an interstellar visitor could create the orbits we see today is 1 in 100, a probability far better than other theories. Using simulations and approximations of the visitor's characteristics, the team concludes that the theory is the most plausible to date.
Source: A substellar flyby that shaped the orbits of giant planets
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