Studies of Other Solar Systems
If the development of planets preceded the genesis of stars other than the Sun, astronomers have long speculated. By removing the limitation of being able to analyze only one example, the finding of extrasolar planets—planets surrounding other stars—would assist explain their theories regarding the development of the Earth’s solar system.
Extrasolar planets were thought to be difficult to observe directly with telescopes situated on Earth because they are typically covered by the light from the stars they circle. Instead, efforts were made to indirectly observe them by noting the gravitational effects that they had on their parent stars.
For instance, small periodic changes in some aspects of the star’s radiation that were brought on by the planet pulling the star first toward and then away from the direction of Earth were observed. By observing the shift in a star’s apparent brightness as an extrasolar planet passes in front of it (transits), it is also possible to identify extrasolar planets indirectly.
After decades of looking for extrasolar planets, astronomers discovered three worlds orbiting PSR B1257+12, a fast-rotating neutron star, in the early 1990s. In 1995, the existence of a large planet orbiting the star 51 Pegasi was confirmed.
This was the first time a planet orbiting a less unusual, more sun-like star had been found. By the end of 1996, astronomers had inferred the existence of a number of additional planets orbiting other stars, but it wasn’t until 2005 that they were able to take the first direct images of what seemed to be an extrasolar planet. There are hundreds of known planetary systems.
These numerous discoveries included systems with enormous planets the size of multiple Jupiters orbiting their stars at closer distances than the planet Mercury is from the Sun. They looked to defy a fundamental principle of the formation process outlined above, which states that massive planets must form far enough from the hot core condensation to allow ice to condense.
Giant planets being able to form swiftly enough to leave a significant amount of matter in the disk-shaped solar nebula between them and their stars has been proposed as a possible answer to this conundrum. The planet may progressively spiral inward as a result of tidal interaction with this matter, halting after the star has consumed all of the disk material within that distance. Astronomers are divided on whether this mechanism is the best explanation for the observable facts, despite the fact that it has been demonstrated in computer simulations.
Additionally, as was said above with relation to the Earth’s solar system, the relatively high temperature that must have occurred in the area around the snow line during the planet’s formation is at odds with the enrichment of argon and molecular nitrogen that was discovered on Jupiter by the Galileo mission.
This study raises the possibility that the snow line is not absolutely necessary for the creation of massive planets. Ice availability is undoubtedly important for their evolution, but it’s possible that this ice formed very early, when the nebula’s midplane was less than 25 K. There may not have been enough material in the solar nebula at those distances for a massive planet to form, even though the snow line may have been much closer to the Sun at that time than Jupiter is today.
A decade or two after the initial findings, the majority of the extrasolar planets were found, and most of them had masses comparable to or higher than Jupiter. Astronomers will learn more about the formation and evolution of planetary systems, including the Sun’s, when methods for finding smaller planets are developed.