Since Copernicus, scientists have been slowly moving the Earth away from its predetermined "center of the universe." Scientists now admit that the Sun is an ordinary star, not too hot, not too cold, not too bright, not too dim, located in a random place in an ordinary spiral galaxy. So when the Kepler telescope began its hunt for planets in 2009, scientists expected to find planetary systems that would resemble our solar system.
Instead, Kepler discovered the types of planets missing in our solar system. It turned out that there are many more exoplanets than we thought: from "hot Jupiters" (planets the size of Jupiter) to "super-earths" (massive solid planets that are larger than our own). Of the 1,019 confirmed planets and 4,178 candidates discovered to date, only one system resembles our own: with terrestrial planets near the star and giant planets a little further away.
“We have no idea why our solar system is different and we would like to get an answer,” planetary scientist Kevin Walsh of the Southwestern Research Institute in Colorado told Astrobiology magazine.
In an attempt to compare the Sun and its planets with the newfound stellar systems discovered by Kepler, a pair of astronomers suggested that as a young man, our solar system may have contained as many as four planets orbiting closer to the Sun than Venus, and that after a series of catastrophic collisions, only Mercury survived. …
“One of the problems in our solar system is that by Kepler's standards, Mercury is too far from the Sun,” said planetary scientist Katrin Volk of the University of British Columbia.
Wolf and her colleague Brett Gladman of the same university suggested that at the beginning of life, most stars are surrounded by "systems of tightly packed inner planets" (STIP). Over time, collisions destroy many of these planets, leaving them near 5-10% of the stars observed today.
But although only a few of the observed systems contain STIPs, Wolf believes that they once prevailed - and the Sun could be one such system, the original inner planets of which were destroyed.
“If the STIP formed easily, it could be possible to find them around all the stars, after which 90% of them were destroyed,” says Wolf.
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Walsh was not involved in this study, but welcomes Wolf's work in matching the solar system with other planetary systems through the use of models to search for invisible planets that may have been in the past.
“We can say that we have never thought about it before. We have always tried to match the planets that we saw, but not those that we did not see. Now we see it around other stars, so it's a good question."
Wolf and Gladman realized that a small number of STIPs could shed light on why our solar system is so different. A pair of scientists took 13 Kepler-observed systems that contain more than four inner planets and ran a 10-million-year-long simulation of them. On ten occasions, the minor planets experienced violent collisions that changed the structure of the planetary system. According to scientists, the remnants are likely to remain stable for more than 10 million years.
The team then ran another series of simulations over a long period of time to understand how systems evolved as they became more stable and how collisions were distributed over time. They found that half of the systems collided but showed no signs of disaster beforehand. Collisional systems remained stable for almost their entire life before the planets began to collide with each other.
Modeling showed that after 5 million years, approximately 5-10% of the STIPs in the sample still did not achieve stability. Since STIPs were only seen in 5-10% of planetary systems observed by Kepler, this could mean that they were all born with STIP, but 90% of STIPs were destroyed by the time Kepler observed them.
“If every star once had a STIP system, that would mean that we (the fashion designers) simply didn’t make it by the time the planets existed,” says Walsh. - We have always tried to build models to get our four solid planets, ignoring the possibility of three to five planets forming even more Earth inside the orbit of Mercury. It would be amazing!.
If everything were so, the Earth would cease to be a strange exception to the rules of planet formation, as random observations show. Instead, it would fit perfectly and would not require a special explanation for its existence. If the solar system - and the earth, therefore, is rare, this could affect the prevalence of life in the universe; but if it follows the usual processes of the formation of planetary systems, then there will be nothing so unusual about it.
Mercury has long been a problem for planetary scientists. In addition to being farther from the Sun than most planets seen by Kepler, Mercury is densely packed with heavy elements. One hypothesis regarding its strange composition includes a collision that swept away a light crust from the planet and left behind a dense layer of iron.
At the same time, models of the solar system returned too much material to explain Mercury alone. To form a single planet orbiting Mercury, simulations require an unusual gap - an artificial boundary - in the dust surrounding the young Sun, which would stretch nearly halfway to Earth's current orbit. If the gap stretched all the way to the star, as most scientists believe, this disk must have contained too much material.
If most planetary systems contained STIPs when they formed, the young solar system might have had one too. According to Wolf, such a scenario would eliminate the need for an artificial gap to the inner disk and would explain an iron-rich planet. The collisions would also allow for the dense composition of Mercury.
To test this possibility, Wolf and Gladman performed simulations that added four planets with masses of the Moon and orbits less than half the distance from the Earth to the Sun. These planets would not have affected the formation of Venus, Earth, and Mars for 500 million years, despite the collisions that took place between their solid neighbors. Kepler came to this scenario during the first simulations.
“It's not uncommon to have a couple of unstable planets and the others don't feel anything,” says Wolf.
As the small inner planets collided with each other, they met one of two destinies. In some cases, the mass of the colliding planets was shot out, but then consolidated into several bodies. In other, more destructive scenarios, less than 10% of the original mass remained, and the rest exploded into small pieces, spiraling towards a star or other planets. The difference often depends on how fast the planets are moving, colliding with each other; as with a car collision, high speed leads to great destruction.
Although Kepler's other observations of STIP systems showed that three or more large bodies were consolidated into one or two short-period planets, our solar system apparently wrecked to the end. We only have one survivor left.