Most planets can exist for a long, long time, but they can not last forever. Hungry stars and violent planetary neighbors can completely destroy a world, while impacts and excessive volcanism can sterilize a habitable world by stripping the planet of its waters. There are also many theoretical ways that could mean the end of a planet, but we know that has not happened yet.
"Planets are dying all the time right in our galactic neighborhood," says Sean Raymond, a planetary modeler at the Laboratoire d 'Astrophysique de Bordeaux in Bordeaux, France, in his blog series How Planets Die . Raymond has explored a variety of ways in which planets could come to an end. While not all planets die, most eventually find their way to the morgue of the planet.
Earth's climate cycle plays an important role in ensuring that the planet is neither too hot nor too cold to sustain life. But it does not take much to bring the climate out of balance in a rocky world like Earth, triggering events that lead either to an incredibly hot planet or a snowball world.
On Earth, the temperature is regulated by the temperature amount of carbon dioxide in the atmosphere. Carbon dioxide and other greenhouse gases in the atmosphere (such as water, methane and nitrous oxide) act as a blanket and keep the planet warm by slowing down how much solar radiation escapes into space. When carbon dioxide accumulates in the atmosphere, it warms the planet's surface, making it rain more . The precipitate then removes some carbon dioxide from the atmosphere and deposits it in the carbonate rocks of the ocean floor, and the planet begins to cool.
When carbon dioxide accumulates more quickly in the atmosphere than can be absorbed in the rocks, something like increased volcanic activity can trigger a runaway greenhouse effect, for example. Temperatures can rise above the boiling point of water, which can be a problem for maintaining life, since all life, as we know it, requires water. Rising temperatures can also cause the atmosphere to escape into space. This removes the shield that deflects the sun's radiation from a planet and other stars.
"Greenhouse heating is a fact of life for an atmosphere and to some extent desirable," wrote Raymond. "But things can get out of hand."
The climate can not be killed only by heat. When a planet becomes cold enough, this body turns into a snowball world a rocky object covered in ice. Ice and snow are bright and reflect much of the heat of a star back into space, making the world even cooler. In a world of surface volcanoes, outbreaks can channel carbon dioxide and other gases back into the atmosphere and heat up the world again. When the snowball conditions occur on a planet lacking plate tectonics ̵
According to Raymond, all potentially life-sustaining planets are at risk . Climate catastrophe that can make a planet uninhabitable, but not completely destroy it.
Lava or Life
The tug of neighboring worlds can pull the orbit of a planet, thereby pressurizing the interior of the planet and increasing the heat of the middle layer of the Earth's mantle. This heat has to find a way to escape, and the most typical method is a volcano.
Volcanic activity can significantly affect a planet's environment. According to the University Society of Atmospheric Research gas and dust particles thrown into the atmosphere by a volcano can affect the atmosphere of a planet, cool the planet, and shade it from the incoming radiation. The eruption of Mount Tambora (19459005), the largest eruption in Earth's history, produced so much ashes in 1815 that global temperatures were lowered, turning 1816 into the so-called "year without a summer".
Volcanoes can also cause the opposite effect – global warming – as they release greenhouse gases into the atmosphere. Frequent and large volcanic eruptions could trigger a runaway greenhouse effect that would turn a habitable world like Earth into something more like Venus .
We do not have to look far for an example of real life volcanic world. Jupiter's moon Io is the most volcanically active body in the solar system, with hundreds of volcanoes erupting constantly. If the earth were dragged as heavily as Io is dragged by the gravity of Jupiter, the earth would have 10 times more volcanic activity than Io, according to Raymond.
Asteroids and icy comets are planetary "crumbs" This can cause significant problems for their neighbors, especially when hurled by ice and gas giants.
As the planets settle in their final orbits, their gravity tractors can move asteroids and comets. Some may be pushed into the outer reaches of the planetary system, while others may be thrown inward and ultimately collide with rocky worlds where life tries to develop.
In our outer solar system, Neptune's last movements pushed several comets inward as they settled in their permanent orbit and drove them from planet to planet until they reached Jupiter. Jupiter threw some of these icy bodies outward, others were hurled inward at a time known as Late Late Bombardment .
Today, the Earth is constantly collecting about 100 tonnes (90 tons) of interplanetary material in the form of dust every day. Objects larger than about 330 meters (100 meters) will surface only about every 10,000 years, while bodies larger than two-thirds of a mile will crash only once every 100,000 years, according to NASA ] Center for Near Earth Objects Studies .
When giant planets throw these destructive crumbs toward the sun, clashes and clashes occur more frequently. Medium sized objects can release dust and debris into the atmosphere, which can disturb the atmospheric processes. Huge impacts can have even worse effects, not only because of the devastation at zero, but also because they can throw enough debris to hit the winter which throws the planet into a mini-glacial period. After sufficient impacts had been shot down in a series, the climate effects could build on each other until they finally made the world uninhabitable.
Based on observations of planetary remains found at other stars, Raymond calculated that about 1 billion Earth-like planets in the galaxy would eventually be destroyed by a bombardment of asteroids.
A Bad Big Brother
As the most massive object in the solar system after the sun, Jupiter acts like a protective big brother . The smaller rocky planets are protected from debris, and giants in other worlds are likely to play the same role. However, if a gas giant like Jupiter becomes unstable, it could have devastating effects on the smaller worlds.
After star formation the disc of leftover material leads to planets. Gravity tractors from the gas and dust in the disc exert a force on the planets and can keep gas giants in line for the first million years. But once it's gone, the planets can more easily change their orbits. Because giant planets are much smaller than their stony siblings, their gravitational thrusts can make a significant difference in the orbit shift of smaller planets. But big worlds are not immune. Two huge planets can pull each other and even get extremely close to each other. According to Raymond, these giants rarely collide, instead of mutually grappling each other. At some point, some worlds could be wholly out of orbit and pushed into space to tie themselves to no stars .
Raymond calculated that about 5 billion rocky worlds were destroyed by gas giants. Most of the destruction was probably shortly after planet formation. A handful, however, probably occurred later in the life of the system after life had evolved. If only 1% of gas giants became unstable later in their planet life, it is possible that 50 million planetary systems have destroyed inhabited worlds by throwing them into their star.
Like planets, stars can end and their transformation can have drastic effects on the planets orbiting them.
For example, Red Dwarf Stars may take more than 100 million years to reach their long-term brightness, ten times longer than our Sun. Planets orbiting a red dwarf can be in the habitable zone for several million years, but as the star brightens, all life-sustaining water can evaporate under the higher temperatures.
But planets orbiting a hot red dwarf could still be alive. "We do not know if this process completely dehydrates planets or just removes some outer layers of the ocean," Raymond wrote. "If enough water is trapped inside a planet (it is believed that the surface of the Earth has the surface water in the mantle a few times), it could withstand the loss of its oceans by later blowing out new ones." It's a complex interplay between geology and astronomy the result is unknown – for now. " Raymond estimated that perhaps 100 billion planets had dried up by their red dwarf.
Sun-like stars give livable planets more time to hold on to the water, giving life a chance. But also the temperature of the sun changes and slowly gets brighter over billions of years. In a billion years, Raymond said, the planet will no longer be in the habitable zone. Water does not remain liquid on the earth's surface. Instead, the planet will go through a rapid greenhouse effect and ultimately look like Venus.
When a sun-like star becomes 10 billion years old, it will run out of hydrogen and it will be between 100 and 200 times its size. (Our sun is 4.5 billion years old, so we still have some time before this happens.) In the solar system, Venus and Mercury are swallowed by the star while the changing gravitational force of the sun is Mars and the Earth pushes out outer planets further. The earth is right on the edge and can either suffer the fate. About 4 billion rocky worlds are probably consumed by a slowly brightening star.
The most massive stars explode in fiery supernova after a relatively short lifetime of several million years. No planets were found around these massive stars, but that might be because there are so few massive stars to look for, and exoplanets are hard to find, Raymond wrote. In any case, planets around these huge stars are likely to be destroyed by the explosive death of the star.
This article was inspired by the series of astronomer Sean Raymond about How Planets
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