Most planets can exist for a long, long time, but they can not last forever. Hungry stars and violent planetary neighbors can completely destroy the world, while impacts and excessive volcanism can make a habitable world sterile by stripping the planet of its water. There are also many theoretical ways that could spell the planet's end but not, as far as we know.
"Planets die all the time right in our galactic neighborhood", Sean Raymond, a planetary modeler at Laboratoire d 'Astrophysique de Bordeaux in Bordeaux, France, wrote in his blog series about how planets die . Raymond has investigated many ways that planets might meet their end.
The Earth's climate cycle plays a major role in making sure that the planet is not too hot or too cold to sustain life.
On Earth, the temperature is regulated by the 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, keeping the planet warm by slowing down how much of the sun's radiation escapes back into space. When carbon dioxide builds in the atmosphere, it warms the surface of the planet, causing it to rain more . Rainfall then removes some of the carbon dioxide from the atmosphere and deposits it in the carbonate rocks on the sea floor, and the planet begins to cool.
If the carbon dioxide accumulates in the atmosphere faster than it can be reabsorbed in the rocks, because of something like increased volcanic activity, for example, it can trigger a runaway greenhouse effect. Temperatures can rise above the boiling point of water, which can be a problem for sustaining life, seeing as all life as we know it requires water. Rising temperatures can also allow the atmosphere to escape into space, removing the protective shield that deflects radiation from planet's sun and other stars.
"Greenhouse heating is a fact of life for an atmosphere, and it is desirable to some degree," Raymond wrote. "But things can get out of hand."
Heat is not the only way the climate can turn deadly. When a planet gets cold enough, that body turns into a snowball world a rocky object covered in ice. Ice and snow are bright and reflect a lot of a star's heat back into space, causing the world to cool down even further. On a world with surface volcanoes, eruptions can dump carbon dioxide and other gases back into the atmosphere, heating the world back up.
According to Raymond, all potentially life-bearing planets run the risk of but, if the snowball conditions occur on a planet that lacks plate tectonics ̵
Lava or life
The tug of neighboring worlds can pull on a planet's orbit, which puts pressure on the planet's interior and increases the heat. of the Earth's middle layer, the mantle. That heat must find a way to escape, and the most typical method is through a volcano.
Volcanic activity can significantly affect the environment of a planet. According to the University Corporation for Atmospheric Research gas and dust particles thrown into the atmosphere by a volcano can affect a planet's atmosphere, cooling the planet and shading it from incoming radiation. In 1815, the eruption of Mount Tambora the largest eruption in Earth's recorded history, threw so much ash that it lowered global temperatures, making 1816 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 a real-life example of a volcano world Jupiter's Moon Io is the most volcanically active body in the solar system, with hundreds of volcanoes that are continuously erupting. According to Raymond, according to Raymond, Earth was trapped as much as Io was tugged by the gravitational force of Jupiter.
Rocky asteroids and ice comets are planetary "crumbs" which can cause significant problems to their neighboring worlds, especially when they are thrown by ice and gas giants.
As the planets settle into their final orbits, their gravitational pullers can move asteroids and comets around. Some can be pushed into the outskirts of the planetary system, while others are hurled inward, eventually colliding with rocky worlds, where life may be trying to evolve.
In our outer solar system, the Neptune's final movements as it settled into its permanent orbit shoved multiple comets inward, passing them from planet to planet until they reached Jupiter. Late Heavy Bombardment .
Today, Earth is constantly accumulating about 100 tons (90 metric tons) of interplanetary material each day in the form of dust. Objects larger than about 330 feet (100 meters), crash down to the surface only about once every 10,000 years, while bodies larger than two-thirds of a mile (1 kilometer) crash down only once every 100,000 years, according to NASA's Center for Near Earth Objects Studies .
When giant planets are tossing these destructive crumbs toward the sun, collisions spike and impacts happen more often. Medium-sized objects can toss up dust and debris into the atmosphere, which can interfere with atmospheric processes. Giant impacts can cause even more dire effects, not only because of the devastation at ground zero, but also because they can throw up enough debris to cause an impact winter throwing the planet into a mini ice age.
Based on the observations of the planetary leftovers found around other stars, Raymond calculated that about 1 billion Earth-like planets In the galaxy will 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 Shielding the smaller rocky planets from the rubble, and giants around other worlds may play the same role. But if a gas giant like Jupiter were to become unstable, it could have a devastating effect on the smaller worlds around it.
After stars form, the disk of leftover material gives rise to planets. Gravitational tugs from the gas and dust in the disk exert a force on the planets and can keep gas giants in the first few million years. Once it is gone, however, the planets can change their orbits more easily. Because giant planets are much smaller than their rocky siblings, their gravitational pushes can make a significant difference in shifting the orbits of smaller planets. But large worlds are not immune; Two giant planets can be tug at each other, and may even pass very close to each other. According to Raymond, these giants rarely collide, instead of providing gravitational kicks to one another. Raymond calculated that roughly 5 billion rocky worlds have been destroyed by gas giants. Most of the destruction probably happened soon after the planets formed. However, a handful probably happened later in the system's lifetime, after life had time to evolve. If only 1% of the gas giants became unstable later in their planetary lifetime, then it's possible that 50 million planetary systems have destroyed the inhabited worlds by tossing them into their star.
Like planets, stars can come to an end, and their transformation can have drastic effects on the planets that orbit them.
Red dwarf stars for example, may take more than 100 million years to reach their long-term brightness, ten times longer than our sun. Planets orbiting a red dwarf may be within the habitable zone for several million years, but as the star grows brighter, any life-sustaining water can evaporate under higher temperatures.
But planets orbiting a hot, red dwarf could still sustain life. "We do not know if this process dries out the planets completely or just strips off some of the outer layers of the ocean," Raymond wrote. "If a planet has enough water trapped in its interior (Earth is thought to have a few times its surface water in the mantle), then it could withstand losing its oceans by later outgassing new ones. It's a complex interplay between geology and astronomy and the outcome is unknown – for now. " Raymond estimated that 100 billion planets may have been dried out by their red dwarf.
Sunlike-stars give habitable planets more time to spend on water, giving life a chance. But the sun's temperature is also changing, slowly brightening over billions of years. In a billion years, Raymond said the planet will no longer be in the habitable zone; water will no longer be liquid on Earth's surface. Instead, the planet will undergo a rapid greenhouse effect and eventually wind up looking like Venus.
When a sun-like star reaches 10 billion years old, it will run out of hydrogen and expand to somewhere between 100 and 200 times its current size (Our sun is 4.5 billion years old, so we have some time before this happens.) In the solar system, Venus and Mercury will be swallowed by the star while the sun's changing gravity will push Mars and the external planets farther out Earth is right on the edge and may suffer either fate. Roughly 4 billion rocky worlds are consumed by a slowly brightening star.
The most massive stars explode in the fiery supernova after a relatively short lifetime of a few million years. Raymond wrote that no massive stars have been found around the planets, but that might be because there are so few massive stars to search and exoplanets still hard to find. Either way, any planets around these giant stars will likely be destroyed by the star's explosive death.
This article was inspired by astronomer Sean Raymond's series on How Planets Die .
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