Weird, newly theorized “eggshell planets” may possess ultra-thin outer layers with ultra-smooth surfaces unlike those seen in any world to date, a new study reports.
Astronomers may have already detected at least three eggshell planets, the scientists noted.
In the past 25 years or so, astronomers have confirmed the existence of more than 4,500 exoplanets, worlds orbiting other stars. Many of these worlds are not like any of the planets in the solar system. For example, so-called “hot Jupiters” are gas giants that orbit closer to their host stars than Mercury does to the sun.
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In the new study, the researchers wanted to investigate what might be possible in terms of a planet’s crackable outer layer, known as the fragile lithosphere. They modeled the different characteristics of a rocky planet and its Star could influence the thickness of its fragile lithosphere.
The new models predicted that worlds small, old, or far from their star would likely have thick, rigid outer layers. However, under the right circumstances, exoplanets could possess a fragile lithosphere only a few kilometers thick – so-called eggshell planets.
The extremely thin, fragile lithospheres of eggshell planets may not prove to be stiff enough to support high-altitude mountains, leading to relatively smooth surfaces. In addition, their outer layers may not prove to be strong enough to produce the dense and strong plaques necessary for tectonic plates, which causes continental drift and the formation of mountains on Earth.
“I like the idea that there are big rocky worlds with surfaces that can look completely different from what we’re used to because of these particular combinations of size, surface temperature, and age,” he said. said lead author of the study, Paul Byrne, a scientist in planet science at the University of Washington in St. Louis, told Space.com. “The possible types of planets are considerably beyond what we see in the solar system.”
The absence of plate tectonics suggests that eggshell planets may not prove to be habitable for life as we know it. Among other things, plate tectonics help ensure that the minerals that draw carbon from their air get trapped inside the Earth. As such, plate tectonics help control atmospheric levels of carbon dioxide, a gas that warms the planet, which helps prevent a planet from experiencing the kind of runaway. Greenhouse effect who dedicated Venus to a climate of hell.
“Plate tectonics help regulate the temperature of the Earth, which in turn helps it maintain relatively comfortable temperatures on the surface,” Byrne said. “We don’t know if plate tectonics is a necessity for a world to be considered habitable, but it certainly helps.”
The agitation of the magma in the mantle layer below the surface of the eggshell planets could cause some kind of deformation. “Places where the mantle comes up might stretch the top surface and places where mantle sinks might push parts of the crust together,” Byrne said. “But the style, the appearance, of this surface deformation probably wouldn’t resemble tectonic plates as we know them on Earth.”
Previous astronomical studies have detected at least three exoplanets that could be eggshell planets, Byrne said. Although scientists are far from directly imagining the surfaces of these eggshell planets, he noted that they could resemble the plains on Venus, which contain large expanses of lava but have little high relief, as the lithosphere is thin there due to scorching surface temperatures.
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It’s still unclear what effects major disturbances could have on eggshell planets, such as giant cosmic impacts, or the type of gravitational pull from a nearby body like a moon that drives tides to Earth.
“Our results suggest that anything that is capable of applying stress to this outer shell over long periods of time, such as tides, would not result in the types of structures we know of on other bodies in the solar system,” like fractures – think of from Europe broken and brittle icy shell, ”Byrne said, referring to Jupiter’s potentially habitable moon.
“Events such as impacts can generate fractures and topography, because at very short timescales even normally ductile rock will break apart, but over geological time our prediction is that any resulting topography will eventually disappear at as the rock flows to level again, ”Byrne added. . “Whether tides, impacts or other forces can generate sustained tectonic activity remains to be determined, but I guess not. “
Planned and future telescopes could help analyze exoplanets to see if they are eggshell worlds.
“What we have presented here is essentially a how-to guide or how-to manual,” Byrne said in a press release. “If you have a planet of a given size, a given distance from its star and a given mass, then with our results you can make estimates for a variety of other characteristics – including whether it may have plate tectonics. “
Scientists detailed their findings online Oct. 20 in the Journal of Geophysical Research: Planets.