Eggshell planet

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An eggshell planet is a type of exoplanet characterized by its ultra-thin outer brittle layer and minimal topography. The term was introduced in scientific discussions to describe a subset of rocky exoplanets with specific geological and tectonic characteristics. These planets pose questions regarding their potential habitability due to the unlikelihood of them having plate tectonics. [1] [2] [3]

Contents

Characteristics

The defining characteristic of an eggshell planet is its exceptionally thin lithosphere. The lithosphere of a planet is the rigid outermost shell, and its thickness can influence various geological processes, including the formation of mountains and plate tectonics. The thickness of the lithosphere is determined by a myriad of factors including the planet's size, interior temperature, and composition. [1] [4] [5]

While plate tectonics is considered essential for maintaining Earth's habitability through temperature regulation, eggshell planets are thought to lack this process. This lack of tectonic activity is significant because plate tectonics is believed to be crucial for a planet's long-term habitability. [1] [4]

Discovery and research

Eggshell planets became a topic of interest following a series of studies examining the variety of exoplanets. Paul Byrne, an associate professor in the Department of Earth and Planetary Sciences at Washington University in St. Louis and a faculty fellow of the McDonnell Center for the Space Sciences, conducted the studies with his team. [6] Through extensive modeling, Byrne and his team ran thousands of simulations to understand the parameters affecting the lithospheric thickness of rocky exoplanets. [7] [8]

Their research identified surface temperature as the primary determinant of the lithosphere's thickness. Other influential factors include planetary mass, distance from its host star, and age. As per their models, planets that are small, old, or distant from their star are likely to possess thick, rigid lithospheres. However, under certain conditions, some planets might have lithospheres only a few kilometers thick, leading to the "eggshell" designation. [8] [3]

These planets may bear similarities to specific regions on Venus, known for its vast lava plains and minimal high-standing terrain due to its scorching surface temperatures resulting in a thin lithosphere. [7] [8]

Potential habitability

The primary concern regarding eggshell planets is their suitability for life. As these planets are believed to lack plate tectonics—a process that might be essential for a rocky planet's long-term habitability—their capacity to support life becomes questionable. While the research is still ongoing, initial findings suggest that the thin lithospheres on these worlds make them less ideal candidates when searching for Earth-like conditions elsewhere in the universe. [4] [9]

Future studies

Scientists are keen on studying eggshell planets further with the help of upcoming space telescopes. [7] These future missions may provide more detailed observations, confirming the geological characteristics and potentially shedding light on the actual number of such planets in the universe. By studying these unique planetary bodies, scientists aim to discern the uniqueness or commonality of Earth-like conditions in the cosmos. [2]

Related Research Articles

<span class="mw-page-title-main">Plate tectonics</span> Movement of Earths lithosphere

Plate tectonics is the scientific theory that Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since about 3.4 billion years ago. The model builds on the concept of continental drift, an idea developed during the first decades of the 20th century. Plate tectonics came to be accepted by geoscientists after seafloor spreading was validated in the mid-to-late 1960s.

<span class="mw-page-title-main">Crust (geology)</span> Outermost solid shell of astronomical bodies

In geology, the crust is the outermost solid shell of a rocky planet, dwarf planet, or natural satellite. It is usually distinguished from the underlying mantle by its chemical makeup; however, in the case of icy satellites, it may be distinguished based on its phase.

<span class="mw-page-title-main">Lithosphere</span> Outermost shell of a terrestrial-type planet or natural satellite

A lithosphere is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time scales of up to thousands of years or more. The crust and upper mantle are distinguished on the basis of chemistry and mineralogy.

<span class="mw-page-title-main">Subduction</span> A geological process at convergent tectonic plate boundaries where one plate moves under the other

Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the heavier plate dives beneath the second plate and sinks into the mantle. A region where this process occurs is known as a subduction zone, and its surface expression is known as an arc-trench complex. The process of subduction has created most of the Earth's continental crust. Rates of subduction are typically measured in centimeters per year, with rates of convergence as high as 11 cm/year.

<span class="mw-page-title-main">Sedimentary basin</span> Regions of long-term subsidence creating space for infilling by sediments

Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock. They form when long-term subsidence creates a regional depression that provides accommodation space for accumulation of sediments. Over millions or tens or hundreds of millions of years the deposition of sediment, primarily gravity-driven transportation of water-borne eroded material, acts to fill the depression. As the sediments are buried, they are subject to increasing pressure and begin the processes of compaction and lithification that transform them into sedimentary rock.

<span class="mw-page-title-main">Tectonics</span> Process of evolution of the earths crust

Tectonics are the processes that result in the structure and properties of the Earth's crust and its evolution through time.

<span class="mw-page-title-main">Rare Earth hypothesis</span> Hypothesis that complex extraterrestrial life is improbable and extremely rare

In planetary astronomy and astrobiology, the Rare Earth hypothesis argues that the origin of life and the evolution of biological complexity such as sexually reproducing, multicellular organisms on Earth required an improbable combination of astrophysical and geological events and circumstances.

<span class="mw-page-title-main">Oceanic crust</span> Uppermost layer of the oceanic portion of a tectonic plate

Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumulates. The crust overlies the rigid uppermost layer of the mantle. The crust and the rigid upper mantle layer together constitute oceanic lithosphere.

<span class="mw-page-title-main">Earth's mantle</span> A layer of silicate rock between Earths crust and its outer core

Earth's mantle is a layer of silicate rock between the crust and the outer core. It has a mass of 4.01×1024 kg (8.84×1024 lb) and thus makes up 67% of the mass of Earth. It has a thickness of 2,900 kilometers (1,800 mi) making up about 46% of Earth's radius and 84% of Earth's volume. It is predominantly solid but, on geologic time scales, it behaves as a viscous fluid, sometimes described as having the consistency of caramel. Partial melting of the mantle at mid-ocean ridges produces oceanic crust, and partial melting of the mantle at subduction zones produces continental crust.

<span class="mw-page-title-main">Earth's crust</span> Earths outer shell of rock

Earth's crust is its thick outer shell of rock, referring to less than 1% of the planets radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper part of the mantle. The lithosphere is broken into tectonic plates whose motion allows heat to escape the interior of the Earth into space.

<span class="mw-page-title-main">Planetary habitability</span> Known extent to which a planet is suitable for life

Planetary habitability is the measure of a planet's or a natural satellite's potential to develop and maintain environments hospitable to life. Life may be generated directly on a planet or satellite endogenously or be transferred to it from another body, through a hypothetical process known as panspermia. Environments do not need to contain life to be considered habitable nor are accepted habitable zones (HZ) the only areas in which life might arise.

<span class="mw-page-title-main">Super-Earth</span> Planet with a mass between Earth and Uranus

A Super-Earth is a type of exoplanet with a mass higher than Earth's, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17 times Earth's, respectively. The term "super-Earth" refers only to the mass of the planet, and so does not imply anything about the surface conditions or habitability. The alternative term "gas dwarfs" may be more accurate for those at the higher end of the mass scale, although "mini-Neptunes" is a more common term.

A river anticline is a geologic structure that is formed by the focused uplift of rock caused by high erosion rates from large rivers relative to the surrounding areas. An anticline is a fold that is concave down, whose limbs are dipping away from its axis, and whose oldest units are in the middle of the fold. These features form in a number of structural settings. In the case of river anticlines, they form due to high erosion rates, usually in orogenic settings. In a mountain building setting, like that of the Himalaya or the Andes, erosion rates are high and the river anticline's fold axis will trend parallel to a major river. When river anticlines form, they have a zone of uplift between 50-80 kilometers wide along the rivers that form them.

<span class="mw-page-title-main">Geodynamics of terrestrial exoplanets</span>

The discovery of extrasolar Earth-sized planets has encouraged research into their potential for habitability. One of the generally agreed requirements for a life-sustaining planet is a mobile, fractured lithosphere cyclically recycled into a vigorously convecting mantle, in a process commonly known as plate tectonics. Plate tectonics provide a means of geochemical regulation of atmospheric particulates, as well as removal of carbon from the atmosphere. This prevents a “runaway greenhouse” effect that can result in inhospitable surface temperatures and vaporization of liquid surface water. Planetary scientists have not reached a consensus on whether Earth-like exoplanets have plate tectonics, but it is widely thought that the likelihood of plate tectonics on an Earth-like exoplanet is a function of planetary radius, initial temperature upon coalescence, insolation, and presence or absence of liquid-phase surface water.

<span class="mw-page-title-main">Superhabitable planet</span> Hypothetical type of planet that may be better-suited for life than Earth

A superhabitable planet is a hypothetical type of exoplanet or exomoon that may be better suited than Earth for the emergence and evolution of life. The concept was introduced in 2014 by René Heller and John Armstrong, who have criticized the language used in the search for habitable planets and proposed clarifications. According to Heller and Armstrong, knowing whether or not a planet is in its host star's habitable zone (HZ) is insufficient to determine its habitability: It is not clear why Earth should offer the most suitable physicochemical parameters to living organisms, as "planets could be non-Earth-like, yet offer more suitable conditions for the emergence and evolution of life than Earth did or does." While still assuming that life requires water, they hypothesize that Earth may not represent the optimal planetary habitability conditions for maximum biodiversity; in other words, they define a superhabitable world as a terrestrial planet or moon that could support more diverse flora and fauna than there are on Earth, as it would empirically show that its environment is more hospitable to life.

<span class="mw-page-title-main">Earth's crustal evolution</span>

Earth's crustal evolution involves the formation, destruction and renewal of the rocky outer shell at that planet's surface.

Heat-pipe tectonics is a cooling mode of terrestrial planets and moons in which the main heat transport mechanism in the planet is volcanism through the outer hard shell, also called the lithosphere. Heat-pipe tectonics initiates when volcanism becomes the dominant surface heat transfer process. Melted rocks and other more volatile planetary materials are transferred from the mantle to surface via localised vents. Melts cool down and solidify forming layers of cool volcanic materials. Newly erupted materials deposit on top of and bury older layers. The accumulation of volcanic layers on the shell and the corresponding evacuation of materials at depth cause the downward transfer of superficial materials such that the shell materials continuously descend toward the planet's interior.

Diana Valencia is a Colombian planetary scientist and astrophysicist. She is an associate professor of Physics and Astrophysics, University of Toronto, Scarborough, and of Astronomy & Astrophysics, University of Toronto.

<span class="mw-page-title-main">Exoplanet interiors</span> Exoplanet internal structure

Over the years, our ability to detect, confirm, and characterize exoplanets and their atmospheres has improved, allowing researchers to begin constraining exoplanet interior composition and structure. While most exoplanet science is focused on exoplanetary atmospheric environments, the mass and radius of a planet can tell us about a planet's density, and hence, its internal processes. The internal processes of a planet are partly responsible for its atmosphere, and so they are also a determining factor in a planet's capacity to support life.

References

  1. 1 2 3 Gough, Evan (2021-11-18). "Eggshell Planets Have a Thin Brittle Crust and No Mountains or Tectonics". Universe Today. Retrieved 2023-08-08.
  2. 1 2 "Eggshell Exoplanets: Rocky Worlds with Ultra-Thin Brittle Lithospheres Could Theoretically Exist | Sci.News". Sci.News: Breaking Science News. 2021-11-11. Retrieved 2023-08-08.
  3. 1 2 "'Eggshell Planets' -- Earth-like exoplanets orbiting distant stars". Brighter Side News. 2021-11-11. Retrieved 2023-08-08.
  4. 1 2 3 Ogliore, Talia (2021-11-11). "'Eggshell planets' are probably not right for life". Futurity. Retrieved 2023-08-08.
  5. ↑ "Scientists discover 'eggshell' planets with brittle crust and smooth exteriors". Rapid City Journal. 2021-11-15. Retrieved 2023-08-08.
  6. ↑ https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2021JE006952
  7. 1 2 3 Q. Choi, Charles (2021-11-29). "Strange 'eggshell' exoplanets may have ultra-smooth surfaces". Space.com. Retrieved 2023-08-08.
  8. 1 2 3 Starr, Michelle (2021-11-15). "These Strange, Brittle 'Eggshell' Exoplanets Could Be Orbiting Alien Stars". ScienceAlert. Retrieved 2023-08-08.
  9. ↑ "Bizarre, brittle exoplanets could feel like walking on alien eggshells". SYFY Official Site. 2021-11-17. Retrieved 2023-08-08.
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