A new study has revealed that ‘Eggshell Planets’ may orbit other stars with a thin outer brittle and very little topography.
Researchers say at least three of these unusual eggshell ‘exoplanets’ – planets outside our solar system – may already be known, but even more could exist.
This rare world is likely to be only a few thousand miles in thickness, unlikely to experience plate tectonics and could or might not be habitable.
Additionally, they are more likely to be younger and larger than exoplanets that have thicker outer layer layers. This could make them potentially part of the same solar systems.
Eggshell planets’ surface could look like Venus’ lowlands, featuring vast lavas and scorching hot temperatures, but with very little terrain.
‘Eggshell planets’ are rocky worlds that have an ultra-thin outer brittle layer and little to no topography. Pictured is an artist’s rendering of such an exoplanet
According to the study, strange planets that have outer layers similar to eggshells make up a large number of possible exoplanets.
Paul Byrne (a Washington University in St. Louis planetary geologist) led the new study.
Byrne, along with his international team of collaborators, wanted to find out which cosmic elements play the greatest role in determining the thickness a planet’s outer brittle layers. This is known as The Lithosphere.
This thickness helps determine whether, for example, a planet can support high topography such as mountains, or has the right balance between rigidity and flexibility for one part to subduct beneath another – the hallmark of plate tectonics.
This process is what keeps Earth’s temperature stable over time. It is why plate tectonics has been considered a crucial factor in determining whether or not a planet can be habitable.
Professor Byrne stated that understanding whether there is plate tectonics on a planet is crucial because it may require plate tectonics for large, rocky planets to become habitable.
“It is therefore particularly important when looking for Earth-like planets around other stars, and when characterising planetary habitability in general.
Astronomers have so far discovered over 4,000 exoplanets orbiting stars in the galaxy.
But it is difficult to say what the exoplanets may be made of or how they might look like Earth.
The thickness of the lithosphere – the outermost shell of a planet – plays a key role in geological processes that determine their characteristics, the team say.
The surface of eggshell planets could resemble the lowlands on Venus (pictured here in a false-colour radar image mosaic). These are tectonic structures. The darker areas with more peach-colored lines, are volcanic plains. A few small volcanoes can be seen near the centre. This image was made with radar data returned by NASA’s Magellan mission, which operated between 1990 and 1994, and shows an area about 1,400 km (870 miles) across
The team modelled multiple combinations planetary mass and surface temperature as well as energy flow to better understand the influence of stellar and planetary factors on lithosphere thickness.
Scientists used as their starting point a generic Earth-sized sized rocky planet for modeling.
Byrne explained, “And then they spun the dials.” We literally had thousands upon thousands of models.
The results show that surface temperature plays the largest role in determining the thickness of the fragile layer, but planetary mass and distance from its star, as well as the age of the planet, all have an impact.
Larger and more mature planets tend to have thicker brittle geospheres. This is similar to Mercury and Mars’s. However, smaller and younger planets may have thinner brittle zones that are comparable to Venus’ lowlands.
The team believes that it is possible for certain parameters to produce worlds with “exceedingly thin, brittle layers”.
These eggshell-shaped planets have not been directly imaged by researchers. This means that we don’t really know their looks, except for speculating on similarities with Venus.
‘We have imaged a few exoplanets, but they are splotches of light orbiting a star,’ Byrne said. “We don’t yet have the technical capabilities to observe exoplanets from space.
Future and planned space telescopes will be used by the scientists to observe exoplanets closer and confirm their geological features.
More than 4000 exoplanets have been discovered by astronomers so far. This is an artist’s rendition of an exoplanet with its moon.
Byrne explained that the published data shows that some exoplanets have extreme weather conditions.
They might be close to their star or much bigger or might have hotter surfaces than planets in our system.
“Ultimately, we wish to contribute to the identification of properties that make a planet habitable.
“And not only temporarily, but habitable over a period of time because life may take a while before it becomes sustainable.”
This study was published in Journal of Geophysical Research: Planets.
Hubble, a large space satellite used by scientists for studying the atmosphere of exoplanets distant from Earth allows them to do so using huge space satellites.
Many conditions exist between distant stars, and the orbiting planets of these star systems.
Scientists need to know the composition of their atmospheres in order to understand and comprehend these new worlds.
They use a telescope like Nasa’s Hubble Telescope to do it.
These huge satellites look up at the sky, and they lock onto exoplanets Nasa considers interesting.
These sensors can perform many types of analysis.
The most valuable and effective is absorption spectroscopy.
This analysis looks at the amount of light coming from a planet’s atmosphere.
A gas can absorb a slight variation in the wavelength of light. This is what causes a blackline to appear on the complete spectrum.
These lines indicate a specific molecule’s presence on Earth.
They are often called Fraunhofer lines after the German astronomer and physicist that first discovered them in 1814.
Scientists can combine all wavelengths of light to determine the chemical composition of the planet’s atmosphere.
It is important to remember that the missing information is what leads you to what is actually there.
This is crucial because the Earth’s atmosphere could interfere with it.
It is possible for light to be absorption by chemicals to skew samples.
This can be used to find helium and sodium in other atmospheres.
This diagram shows how light passing from a star and through the atmosphere of an exoplanet produces Fraunhofer lines indicating the presence of key compounds such as sodium or helium