Scientists have puzzled over a massive planet named GJ 523b, which is over twice the size of Earth but lacks a thick atmosphere. Despite its size, researchers expected it to have accumulated a substantial gaseous layer. GJ 523b, located around 170 million years from its star, measures more than 2.5 times the size of Earth and weighs approximately 23 times more.
According to the University of Wisconsin-Madison, GJ 523b’s composition consists of dense rock surrounding a large core. This revelation comes from a study led by Max Kroft, a graduate student, and supervised by Professor Thomas Beatty from UW-Madison’s Astronomy department.
Characteristics of a Mega-Earth
A Mega-Earth is a large, dense planet outside our solar system. It exceeds the mass of a typical super-Earth and primarily consists of rock and metal. Beatty explains that GJ 523b provides a clearer definition of this category, having been described as a Mega-Earth for a decade without a concrete example.
Investigating GJ 523b requires knowledge beyond astronomy. Geologists will study how iron and rock behave under extreme pressures that Earth’s laboratories cannot replicate. Atmospheric scientists will evaluate how much of the planet is pure rock.
First identified by NASA’s Transiting Exoplanet Survey Satellite (TESS), GJ 523b was detected by the periodic dimming of starlight, a sign of a planet transiting in front of its star. “We think that’s a planet passing in front of the star and transiting,” Kroft stated, indicating a decrease in starlight.
Further analysis was conducted by Kroft using Arizona’s WIYN telescope and complemented with data from the James Webb Space Telescope, focusing on the planet’s density and atmospheric properties.
Exploring Its Thin Atmosphere
Generally, growing rocky planets gather a hydrogen-rich atmosphere. In our solar system, planets like Jupiter and Saturn developed large atmospheres beyond 20 times Earth’s mass. Researchers question why GJ 523b, at over 20 times Earth’s mass, didn’t follow this pattern.
The team suggests several theories. One possibility is that GJ 523b’s orbit brought it too close to its star, with high temperatures stripping away much of its atmosphere. Another scenario involves a collision of two planets, with the heat from the impact dissipating atmospheric gases.
A planet can’t hold on to its atmosphere if it’s really hot, resulting in a large rocky mass with minimal atmosphere,
Kroft added, explaining the potential consequences of such a cosmic event.