Astronomers discover rocky 170-million-year-old 'mega-Earth' that defies planet formation theories
Washington DC, August 20
In a discovery that challenges current theories of planetary formation, astronomers have discovered an unusually dense, giant exoplanet that boasts 23 times the weight of Earth while remaining predominantly rocky. The 170-million-year-old planet is more than 2.5 times larger than Earth!
The celestial body, named GJ 523b, has been informally dubbed a "mega-Earth"- a rare category of exceptionally massive, dense, rocky worlds.
According to research led by Max Kroft at the University of Wisconsin-Madison, the exoplanet is approximately 2.5 times wider than Earth (with a radius roughly 2.55 times larger), but packs an extraordinary amount of matter into its size, resulting in a staggering density of about 126.82 grams per cubic inch.
GJ 523b was initially flagged by NASA's Transiting Exoplanet Survey Satellite (TESS) as it crossed in front of its host star. Researchers subsequently confirmed its existence and calculated its immense mass using ground-based instruments, including the WIYN 3.5-meter Telescope at Kitt Peak National Observatory in Arizona.
According to data, GJ 523b completes an orbit around its star every 17.75 days. The planetary system itself is relatively young, estimated at around 170 million years old.
The discovery has left scientists puzzled. Traditional planetary formation models suggest that once a rocky core grows to roughly 20 times the mass of Earth, its gravitational pull becomes strong enough to rapidly draw in massive amounts of gas from surrounding space, evolving into a gas giant similar to Jupiter or Saturn.
However, despite crossing this mass threshold, GJ 523b retained an ultra-dense rocky composition with relatively little atmosphere.
"This isn't what we expected at all," said Max Kroft, lead author of the study, in a press statement. "Dense planets like this aren't uncommon, but they're usually small rocky planets similar to Earth or Mercury. The question is, why didn't this planet do that, if it's 20 times the size of Earth?"
Astronomers have proposed two leading theories to explain the anomaly.
The first, they say, could be 'Atmospheric Stripping'. The planet may have originally formed with a thick gas envelope that was later blasted away by stellar activity or cosmic events.
Another theory they have proposed is the 'Giant Impact'. The planet could have been created by a catastrophic collision between two large rocky protoplanets, which merged their dense cores while blowing off their light gaseous layers.
The research paper detailing the discovery has been submitted to The Astronomical Journal. Astronomers hope to identify more such "mega-Earths" in the future to better understand whether GJ 523b is a solitary cosmic outlier or part of a previously unrecognized class of exoplanets.
— ANI
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