This young 'mega-Earth' is 23x more massive than our planet
What's the story
Astronomers have discovered an unusually massive and dense exoplanet, named GJ 523b. The planet is about 2.5 times wider than Earth and has a mass nearly 23 times greater. Such large and dense worlds are informally referred to as "mega-Earths," which challenges conventional ideas about how rocky planets form. GJ 523b's high density suggests it has relatively little atmosphere, contrary to what astronomers would usually expect for a planet of this size.
Planet profile
Discovery and characteristics of GJ 523b
GJ 523b was first spotted by NASA's Transiting Exoplanet Survey Satellite (TESS).
Further observations with WIYN 3.5-meter Telescope at Kitt Peak National Observatory in Arizona confirmed its existence.
The team found that GJ 523b has a mass 23.5 times that of Earth, a radius 2.55 times larger, and a density of about 126.82g per cubic inch.
It orbits its star every 17.75 days and is part of a relatively young planetary system, estimated to be nearly 170 million years old.
Formation puzzle
Planet's youth and size challenge conventional formation theories
The size, mass, and youth of GJ 523b pose a challenge for planet formation models.
These models suggest that planets start by forming cores of rock and metal, which then attract hydrogen and helium from the surrounding gas and dust disk.
In our solar system, giant planets like Jupiter and Saturn are thought to have started rapidly accumulating their massive gaseous envelopes once their growing cores reached about 20 times Earth's mass.
However, GJ 523b already exceeds this threshold but has not evolved into a gas-rich world.
Evolution theories
Possible explanations for GJ 523b's unusual characteristics
The unusual high density of GJ 523b raises questions about its evolution.
One theory suggests that the planet may have formed with a thick atmosphere that was later stripped away.
Another possibility is that it was created by a collision between two planets, resulting in a larger rocky world while ejecting much of their gaseous envelopes into space.
These theories could explain why this planet took such an unusual evolutionary path.
Formation insights
Mega-Earths and their significance in exoplanet research
The term "mega-Earth" has been used for over a decade to describe supermassive rocky worlds, but it has never been a formally defined class of exoplanets.
Discovering more planets like GJ 523b could help astronomers understand if these strange worlds are rare anomalies or part of a larger population.
"It's hard to infer things about planet formation in general from a sample size of one," said Max Kroft, lead author of the study.