Astronomers have found an unusually massive, dense exoplanet that challenges standard concepts about how rocky planets type.
Called GJ 523b, the exoplanet is about 2.5 times wider than Earth however packs roughly 23 times our planet’s mass into that comparatively compact dimension. Worlds this huge and dense are typically known as “mega-Earths,” an off-the-cuff time period for unusually massive, predominantly rocky planets. GJ 523b’s excessive density suggests it accommodates comparatively little environment regardless of being massive sufficient that astronomers would usually count on it to have collected a substantial gaseous envelope, based on a assertion from the University of Wisconsin–Madison.
“This isn’t what we expected at all,” Max Kroft, lead writer of the research, mentioned in the statement. (*23*)
GJ 523b was initially recognized as a candidate by NASA’s Transiting Exoplanet Survey Satellite (TESS), which searches for periodic dips in starlight brought about when planets cross, or transit, their host stars. Researchers adopted up with observations from the ground-based WIYN 3.5-meter Telescope at Kitt Peak National Observatory in Arizona, utilizing a spectrograph to measure the planet’s gravitational tug on its star.
Combining these observations, the crew calculated that GJ 523b has a mass about 23.5 times that of Earth, a radius 2.55 times bigger and a density of about 126.82 grams per cubic inch. It circles its star each 17.75 days. The planetary system can be comparatively younger, at an estimated almost 170 million years outdated, based on the research.
That mixture of dimension, mass and youth poses a puzzle for planet formation fashions. Planets start by constructing cores of rock and steel, which might then pull in hydrogen and helium from the disk of gasoline and dirt surrounding a younger star. In our personal solar system, big planets reminiscent of Jupiter and Saturn are thought to have begun quickly accumulating their massive gaseous envelopes as soon as their rising cores reached roughly 20 times Earth’s mass.
GJ 523b is already about 23 times Earth’s mass, placing it past that threshold. Yet as a substitute of creating into a gas-rich world, its unusually excessive density suggests it has comparatively little gasoline and stays predominantly rocky — elevating the query of why it adopted such a completely different path.
“The question is, why didn’t this planet do that, if it’s 20 times the size of Earth?” Kroft mentioned within the assertion.
One chance is that GJ 523b initially fashioned with a thick environment that was later stripped away. Another is that it fashioned by a collision between two planets, creating a bigger rocky world whereas blasting a lot of their gaseous envelopes into area, based on the assertion.
Astronomers have used the time period “mega-Earth” for more than a decade to explain exceptionally massive rocky worlds, although it has by no means represented a formally established class of exoplanets. Finding more examples like GJ 523b might assist reveal whether or not these uncommon worlds are uncommon exceptions or a part of a broader inhabitants.
“It’s hard to infer things about planet formation in general from a sample size of one,” Kroft mentioned within the assertion. “We’re not going to get to 10,000 of these overdense planets, but if we can get to 20 or 30, maybe some trends might pop out.”
The findings have been submitted to The Astronomical Journal and are currently available on the preprint server arXiv and haven’t but been peer reviewed.