A University of Georgia astrophysicist has won more than $365,000 in NASA funding to test the two rival theories of how giant planets form, and whether, as new observations suggest, they can form millions of years faster than textbooks predict.
Assistant professor Cassandra Hall, a computational astrophysicist in the Franklin College of Arts and Sciences and a faculty member in the Center for Simulational Physics, will use computer simulations to determine how the two formation pathways interact in a young planetary system's earliest stages, according to the university's announcement.
More than 6,000 exoplanets have now been confirmed, ranging from small rocky worlds to giants nearly massive enough to be stars. The standard theory, core accretion, builds a planet slowly: pebbles and dust gather around a young star over millions of years. The rival theory, gravitational instability, has a massive disk collapse directly into dense clumps, forming planets in hundreds to thousands of years.
Hall's project tackles the possibility that the two methods are not rivals at all but phases, with disk collapse and core growth interacting in the same system. The answer matters for reading the flood of exoplanet data: a planet's formation speed is written into its composition and orbit, and misreading it misdescribes the system.
It is also a state-university story. The simulation work happens at Georgia's public flagship, funded by a federal agency, training graduate students in computational physics. Astronomy's golden age of data is being interpreted, in large part, at desks like these.
The simulations will run against a growing observational record: thousands of exoplanets whose masses, orbits and atmospheres are now measured well enough to discriminate between formation stories. A theory that cannot reproduce the observed population fails, however elegant, and Hall's interacting-models approach is designed to fail or survive against exactly that evidence.
The grant, more than $365,000, funds the simulation programme and the researchers who run it, part of NASA's investigator programme that keeps fundamental theory work distributed across the country's universities rather than concentrated at the agency's own centres.
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