Uncovering the Secrets of Baby Planets: A Study of 30 Stellar Nurseries with ALMA
Introduction: When infant planets are born, they quickly devour the remaining gas and dust clouds that surround them. These protoplanetary disks disappear within just a few million years, but astronomers now have a better understanding of this process thanks to a new study conducted by an international team using the Atacama Large Millimeter/submillimeter Array (ALMA). The research, part of the ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO) program, studied 30 protoplanetary disks around sunlike stars and found that the gas and dust components in these disks evolve at different rates. The amount of gas left over determines the type of planets these systems produce.
The AGE-PRO Results: The AGE-PRO results have given rise to 12 research papers by different teams, showing just how ground-breaking the discovery is. "These studies have revealed how protoplanetary disks evolve over time," said AGE-PRO researcher Anibal E. Sierra Morales of the Mullard Space Science Laboratory at University College London (UCL). "The extraordinary results are an essential step toward understanding the initial conditions that lead to the formation of Earth-like planets."
The Formation of Protoplanetary Disks: The story of protoplanetary disks begins when clumps of overdense, cool gas collapse under their own gravity in interstellar molecular clouds, birthing stars. These infant stars, or "protostars," continue to gather matter from their prenatal envelope of gas. Eventually, what is left behind is a main sequence star surrounded by a flattened, swirling cloud of gas and dust—a protoplanetary disk. Within this disk, conglomerations of material bump together and stick, gathering mass until they form planetesimals. These planetesimals continue to gather material from the protoplanetary disk, and it is from this process that planets grow.
The Role of Gas and Dust: It's estimated that protoplanetary disks surround infant stars for several million years, setting the time that giant planets have available to form. The initial size and mass of the protoplanetary disk and its angular momentum determine the kind of planets it is capable of birthing. The lifespan of gas in the disk then determines how long the clumps have to gather and grow into bodies the size of asteroids or planets. Additionally, these factors can also determine if planets migrate through the planetary disk during their youth, moving from their birthplaces closer to or farther away from their star.
The AGE-PRO Study: Before this new study, researchers had analyzed how the dust content of protoplanetary disks evolves, but the way the gas content changes over time was not as well understood. "AGE-PRO provides the first measurements of gas disk masses and sizes across the lifetime of planet-forming disks," said research principal investigator Ke Zhang of the University of Wisconsin-Madison. Using ALMA, the team zoomed into 30 protoplanetary disks of different ages, ranging from 1 million years old to over 5 million years old. These disks were located in the star-birthing regions of the constellations Ophiuchus, Lupus, and Upper Scorpius. The sensitivity of ALMA allowed the team to track particular chemical "tracers" that reveal gas and dust masses during vital stages of protoplanetary disk evolution, from initial formation to their inevitable disintegration millions of years later.
Conclusion: The AGE-PRO program has provided unprecedented insights into
