From Stardust to Stone: Windswept Grains Hold Clues to Planet's Beginnings
By National Radio Astronomy Observatory
The Atacama Large Millimeter/submillimeter Array (ALMA) has uncovered a key piece of the puzzle in how rocky planets, such as Earth, form around young stars. For decades, scientists have struggled to explain how dust grains in the disks around newborn stars grow from tiny dust grains to planet-building "pebbles" without either spiraling into the star or shattering in collisions—a challenge known as the "meter-size barrier."
A team of more than 50 astronomers and chemists from the world's leading scientific institutes used ALMA for this large program of research, known as the "Fifty AU STudy of the chemistry in the disk/envelope systems of Solar-like protostars" or FAUST. The team studies the chemistry of the dense molecular gas in the envelopes of a representative sample of solar-like protostars, and now, for the first time ever, have directly observed millimeter-sized dust grains—about 10,000 times larger than typical interstellar dust—embedded in the walls of a protostellar outflow cavity.
The Discovery of Millimeter-Sized Dust Grains
These grains appear to have been lifted from the dense inner protostellar disk by winds and then deposited farther out, away from where they can fall back onto the disk, allowing them to continue growing. This process gives the grains more time and space to stick together, potentially overcoming a long-standing barrier to planet formation.
Implications for Planet Formation
Astronomers directly observed these millimeter-sized dust grains in the walls of the protostellar outflow cavity of the young L1551 IRS5 binary system. This observation shows that these grains can grow much larger than previously thought in the early stages of planet formation. The findings, published in the journal Astronomy & Astrophysics, offer new insight into the processes that may have led to the formation of our own solar system and highlight a previously underestimated pathway for planet formation.
"This discovery not only provides a new mechanism for building planets but also offers a glimpse into how our own solar system may have formed," said Giovanni Sabatini, a scientist with the National Institute for Astrophysics (INAF) at the Arcetri Astrophysical Observatory in Florence, and leader of this research.
Broader Significance
"The findings open exciting new questions about the diversity of planetary systems in our galaxy and bring us closer to understanding our cosmic origins," adds Claire Chandler, NSF NRAO scientist and a co-PI of the FAUST collaboration.
Conclusion
This research underscores the importance of studying dust grains in the formation of planetary systems and their implications for understanding the early histories of such systems.
For more information:
G. Sabatini et al, FAUST XXIV. Large dust grains in the protostellar outflow cavity walls of the Class I binary L1551 IRS5, Astronomy & Astrophysics (2025). DOI: 10.1051/0004-6361/202554750
