Astronomers have, for the first time, captured a gallery of detailed snapshots of planetary systems during their "teenage years," an era long shrouded in mystery. The ALMA survey to Resolve exoKuiper belt Substructures (ARKS), using the Atacama Large Millimeter/submillimeter Array (ALMA), has produced the sharpest images ever of 24 debris disks, the dusty belts left after planets finish forming. These disks are the cosmic equivalent of teenage planetary systems, somewhat more mature than newborn planet-forming disks but not yet settled into adulthood (a regime with stable planets and a dissipated dust disk like our own solar system). This teenage stage, on the contrary, is quite chaotic, with objects and dust colliding frequently.
Our own solar system's counterpart to this phase is the Kuiper Belt, a ring of icy debris beyond Neptune that preserves a record of massive collisions and planetary migrations from billions of years ago. By imaging 24 exoplanetary debris belts nearby in the Milky Way, the ARKS team has opened a window into what our solar system went through as the Moon was forming and as planets jostled for their final places, sometimes even trading orbital positions.
The ARKS collaboration has now produced 10 related papers about these extrasolar planetary systems, including one led by Caltech postdoctoral scholar Yinuo Han and appearing in the journal Astronomy & Astrophysics on January 20.
"These images are showing us dust and gas from rings of comets orbiting stars, much like alien versions of our own solar system's Kuiper Belt," says Han. "We've been studying their structure over the past three years, trying to understand how planetary systems formed by looking at these solar system 'cousins' at different ages."
Han's paper examines how these dusty rings surrounding stars are structured in order to better understand the formation of planetary systems. Many disks show evidence for zones of calm and zones of chaos, with vertically "puffed-up" regions, akin to our solar system's own mix of serene classical Kuiper Belt objects and those scattered by Neptune's long-ago migration.
"We see a range of structures among these dust belts," he adds. "Some of them are asymmetric or have gaps, which is interesting because they potentially point to planets that are perturbing the belt with their gravity or carving out those gaps. These techniques are sensitive to a population of planets that have so far been difficult to detect because they are generally too small and have long orbits. The complexity of these disk structures reflect the diversity among exoplanetary systems."
Like teenagers dodging their parents' cameras, these faint disks have managed to hide from astronomers for years. But thanks to ALMA, astronomers can now see their complex structures: belts with multiple rings, smooth and wide halos, sharp edges, and even unexpected arcs and clumps. ALMA captured these elusive images by scanning the exoplanetary systems in long wavelengths of light around a millimeter, about 2,000 times longer than visible light. In this regime, the hot, bright star at the center of the system is dim, and the cooler surrounding disk is luminous.
The ARKS results show this teenage phase is a time of transition and turmoil. By looking at dozens of disks around stars of different ages and types, ARKS helped decode whether the chaotic features are inherited, sculpted by planets, or arise from other cosmic forces. Answering these questions could reveal whether our solar system's history was unique or the norm.
The ARKS survey's findings are a treasure trove for astronomers hunting for young planets and seeking to understand how planetary families, like our own, are built and rearranged.
"As we continue to interpret the ARKS survey, these results will form the foundation for future observations to grow the sample and put theories of planet formation to the test," Han says.
The ARKS survey is the work of an international team of approximately 60 scientists, led by the University of Exeter, Trinity College Dublin, and Wesleyan University.
This information was adapted from a press release shared by the US National Science Foundation National Radio Astronomy Observatory (NRAO), which is a partner of ALMA.
