A new international study has revealed that planet-forming disks around young stars lose their gas much faster than their dust, challenging long-standing ideas about how planets like Jupiter form.
This discovery comes from a major observing program called AGE-PRO, which used the powerful ALMA telescope in Chile to study 30 protoplanetary disks—swirling clouds of gas and dust that eventually form planets.
The research, led by scientists from the University of Arizona, the University of Wisconsin-Madison, and several other institutions, was published in a special issue of the Astrophysical Journal.
AGE-PRO is the first large-scale study to closely track how gas behaves in planet-forming disks over time.
Previous studies mostly focused on dust, since gas is much harder to observe and requires long hours of telescope time.
One of the most surprising findings is that gas disappears much more quickly than dust as these disks age. In their early stages—within the first million years—these disks can hold several times the mass of Jupiter in gas.
But as time goes on, the gas thins out rapidly, while the dust lingers much longer. This shift in the gas-to-dust ratio could significantly affect the types of planets that form.
For example, it might be harder for massive gas giants like Jupiter to form in older disks, leaving more time for smaller rocky planets to take shape.
The researchers found that even though many disks lose their gas quickly, the ones that survive longer tend to have more gas than expected. This raises new questions about how and when gas giant planets are able to form before their fuel runs out.
The AGE-PRO team used ALMA’s incredible sensitivity to detect faint molecular “fingerprints” that help identify different gases in the disks.
These included common gases like carbon monoxide and more unusual ones like diazenylium (N₂H⁺), formaldehyde, and methyl cyanide. By analyzing the light from these molecules, scientists could estimate the amount of gas in each disk, even in very faint or small ones that had never been studied in such detail before.
The study focused on three nearby star-forming regions that represent different stages in disk evolution: Ophiuchus (the youngest), Lupus (1–3 million years old), and Upper Scorpius (the oldest, at up to 6 million years old).
ALMA observations provided a clearer picture of how gas and dust evolve together over time, with important implications for how planets grow and move in these systems.
One key insight is that the gas-to-dust mass ratio is more stable across disks of different sizes than researchers had assumed. This means that both large and small disks may follow similar patterns when it comes to gas loss—contrary to previous theories that suggested small disks might lose gas more quickly.
This groundbreaking survey not only improves our understanding of planet formation but also provides a valuable archive of gas data for future researchers. With better tools to measure gas in these dusty birthplaces of planets, astronomers are now closer to understanding how solar systems like ours come to be.
Source: University of Arizona.
