The Atacama Large Millimeter/submillimeter Array (ALMA) has captured high-resolution images of protoplanetary disks. ALMA’s observations have revealed substructures in protoplanetary disks, such as rings and gaps. This evidence suggests that planets are forming and sweeping up material from the disk. 

ALMA’s dust polarization image of a protoplanetary disk is the deepest ever captured. ALMA has also set new standards for observing dust in protoplanetary disks. 

Protoplanetary disks are made up of: 

• Gas: 99% by mass, mainly molecular hydrogen and helium 
• Dust particles: 1% by mass 
• Other molecules: Trace amounts of CO and other molecules 

Protoplanetary disks typically last about 2–3 million years

ALMA has also observed: 

• Water ALMA detected water being inherited into a protoplanetary disk without significant changes to its composition. This suggests that the water in our Solar System formed billions of years before the Sun. 
• Planetary systems ALMA observed two rings of dust around a star, at distances comparable to the asteroid belt and the orbit of Neptune. This suggests that we are witnessing the formation of a planetary system similar to our own. 
• Tracks and grooves ALMA revealed that tracks and grooves in protoplanetary disks are common. This suggests that planets may be born earlier than formation theories.

Recent observations of protoplanetary disks have revealed: 

• Hot, dense water vapor 
• Substructures such as rings, gaps, spirals, and crescents 
• CO gas abundance 

The structure of protoplanetary disks can provide clues to where planets form and whether they change orbits after formation. 

Protoplanetary disks evolve over millions of years through accretion, outflows, photoevaporation, and condensation into larger bodies. They often develop a flared torus shape due to a combination of heat and radiation pressure from the central star.

Studying other stars can help us understand how our solar system formed. By observing other stars, we can: 

• See different paths of planetary system formation 
• See planetary systems at different stages of formation 
• Validate the core accretion theory 
• Learn why our solar system has small, rocky planets near the Sun and gas giant planets far away 
• Learn why Earth has conditions that support life 
• Learn why conditions on other planets are hostile to life 
• Better understand the life cycle of stars 

The Sun and planets formed together 4.6 billion years ago from a cloud of gas and dust called the solar nebula. A shock wave from a nearby supernova explosion may have caused the solar nebula to collapse.

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