Is our Solar System comparable to other solar systems? What do other systems look like? We know from exoplanet studies that many other systems have hot Jupiters, massive gas giants that orbit extremely close to their stars. Is that normal, and our Solar System is the outlier?

One way of addressing these questions is to study the planet-forming disks around young stars to see how they evolve. But studying a large sample of these systems is the only way to get an answer. So that’s what a group of astronomers did when they surveyed 873 protoplanetary disks.

Mass is the critical piece in a new study into planet-forming disks. The disk’s mass determines how much matter is available to form planets. By measuring the disks’ mass around young stars, astronomers can constrain the total mass of planets that might form there and get one step closer to understanding solar system architecture.

The new study is “Survey of Orion Disks with ALMA (SODA): I. Cloud-level demographics of 873 protoplanetary disks.” It’s published in the journal Astronomy and Astrophysics, and the lead author is Sierk van Terwisga, a scientist at the Max Planck Institute for Astronomy in Heidelberg, Germany.

“Up to now, we didn’t know for sure which properties dominate the evolution of planet-forming disks around young stars,” van Terwisga said in a press release. “Our new results now indicate that in environments without any relevant external influence, the observed disk mass available for forming new planets only depends on the age of the star-disk system.”

The dust mass not only tells astronomers the mass of planets that might form from a disk. Depending on the disk’s age, it could also tell astronomers what planets have already formed.

But other factors affect disk mass too, and those factors vary from disk to disk. Things like stellar wind and irradiation from nearby stars outside the disk can also affect mass. So how were the researchers able to isolate those effects in such a large sample?

They focused on a well-known region of protoplanetary disks called the Orion A cloud, which is part of the Orion Molecular Cloud Complex (OMCC). The OMCC is about 1350 light-years away and home to the well-studied Orion Nebula, a feature even backyard astronomers can see.

This image of the giant Orion A star-forming cloud was captured by the Herschel Space Telescope. It traces the large-scale distribution of cold dust. Orion A is about 1350 light-years away and consists of individual star-forming regions indicated by their labels. The locations of planet-forming disks (+) observed with ALMA are indicated, while disks with dust masses above an equivalent of 100 earth masses appear as blue dots. The famous Orion Nebula, visible to the naked eye in the sky, hosts the Orion Nebula Cluster (ONC), including several massive stars emitting intense radiation. Image: S.E. van Terwisga et al./MPIA
The Herschel Space Telescope captured this image of the giant Orion A star-forming cloud. It traces the large-scale distribution of cold dust. Orion A is about 1350 light-years away and consists of individual star-forming regions indicated by their labels. The locations of planet-forming disks (+) observed with ALMA are indicated, while disks with dust masses above 100 earth masses appear as blue dots. The famous Orion Nebula, visible to the naked eye in the sky, hosts the Orion Nebula Cluster (ONC), including several massive stars emitting intense radiation. Image: S.E. van Terwisga et al./MPIA

Álvaro Hacar is a co-author of the study and a scientist at the University of Vienna, Austria. “Orion A provided us with an unprecedented large sample size of more than 870 disks around young stars,” Hacar said. “It was crucial to be able to look for small variations in the disk mass depending on age and even on the local environments inside the cloud.”

This is a good sample because all disks belong to the same cloud. That means their chemistry is uniform, and they all have the same history. The nearby Orion Nebular Cluster (ONC) hosts some massive stars that could affect other disks, so the
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