Last October a picture of the system HL Tauri captured by ESO’s ALMA (Atacama Large Millimeter / submillimeter Array) telescope was published. It showed a disk of dust that is slowly coalescing and was one of the sharpest images ever made at sumbillimetric wavelengths. According to many scientists there are planets that are forming in the system but others were skeptical and that created a debate. Now a team of astrophysicists from the University of Toronto led by Daniel Tamayo brought new evidence that there really are planets forming, published in the journal “Astrophysical Journal”.

The skepticism about the planets in formation in the HL Tauri system, whose star has an age estimated in less than a million years, is due to the fact that the gaps in the dust disk where planets may be forming are too close. Planets massive enough to create those gaps in the disk would be expelled from the system because of the violent gravitational effects due to the proximity between them.

The team led by Daniel Tamayo took example of what happens between Neptune and Pluto to argue that the HL Tauri system there’s a resonant configuration among the proto-planets that keeps them separate. In essence, these planets have specific orbital periods so they don’t crash into each other because of that reason, just as it happens for Neptune and Pluto, whose orbits actually cross one another.

However, this type of gravitational balance isn’t stable. The HL Tauri system is very young but over the next billion years there could be violent changes. The orbits of many planets may change considerably, so much that some of them probably will be ejected from the system. Other planets will remain in much more elliptical orbits, such as those of exoplanets found in other star systems that are much older.

This type of research is allowing us to understand better and better the dynamics existing in the formation of star systems. Many systems discovered in recent years have characteristics very different from ours and scientists are trying to understand why. Simulations with supercomputers are increasingly accurate but direct observations keep on being crucial to understand how our solar system was formed and evolved.

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