A new planet begins life in a rotating ring of gas and dust, a cradle known as a protostellar disk. My colleagues and I used computer simulations to show that newborn gas planets in these disks likely have surprisingly flattened shapes. This discovery was published on: Astronomy and Astrophysics LettersIt could contribute to our understanding of exactly how planets form.

It is extremely difficult to observe newly formed protoplanets that are still within protostellar disks. Only three young protoplanets of this type have been observed so far, and two of them are located in the same system, PDS 70.

We need to find systems that are young enough and close enough that our telescopes can detect the faint light of the planet and distinguish it from the light of the disk. The entire process of planet formation only takes a few million years; This is a blink of an eye on an astrophysical scale. This means we have to be lucky enough to catch them in the making.

Our research group performed computer simulations to determine the properties of gaseous protoplanets under various thermal conditions in planetary cradles. The simulations have sufficient resolution to follow the evolution of protoplanets in the disk from the early stage when condensation occurs within the disk. Such simulations are computationally intensive and have been carried out at DiRAC, the UK’s Astrophysics Supercomputing Centre.

As a rule, several planets are formed inside the disk. The study found that the protoplanets, rather than being spherical, had a shape known as flat spheroids, like Smarties or M&Ms. They grow by drawing gas from their poles rather than the equator.

Technically, the planets in our solar system are also oblate spherical, but their oblateness is negligible. Saturn is flattened by 10%, Jupiter is flattened by 6%, and Earth is flattened by only 0.3%. For comparison, the typical flattening of protoplanets is 90%. Such flattening would affect the observed properties of protoplanets and should be taken into account when interpreting the observations.

How do planets begin?

The most common theory of planet formation is the “core growth” theory. According to this model, dust particles smaller than sand collide with each other, gather together, and gradually turn into larger objects. In fact, this is what happens if the dust under your bed is not cleaned. It creates a fairly large dust core and absorbs gas from the disk, forming a gas giant planet. This bottom-up approach will take several million years.

The opposite of the top-down approach is the disk imbalance theory. In this model, protostellar disks accompanying young stars are gravitationally unstable. In other words, they are too heavy to be moved and break apart into planets.

The theory of nucleus accretion has been around for a long time and can explain many aspects of the formation of our solar system. However, disc instability may better explain some of the exoplanetary systems we have discovered in recent years, such as systems in which a gas giant planet orbits far, far away from its host star.

The appeal of this theory is that planet formation occurs very rapidly over several thousand years; This is consistent with observations suggesting the presence of planets in very young disks.

Our study focused on gas giant planets formed using the disk instability model. They have become flat because they were formed by the compression of an already flat structure, that is, the protostellar disk, and due to the way they rotate.

There is no flat Earth

Although these protoplanets were generally very flattened, their cores, which would later become the gas giant planets we know, were less flattened; only around 20%. This is only twice that of Saturn. They are expected to become more global over time.

Rocky planets like Earth and Mars cannot form due to disk instability. They are believed to form when dust particles gradually coalesce into pebbles, rocks, kilometer-sized objects, and eventually planets. They are too dense to flatten significantly even when newborn. It is impossible for the Earth to have become this flat in its youth.

However, our study confirms the role of disk instability on some worlds in some planetary systems.

We are now moving from the age of exoplanet discoveries to the age of exoplanet descriptions. Many new observatories are planned to become operational. This will help detect more protoplanets embedded in their disks. Predictions based on computer models are also becoming increasingly complex. Comparing these theoretical models and observations brings us closer to understanding the origin of our solar system.