New research suggests that newborn gas planets may be surprisingly flat

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An artist's impression of a „solar Jupiter” exoplanet. Credit: NASA/JPL-Caltech

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An artist's impression of a „solar Jupiter” exoplanet. Credit: NASA/JPL-Caltech

A new planet begins its life in a swirling circle of gas and dust called a cradle Protostellar disc. My colleagues and I used computer simulations to show that newborn gas planets in these disks have surprisingly flat shapes. This discovery, Published in Astronomy and Astrophysics LettersLet's add to our picture how planets form.

Protoplanets that have just formed and are still inside their protostellar disks are more difficult to observe. Only three young protoplanets have been observed so far, two of which are in the same system, PDS 70.

Our telescopes should detect faint light from the planet itself and find systems that are young and close enough to distinguish from the disk. The entire process of planet formation takes only a few million years, which is nothing more than a blink of an eye on astrophysical scales. This means we have to be lucky enough to catch them in the act of creating.

Our research team performed computer simulations to determine the properties of gaseous protoplanets under various thermal conditions in planetary cradles.

The simulations have sufficient resolution that it is possible to follow the evolution of a protoplanet in the disc from its earliest stages, when it is just condensation within the disc. Such simulations are computationally demanding and driven TRAC, UK's Astrophysics Supercomputing Facility.

Typically, multiple planets form within a disc. The study found that protoplanets have a shape called oblate spheroids, like Smarties or M&Ms, rather than spheres. They grow by drawing gas mainly through their poles rather than their equators.

Technically, the planets in our solar system are also oblate spheroids, but their flatness is smaller. Saturn is 10%, Jupiter 6%, and Earth is only 0.3% flat.

By comparison, the typical flatness 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 widely accepted theory for planet formation That's „Key Accumulation”.. According to this model, dust particles smaller than sand collide with each other, group together, and gradually grow into larger and larger bodies. This effectively happens when you don't clean the dust under your bed.

A dust core that forms massive enough that it pulls gas from the disk to form a gas giant planet. This bottom-up approach takes a few million years.

The opposite, top-down approach Disc Instability Theory. In this model, protostellar disks attending young stars are gravitationally unstable. In other words, they are too heavy to maintain, and so fragment into pieces, forming planets.

The core accretion theory has been around for a long time, and it explains many aspects of how our solar system formed. However, disk instability can better explain some of the exoplanetary systems we've discovered in recent decades, such as a gas giant planet orbiting far from its host star.

The appeal of this theory is that planet formation occurs very rapidly within a few thousand years, which is consistent with observations that suggest planets exist in very young disks.

Our study focused on gas giant planets formed via the disc instability model. They form from the contraction of the protostellar disc, an already flat structure, but are also flattened by how they spin.

There are no flat earths

Although these protoplanets are generally very flat, their cores, as we know them, will eventually form into the gas giant planets, which are less flat – only about 20%. It is twice the surface area of ​​Saturn. They are expected to become more spherical over time.

Rocky planets like Earth and Mars could not have formed via disc instability. They are thought to form by the slow accretion of dust particles into pebbles, rocks, kilometer-scale objects, and eventually planets. Even newborns are very dense. It is unlikely that the earth was so flat when it was young.

But our study supports a role for disk instability in the case of some worlds in some planetary systems.

We are now moving from the era of exoplanet discovery to the era of exoplanet characterization. Many new observatories have come into operation. These will help detect many protoplanets embedded in their disks. The predictions of computer models are also becoming more sophisticated.

Comparison between these theoretical models and observations brings us closer and closer to understanding the origin of our solar system.

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