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Weekend Image: The Birth of a Planet-Forming Star System





A team led by Daniel Tamayo from the Centre for Planetary Science at University of Toronto Scarborough and the Canadian Institute for Theoretical Astrophysics, found that circular gaps in a disk of dust and gas swirling around the young star HL Tau are in fact made by forming planets. “HL Tau likely represents the first image taken of the initial locations of planets during their formation,” said Tamayo. “This could be an enormous step forward in our ability to understand how planets form.”

The image of HL Tau, taken in October 2014 by the state-of-the-art Atacama Large Millimeter/submillimeter Array (ALMA) located in Chile’s Atacama Desert, sparked a flurry of scientific debate.

While those who observed the original image claimed that planets were most likely responsible for carving the gaps, some remained skeptical. It had been suggested that the gaps, especially the outer three, could not represent forming planets because they are so close together. It was argued that planets massive enough to carve such gaps should be scattered violently by the force of gravity and ejected from the system early on in its development.

But Tamayo’s study is the first to suggest the gaps are evidence of planetary formation because the gaps are separated by amounts consistent with what’s called a special ‘resonant configuration.’ In other words, these planets avoid violent collisions with each other by having specific orbital periods where they miss each other, similar to how Pluto has avoided Neptune for billions of years despite the two orbits crossing one another.

photo of Daniel Tamayo with computer“The system can be much more stable in a resonant configuration and it’s a natural state for planets in the HL Tau system to migrate to,” said Tamayo (pictured at right).

The HL Tau system is less than a million years old, about 17.9 billion kilometres in radius and resides 450 light years from Earth in the constellation Taurus.

Since young systems like HL Tau are shrouded by a thick cloud of gas and dust, they can’t be observed using visible light. ALMA resolves that issue by using a series – or an ‘array’ – of telescopes located 15 kilometres apart that use much longer wavelengths. The result is unprecedented access to high resolution images that Tamayo says will continue to revolutionize the study of planetary formation.

“We’ve discovered thousands of planets around other stars and a big surprise is that many of the orbits are much more elliptical than those found in our solar system,” said Tamayo.

“This and future ALMA discoveries may be the key to connecting these discovered planets to their original birth locations.”

While the HL Tau system remains stable in its relatively young age, Tamayo says over billions of years it will act as a “ticking time bomb.” Eventually the planets will scatter, ejecting some and leaving the remaining bodies on elliptical orbits like the ones found around older stars.

Our solar system does not seem to have undergone such a dramatic scattering event, Tamayo said. Future observations could also go a long way in determining whether our solar system is typical or an oddity ideally suited for life.

“If further observations show these to be the typical starting conditions around other stars, it would reveal our solar system to be a remarkably special place.”

Tamayo created two videos based on computer simulations to show how HL Tau would appear in both resonant and non-resonant configurations.

The findings are available online and will be published in the upcoming edition of Astrophysical Journal.

The Daily Galaxy via University of Toronto


1. Planets form in the protodisk, center of which is forming a star as well. Aout 98%-99.5% of the total disk material gets to be a star, the rest is planets, proto planets that become moons of larger planets (such as some moons of the large gas planets of our own system) or impact/merge with formed planets or reform and add to them and/or create moons (such as our moon was created by a merge of a smaller planet), and comets and left overs akin to our Kuiper and Oort. Fine.

But as a planet forms, acquiring mass, it's orbit simply has to change OUTWARD in orbit, i.e. go away from the star/protostar into a further orbit, the more massive it gets. If the planet forming acquires mass too fast, it's likely to be either ejected from the system or acquire a much further from the star orbit, orbital mechanics are like that. The alternative is also that as the planet acquires mass it spirals into the protostar if the orbit doesn't or can't change outward and its speed of orbit isn't increased.

I think I have this right so looking for an edit comment here please.

2. As to why it's thought our solar system didn't do so much of that orbit adjustment and mayhem, naw, it's been theorized that for example Jupiter was much closer to the sun than now and migrated outward, (slingshoting with another large body or acquiring mass from gulping up other planets AND slingshoting as well by coincidence) raising mayhem with the rest of the planets in the process due to Jupiter's massive gravity pulling all other planets here and there adjusting their orbits or sending them to the sun. It's also theorized that a number of rocky planets were so perturbed in orbit they simply lost it and spiraled into the sun.

So the thought that our solar system was a peaceful innocent one is now theorized to be wrong.

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