Chapter 1: What mysteries about solar system formation are still unsolved?
Over the centuries, scientists have solved countless mysteries about the cosmos, through careful observation and experimentation. But one of the most enduring mysteries is closest to home. We still have never seen how a solar system like our own is born.
Our current model of how planetary systems form is mostly based on extrapolation of data from meteorites and observations of our neighbouring planets. And for the most part, scientists think we've broadly got it right. At least the models we've built seem to make sense. There are, however, stages that have remained somewhat mysterious. Exactly how, when, and where planets form being the big one.
But that's about to change. Earlier this year, the James Webb Space Telescope found a baby star hidden in a cocoon of gas, and amongst that gas and dust, planets are being made. For the first time, we've been able to see the very earliest phases of planetary formation,
So not only are we finally getting to the bottom of the puzzle, it could even show us something about how our own solar system's planets came to be. I'm Alex McColgan, and you're watching Astrum.
Join me today as we unravel the secrets of HOPS 315, consider what its future planetary system might look like, and dive into how this discovery is reframing our understanding of planet formation across the universe.
Given that we live on a planet, have visited seven others in our solar system, and found more than 6,000 beyond that, you'd think that we should have a pretty good idea as to how planets form. Well, unfortunately, that's not necessarily the case.
Much of what we know today is thanks to the analysis of meteorites that have landed on Earth, and observations we've made of the planets in our own solar system as they are now. The rest of it has been left up to models and simulations. Why? Well, it turns out the earliest stages of star and planetary formation are extremely difficult to see.
It all starts with huge molecular clouds made up of dust and gas particles. As they move around, they create thermal pressure pushing outward on the cloud, But these particles also have to obey the laws of gravity, just like everything else, so they also pull each other, and the cloud, inward. This push and pull remains in perfect balance for millions of years, keeping the nebula stable.
But a nearby cosmic event, for instance the shockwave resulting from a supernova explosion, can suddenly send everything into disarray. If gravity starts pulling this gas cloud inward faster than the pressure of its moving particles can push back, we get a runaway effect, a gravitational collapse. The dust and gas from the outer regions begin raining inward.
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Chapter 2: How did the James Webb Space Telescope contribute to our understanding of planetary formation?
That is, until now. 1,300 light years away, in that Orion Nebula, a baby solar system is being born. And we're watching it with our own eyes. Well, James Webb's lens. This is HOPS 315, a star that's less than 150,000 years old and 0.6 solar masses. It's still growing, feeding on an envelope of dust and gas that hides in a cloudy veil.
But incredibly, researchers found a gap in the clouds and managed to snap a photo, and they saw something extraordinary. Webb's infrared spectra showed the presence of both warm silicon monoxide gas and tiny silica crystals near the young star. we were witnessing the moment gas condenses into a solid for the first time.
This is a big deal, because as a protoplanetary disk starts to cool, compounds begin crystallizing in a specific order based on their condensation temperatures. This is known as a condensation sequence. We can infer this sequence from our understanding of chemistry and our analyses of primordial asteroids, which are like time capsules of our early solar system.
The oldest condensates trapped in these asteroids are calcium-aluminium inclusions, or CAIs, and crystalline silicate materials. The fact that we saw both silicon monoxide gas and solid crystalline silicates around HOPS 315 indicates that this star and its system are at the very beginning of their formation.
In other words, we were watching the very first stage of planet formation as it's happening for the very first time. This was a major breakthrough, and as lead author of the landmark paper Melissa McClure puts it, For the first time, we've identified the earliest moment when planet formation is initiated around a star other than our Sun.
They wanted to explore further, so professors Melissa McClure and Meryl Vanthoff focused the Atacama Large Millimeter-Submillimeter Array Telescope, or ALMA, on this baby star.
Whilst James Webb Space Telescope revealed the warm inner regions of a young star through infrared light, ALMA specialises in observing much colder material, the dust and gas that emit millimetre and submillimetre wavelengths of electromagnetic radiation. This allows astronomers to trace the chemical composition and structure of molecular clouds.
By combining the two observatories, McClure and Van't Hoff could connect the dots. James Webb found the evidence of early planetary formation, and ALMA pinpointed where in the disk that process was taking place. What's most interesting about this is that it's roughly in the same region around HOPS 315, as asteroids made of similar materials are found around our Sun.
We don't know exactly what this means yet, but it suggests that the same early building steps for planets may happen in many young systems, and there's more. It's worth mentioning that although silicates were found, the outflow jet they studied is actually suspiciously low in silicon, the most important element for making silicates, and therefore planets.
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