All things solar system evolution: Planet formation, composition, and asteroid deflection

In today’s episode we look at a variety of new results related to observing how planetary systems form, where planet ends up in solar system’s (including in our own Jupiter’s atmosphere!), and how rocks get flung at Earth even today.

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Today’s Top Stories

• How Newborn Stars Prepare for the Birth of Planets
• Findings From NASA’s Juno Update Jupiter Water Mystery
• MIT engineers devise a decision map to identify the best mission type to deflect an incoming asteroid.
• Rare ice volcanoes captured erupting on Lake Michigan beach but may not stick around

One of the things we talk about is planet formation. Or, more importantly, how we really don’t understand planetary formation. Part of the problem is, we only had one example of a solar system for the nearly 400 years between when Galileo started making scientific observations and when 51 Peg was discovered to have a planet in 1995. Four-hundred years is a lot of years during which theorists could theorize about how to create solar systems just like our own. In the years since extrasolar planets were discovered, people have flailed about trying to explain the great diversity of solar systems we are now finding. Along the way, lots of contradictory ideas have been put forward. Part of the problem is we don’t have a lot of data to describe the in between steps in solar system formation. We see the big picture of star forming regions becoming star clusters. We see the proplyd step, where baby solar systems are cocooned in gas and dust. With radio telescopes we have started to see disks with what we think are forming planets. With missions like Kepler, we see fully formed solar systems in every possible configuration. What we haven’t had are observations of the intermediate step between proplyd and planetary disk. At least we haven’t had them until now.

A team of observers using the Very Large Array and the Atacama Large Millimeter Array have now observed more than 300 baby planet forming disks that are just starting to spin up. All these systems are part of the Great Orion Star Forming Region. As astronomers, we will often say things like “all the stars in a star cluster form at the same time” but the truth is, they may gradually come into existence over a million or millions of years, which from the perspective of cosmic time and stellar evolution is only a moment. From the perspective of planet formation, however, a difference of a million years can be the difference between no planets and a mostly-finished solar system. Only by looking at many different young systems did this team have any possibility of catching systems in the act of just starting to form worlds.

Out of their collection of more than 300 systems, the research team identified 4 protostars just starting to turn on; systems estimated to be less than 10,000 years old. These system’s stars have just started to form, and have slow moving jets, and they appear irregular and blobby in radio light. According to team researcher Nicole Karnath, “We think that they are in one of the earliest stages of star formation.” By studying these stars we can begin to build a detailed film of what star systems look like during a new stage of their development. 

While it may seem like a waste to observe more than 300 systems to find just 4 special systems, we want to assure you that no piece of data in this survey will go unused. This work has already produced 2 new papers appearing in the Astrophysical Journal, and has detailed how the size of protoplanetary disks evolves as the forming star in each system grows by stealing material away from the disk. It’s literally a star eat planet-forming material universe out there. 

The interplay between forming stars and their planetary disks can have profound effects on how planets form. We observe young stars blasting their inner solar systems with light; so much light that it can push material outwards and dry up the inner solar system. Just how far things get dried out is still being sorted, but we do see where all the water went – and that place is the outer solar system. What we observe is a difference of composition, with the Sun having far fewer atoms capable of combining to form water than we see of actual water in the atmosphere of worlds like Jupiter. In new data coming to us from the Juno mission, observations of Jupiter’s equatorial region show the atmosphere is roughly 0.25% water, which is 3 times what we see in the composition of the Sun. This data comes from looking at Jupiter in microwave colored light, which is readily absorbed by water. Using Juno’s Microwave Radiometer, scientists can study Jupiter’s water content at a variety of atmospheric depths to get at these water-rich results. These results don’t necessarily reflect the composition of the entire world, and future orbits will allow these same kinds of observations to be made of Jupiter’s polar regions, which have a different temperature structure and observationally don’t have the same puffy white water clouds we see in the equatorial regions. Over time, Juno is going to allow us to build a  detailed map of Jupiter’s atmosphere, but for now, it’s cool to just know there be water in them there clouds.

One of the complexities we have to deal with in trying to understand planet formation is things don’t stay where you put them. Worlds that start in one orbit may end up somewhere entirely different, as objects ranging from comets to ice giants to rocky asteroids all get tossed about through gravitational interactions. At more than 5 billion years old, our solar system has moved past the worst of its rock flinging days, but there are still objects out there hitting our planet on a regular basis. Earlier this week, a meteor fell in Europe, and it sometimes seems that every month a new object is found passing between the Earth and the Moon. While we haven’t found anything truly dangerous yet, at some point we are likely to find a city of civilization killer. Trying to figure out how to protect our planet is a top priority for a lot of scientists and in a new paper in Acta Astronautica, a team of MIT researchers describe a new algorithm for deciding how different kinds of asteroids should be deflected, based on their composition, orbit, and how far away they are when they are detected. Now… we just have to develop the technology this algorithm counts on if we want to actually be able to take its advice. But that’s a problem for another day.

For now, I’d like to round up today’s episode, but before I do I want to say that folks around Sagatuk, Michigan which is vaguely near Grand Rapids, are observing on ice volcanoes on the beaches of Lake Michigan. These amazing piles of ice are geysering slush in ways we talk about happening on other worlds and we can now see on our own. I’m not going to try and describe these fabulous mounds of hydraulic forces, instead I’m going to recommend you go check out the story