Postdoc Spotlight: Matt Clement Explains New Evidence for How Jupiter and Saturn Formed

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Tuesday, October 27, 2020 

One feature of our Solar System is that our planets come in many different sizes and compositions—ranging from tiny rocky Mercury to the gas giant Jupiter. However, over the past decade, astronomers began to study planetary systems outside of our own and were surprised to find that, in most cases, they don’t look like ours. A lot of systems seem to have equally spaced planets of a similar size

This difference has brought up some crucial questions, like: Was our Solar System ever this orderly? If so, what upset the lineup so dramatically? When did it happen? Why are we different? Was it that difference that led Earth to develop life?

The current theory is that early in the Solar System’s development, there was an instability—likely led by the push and pull of the system’s gas giants—that ultimately brought about our current planetary configuration. 

Matt Clement is a Postdoctoral astrophysicist at the Earth & Planets Laboratory who uses computer modeling to piece together this complex story of how our early Solar System formed. As Clement puts it, trying to figure out what happened “is a bit like trying to understand how to make a smoothie only by tasting the final product.” 

Recently, Clement published a paper entitled, Born eccentric: Constraints on Jupiter and Saturn’s pre-instability orbits. In this paper, Clement presents new birth conditions for Jupiter and Saturn and how this further information can help explain the current configuration of our Solar System.

For this Postdoc Spotlight, we sat down with Clement to discuss this recent work, the Solar System, and how he became interested in this area of research. Read the full interview below. 

1) Who are you, and what do you do here at the Earth and Planets Laboratory (EPL)?  

Hi, I’m Matt Clement, and I’m an astronophysics Postdoc at EPL.  

2) What is your area of research, and why is it important? 

I use computer simulations to study the formation and dynamical evolution of the Solar System and other similar planetary systems. In particular, my research focuses on the formation of the Solar System’s terrestrial planets. 

Astronomers think that the Earth’s genesis was sculpted and regulated by early orbital disturbances from the giant planets—namely Jupiter and Saturn. I have been working to reconcile our understanding of the conditions that gave rise to these massive giants and how they ended up in their current configuration. 

This work is important because the evolutionary path that Jupiter and Saturn embark on significantly affects the young Earth. Understanding how our giant planets might have evolved differently than those in other planetary systems helps us understand and characterize the habitability requirements elsewhere in the cosmos. 

3) Why study our Solar System? 

Studying the early evolution of the Solar System helps us better understand the Earth and its overall place in the universe. 

While exoplanet science has undoubtedly revolutionized our knowledge of planetary systems, the Solar System's geologic and observational accessibility makes it an unparalleled laboratory in which to study planet formation.

4) How did the Solar System form? 

We are reasonably sure the giant planets (Jupiter, Saturn, Uranus, and Neptune) formed much quicker than the terrestrial planets (Mercury, Venus, Earth, and Mars) and were born in a more compact configuration, closer to one another than they exist in today. Sometime after their formation, we think that the entire Solar System experienced a global orbital instability, wherein the orbits of the planets changed drastically and rapidly.  

Through this process, the Solar System likely lost one or more planets, and the outer Solar System was rapidly reshaped from its primordially compact architecture into the diffuse collection of orbits that we observe today.  Much of the record of the Solar System’s birth was erased in this instability, so we must use large numbers of computer simulations (>6,000 in our recent paper) to decode what happened during the instability, how it perturbed different objects like asteroids and the tiny terrestrial worlds, and what the conditions were when the planets were born.  

This animation shows how the instability event ultimately sculpted the formation of the terrestrial planets. Credit: Matthew Clement. 

This is a bit like trying to understand how to make a smoothie only by tasting the final product.  Most of the information about how the ingredients went in is lost during the mixing process, and you have to try and reverse engineer what the recipe was

5) You recently published research that constrains Jupiter and Saturn's "birth" location. Can you summarize your findings? 

One problem that has plagued instability models for a while now is understanding how Jupiter’s orbit got so eccentric and elliptical (non-circular).  

In the past, simulations that can reproduce Jupiter’s current orbital shape tend to push Saturn too far out into the outer Solar System, beyond where Uranus is today. So we focused on that problem for this research. 

We used initial conditions consistent with models of the giant planets forming in gaseous protoplanetary disks to more consistently generate Jupiter and Saturn-like orbits. 

Our research indicates that the Solar System isn’t all that different from other detected systems in terms of the orbits on which Jupiter and Saturn were born. 

6) You found that Jupiter and Saturn likely started forming in a 2:1 resonance instead of the previously thought 3:2 resonance. What does that mean, and how does it affect what we know about these two planets? 

As giant planets form in their primordial gaseous nebula, they experience various forces that cause them to radially migrate in the disk. They move around, and their orbits get smaller and larger. As they move around in the gas disk, more massive planets like Jupiter and Saturn can fall into what we call “resonances” with one another. We see this all the time in our Solar System and other planetary systems.  

So, in the simplest terms, this type of orbital resonance is where the planets’ orbit is an exact integer ratio to each other (2:1, 3:2). To get a picture of this, imagine Jupiter going around the Sun exactly two times for every one time that Saturn goes around. 

To understand our Solar System, we must understand which resonance Jupiter and Saturn formed in.

Early work favored a situation in which Jupiter went around the Sun two times every three times Saturns went around. So, they would start forming relatively close to each other. One of the consequences is that they are so close that they never develop their own isolated gap in the gas disk, and they end up on very circular orbits, which they don’t have today.  

Our recent work indicates that a  2:1 resonance is more likely. The advantage of being in the 2:1 is that the two giants can carve out their own groove in the gas, and their orbits start to get less circular and more elliptical. In this configuration, we found that they are more likely to end up in the arrangement we see today.  

Essentially, by not starting as close to each other, they don’t perturb each other as wildly when the instability kicks off, and Saturn doesn’t get pushed out deeper into the outer Solar System.  

7) Does this work change how we look at the way our Solar System and planets formed? Why is this important? 

Understanding how Jupiter and Saturn acquired their orbital shapes and mutual spacing may not seem like that big of a deal. However, it turns out that the interplay of the two gas giants' orbits drives a fair amount of the Solar System’s evolution as a whole.  

Jupiter makes up about 2/3 of all the total mass in planets, asteroids, and comets in the Solar System, and Saturn comprises the majority of the rest of the material. The orbital dance that Jupiter and Saturn perform today drives many dynamical effects in the Solar System and likely affected the Earth’s growth in the past. 

Our new work does a much better job of consistently replicating the current Solar System in our models. We now have a handy set of simulations that we can take and study to understand Jupiter and Saturn’s effect on the terrestrial planets, their impact on the outer Solar System, and their effect on comets and asteroids. 

This could help us understand why Earth is a nice temperate and water-rich place where we can live, while Mars and Venus are quite inhospitable to life as we know it.

8) What inspired you to start looking at this question? 

My Ph.D. research involved studying how the Solar System’s instability sculpted the terrestrial planets. In particular, we found that Jupiter’s orbital influence likely stunted Mars’ growth (Mars is only about 10% the mass of Earth, and this is a big reason why the two worlds are so different) and was responsible for delivering water-rich asteroids to the Earth.  

However, we found it very difficult to accurately match Jupiter and Saturn’s orbits with conventional models, which led us to begin looking at these problems with the instability in more detail. 

7) How would you say your background influences your research? 

Before grad school, I spent five years on active duty in the Navy on a submarine. I spent a good amount of my time maintaining the ship’s nuclear reactor and the various mechanical and electrical systems that support its operation. I think this “engineering mindset” helps influence my approach to research today. 

8) When you're not simulating Solar System evolution, what do you do for fun? 

I spend most of my free time just hanging out with family and friends. I also find car and house projects very satisfying.  I enjoy playing guitar, though I don’t really have the free time to play with other people as much anymore. 

Matthew Clement (middle) plays guitar with the Dielectric Breakdown. Credit: Matthew Clement. 

Back when I was in the Navy, I was in a cover band and played some bar gigs with some of my classmates in nuclear power school in Charleston, SC.  We called ourselves “Dielectric Breakdown,” which we settled on by going through the index sections of our various textbooks to find a term that would make the coolest sounding band name. 

9) If you could meet one of your science heroes, who would it be? 

I have always been very interested in the Apollo space missions. I got a chance to see Neil Armstrong give a talk as an undergrad a couple of years before he passed away.  I also met with Harrison Schmitt, who walked on the moon on Apollo 17, with a group of around ten undergrads.  

I’ve read most of the various Apollo astronauts’ books, and my favorite is Mike Collin’s book “Carrying the Fire.”  It does a great job of telling the story of a regular person going on the amazing journey of Apollo 11. So I’d say it would be incredibly cool to meet him.

10) Do you have any advice for current grad students in your field? 

I’d say to remember that Rome was not built in a day, and thus your thesis can’t be written in a day. I think some students can end up losing the forest for the trees when it comes to getting through grad school.  It helped me to try and focus on moving forward towards the goal of finishing.   

I tried my hardest to have a goal every day of what I wanted to accomplish, in addition to weekly, monthly, and yearly milestones. You layout the essential things to help you build your thesis and be marketable on the backend.  In a given year, I’d have a big project I was focusing on completing and publishing, a couple I was focusing on getting off the ground, and also goals for smaller things that are still important for getting your research out there and getting a job in astronomy: like going to a certain number of conferences, talking to a certain number of people while there, and so on.

You can learn more about Matthew Clement and his research on his website.