Finding other Earths—the chemistry of star and planet formation

April 1, 2016 by Anika Radiya-Dixit, Duke University
Finding other Earths—the chemistry of star and planet formation
The Milky Way rising above the Pacific Ocean off a coast in California.

In the last two decades, humanity has discovered thousands of extrasolar planetary systems. Recent studies of star- and planet-formation have shown that chemistry plays a pivotal role in both shaping these systems and delivering water and organic species to the surfaces of nascent terrestrial planets. Professor Geoffrey A. Blake in Chemical Engineering at the California Institute of Technology talked to Duke faculty and students over late-afternoon pizza in the Physics building on the role of chemistry in star and planet formation and finding other Earth-like planets.

In the late 18th century, French scholar Pierre-Simon Laplace analyzed what our could tell us about the formation & evolution of planetary systems. Since then, scientists have used the combination our knowledge for small bodies – asteroids – and large bodies – planets – to figure out how solar systems and planets are formed.

In 2015, Professor Blake and other researchers investigated more into ingredients in planets necessary for the development of life. Using the Earth and our solar system as the basis for their data, they explored the relative disposition of carbon and nitrogen in each stage of star and planet formation to learn more about core formation and atmospheric escape. Analyzing the carbon-silicon atomic ratio in planets and comets, Professor Blake discovered that rocky bodies in the solar system are generally carbon-poor. Since carbon is essential for our survival, however, Blake needed to determine the range of carbon content that terrestrial planets can have and still have active biosystem.

Finding other Earths—the chemistry of star and planet formation
The “Astronomer’s periodic table,” showing the relative contents of the various elements present in stars.

With the Kepler mission, scientists have detected a variety of planetary objects in the universe. How many of these star-planet systems – based on measured distributions – have 'solar system' like outcomes? A "solar system" like planetary system has at least one Earth-like planet at approximately 1 astronomical unit (AU) from the star – where more ideal conditions for life can develop – and at least one ice giant like Jupiter at 3-5 AU in order to keep away comets from the Earth-like planet. In our galaxy alone, there are around 10 billion stars and at least 10 million planets. For those stars similar to our sun, there exist over 4 million planetary systems similar to our solar system, with the closest Earth-like planet at 20 light years away. With the rapid improvement of scientific knowledge and technology, Professor Blake estimates that we would be able to collect evidence within next 5-6 years of planets within 40-50 light years to determine if they have a habitable atmosphere.

How does an Earth and a Jupiter form at their ideal distances from a star? Let's take a closer look at how stars and planets are created – via the astrochemical cycle. Essentially, dense clouds of gas and dust become so opaque and cold that they collapse into a disk. The disk, rotating around a to-be star, begins to transport mass in toward the center and angular momentum outward. Then, approximately 1% of the star mass is left over from the process, which is enough to form planets. This is also why planets around stars are ubiquitous.

How are the planets formed? The dust grains unused by the star collide and grow, forming larger particles at specific distances from the star – called snowlines – where water vapor turns into ice and solidifies. These "dust bunnies" grow into planetesimals (~10-50 km diameter), such as asteroids and comets. If the force of gravity is large enough, the planetesimals increase further in size to form oligarchs (~0.1-10 times the mass of the Earth), that then become the large planets of the solar system.

Finding other Earths—the chemistry of star and planet formation
Analysis of C/Si ratios in extraterrestrial bodies revealed low carbon content in the formation of Earth-like planets. Graph displaying the locations of Earth-like planets found at 0.01-1 AU from a star, and Jupiter-like planets at 0.01-50 AU from a star.

In our solar system, a process called dynamic reorganization occurred that restructured the order of our , putting Uranus before Neptune. This means that if other solar systems did not undergo such dynamic reorganization at an early point in formation of solar system, then other Earths may have lower organic and water content than our Earth. In that case, what constraints do we need to apply to determine if a water/organic delivery mechanism exists for exo-Earths? Although we do not currently have the scientific knowledge to answer this, with ALMA and the next generation of optical/IR telescopes, we will be able image the birth of solar systems directly and better understand how our universe came to be.

To the chemistry students at Duke, Professor Blake relayed an important message: learn chemistry fundamentals very carefully while in college. Over the next 40-50 years, your interests will change gears many times. Strong fundamentals, however, will serve you well, since you are now equipped to learn in many different areas and careers.

The Astrochemical Cycle: how solar systems are formed.
Finding other Earths—the chemistry of star and planet formation
Depiction of the snow line for planet formation.

Explore further: Newly discovered planet in the Hyades cluster could shed light on planetary evolution

More information: Edwin A. Bergin et al. Tracing the ingredients for a habitable earth from interstellar space through planet formation, Proceedings of the National Academy of Sciences (2015). DOI: 10.1073/pnas.1500954112

Related Stories

What kinds of stars form rocky planets?

December 3, 2015

As astronomers continue to find more and more planets around stars beyond our own Sun, they are trying to discover patterns and features that indicate what types of planets are likely to form around different kinds of stars. ...

Largest rocky world found

February 11, 2016

We thought we understood how big rocky planets can get. But most of our understanding of planetary formation and solar system development has come from direct observation of our own solar system. We simply couldn't see any ...

Jupiter twin discovered around solar twin

July 15, 2015

Astronomers have used the ESO 3.6-metre telescope to identify a planet just like Jupiter orbiting at the same distance from a Sun-like star, HIP 11915. According to current theories, the formation of Jupiter-mass planets ...

Jupiter's movements made way for Earth

June 23, 2015

There's something about our solar system that appears to be unusual. For some reason, most of our bigger planets are far away from our host star, while closer in are smaller, rocky worlds, including Earth itself.

Recommended for you

Coffee-based colloids for direct solar absorption

March 22, 2019

Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal ...

EPA adviser is promoting harmful ideas, scientists say

March 22, 2019

The Trump administration's reliance on industry-funded environmental specialists is again coming under fire, this time by researchers who say that Louis Anthony "Tony" Cox Jr., who leads a key Environmental Protection Agency ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

wduckss
1 / 5 (2) Apr 01, 2016
"Essentially, dense clouds of gas and dust have become opaque and cold that they collapse into a disk. The disk, rotating around a to-be old, begins to transport mass and toward the center and angular momentum outward. Then, approximately 1% of the old mass is left over from the process, which is enough to form planets. this is also why planets around stars are ubiquitous. "

Why rotating cloud? What is in the center of the cloud which causes "collapse"? Why the composition of the stars emerged in the center of the cloud (99% of matter) is hydrogen, helium and ~ 1% of these particles and the planet (the other 1%) have the same (gaseous planets) and a completely different composition (other bodies)?
How does the factory for the creation of more complex elements, and why is has somewhere, and somewhere in there is no? ..

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.