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Less Shine on the Crazy Diamond

By Gregg Sangillo

AU alumna Johanna Teske was part of a team whose research refuted the existence of the so-called “diamond planet.”

AU alumna Johanna Teske was part of a team whose research refuted the existence of the so-called “diamond planet.”

Johanna Teske is getting ready to defend her doctoral dissertation in the spring. It’s an arduous process for any graduate student, but Teske has already demonstrated a knack for innovative scholarly research. In October of this year, she made national news.

Teske, who earned her bachelor’s degree in physics from American University in 2008, is now a graduate student in astronomy at the University of Arizona. She’s done extensive research on exoplanets—planets that exist outside our Solar System—and their host stars. Teske took an interest in one host star in particular, 55 Cancri, which has five planets orbiting it, including a 'super-Earth' 55 Cancri e.  

Earlier research in 2010 on the host star, and in 2012 on its super-Earth exoplanet, suggested that 55 Cancri e had an abundance of carbon, the chemical element that makes up diamonds. And so a glorious, almost mythical notion of a “diamond planet” was born.

However, there’s now a little less shine on the diamond planet. Teske and a team of researchers observed the host star and determined that the planet may be less carbon-rich than previously assumed. An article on the group’s findings appeared on and was picked up by

“For a graduate student to get national press for one of her research projects is quite rare,” says Nathan Harshman, an AU physics professor who served as Teske’s internship adviser and mentor while she was an undergraduate.

The Devil in the Details

So how did Teske make her discovery? With any research of this magnitude, the devil is in the details.

Scientists can determine a planet’s composition by its density, which is derived from its mass and radius. Another way to understand the interior makeup of a planet is by analyzing the composition of its host star (the same material that makes up a star is also found in its planets).

A 2010 paper by scientist Elisa Delgado Mena and others measured the composition of 55 Cancri, finding a high carbon-to-oxygen ratio. A subsequent paper in 2012 led by Nikku Madhusudhan combined this assumption about the host star with detailed modeling of the super-Earth exoplanet to derive a “diamond-rich” composition.

Teske noted that the 55 Cancri star is cooler and more metal-rich than the sun, and configuring the carbon-to-oxygen ratio is a bit more complicated in this instance. “I saw that this prediction of the planet being a diamond planet was based pretty heavily on this star being carbon-rich, and so I thought, ‘Is that a good assumption?’” she explains.

So Teske realized that she needed to dig a little deeper and use a wider base of information to determine the carbon-to-oxygen ratio. Through archival data, she examined the light and energy as it emanates from the star.

Not all of the star's light makes it out of its atmosphere, creating lines in the star’s spectrum. These lines correspond to different chemical elements, acting like fingerprints and helping the researcher more accurately measure the elements in a particular star.

Teske used a larger number of lines that indicate the abundances of carbon and oxygen, as well as higher-quality data, to make her measurement. Through this, she concluded that the star’s carbon-to-oxygen ratio was significantly lower than the 2010 paper reported, calling into question a key piece of evidence for the carbon-rich diamond planet.

From a Small Town

Teske was born in Harrisburg, Pa., where she lived before moving with her family to the small farming town of Palmyra in Lebanon County. Growing up, she didn’t even have a working telescope, and she wasn’t planning on a career in astronomy. But she was inclined towards the sciences, developing an interest in cosmology and devouring the work of Stephen Hawking.

“When I was a kid, I was always asking questions. And I liked museums a lot and I read a lot of books. And that’s continued. I like to know how things work, and why they work certain ways. That’s always been my motivation,” she says.

AU Undergraduate Years

After getting a scholarship to AU, Teske majored in physics but also took a heavy load of chemistry classes. She speaks fondly of her time at AU, and she appreciated the special attention she got in the Physics Department.

“I knew all my professors really well, and they were available a lot of the time to give me help and advice. And it was just a very tight-knit community.”

The feeling was mutual, as professors in the Physics Department were particularly impressed with Teske. “She was doing mature, independent research as an undergraduate,” says Harshman. “She was remarkable from day one.”

The Path to Discovery

These days, Teske is applying for a number of post-doctoral positions. She plans to continue doing high-level research, and hopes to combine this with teaching opportunities.

Teske is motivated by a passion for her work. She says research can be tedious, with hour upon hour spent analyzing data in front of a computer screen. Unlike in the movies—when a scientist or researcher expresses euphoria at the moment of breakthrough—Teske doesn’t immediately bask in her success.

“In terms of ‘aha’ moments, I don’t really have a lot of those. Even when you make a measurement, there’s a lot of necessary work after that to make sure it’s not wrong,” she says. “Most of the time for me, it’s a much more gradual process of discovery.”