UND astronomers use novel approach to detect elements on exoplanets

Recent publication in The Astronomical Journal details techniques used to detect sodium in atmosphere of KELT-10b, a distant ‘hot Jupiter’ planet

Imagine capturing a photo of a fly buzzing past a light bulb, and how delightful that would be for a bug-obsessed entomologist.

The brightness of the bulb would highlight impressive details about the creature – how its translucent wings are structured, or how many tiny hairs surround its legs. Observers would have a fresh new perspective on their subject of study.

Discovered in 2015, KELT-10 is a little younger, slightly hotter and 40 percent brighter than our sun. But KELT-10b, the only planet orbiting the star, is a gas giant like Jupiter that orbits its star ten times closer than Mercury’s path around the sun. A year lasts merely four days on KELT-10b.

Now apply that imagery to a situation occurring more than 600 light years from Earth, where a star much like our own is telling UND astronomers about a planet unlike anything we’d find in our solar system.

At UND’s Department of Space Studies, observations of this “Hot Jupiter” planet are being used to better understand the formation and characteristics of exoplanets – planets and planetary systems beyond our own.

In turn, their work will help fellow exoplanet experts more efficiently interpret data collected by ground-based telescopes that have to regularly contend with Earth’s atmosphere.

Ph.D. student Sean McCloat and Assistant Professor Sherry Fieber-Beyer at the John D. Odegard School of Aerospace Sciences recently published “Atmospheric Transmission Spectroscopy of Hot Jupiter KELT-10b using Synthetic Telluric Correction Software” in The Astronomical Journal. The two collaborated with Assistant Professor Carolina von Essen of Aarhus University, a co-author of the article.

As KELT-10b celebrated “New Year’s Eve” by passing in front of its star, relative to Earth, McCloat used novel software techniques to detect elements in KELT-10b’s hot, gaseous atmosphere.

McCloat employed the “fly and lightbulb” analogy to explain the nature of transit spectroscopy, the term for observing the electromagnetic signature of a planet passing in front of its star.

“In this project, we were in effect waiting for the light to shine through the fly’s wings, so we could figure out what those wings are made of,” he said.

Searching for signs of life

A key reason for studying exoplanets for McCloat and his faculty mentor, Fieber-Beyer, is the search for extraterrestrial life. By studying the elements found in exoplanet atmospheres, astronomers can look for signifiers of life – elements that correlate with what we know as bio-signatures.

KELT-10b, with its extremely close proximity to a star, is obviously out of the running for harboring life as we know it. But the peculiar planet is an excellent proving ground for refining the way scientists observe exoplanets more broadly, according to McCloat and Fieber-Beyer.

Simply put, it’s a big, gassy planet that passes in front of its star very often. When the planet passes, what we see on the electromagnetic spectrum changes, and those changes can be further interpreted to identify elements.

By using a 2018 observation of KELT-10b, plus software that adjusted the telescope data for Earth atmosphere conditions at the time, McCloat was able to detect the presence of sodium 614 light years away from UND.

“Getting this type of spectral fingerprint is a very new technique in observing exoplanets,” Fieber-Beyer said. “And through what Sean has developed in the correction software, we can potentially observe exoplanets as finely as our own solar system.”

“This work shows the important research our students and faculty are doing in atmospheric composition of exoplanets, which is a completely new area,” said Pablo de León, professor and chair of the Department of Space Studies. “This knowledge is being developed right here, in North Dakota, and will help us to better understand our universe.”

To get past the noise

To redeploy the “fly and lightbulb” analogy, imagine trying to look through a glass of water at the fly passing the bulb. That’s what it can be like to use telescopes on Earth’s surface to look at distant objects, according to McCloat. The atmosphere creates extensive noise and interference on the electromagnetic spectrum.

Typically, ground telescopes – such as the Very Large Telescope (VLT) responsible for the 2018 readout used by McCloat in the project – have relied on observing “standard stars” to account for Earth-bound interference when looking at other stars and exoplanets. This meant using precious, expensive telescope time to look at very well known stars for the sake of corrective measurements.

“What we did was use software to create a model of what the atmosphere looked like at that time, and at the location of observation,” McCloat said.

In the case of the VLT, McCloat’s software used data from the National Oceanic and Atmospheric Administration to approximate conditions high up in the Atacama Desert of Chile, at the Paranal Observatory.

Operated by the European Southern Observatory, the VLT’s 2018 data was made available to McCloat by von Essen, who’s a fellow astronomer in Denmark and a co-author of the published study.

Alien worlds abound

Sodium is particularly easy to see, with respect to the way it appears in the electromagnetic spectrum, McCloat said. The first measurement of an exoplanet atmosphere, published in 2002, was of sodium.

“But that was done by the Hubble Space Telescope,” McCloat remarked. Now, techniques are advancing to make this work possible on the ground, between a larger variety of telescopes. That’s important, because sodium’s signature can illustrate broader qualities of the planet in question. A strong sodium signal suggests an extensive atmosphere and larger planet, and so on.

“This type of research will help us understand more about how planets form and how systems of planets change over time,” McCloat said. “Until recently, we’ve only known Jupiter-type planets to exist farther from the star. In a very real sense, KELT-10b is alien to us.”

Another implication of the paper – published in one of the world’s foremost astronomical journals – is that by learning how to be more efficient in accounting for Earth’s atmosphere, it will be easier to start looking at Earth-like planets.

Thus, as astronomers continually eliminate electromagnetic “noise” from our telescopes, the search for life elsewhere can continue in earnest.

Career highlight

Fieber-Beyer was proud to see McCloat work through the data and earn first billing on the research article. In her words, he put in the work to deserve the authorship.

“He’s been really great as a student and instructor in our department, and he came up with phenomenal results,” Fieber-Beyer said. “I’m very proud of what he’s achieved through his years of research.”

McCloat said that the accomplishment of finishing and publishing the paper is a highlight of his career as a graduate student. He’s been working on the paper since the original KELT-10b data was obtained in 2018, he said.

“The work I’ve been doing with Dr. Fieber-Beyer and UND’s own telescopes has built my understanding to the point where I could do a project like this,” McCloat said. “And it’s really a big building block on top of what I’ve already built at UND.

“It feels very good to have these past few years of work acknowledged with the first author publication.”

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