It's been almost a decade since Dr. Stefan Cartledge introduced PHYS 324: Astrophysics – Origins of Planetary Systems to students at MacEwan University. That's a long time, considering that the existence of exoplanets (planets that go around stars that aren't our sun) was only proven 27 years ago.

"Back when films like Star Wars and Star Trek were released, we couldn't prove that there were planets beyond our solar system," says the assistant professor in the Department of Physical Sciences.

Dr. Cartledge always kicks off the course, one of only a few of its kind in Canada offered to undergraduates, with the terminology of star systems and a lesson on how stars and planets form. He describes the process of exoplanet formation like a recipe. The ingredients are the elemental gases and dust that exist in clouds within the interstellar medium (ISM), and that collide and stick together as they orbit a star. The ISM, areas in between solar systems, has been the focus of Dr. Cartledge's research since grad school. 

"I get to tell my students that I came up with part of the recipe," he says with a smile. For years, Dr. Cartledge has focused his research on distant stars in the galaxy, trying to figure out the amounts of certain elements – oxygen, krypton, germanium, iron and silicon – that existed around them in different directions. 

The goal – and Dr. Cartledge's contribution to "the recipe" – was demonstrating how well-mixed the elements are within the galaxy. He began with a study that looked at the material in the gas space – big clouds of gas between the stars – then researched solid material in the dust space. 

"If we measure a certain amount in gas based on what we know about how the amounts vary from star to star, we can infer the total, which is gas plus dust, should be well mixed in the area of the galaxy that's near the Earth." 

Knowing that the ISM is well-mixed makes it possible for researchers to more easily identify anomalies – and study the cause of those differences. Among astrophysicists, the ISM isn't considered particularly exciting, confesses Dr. Cartledge, but it's what comes from all that gas and dust that captures his interest. 

"I  think it's the idea of seeing something that nobody's seen before – that innate human desire to see what's beyond the next hill or on the other side of that body of water. Space plays into our explorer instincts."

Sharing his fascination with exoplanets was the inspiration for PHYS 324. With help from his research partner, Dr. Martin Connors, at Athabasca University (AU), Dr. Cartledge's students use the AU's robotic telescope to observe a known exoplanet. They use the transit method, the easiest and most informative of the five key ways to detect extrasolar planetary systems.

"If you stare at a star long enough, if there's a planet going around it and if that planet's orbit lines up with your line of sight, you'll see a shadow as it travels in front of the star," explains Dr. Cartledge. "That's a transit." 

Students use their observations to figure out the planet's characteristics, which connects to conversations in the class about determining whether a planet is habitable. 

"NASA scientists are suggesting that within 20 years, we may be able to find a planet that's close enough to Earth-like to be habitable," says Dr. Cartledge. "With studies suggesting there could be as many as 20 billion Earth-like planets in our galaxy, the odds that we're the only planet that has life seems pretty slim." 

While Dr. Cartledge isn't currently on the hunt for new exoplanets, he does work with student researchers to confirm the existence of those found by others. In Winter 2023, he has two students working on independent studies – one who is developing better tools to observe exoplanets and another who is observing supernovas near giant molecular clouds in the ISM.

"If these courses had existed when I was an undergrad, I would have taken them like a shot," says Dr. Cartledge. "It's exactly what I wanted to know growing up watching re-runs of Star Trek and imagining myself on the Enterprise going to all these different places, seeking out new life and new civilizations."