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Dr. Ernst De Mooij, University of Toronto – Exoplanet Atmosphere Detection

In today’s Academic Minute, Dr. Ernst De Mooij of the University of Toronto reveals how we can explore the atmospheres of planets beyond our solar system without ever leaving Earth.

Dr. Ernst de Mooij is a post-doc at the Department of Astronomy and Astrophysics at the University of Toronto. He obtained his PhD in 2011 from the University of Leiden. His main research focuses on the study of exoplanet atmospheres using ground-based telescopes.

Ernst De Mooij – Exoplanet Atmosphere Detection

Tau Bootis b is one of the first planets discovered to orbit a star outside of our solar system. It belongs to the class of planets known as hot Jupiters, giant planets orbiting extremely close to their star which causes their day-side temperatures to be thousands of degrees. Although Tau Bootis b was not seen directly, it was discovered by measuring tiny variations in the velocity of its host-star due to the gravitational pull of the planet. Although many attempts have been made over the years to directly detect the planet itself, it has remained elusive.

Last year we observed the Tau Bootis system for 18 hours with the 8 meter Very Large Telescope in Chile. By using a new technique we were able to disentangle the light from the planet from that of its star, enabling us for the first time to detect the light from this planet. Our observations targeted a specific molecule in the planet's atmosphere: Carbon Monoxide.

By measuring the shift in wavelength of the carbon-monoxide absorption as the planet orbits its star we were able to determine both the planet's true mass, approximately 5 times the mass of Jupiter, as well as the angle of its orbit as we see it from Earth: we see the orbit under an angle of
45 degrees – half-way between face-on and edge-on.

Furthermore, our detection of Carbon-Monoxide enabled us to determine how the temperature changes with altitude in the atmosphere of Tau Bootis b. As it turns out, the temperature drops towards higher altitudes. This is also the case in the Earth's troposphere, but different for other hot Jupiters that have been observed to show an increase in temperature high up in their atmospheres – an inversion layer – just as the Earth's stratosphere. Why this temperature gradient differs from planet to planet is still a puzzle.

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