Daniel Apai
Daniel Apai

The Italian priest Giordano Bruno was burned at the stake in 1600 for, among other things, imagining an infinite number of other worlds, and claiming that “Innumerable suns exist; innumerable Earths revolve about these suns.”  Modern astronomers are proving Bruno right—there really are innumerable suns with innumerable planets revolving around them.

An extrasolar planet, or exoplanet, is a planet outside our Solar System.  As of early September, a total of 836 exoplanets have been found. Astronomers now believe that more than half of all sun-like stars harbor at least one planet, leading to the estimate of at least 160 billion exoplanets in our own Milky Way galaxy.

The question that immediately comes to mind: Among all these planets, are there any other Earths?

Daniel Apai, a foremost researcher on exoplanets and a professor at the University of Arizona, will speak about the properties of the known exoplanets and the prospects for habitable planets at the Academy Village on Thursday afternoon, Oct. 4th.

Direct imaging of exoplanets is extraordinarily difficult because the brightness of the parent star overwhelms the faint light from the planet.  So most planets are found by indirect methods, such as looking for wobbles of the star position as the planet tugs on it, or sudden drops in starlight as the planet passes in front of the star.  The Kepler satellite watches thousands of stars, looking for dips that would signal a planet.

Apai and his group of students and postdoctoral scientists study exoplanets by high-contrast imaging, by observing exoplanetary transits and eclipses, and by theoretical modeling of the conditions for formation of exoplanets.

Apai is particularly interested in the formation of habitable planets and the characterization of their atmospheres, including the search for biomarkers—chemical signatures for the existence of life.

He studied physics at the University of Szeged in Hungary and obtained a Ph.D. in astrophysics from the University of Heidelberg for research carried out at the Max Planck Institute for Astronomy. He has been a postdoctoral researcher at the University of Arizona and an assistant astronomer at the Space Telescope Science Institute, before becoming an assistant professor of astronomy and planetary sciences at the University of Arizona

Planets Outside Our Solar System: Oct. 2012
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