White dwarfs’ exoplanets – what do we know about them?

A booming area of space science is the study of “exoplanets”, the term for planets outside our Solar System. Telescopes like the Transiting Exoplanet Survey Satellite (known as TESS) are showing us how common exoplanets are. Scientists employ many approaches when studying exoplanets. One approach is to study the composition of rocky material orbiting white dwarfs. We spoke with Alexandra Doyle, a UCLA graduate student, to learn more about this approach.

What do your studies tell us about the presence of Earth-like planets in other planetary systems?

The reason we want to look at rocky bodies in other planetary systems is so that we can compare them to rocky planets in our Solar System and see how similar they are. Specifically, the geochemistry and geophysics of interiors of exoplanets are crucial, because they can determine important parameters for habitability of a planet, such as, whether or not it has a magnetic field, what the atmosphere will look like, and the existence of plate tectonics. The geochemistry that we examine in this study can affect all of these parameters and we show that this parameter is similar, for the rocks forming around other stars, to those in our Solar System. The more similar rocks around other stars look like the rocks that made Earth, the more likely it is that there are habitable planets like Earth out there. This is an important piece in the habitability puzzle.

How does this research fall into the larger body of scientific work being done on exoplanets?

Many of the studies trying to define the geochemistry of rocky exoplanets use either mass-radius relationships or use the chemistry of the star that the bodies are orbiting. One of the neat things about using white dwarf stars is that we know that the elements we are measuring are coming from the rocks themselves. So, we are directly probing the geochemistry of the rocky bodies, without having to make so many inferences.

How did you become interested in studying exoplanets?

I actually have a background in geology and mathematical economics! When I began in the Earth, Planetary, and Space Science department at UCLA, I was amazed at how interdisciplinary our department was, and how often my advisor collaborated with the Astronomy department. This isn’t very common. But, between the geochemistry know-how of myself and the other corresponding author, Ed Young, and the vast knowledge of astrophysics, statistics and white dwarfs of the other co-authors, our group at UCLA has constrained, and is continuing to constrain, very specific geochemical parameters in rocky bodies that used to orbit these white dwarf stars. It only took one discussion about the topic for me to realize that I wanted to be a part of it!