Heather Knutson

Properties of Exoplanets

Heather Knutson

For centuries, astronomers had expected that planetary systems around other stars should echo our own, with small, rocky planets orbiting close to the star and more massive gas giant planets farther out. It therefore came as a surprise when the first planets discovered around nearby stars turned out to be massive gas giants similar to Jupiter orbiting extremely close to their parent stars. Nearly two decades later, these “hot Jupiters” have turned out to be merely the tip of the iceburg; we currently know of more than two thousand extrasolar planets and planet candidates with a diverse array of properties that continue to defy our expectations of what should be out there.

For many of these planets, we know little more than their masses, orbital periods, and sometimes their radii. I use observations of eclipsing systems, where the planet periodically passes in front of its host star, to build up a more detailed picture of the properties of these alien worlds. Although much of my present-day work focuses on hot Jupiters, which are more easily observed due to their large sizes and high temperatures, my ultimate goal is to carry out similar studies on smaller and more earth-like planets.

Hot Jupiter

Current research topics include:

  1. Atmospheric circulation on short-period, tidally locked hot Jupiters. I use the Spitzer Space Telescope to measure changes in the brightness of the planet as a function of orbital phase, which indicates the size of the temperature gradient between the perpetually-illuminated day side and the darker, colder night side. By comparing circulation patterns on a diverse sample of hot Jupiters, I aim to learn more about the physical processes that shape these atmospheres.
  2. Non-equilibrium chemistry and haze formation in the atmospheres of cooler (< 1000 K) gas giant exoplanets. I use the Spitzer and Hubble Space Telescopes to search for absorption features from common molecules such as water, methane, carbon monoxide, and carbon dioxide in the spectra of these planets, and to compare the measured abundances of these molecules to the predictions from equilibrium models. These same kinds of observations can also indicate the presence of high-altitude clouds or hazes.
  3. A search for new low-mass eclipsing planets around bright nearby stars. This program focuses on planets that have already been detected using the Doppler or radial velocity technique and checks for eclipses using Spitzer photometry.
  4. Hot Jupiter migration mechanisms. We know that hot Jupiters must have formed farther out in the disk and then migrated inward, but the mechanism by which they migrated is still the subject of ongoing debate. The goal of this program is to test competing migration theories by searching for evidence of massive, long-period stellar or planetary companions in systems with hot Jupiters using the Keck Observatory.

[Image is an artist's impression of a Hot Jupiter. Image credit: ESA, NASA, and G. Tinetti.]