As the planet transits across its star a small portion of the starlight will filter through the atmosphere before reaching our telescopes. Imprinted on this light are the fingerprints of different atoms and molecules in the planets atmosphere. We measure the transmission spectra of exoplanets to determine their composition and gain an understanding of their origin and evolution.

Our ability to identify the consituent chemicals in exoplanet atmospheres now allows us to test theories planet formation. Hot Jupiters, large gaseous planets close to their host stars, are not believed to have formed at their current locations, instead arriving there through disk migration or scattering by other planets or nearby stars. The BOWIE-ALIGN program (JWST GO 3838), led by Dr. James Kirk of Imperial College London and Dr. Eva-Maria Ahrer of the Max Planck Institute for Astronomy, seeks to find observational signatures differentiating these migration mechanisms. Dr. Ahrer also leads a complementary program looking at the hot Jupiter WASP-94Ab (JWST GO 3154) seeking to further understand the origins of these planets

While there is significant focus on hot Jupiters in the astronomy community, members of the BOWIE+ collaboration have also been investigating temperate ("Chemistry and Clouds of a Temperate Jupiter"; GO 4227, with PIs Alastair Claringbold and Prof Peter Wheatley, both of the University of Warwick) and warm Jupiters ("Warm Jupiters: the next step in uncovering giant planet formation and migration"; GO 7982, with PIs Alastair Claringbold of Warwick and Prof James Owen of Imperial College) using transit spectroscopy as a way to understand these understudied populations of exoplanets.

When the planet passes behind the star from our point of view we can measure the difference between the light before and after the planet is eclipsed. The difference between the eclipsed light (just the star) and the light just prior/after (star+planet) will be just the planet emission. Depending on the wavelength of light we will measure the reflection or emission which can tell us about the thermal structure and the albedo.

A phase curve is the measure of the light from the combined star + planet system over a full or half orbit of the planet around the star. As the planet orbits the star different phases of the planet will appear which contribute more or less light to the measured total flux. Measurements of a planets phase curve can inform us about the redistribution of energy in the planets atmosphere, and changing thermal structure from day-to-night side.