Characterizing Planetary Atmospheres

How can we identify and learn about an exoplanet's atmosphere?

The Transit Method

Simply put, a transit is an event where a planet passes between it's host star and an observer.

A transit allows us to see an exoplanet from many, many light years away not through direct imaging by seeing the planet itself, but seeing dimming of the star's brightness during the transit period.

This dimming can yield a surprising amount of data about a planet and can tell us about the planet's orbit, it's size, and even the planet's atmospheric composition.

The most successful method of exoplanet detection

To date, over 4,000 exoplanets have been discovered by astronomers all over the world. The bulk of these discoveries (around 75%) were made using the transit method.

Characterizing Atmospheres

Exoplanet atmospheres can be studied by observing their transits at different wavelengths. For instance, planets with atmospheres similar to Earth may produce deeper transits at shorter (bluer) wavelengths. You can see this phenomenon in action below!

POET will use this technique -- known as transit spectroscopy -- to detect whether an exoplanet has an atmosphere and provide important clues about what it is made of. These observations will be used to identify exoplanets that are suitable for further, more detailed atmospheric characterization studies using the James Webb Space Telescope.

Questions POET will investigate:

• What are the statistical properties of exoplanet atmospheres?
• Are most exoplanet atmospheres hazy like on Venus or clear like on Earth?
• When does an atmosphere transition from cloudy to clear?
• How does atmospheric scattering depend on the amount of energy the planet receives from its host star?

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