The Universal Presence of Nightside Clouds on Hot Jupiters Assistant Astronomer Steward Observatory – University of Arizona Thomas G. Beatty tgbeatty@email.Arizona.edu

From optical Hubble observations, we know that clouds exist at planetary dusk and dawn Sing et al. (2015)

? ? But we did not know: How common are clouds on hot Jupiters? What are the cloud properties of the daysides and nightsides? Where does cloud formation occur? ? ?

Phase curves watch an exoplanet for an entire orbit, and show day-to-night atmospheric changes

Phase curves are the main way we study the global climates of hot Jupiters

A main result from the last few years of study has been that hotter planets show larger day-night temperature contrasts Beatty et al. (2018)

faster heat re-radiation transport This has been thought to occur because of the changing balance between heat transport and re-radiation in planetary atmospheres Beatty et al. (2018)

But it also requires fine tuning to work for all hot Jupiters… faster heat re-radiation transport This balancing act should to tell us something about the atmospheric dynamics. But it also requires fine tuning to work for all hot Jupiters… Beatty et al. (2018)

Spitzer phase curves of the hot brown dwarf KELT-1b Beatty et al. (2018)

Because KELT-1b is 28 MJ, the IR photosphere is at much higher pressure than for a typical hot Jupiter We expected to see a much smaller day-to-night temperature contrast than for a typical hot Jupiter.

But KELT-1b matches the hot Jupiter trend Beatty et al. (2018)

The temperatures shows that all the nightsides are roughly the same at 1000K! clear daysides cloudy nightsides Nightside clouds are clamping the nightside emission to 1000K Beatty et al. (2018)

So instead of a delicate thermal balancing act… faster transport faster re-radiation Beatty et al. (2018)

nightside clouds The universal presence of nightside clouds naturally explains this trend, by forcing us to see all the nightsides at 1000K Beatty et al. (2018)

? ? How common are clouds on hot Jupiters? What are the cloud properties of the daysides and nightsides? Where does cloud formation occur? ? ?

How common are clouds on hot Jupiters? What are the cloud properties of the daysides and nightsides? Where does cloud formation occur? Clouds appear to be present on the nightsides of all hot Jupiters. Based on the 1000K temperature, probably silicate or manganese clouds Clouds most likely form near planetary dusk, and burn-off near dawn.

And stay tuned for Hubble observations where we try to measure the cloud properties directly!