English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

As brown dwarfs and young giant planets cool down, they are known toexperience various chemical transitions --- for example from CO rich L-dwarfsto methane rich T-dwarfs. Those chemical transitions are accompanied byspectral transitions whose sharpness cannot be explained by chemistry alone. Ina series of articles, Tremblin et al. proposed that some of the yet unexplainedfeatures associated to these transitions could be explained by a reduction ofthe thermal gradient near the photosphere. To explain, in turn, this moreisothermal profile, they invoke the presence of an instability analogous tofingering convection -- compositional convection -- triggered by the change inmean molecular weight of the gas due to the chemical transitions mentionedabove. In this short note, we use existing arguments to demonstrate that anyturbulent transport, if present, would in fact increase the thermal gradient.This misinterpretation comes from the fact that turbulence mixes/homogenizesentropy (potential temperature) instead of temperature. So, while increasingtransport, turbulence in an initially stratified atmosphere actually carriesenergy downward, whether it is due to fingering or any other type ofcompositional convection. These processes therefore cannot explain the featuresobserved along the aforementioned transitions by reducing the thermal gradientin the atmosphere of substellar objects. Understanding the microphysical anddynamical properties of clouds at these transitions thus probably remains ourbest way forward.

Why compositional convection cannot explain substellar objects sharp spectral type transitions