Exometeorology

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Not to be confused with space weather.
Gliese 1214 b
showing clouds covering the planet's surface. Because there are such a wide variety of exoplanets, air and cloud compositions and circulation patterns can vary greatly from exoplanet to exoplanet.

Exometeorology is the study of atmospheric conditions of exoplanets and other non-stellar celestial bodies outside the Solar System, such as brown dwarfs.[1][2] The diversity of possible sizes, compositions, and temperatures for exoplanets (and brown dwarfs) leads to a similar diversity of theorized atmospheric conditions. However, exoplanet detection technology has only recently[when?] developed enough to allow direct observation of exoplanet atmospheres, so there is currently very little observational data about meteorological variations in those atmospheres.

Observational and theoretical foundations

Modeling and theoretical foundations

GJ 1214b, and Kepler-1649b, a theorized Venus analog.[3][4][5][6]

These models assume that the exoplanet in question has an atmosphere in order to determine its

insolation from its star.[7] Additionally, the main causes of weather - air pressure and air temperature differences which drive winds and the motion of air masses - can only exist in an environment with a significant atmosphere, as opposed to a tenuous and, consequently, rather static atmosphere, like that of Mercury.[8] Thus, the existence of exometeorological weather (as opposed to space weather
) on an exoplanet depends on whether it has an atmosphere at all.

Recent discoveries and observational foundations

The first exoplanet atmosphere ever observed was that of

Gliese 1132 b.[11]

However, measuring traditional meteorological variations in an exoplanet's atmosphere — such as precipitation or cloud coverage — is more difficult than observing just the atmosphere, due to the limited resolutions of current telescopes. That said, some exoplanets have shown atmospheric variations when observed at different times and other evidence of active weather. For example, an international team of

shockwave-like windstorms that reverberate around the planet and distribute the sudden heat influx.[14]

Theorized weather

Artist's impression of HD 189733b, depicting a blue gas giant with white cloud tops streaking horizontally away from the tidally-locked planet's subsolar point. This exoplanet has numerous observed and theorized weather conditions, including variations in the escape speed of atmospheric hydrogen, 2 km/s winds in a jet around its equator, and rains of molten glass.
Artist's impression of HD 189733b. This exoplanet has numerous observed and theorized weather conditions, including variations in the escape speed of atmospheric hydrogen, 2 km/s winds in an easterly jet around its equator, and rains of molten glass.[15]

Empirical observations of

HD 189733b[12] or just the speeds of globally circulating winds on that same planet.[16]
However, a number of other observable, non-meteorological properties of exoplanets factor into what exoweather is theorized to occur on their surfaces; some of these properties are listed below.

Presence of an atmosphere

As mentioned previously, exometeorology requires that an exoplanet has an atmosphere. Some exoplanets that do not currently have atmospheres began with one; however, these likely lost their primordial atmospheres due to atmospheric escape

giant impacts[18]
stripping the exoplanet's atmosphere.

Some exoplanets, specifically

vaporizes and forms an atmosphere on the day side of the planet. Strong winds attempt to carry this new atmosphere to the night side of the planet; however, the vaporized atmosphere cools as it nears the planet's night side and precipitates back down to the surface, essentially collapsing once it reaches the terminator. This effect has been modeled based on data from transits of K2-141b[19] as well as CoRoT-7b, Kepler-10b, and 55 Cancri e.[20] This unusual pattern of crustal evaporation, kilometer-per-second winds, and atmospheric collapse through precipitation might be provable with observations by advanced telescopes like Webb.[19]

Exoplanets with full atmospheres are able to have diverse ranges of weather conditions, similar to weather on the terrestrial planets and

HD 189733b,[16] and atmospheric precipitation and collapse on tidally-locked worlds.[21]

Orbital properties

One of the most important factors determining an exoplanet's properties is its orbital period, or its average distance from its star. This alone determines a planet's effective temperature (the baseline temperature without added insulation from an atmosphere)[7] and how likely the planet is to be tidally locked.[22] These, in turn, can affect what chemical compositions of clouds can be present in a planet's atmosphere,[13] the general motion of heat transfer and atmospheric circulation,[23] and the locations where weather can occur (as with tidally-locked lava worlds with partial atmospheres).

For example, a

insolation than the planet's unending gravitational contraction, then it will have advective circulation patterns; if the opposite heat source is stronger, it will have convective circulation patterns, as Jupiter exhibits.[13]

Additionally, an exoplanet's average incident stellar radiation, determined by its orbital period, can determine what types of chemical cycling an exoplanet might have. Earth's water cycle occurs because our planet's average temperature is close enough to water's triple point (at normal atmospheric pressures) that the planet's surface can sustain three phases of the chemical; similar cycling is theorized for Titan, as its surface temperature and pressure is close to methane's triple point.[24]

Similarly, an exoplanet's

perihelion) is so large that the planet's effective temperature varies greatly throughout its orbit.[14] A less extreme example is eccentricity in a terrestrial exoplanet's orbit. If the rocky planet orbits a dim red dwarf star, slight eccentricities can lead to effective temperature variations large enough to collapse the planet's atmosphere, given the right atmospheric compositions, temperatures, and pressures.[21]

See also

References

  1. ^ Allers, Katelyn (2019-10-10). "Exometeorology: Determining atmospheric ..., Dr. K. Allers". Western Events Calendar. The University of Western Ontario. Archived from the original on 2023-03-14. Retrieved 2023-03-14.
  2. ^ "Exoplanets subject to meteorological variations". ScienceDaily. Délégation Paris Michel-Ange. 2012-07-10. Archived from the original on 2023-03-14. Retrieved 2023-03-14.
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  17. ^ Gianopoulos, Andrea (3 February 2022). "Puffy Planets Lose Atmospheres, Become Super Earths". NASA. Archived from the original on 26 May 2023. Retrieved 15 April 2023.
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  19. ^ a b Bartels, Meghan (5 November 2020). "This bizarre planet could have supersonic winds in an atmosphere of vaporized rock". Space.com. Archived from the original on 12 May 2021. Retrieved 15 April 2023.
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