Astrophysics (Index)About

atmosphere

(envelope)
(gas surrounding astronomical object)

An atmosphere is basically any gas surrounding a celestial body such as a star or a planet. It is sometimes referred to as an envelope around the body. (For planets, the term envelope is sometimes used to mean the material above the core, a common usage in discussions of planet formation and early life, in which case the term is sometimes qualified, e.g., gaseous envelope.) A stellar atmosphere is the star's photosphere and outward, i.e., the part that directly emits or modifies the electromagnetic radiation sent into space. A planet or moon's atmosphere may be a significant portion of its mass, e.g., a gas giant, or nearly nothing, e.g., the Moon.

bodyfraction which is gas
Jupiter>95%
Uranus and Neptune~10%
Venus0.01%
Earth1/1,000,000
Moon3×10-19

The body's atmosphere is of interest in itself as well as the hints it provides regarding the character of the body, and also as a factor in habitability and biosignatures. Emitted EMR and transmission spectroscopy are hints to its makeup, and any evidence of chemical mixtures that should not last, i.e., out of chemical equilibrium, indicates something replenishing the mixture, e.g., a reaction with the surface, or a emission from inside the planet, or life. Atmospheric models and climate models (e.g., one dimensional climate models or MarsWRF) are created to study and explain planetary atmospheres.

The Earth's atmosphere serves as a well-studied example of a planetary atmosphere. Its effects on astronomical observation (atmospheric windows and seeing) have motivated analysis also useful for understanding other atmospheres.

Atmospheric retention and its lack (atmospheric escape) are of interest, both to explain observations of a body's atmosphere (or its lack) and to establish that an atmosphere is being replenished, if it ought to be gone. Its temperature, the body's gravity, and the mass of the molecules determine if some molecules reach escape velocity and are lost: for example, hydrogen molecules are sufficiently light that the Earth's temperature assured they haven't remained. Photodissociation can break molecules into smaller units, affecting retention, as can gravitational separation, i.e., chemical differentiation, stratification of the atmosphere by molecular weight.

The phrase bulk atmosphere (and similar phrases, such as bulk planetary atmosphere) refers to the entire atmosphere, e.g., when speaking of its composition, it can indicate you're speaking of components of the entire atmosphere rather than what is at some particular portion.


(planets,stars,Sun,gas)
Further reading:
http://en.wikipedia.org/wiki/Atmosphere
http://en.wikipedia.org/wiki/Stellar_atmosphere
http://en.wikipedia.org/wiki/Extraterrestrial_atmosphere

Referenced by pages:
abiotic oxygen
ablation
absorption
absorption line
admittance
advection
aerosols
airglow
airmass
air shower
albedo
adaptive mesh refinement (AMR)
antimatter
adaptive optics (AO)
apparent magnitude (m)
ARGOS
atm
atmosphere formation
atmospheric escape
atmospheric model
atmospheric temperature profile
atmospheric tide
aurora
autoconversion rate
Black Widow Pulsar (B1957+20)
bar
baroclinicity
black hole merger
biosignature
bow shock
brown dwarf (BD)
Brunt-Väisälä frequency
BT-Settl
carbonate-silicate cycle
carbonate system
carbon star (C)
Cassini
CCAT-prime (CCAT-p)
chemical equilibrium (CE)
methane (CH4)
Cherenkov detector
Cherenkov radiation
chromosphere
CMB anisotropies
carbon dioxide (CO2)
cold trap
Colossus Telescope
comet
Coriolis force
corona
Cherenkov Telescope Array (CTA)
diffraction limited
DISORT
diffractive interstellar scintillation (DISS)
deformable mirror (DM)
Dragonfly
radial-drift barrier
drogue chute
dynamical instability
Earth
earthshine
eccentricity (e)
exoplanet eclipse light curve
eclipse mapping
emission
ethylene (C2H4)
extreme ultraviolet (EUV)
evaporation
ExoCTK
exosphere
extinction
fluorescence
focal plane tilt
forbidden line
forward model
free streaming
gas flow
G-CLEF
general circulation model (GCM)
Gemini Observatory
geosignature
giant planet
GJ 1132 b
GJ 1214 b
gray atmosphere
greenhouse effect
molecular hydrogen dissociation front (H2 dissociation front)
habitability
Hadley cell
High-altitude Water Cherenkov Observatory (HAWC)
acetylene (C2H2)
HD 80606 b
helium planet
helium rain
HITRAN
homopause
humidity
hydrodynamic equations
hydrodynamic escape
hydrodynamics
hydrology
hydrostatic equilibrium
image stabilization
internal gravity wave
ionosphere
intertropical convergence zone (ITCZ)
Infrared Telescope Maffei (ITM)
Jeans escape
Jeans parameter (λ)
Juno
Jupiter
Kuiper Airborne Observatory (KAO)
Kelvin waves
Kelvin-Helmholtz instability (KHI)
Lyman-break galaxy (LBG)
lattice Boltzmann method (LBM)
light pollution
limb
limb darkening
liquid planet
Lorentz force
lucky imaging
lunar water
magnetometer
Mars
Mars 2020
Mars Express
mass density
mass extinction
mass spectrometer
Mauna Kea
MAVEN
M dwarf
Mercury
meridional flow
metallicity (Z)
meteoroid
magnetohydrodynamics (MHD)
microwave
Mie scattering
MITgcm
mixing length theory
mixing ratio
MUSCLES
Neptune
numerical weather prediction (NWP)
occultation
one dimensional climate model
optical depth (τ)
Orbiting Wide-angle Light Collectors (OWL)
PAH emissions
PanCET
passive dust
planetary boundary layer (PBL)
post-common envelope binary (PCEB)
pointing error (PE)
phase curve
PHOENIX stellar model
photoevaporation
photometry
plane-parallel atmosphere
planetary differentiation
planetary protection
planetary science
planet formation
planet structure
plane wave
Pioneer Venus Orbiter (PVO)
precipitable water vapor (PWV)
radioactive dating
ram pressure
Rayleigh scattering
red noise
reducing atmosphere
regolith
retrieval
Reynolds decomposition
Reynolds number (Re)
radiative forcing (RF)
Richardson number (Ri)
Rossby number (Ro)
rocky planet
Rossby radius of deformation
Rossby waves
radiative transfer code (RT code)
radial velocity method
scale height (H)
supercritical fluid (SCF)
Solar Dynamics Observatory (SDO)
spectral energy distribution (SED)
seeing
solar constant
sounder
stationkeeping
stellar atmosphere
stellar structure
stellar temperature determination
strewn field
subgrid-scale physics
sublimation
Sun surface features
super-Earth
superrotating wind
surface reaction
surface temperature
TAM
Taylor-Proudman theorem
telescope
telluric line
telluric star
Trace Gas Orbiter (TGO)
thermal wind
three dimensional model
tide
TIMED
timescale (t)
Titan
time-ordered data (TOD)
tomography
transiting planet
transition region
transit spectroscopy
transmission spectroscopy
turbulence
twinkling
two-stream approximation
Thorne-Żytkow object (TZO)
Upper Atmosphere Research Satellite (UARS)
ultraviolet (UV)
Ultimate Spitzer Phase Curve Survey (USPCS)
Venus
very-high-energy gamma rays (VHEGR)
volatile material
vortex
water lines
water vapor planet
water world
weathering
atmospheric window
Wide Field Infrared Explorer (WIRE)
zonal flow

Index