International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 1

Exosphere Temperature Variability at Earth, Mars and Venus

due to Solar Irradiation

Jeffrey M. ForbesDepartment of Aerospace Engineering SciencesUniversity of Colorado, Boulder, Colorado, USA

Sean L. BruinsmaDepartment of Terrestrial and Planetary Geodesy

Centre Nationale D'Etudes Spatiales,Toulouse, France

QuickTime™ and a decompressor

are needed to see this picture.

International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 2

QuickTime™ and a decompressor

are needed to see this picture.

International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 3

Exosphere Temperature Variability at Earth, Mars and Venus

Earth Mars Venus

Solar Wind Interaction

Solar Irradiation & Planetary Rotation

• In-situ

• Solar Tides Propagating from Below

Solar Radiation Variability

• Long-term

• Solar Rotation

• Day-to-day

200-400K 50-120K 200 K

20-50K ?

800K 180K 40K

50-100K 20-40K 20K

??20-40K

> 20-50K ?

20-200K ? ?

International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 4

81-DAY MEAN EXOSPHERE DENSITY AT MARS, Normalized to 390 km and Derived from Precise Orbit Determination of MGS

(370 x 437 km orbit; perigee -40º to -60º latitude, 1400 LT)

81-day mean density

81-day meanF10.7 solar flux at 1 AU

81-day meanF10.7 solar flux at Mars

Note: Each density determination is made over 3-5 Mars days, and is a longitude average, so thereis no possibility to derive longitude variability, e.g., as seen in MGS accelerometer data.

N. Hemis.

Summer

Equinox EquinoxS.

Hemis.Summer

(1.3

7-1.

66 A

U)

International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 5

T∞ =130.7 +1.53F10.7

−1.14cos Ls( )−13.5sin Ls( )(R=.98)

zonal mean dust optical depth ±30o

latitude avg.

ρ390 = 3.72 + 0.28F10.7 − 1.4 cos Ls( ) − 4.3sin Ls( ) (R = .96)Fit for density (10-18 cm-3):

N. Hemis.

Summer

Equinox EquinoxS. Hemis.

Summer

Least-Squares Fit to Exosphere Temperature Derived fromObserved Densities and DTM-Mars (Lemoine and Bruinsma, 2002)

International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 6

QuickTime™ and a decompressor

are needed to see this picture.

Mars Venus

ΔTΔF10.7

= 4.2

ΔTΔF10.7

= .31

ΔTΔF10.7

= 1.5

ΔTΔF10.7

= 2.9

MG

S D

rag

An

alys

is

Kas

prza

k et

al.

(199

7) P

VO

, Mag

ella

n

NRLM

SISE00

Jacc

hia

(197

0)

Earth

International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 7

QuickTime™ and a decompressor

are needed to see this picture.

Exosphere Temperature Variability due to the Sun’s Rotation

QuickTime™ and a decompressor

are needed to see this picture.

Forbes, J.M., Bruinsma, S., Lemoine, F.G., Bowman, B.R., and A. Konopliv, Variability of the Satellite Drag Environments of Earth, Mars and Venus due to Rotation of the Sun, J. Spacecraft & Rockets, 44, 1160-1164, 2007.

International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 8

QuickTime™ and a decompressor

are needed to see this picture.

QuickTime™ and a decompressor

are needed to see this picture.

QuickTime™ and a decompressor

are needed to see this picture.

Niemann et al., Earth Planets Space, 50, 785-792, 1998.

Solar Irradiation & Planetary RotationIn-situ Thermal Tides

at Mars & Earth

SSMIN ΔT ~ 40K

SSMAX ΔT ~ 120K

SSMIN ΔT ~ 200K

SSMAX ΔT ~ 400K

Mars

Earth

International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 9

QuickTime™ and a decompressor

are needed to see this picture.

Exosphere Temperature Variability due to Sun-SynchronousSemidiurnal Solar Tides Propagating from Below

Marslow dustLs = 270

QuickTime™ and a decompressor

are needed to see this picture.

Earth

QuickTime™ and a decompressor

are needed to see this picture.

QuickTime™ and a decompressor

are needed to see this picture.

Marslow dust Ls = 270

International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 10

Topographic/land-sea Modulation of Periodic Solar Radiation Absorption Gives Rise to Longitude-Dependent Tidal perturbations

≈ 25 Kmax-min variation

with longitude

Diurnally-varying solar radiation

12local time

0 24

Diurnal amplitude of latent heating due to tropical convection

International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 11

QuickTime™ and a decompressor

are needed to see this picture.

Mars Thermosphere Densities at 120 km, 1500 LT, Kg/m3

Longitudinal Structures Due to Vertically-Propagating Thermal Tides Modulated by Topography

MGS Accelerometer Mars GCM, Moudden & Forbes, 2008

International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 12

Conclusions Concerning Exosphere Temperature Responses of the Terrestrial Planets to Changes in

Solar Irradiation

These exosphere temperature responses are determined by

• Magnitude of incoming solar radiation (i.e., orbit) & heating efficiency

• CO2 content, i.e., cooling efficiency

• Dynamics, i.e., adiabatic cooling (ion drag on Earth)

• Rotation rate of the planet

• Solar radiative absorption and heating at lower altitudes, i.e., upward-propagating thermal tides

• Modulating topography