Can Vesta have a polar cap?Can Vesta have a polar cap?

Eleonora AmmannitoINAF/IFSI - Roma

CISAS - Padova

CISAS-UPD

The modelThe model

• Time-dependent, unidimensional partial differential equations, expressing the conservation of energy (heat diffusion) and mass (gas diffusion), in the general form

= density, = flux, Q = source term• PDE's are solved numerically in

discrete time steps on a discrete grid

Qt

The initial conditionsThe initial conditions

70

90

110

130

150

170

190

210

-4 -3 -2 -1 0 1 2 3 4

orbital position

tem

pera

ture

(k)

10 20 30 40 50 60 65 70 75 80 85

semi major axis (a) 2.362 (AU)eccentricity (e) 0.089rotational period (p) 5.342 (h)latitude (theta) 90 ÷ 75 (deg)obliquity* (q) 21.8 (deg)Perihelion argument (w ) 150.27 (deg)

Seasonal variation of the temperature at different latitudes on the surface of Vesta. It was condidered the equilibrium between the solar irradiance at the Vesta’s distance from the Sun at each latitude and the thermal emission of the body.

albedo (al) 0.04IR emissivity (em) 0.9porosity (po) 0.3radius (r) 265 (km)dust thermal conduct. 0.25 ÷ 1.0 (W/(m*K))dust specific heat 1200 ÷ 1300 (J/(Kg*K))n° layers 100thikness of layers 0.001 (m)

Parametri orbitali:

Parametri fisici:

Preliminary indicationsPreliminary indications

-0.15

-0.13

-0.11

-0.09

-0.07

-0.05

-0.03

-0.01

0 100 200 300 400 500 600 700 800 900 1000

vesta's orbits

Po

siti

on

of

the

ice

wrt

th

e su

rfac

e (m

)

90 85 80