MIROMIRO
Continuum Observations of Asteroid (2867)
Steins with the MIRO Instrument
Ringberg Castle
Tegernsee, Germany
February 2528, 2009
S. Gulkis, S. Keihm, L. Kamp, C. Backus,
M. Janssen, S. Lee, B. Davidsson,
+ MIRO SCIENCE TEAM
Jet Propulsion Laboratory
California Institute of Technology
S. Gulkis 2/22/09
OUTLINE
MIRO
* MIRO INSTRUMENT OVERVIEW
* GEOMETRY OF THE ENCOUNTER
* OVERVIEW OF THE OBSERVATIONS
* DUAL CONTINUUM DATA
* DATA ANALYSIS
 SHAPE MODEL
 THERMAL MODEL AND RADIATIVE
TRANSFER
* ERROR ANALYSIS
* RESULTS and CONCLUSIONS
* ACKNOWLEDGEMENT
S. Gulkis 2/22/09
Instrument OvervieOverview
MIRO
Telescope
30 cm diameter
Boresight along zaxis of s/c
Receivers (two)
Continuum 190 GHz (1.6 mm)
563 GHz(0.5 mm)
Spectroscopic (563 GHz)
H2O, CO, NH3, CH3OH
Spectral resolution (44 kHz)
Resolving Power = 1.3 x 10^7
Single linear polarization(crossed)
Flipmirror calibration(warm,cold,sky)
Beam Characteristics
Submillimeter HPBW7.5 arc min
Millimeter HPBW23.8 arc min
STRUCTURAL THERMAL MODEL
S. Gulkis 2/22/09
ROSETTASTEINS FLYBY GEOMETRY
MIRODAY NIGHT
S. Gulkis 2/22/09
Overview of ObservationObservations
MIRO
*
MIRO was powered on for approximately 10 hours centeredon CA
*
Warm and cold calibration targets were observed every 30minutes
*
Instrument performance was nominal
*
Thermal emission from Steins was observed with high S/N inboth mm and smm continuum channels
*
First detection of Steins occurred about 92 s(mm)[44 s smm]
before CA
*
MIRO boresight was significantly displaced from Steins formost of the flyby

Phase coverage of data was limited [~ 31590 deg]
*
Spectroscopic data were obtained but no spectral lines wereobserved
S. Gulkis 2/22/09
Predicted Antenna Temperatures for beam
centers on target center
for beam
centers on target center
MIRO82.9 K590 GHz
29.9 K190 GHz
Peak Observed
Temperatures
1st detection
Last detection
For Planning
Purposes Only
Calibrated Continuum Data
MIRO
Millimeter Submillimeter
S. Gulkis 2/22/09
ANALYSIS
MIRO
* Shape Model of Steins (NEXT SLIDE)
* Important quantities needed in analysis

Subspacecraft and SubSolar positions

Unit surface normals on a grid around the intersection of boresight and Steins
* Intersection of beam boresight with the shape model

Used Walter Sabolo's measurements of Steins in WAC images

Corrected for photometric center of Steins and true body center
* Based on shape model and Lambertian model of scattered sunlight

Corrected for geometrical distortion in WAC image plane using a formula providedby Walter Sabolo
* Distance from Rosetta obtained from SPK kernals

ORHR_______________00077.BSP for Rosetta

ORHO_______________00077.BSP for Steins
* Orientation of asteroid relative to boresight

Used SPK data using calls from Spice
This work carried out by Dr. Lucas Kamp (JPL)
S. Gulkis 2/22/09
Digital Shape Model used in analysis
MIRO
*
Based on data provided by OSIRIS
instrument
*
Digital Shape Kernel (DSK)steins_
shape_model_ver2a.dsk
*
Provided by group at Laboratoire
d'Astrophysique de Marseille,
France (contact Olivier Groussin)
*
Reference: Lamy et al. 2008, A&A
487,1179
S. Gulkis 2/22/09
MIROThermal Models (Top)
Pencil Beam Brightness Temp(Bottom)
* Thermal models use Steins period,
*
*
*
*
1022
304
87
22
smm
mm
albedo (0.4 assumed) and heliocentric
distanceTemperatures are equatorial.
Albedo not well determined
Thermal Inertia (mks units)
 22(lunar powder)
 87(lunar fine)
 304(lunar basalt)
 1022(lunar igneous rock)
Arrows point to pencil beam zenithemission (blackbody equivalent T) for
the two MIRO continuum wavelengths
(0.53 mm & 1.58 mm) for thermal
inertia = 22
Steins thermal model needs to fit
IR(VIRTIS, SPITZER,+) andsubmillimeter data (MIRO)
Calculations by Dr. Steve Keihm (JPL)
S. Gulkis 2/22/09
MIRO BORESIGHTS NEAR CCA
MIROS. Gulkis 2/22/09 11
Estimated Errors
MIRO
Pointing Random Systematic
Range, km +/ 1 arc min All <
[Modeling error] [Meas error] [Meas error]
+/ 3 K mm +/ 1 K mm < 0.9 K mm
820.7 +/ 12 K smm +/ 1 K smm < 2.7 K smm
Maximum CA
1412.6 +/ 1 K mm +/ 1 K mm < 0.3 K mm
Local Minimum +/ 1 K smm +/ 1 K smm < 0.2 K smm
2129.4 +/ 1 K mm +/ 1 K mm < 0.3 K mm
2nd Maximum +/ 12 K smm +/ 1 K smm < 0.8 K smm
S. Gulkis 2/22/09
MODEL PARAMETERS
MIRO
MODEL PARAMETER POWDER ROCK
Density (g/cm^3) 1.25 2.6
Thermal Conductivity (w/cm K) 6 x 10^6 6 x 10^3
Specific Heat (ws/g K) 0.67 0.67
Thermal Inertia MKS (J/K m^2 s^0.5) 22 1022
Dielectric Constant 2.34 5.03
Thermal Skin Depth (cm) 0.22 4.89
Electrical Skin Depth (cm )(smmmm) .24.76 .04.12
Loss Tangent .017 .036
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Observed and Model Ant TemperatureAnt Temperatures
MIRO
RANGE TA(OBS) TA(M) TA(OBS) TA(M)
KM smm smm mm mm
Powder 820.7 82.9 92.4 29.9 25.1
Rock 84.5 24.9
Powder 1013.9 18.6 19.9 15.5 11.3
Rock 19.1 11.4
Powder 1412.6 5.3 1.6 9.2 4.9
Rock 1.6 5.0
Powder 1722.1 11.3 8.0 10.3 6.1
Rock 8.6 6.3
Powder 2129.4 25.7 25.2 9.7 6.2
Rock 28.3 6.4
Powder 2640.1 17.4 17.9 7.2 4.0
Rock 20.4 4.2
S. Gulkis 2/22/09
Pointing based on photographic measurements
Brightness Temperature Models for Steins
at MIRO Wavelengths (0.53 & 1.58 mm)
MIRO
Calculations by Dr. Steve Keihm S. Gulkis 2/22/09
Surface temperature for various model
assumptions (Latitude = 0) assumptions (Latitude = 0)
MIRO
Calculations by Dr. Steve Keihm S. Gulkis 2/22/09
CONCLUSIONS
MIRO
*
Both high and low thermal inertia models, similar to those used for the moon,
can fit the MIRO data within the uncertainties of the data;
*
Principal source of errors is the modeling pointing error, not the measurement
errors; for the peak antenna temperature measured, the error is estimated to be
12 K (smm) and 3 K (mm) for a 1 arc min pointing error;
*
For low thermal inertia models, the ratio of thermal to smm electrical skin
depths is of the order of unity; the thermal wave is attenuated by 1/e at the
depth of penetration
*
For high thermal inertia models, the thermal skin depth is considerably larger
than the smm electrical skin depth and the surface temperature is measured
*
Thermal models for Steins need to fit VIRTIS, SPITZER, and MIRO data; the
high surface temperatures reported by VIRTIS and SPITZER require a low
thermal inertia regolith;
*
There is a suggestion that the emissivity of a low thermal inertia model needs
to be less than that calculated from the dielectric constant itself. We estimate
that emissivity could be as low as .79 but probably not lower. Reduced
emissivity could be produced by subsurface scattering.
*
Reducing the loss tangent doesn't lower the temperature significantly
S. Gulkis 2/22/09
ACKNOWLEDGEMENT
MIRO
The MIRO team would like thank
ESOC and ESAC teams for their technical support
OSIRIS, VIRTIS and ALICE teams for sharing their pre
published data
U. Keller, P. Lamy, O. Groussin, W. Sabolo, M.
Fulchignoni, and A. Barucci for information about their
Steins observations and models
S. Gulkis 2/22/09
MIROMIRO
Backup Figures
S. Gulkis 2/22/09
DOPPLER SHIFT AND ANG DIAM
MIRO
Phase Angle (RosettaSteinsSun)
MIRO
Angular Diameter SteinDiameter Steins
MIRO
MIRO TIMELINE AT STEINAT STEINS
MIRO
Min from CA EVENT
329 Power on
307 CTS/dual continuum
37 Start s/c roll
36.5 End s/c roll
16 Dual continuum
11 Asteroid mode
1.9 ~ 0 solar phase angle
1.5 First mm detection
0.7 First smm detection
0 CA
0.5 Peak mm signal (29.9 K)
0.6 Peak smm signal (82.9 K)
1.7 s/c over morning terminator
10.6 Loss of signal
10.6 Dual continuum
13 CTS/dual continuum
302 Disable science acquision
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Pointing Error Sensitivity
MIROS. Gulkis 2/22/09
Range, km Millimeter
+/ 1 arc min
SubMillimeter
+/ 1 arc min
820.7
Maximum near CA
+/ 3 K +/ 12 K
1412.6
Local Minimum +/ 1 K +/ 1 K
2129.4
2nd Maximum +/ 1 K +/ 12 K
Brightness Temperature Models for Steins
at MIRO Wavelengths (0.53 & 1.58 mm)
MIRO
CW
CCW
k (w/cmK)
rho (gr/cm^3)
Model computed by Steve Keihm (JPL)
S. Gulkis 2/22/09
Science Objectives
MIRO
* Constrain thermal and electrical properties of Asteroid Steins
 k Thermal conductivity (W/cm K)
 c Specific heat
 *r Dielectric constant
 *
Density
 Tan(*) Loss tangent = 2*/*r *
* Observation related quantities
 Thermal skin depth (2k/**c)^0.5 (thermal wave damping to 1/e )
 Thermal inertia (k*c)^0.5
* Assist in the determination of regolith properties
* Detect or set upper limit on abundance of water vapor around Asteroid Steins
S. Gulkis 2/22/09
Thermal and Electrical Skin Depth
Estimates for MIRO Estimates for MIRO
MIRO
* Thermal Skin Depth (amplitude for thermal wave 1/e surface value)
 Thermal skin depth =
2k
"#c
*
2 mm
* Electrical Skin Depth

d=
"
2#tan($)%
 *
5 *
for fine powder (loss tangent = .017)
 d(smm) = 2.4 mm *
1 thermal skin depth
 d( mm) = 7.5 mm *
3 thermal skin depths
S. Gulkis 2/22/09