Mercury Disk Observations by Japanese team

1. Observation of Mercury transit on the solar disk on November 9, 2007 [Dawn-Dusk Asymmetry] by Junya Ono and Ichiro Yoshikawa, University of Tokyo

2. Sodium abundance vs. Mercury’s distance from equatorial plane

[Micro meteoroid and dust distribution vs. Mercury sodium] by Shingo Kameda, ISAS/JAXA

3. Observation of Mercury disk at the time of Messenger flyby in January 2008 by Masato Kagitani and Shoichi Okano, Tohoku University

Hunten and Sprague, 1997

Schleicher et al., 2004

It is impossible to observe both dawn and dusk sides

at a time by ground-based observation.

However, based on statistics, sodium density

on the dawn side is ～ 3 times higher than

that on the dusk side

It is thought that sodium atoms are adsorbed

in the night side (low temp), while they are

released from the dayside.

Dawn-Dusk Asymmetry observed at Mercury transit on November 9, 2006 by Junya Ono and Ichiro Yoshikawa (University of Tokyo)

Dawn-Dusk Asymmetry was observed

at a time of Mercury transit on the solar disk.

Observation was made at Hida Observatory of Kyoto University on November 9, 2006 using a 60-cm vacuum solar telescope and a 10-m spectrograph (R ～ 210,000).

Conditions at a time of observation

Start time (UT)

End time (UT)

Mercury diameter

Mercury-Sun distance

True Anomaly Angle

Mercury-Sun velocity

Rotational velocity of the Sun

Wavelength

Doppler shift

g-factor

22:06

00:04

9.96 arcsec

0.315 AU

329°

5.3 → 5.2 km/s

0.9 → 1.4 km/s

589.592 nm (Na D1)

8.5 → 7.5 pm

0.18 → 0.12

Example of observed Na absorption in a single frame data

far from limb (>2.5”)

close to limb

co-added 6 data at the North polar region (improved S/N)

Column density of Na atoms along a line of sight vs. distance from the limb

Na atoms column densities at limb locations [Na atoms/cm2]

6.1 ± 1.1×1010 Morning

Evening

NorthSouth

4.1 ± 1.8×1010

5.7 ± 1.2×1010

5.4 ± 1.3×1010Morning-Evening asymmetry 1.5 ±0.71

Na temperatures derived from observed line width

Na temperature were also derived from scale height

Atmospheric seeing was determinedfrom shadow region (red lines)

Morning 1.59 arcsec

Evening

North

South

1.76 arcsec

1.73 arcsec

1.72 arcsec

Determined seeing

Temp. from line width Temp. from scale heightscale heightMorning

Evening

North

South

1750 ±500 K

2350 ±900 K

2700 ±950 K

3200 ±1150 K

152 ±30 km

124 ±40 km

128 km

134 km

1560 ±260 K

1300 ±410 K

1320 K

1380 K

Summary of Mercury transit observation on Nov. 9, 2006

1. Morning–Evening asymmetry was ～ 1.5

2. No high densities at polar regions

3. Temperatures derived from line width are different from those derived from scale height. → meaning that the Mercury atmosphere is not in the hydrostatic equilibrium.

・ source process　　 Relation between dust distribution and

atmospheric density

Micro meteoroid and dust distribution vs. Mercury sodium

by Shingo Kameda, ISAS/JAXA #1

Tilt angle of Mercury’s orbit is 7 degrees.Assuming thatdust and micro-meteoroidsare concentrated nearecliptic plane,source rate for meteoroidvaporization will be higher (possibly).

Potter et al., 2007

TAA vsSodium density

Radiation pressure

(Potter et al., 2007)

Radiation pressure isMinimum at the TAA of0 and 180.

Micro meteoroid and dust distribution vs. Mercury sodium

by Shingo Kameda, ISAS/JAXA #2

Sprague et al., 1997

Micro meteoroid and dust distribution vs. Mercury sodium

by Shingo Kameda, ISAS/JAXA #3

TAA vsSodium density

Radiation pressure isMinimum at the TAA of0 and 180.

However,From other results,It is not definite..

Sprague et al., 1997

As a trend,Mercury is away from ecliptic plane small

density

Potter et al., 2007

Micro meteoroid and dust distribution vs. Mercury sodium

by Shingo Kameda, ISAS/JAXA #4

Potter et al., 2007

In Northern side,Heliospheric distance is small large dust density (?)

Micro meteoroid and dust distribution vs. Mercury sodium

by Shingo Kameda, ISAS/JAXA #5

As a trend,Mercury is away from ecliptic plane small

density

Problem:1. Accuracy of absolute value for each observation result2. The cause of significant increase is still unknown.

Potter et al., 2007; Sprague et al., 1997

□: Observation at Haleakala in 2006

Micro meteoroid and dust distribution vs. Mercury sodium

by Shingo Kameda, ISAS/JAXA #6

D=60cm

λ/∆λ~59,000

Platescale:0.92 ”/pix

Japan Iitate observatory

Observation of Mercury disk at the time of Messenger flyby in January 2008 by Masato Kagitani and Shoichi Okano, Tohoku University

Observation

D=60cm

λ/∆λ~59,000

Platescale:0.92 ”/pix

Slit: 2.1”x180”

Fig: Slit configuration

・Long-slit spectroscopy

・High-dispersion Echelle spectrograph

Observation

Date Time(UT)

Seeing (FWHM

)

Quality Day or Night

Jan. 15

8:13 6.9 Mid Night

Jan. 17

8:09 5.0 Mid Day

8:17 6.5 High Day

8:24 6.5 Low Night

8:30 6.9 Low Night

Jan. 19

8:04 7.0 Mid Day

date TAA Phase angle

Ang.-

Diam.

Jan. 15 98 76 5.9”

17 117 88 6.2”

19 120 90 6.4”

Data Reduction

Earth’s sodium emission

Mercury sodium tail

Mercury continuum

Spatial axis

Spe

ctra

l axi

s

Sky

back

grou

nd s

ubtr

acti

on

Sky background

Calibration

To calibrate absolute intensity, Hapke’s reflection model was used.

Hapke’s reflection model

Observed continuum

Seeing convolved Hapke’s reflection model

NaD2

NaD1MR

/nm

(co

ntin

uum

)

MR

(S

odiu

m e

mis

sion

)

Result

Date Time(UT)

Seeing (FWH

M)

Quality Disk NaD2 [MR]

Column density x1010[cm-2]

Total sodium atoms within 3RM [x1028]

Jan. 15

8:13 6.9 Mid 1.17 2.1 4.8

Jan. 17

8:09 5.0 Mid 1.67 2.9 5.2

8:17 6.5 High 1.49 2.6 5.7

8:24 6.5 Low 1.10 1.8 4.4

8:30 6.9 Low 1.18 2.1 4.6

Jan. 19

8:04 7.0 Mid 1.35 2.4 5.1