Near-infrared brightness of the Galilean satellites eclipsed in Jovian shadow

Collaborators：Shirahata M., Minowa Y., Hayano Y.(NAOJ), Arimatsu K.(Univ.of Tokyo), Takahashi Y. Kuramoto K. (Hokkaido Univ.) Nakamoto T. (Tokyo Tech.)Wada T., Matsuura S. (ISAS/JAXA)Nakajima K. (Kyushu Univ.)Kimura J. (ELSI, Tokyo Tech)Honda C. (Univ.of Aizu)Egami E (Arizona Univ.)Jason Surace (Caltech)

TSUMURA Kohji (FRIS, Tohoku Univ.)

JupiterIRCS+AO188 (JHK)2012/Jul./21

(Original) purpose of the observation

Satellite in eclipse

Surrounding sky

ZL

ZL+CIB

• Observations of Cosmic Infrared Background (CIB) to study star formation at the early universe.

SKY brightness = Zodiacal light (ZL) + Galactic light + CIB• Zodiacal light is the strongest foreground

radiation Biggest error source.• CIB observation without ZL subtraction error

using Galilean satellites as occulters.

Galilean satellites： Jovian moons• Io, Europa, Ganymede, Callisto• Io is not suitable owing to volcanoes

The moons are shielded in Jovian shadow• Two observable chances in a year

Eclipse of Galilean satellites

Jupiter

Galilean satellites

EarthSun

Observable seasons

Earth

Io1.76 days

Europa3.55 days

Ganymede7.16 days

Callisto16.69 days

Europa

Ganymede

Europa zoom-in

Jupiter

Straylight from Jupiter Straylight control is very important

• Scattered Jovian light at the earth atmosphere• Scattered Jovian light in the optics

CH4-long band reduces Jovian stray light

Straylight brightness relative to sky

Europa Ganymede

Callisto

Movement of objects• Target ： Europa eclipse• Telescope track: Jupiter• AO guide: Ganymede

All of them are non-sidereal

Thanks to Subaru SAs for success of such a difficult observation

Europa in eclipse

Ganymede(AO guide)

Jupiter

IRCS FoV(Juputer Track)

Special tracking method

Bright in shadow! Ganymede and Callisto are bright in

Jovian shadow• 10-6 of its out-of-eclipse brightness • New discovery of Subaru and HST

Ganymede in eclipse by HST Callisto in eclipse by Subaru

Instrument Date Band Depth Result

Subaru/IRCS 2012/2/21 J-band (1.25µm) ~0.5 Non-detection <1.5 µJy

HST/WFC3 2013/5/5 F139M (1.39µm) 0.54-0.76 Non-detection <5.5 µJy

Subaru/IRCS 2013/11/19 CH4-long band(1.69µm)

>0.4 Non-detection <88 µjy (Bad weather)

HST/WFC3 2014/3/26 F139M (1.39µm) 0.30-0.65 6.0-9.5 µJy

Instrument Date Band Depth Result

Spitzer/IRAC 2012/3/26 Ch.-1 (3.6 µm) >0.87 Non-detection <3.6 µJy

Subaru/IRCS 2012/7/26 J-band (1.25µm) 0.86-0.95 60-100 µJy

HST/WFC3 2013/2/5 F160W (1.60µm) 0.77-0.94 60-80 µJy

HST/WFC3 2013/3/5 F139M (1.39µm) 0.79-0.74 25-35 µJy

Spitzer/IRAC 2013/4/17 Ch.-1 (3.6 µm) >0.67 Non-detection <3.6 µJy

Spitzer/IRAC 2013/4/24 Ch.-1 (3.6 µm) >0.67 Non-detection <3.6 µJy

Europa eclipses

Ganymede eclipses

Instrument Date Band Depth Result

Subaru/IRCS 2013/10/19 J-band (1.25µm) 0.88-0.94 20-40 µJy

Callisto eclipses

Why were they bright in eclipse？

1) Jovian aurora and/or lightning2) Illumination from other satellites3) Emission from the satellites in eclipse 4) Refracted sunlight in Jovian

atmosphere5) Scattered sunlight by hazes in Jovian

atmosphere

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Hypothesis discussed here

Hypothesis ： 1), 2)

1) Jovian aurora/lightning• Europa, nearest to Jupiter,

should be brightnest

2) Illumination from other satellites

• One detected event (Europa) can be explained.

• Detected brightness in other events cannot be explained

JupiterIo

Europa

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× Copyright @ Walter Myers

Hypothesis： 3)3) Emission from the satellites Ganymede aurora emission

is localized• It cannot explain our detected

flat brightness

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McGrath+ (2013)

Atmospheric emission from the satellites cannot explain the detected SED. Assuming OH dominated

airglow.

Hypothesis： 4)4) Refracted sunlight in the atmosphere

• Galilean satellites should be brighter only by refraction effect.

Refraction in the Jovian atmosphere

Dust absorption

4) Refracted sunlight in the atmosphere Galilean satellites should be brighter only by

refraction effect. Absorption by dusts in the atmosphere

(eg. Smith 1980)

Hypothesis： 4)

Hypothesis： 5)4) Refracted sunlight in the atmosphere

• Galilean satellites should be brighter • Dust absorption

5) Scattering by hazes at higer atmosphere(First observational detection of Jovian hazes.)

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Scattering by hazes

Jovian atmosphere modeling Previous studies investigated ~100mbar

range by observations of ingress/egress (e.g. Smith et al.1980)

Scattering at higher range (~10mbar) is required • There are less information

about this pressure range.• Important range for haze

particle generation. • Observational study of Jovian

upper atmosphere by ground based observations of eclipses.

Haze layer 1

Haze layer 2

Gas layer

Jovian atmosphere

Application to Exo-planet transit Atmosphere around exo-

planets are observed by transit.

Little information about transmission spectrum of planetary atmosphere in our solar system.

This method provides us the transmission spectrum of Jovian atmosphere• Standard for classification

of exoplanet atmosphere国立天文台岡山天体物理観測所Webリリース (2013年6月)晴天のスーパーアース？−低質量の太陽系外惑星GJ3470bの大気を初めて観測−

Star

Earth

Earth

Jupiter

Sun

Exo-planet

Transit observation of Exo-planet

Galilean satellite eclipse observationJovian atmosphere

Galilean satellite

Planetary atmosphere

Current Status Two eclipses (Callisto and Ganymede)

were observed in S14B by Gemini/NIRI (Time exchange program)• Bad weather and some troubles.• Unknown stray light

Two eclipses (Callisto and Ganymede) will be observed in S15A by Subaru/IRCS and Gemini/NIRI (Time exchange program)

Summary Deep imaging of Galilean satellite eclipses in

Jovian shadow by Subaru, Hubble, and Spitzer.

Ganymede, and Callisto were bright even in the Jovian shadow at around 1.5 um.• Ganymede: 4e-6, Callisto: 2e-6 relative to their brightness out

of eclipse.• Ganymede was under detection limit at 3.6 um.• Thermal radiation from their 120K surface is neglgible.• Europa is much darker than the others.

What is the light source?• Forward scattering of sunlight at Jovian upper

atmosphere. • We can investigate hazes in the Jovian upper

atmosphere by ground-based observations.

supplement

Light curve

Impact Parameter

衛

Brightness depends on the satellite position

Jovian shadow

0

satellite

11 0.6

あるモデルパラメータでの計算結果