2030年代に向けた光赤外コミュニティーの戦略
Q: 若手は何をしたいか？
—系外惑星探査に期待する立場から—

藤井友香（東京工業大学ELSI）@2019年度光学赤外線天文連絡会シンポジウム

知りたいこと••

地球は宇宙の中でどういう立ち位置なのか？
一般的な岩石惑星はどんな姿で生まれ、どういう進化を辿るのか✓

液体の水が表面にある惑星✓

生命を育む惑星✓

大気圧、大気組成などの多様性✓

統一的な理論的枠組み？

→（それなりの数の）地球型系外惑星の分光観測
天文学や惑星科学の枠を超えて、我々の世界観にインパクト

202

0

Observation Type
Discovery

Bulk Composition(gas/water/mantle/core fraction)

0

Spectroscopy
Details
0204

205

0

Detections

Insights
System architecture
Occurrence rate
Correlation with stellar properties

Mass andRadius
203

太陽型星周りの温暖な岩石惑星

NOW

M型星周りの温暖な岩石惑星0

ガス惑星 or 熱い惑星

201

Characterization

Atmospheric Profiles(Surface Composition)of golden targets

Fig.1 Development of Exoplanet Exploration

Photometric/
SpectroscopicSurvey

見えてきたlow-mass planetsの性質:

質量ー半径の統計的な性質

AA55CH11-Kaltenegger

ARI

3 August 2017

10:25

Kaltenegger 2017

44.0

Annu. Rev. Astron. Astrophys. 2017.55:433-485. Downloaded from www.annualreviews.org
Access provided by Tokyo Institute of Technology on 09/26/17. For personal use only.

Radius [R_earth]

3.5

33.0

Flux(F/F )4,000T(˚K)
2,200

1,000

1,600

400

1,200100900

40700

Cold H2/HeK-11e

KOI-142 b

10500

1300

K-79 cK-29 b
K-29 cK-177 bK-114 c

1.5

0.5

1150%
H2O
25%
H2O

K0095
K0405
K0421
K0421
K0100
K0100
K0253
K0253
K0240
K0098

K-102 eNote.
ﬁlters

K-48 dK-18 b
K-238 f55 Cnc e
K-20 b
K-113 bK-60 b
K-21 b
KOI-94 b
CoRoT-7 b

K-80 eK-99 b
K-338 eK-97 b
K-80 dK-36 b
K-93 b
K-10 b K-406 b LHS 1140 b

K-78 b K-138 c K-409 b
TRAPPIST-1 g
K-138 d TRAPPIST-1 b
GJ 1132 bTRAPPIST-1 f
1.0
TRAPPIST-1 c
EarthVenus
TRAPPIST-1 e
K-102 fK-406 cK-408 b
TRAPPIST-1 d

1

K-80 b

K-289 bK-60 dK-60 cK-414 bK-276 dK-350 dK-106 eHIP 116454 b
K-131 bK-414 cPlanetcandidMgSO3(rock)K-307 b K-106 c
25%
K-348 bK2-38 cFe
K-10 cK-454 bK-68 b50%
HD 97658 b
K-417 bFe
BD+20 594 b

K-98 b

K-11 b

K-80 cK-96 b

K-26 c

K-307 c2.0

K-276 c

GJ 1214 b
K-26 b

K-114 dK-109 bK-20 c

K-223 bK-92 cK-11 f2

Figure 1

K-350 cK-109 c2.5

K-11 dRadius gap

The Astronomical Journal, 156:264 (13pp), 2018 December

100%
H2 O

K-95 b

K-103 bK-305 cK-289 dK2-10 b
GJ 3470 b
WASP-47d
K-305 bK-94 b
K-79 b
K2-95 bK-223 cK-11 cK-100 cK-36 c

K-79 eK-30 bGJ 436 b
UranusK-4 b
NeptuneK-105 cK-100 bK-102 dK-68 cK-131 c5

Mass [M_earth]

100%
Fe(This8.

K2-38 b

岩石惑星多いe.g., Rogers 2015
1010

Mass-radius curves of planets with radii below 4 Earth radii and masses below 30 Earth masses. Planets are color-coded by the stellar
flux they receive (compared with Earth). Hypothetical temperatures for the planets are included to add a common physical entity to theFigure 5. The distribution of close-in planet sizes. The top panel shows thedistribution from Fulton et al. (2017) and the bottom panel is the updated
distribution from this work. The solid line shows the number of planets per starwith orbital periods less than 100days as a function of planet size. A deep
trough in the radius distribution separates two populations of planets withRp >1.7 RÅ and Rp <1.7RÅ . As a point of reference, the dotted line showse.g., Fulton+ 2017

AfterW
properadiu
paramstella
direc
popu
W
efﬁci
the drecovcalcu
in di見えてきたlow-mass planetsの性質:

AA55CH11-Kaltenegger

ARI

3 August 2017

10:25

A few benchmark targetsの大気の特徴づけ
Kaltenegger 2017

44.0

Annu. Rev. Astron. Astrophys. 2017.55:433-485. Downloaded from www.annualreviews.org
Access provided by Tokyo Institute of Technology on 09/26/17. For personal use only.

Radius [R_earth]

3.5

33.0

Flux
(F/F )
4,000

T(˚K)
2,200

1,000

1,600

400

1,200

100900Cold H2/He
K-11e

KOI-142 b

4010K-79 c←

K-29 b700

K-29 cK-177 b500
300

K-100 cK-60 dK-60 cK-414 bK-11 b

LHS 3844b

K-114 c1.5

0.5

Figure 1

11K-102 e
K-48 dK-18 b
K-238 f55 Cnc e
K-20 b
K-113 bK-60 b
K-21 b
KOI-94 b
CoRoT-7 b

K-80 eK-99 b
K-338 eK-97 b
K-80 dK-36 b
K-93 b
K-10 b K-406 b LHS 1140 b

K-78 b K-138 c K-409 b
TRAPPIST-1 g
K-138 d TRAPPIST-1 b
GJ 1132 b
TRAPPIST-1 f
1.0
TRAPPIST-1 c
EarthVenus
TRAPPIST-1 e
K-102 fK-406 cK-408 b
TRAPPIST-1 d

1

K-80 b

K-289 bK-98 b

2.0

K-276 dK-350 dK-106 eHIP 116454 b
K-131 b

50%
H2O
25%
H2O

MgSO3(rock)K-307 b K-106 c
25%
K-348 bK2-38 cFe
K-10 cK-454 bK-68 b50%
HD 97658 b
K-417 b
FeBD+20 594 b

K-307 c2K-80 cK-96 b

K-26 cK-114 dK-109 bK-414 cK-276 cK-92 cK-11 f

K-20 cK-223 b

GJ 1214 b
K-26 b

K-109 c2.5

K-11 dK-350 c100%
H2 O

K-95 b

K-103 bK-305 cK-289 dK2-10 b
GJ 3470 b
WASP-47d
K-305 bK-94 b
K-79 b
K2-95 bK-223 cK-11 c1K-36 c

K-79 eK-30 bAn Earth-radius planet
without an atmosphere

GJ 436 b
UranusK-4 b
NeptuneK-105 cK-100 bK-102 dK-68 cK-131 c5Mass [M_earth]

1010

K2-38 bFigure 1: The 4.5 µm thermal phase curve of LHS 3844b andPlanet-to-star flux binned over 25 equally spaced intervals over th100%
riod (points with 1 uncertainties) compared to the best fit phaseFemalized such that the relative flux is zero when the planet is eclip
0.5. b, The spherical harmonic temperature map used to generate
planet’s substellar point corresponds to the latitude and longitude (ical harmonics model includes north-south temperature variation,
constrained by the data.

confidence). From a joint fit to the Spitzer and TESS transit tim
tral transit to 2458325.22559 ± 0.00025 BJDTDB and the orbital pedays. We also established upper limits for transits of other planets
fit to the TESS andSpitzer data. In theorbital period
range from 0Kreidbreg+
2019
Spitzer
Figure 2: Predicted emission spectrum
for a range of surface
compositions.
The measured
corresponds to 0.6R , and from 6 to 12 days our 3 upper limit isplanet-to-star flux (shown in black) is most consistent with a pure dark basaltic surface. Mixed

Mass-radius curves of planets with radii below 4 Earth radii and masses below 30 Earth masses. Planets are color-coded by the stellar
surface compositions require at least 40% basalt or 75% ultramafic rock to be consistent with theflux they receive (compared with Earth). Hypothetical temperatures for the planets are included to add a common physical entity to the見えてきたlow-mass planetsの性質:

AA55CH11-Kaltenegger

ARI

3 August 2017

10:25

A few benchmark targetsの大気の特徴づけ
Kaltenegger 2017

44.0

Annu. Rev. Astron. Astrophys. 2017.55:433-485. Downloaded from www.annualreviews.org
Access provided by Tokyo Institute of Technology on 09/26/17. For personal use only.

Radius [R_earth]

3.5

33.0

Flux(F/F )
4,000

T(˚K)
2,200

1,000

1,600

400

1,200

100

900

40700

Cold H2/He
K-11e

KOI-142 b

1012.5

K-79 cK-29 b
K-29 cK-177 b←K-11 c300

K-414 b10.5

11K-80 b

50%
H2O
25%
H2O

K-48 dK-18 b
K-238 f55 Cnc e
K-20 b
K-113 bK-60 b
K-21 b
KOI-94 b
CoRoT-7 b

K-105 cDetection of H2O signatures

K-102 eK-289 bK-80 eK-99 b
K-338 eK-97 b
K-80 dK-36 b
K-93 b
K-10 b K-406 b LHS 1140 b

K-78 b K-138 c K-409 b
TRAPPIST-1 g
K-138 d TRAPPIST-1 b
GJ 1132 b
TRAPPIST-1 f
1.0
TRAPPIST-1 c
EarthVenus
TRAPPIST-1 e
K-102 fK-406 cK-408 b
TRAPPIST-1 d

K-276 dK-350 dK-106 eHIP 116454 b
K-131 bK-414 cMgSO3(rock)K-307 b K-106 c
25%
K-348 bK2-38 c
FeK-10 c
K-454 bK-68 b50%
HD 97658 b
K-417 bFe
BD+20 594 b

K-114 dK-114 c1.5K-80 cK-96 b

K-26 cK-60 dK-60 cK-11 b

K-276 cK2-18

K-289 dK-98 b

2.0

K-20 cK-223 b

GJ 1214 b
K-26 b

K-307 c2Figure 1

K-350 c100%
H2 O

K-95 b

K-11 dK-92 cK-109 bK2-10 b
GJ 3470 b
WASP-47d
K-305 bK-103 bK-305 cK-109 cK-11 fK-30 b

K-94 b
K-79 b
K2-95 bK-223 c500

K-100 cK-36 c

K-79 e

GJ 436 b
UranusK-4 b
Neptune100%FeK2-38 bK-100 bK-102 dK-68 cK-131 c5Mass [M_earth]1010

Mass-radius curves of planets with radii below 4 Earth radii and masses below 30 Earth masses. Planets are color-coded by the stellar
flux they receive (compared with Earth). Hypothetical temperatures for the planets are included to add a common physical entity to theBenneke+ 2019; HST

現在~2020年代
サイズ・軌道-ますます活発に。地球型惑星は、少なくとも低質量周りについては、統計的な議論は進むだろう。(→形成論への示唆)

temperate low-mass planetsの大気分光観測-

現在、アメリカの宇宙望遠鏡 (Hubble, Spitzer) が活躍-

JWSTの打ち上げが成功すると、さらに独壇場に？
✓JWSTでは、HZ付近の地球型惑星について、さらにいくつかのマイルストーン的な観測結果が出てくるのではないか•

大気の有無、水素大気への制限、(Earth-analogも?)•

主にM型惑星周りのトランジット惑星の観測によって•日本からは (今のところ、この分野で、) 宇宙望遠鏡へのアクセスが悪い印象→課題（日本の貢献の鍵＝WSO-UV？）

2030年代以降•

反射光、熱輻射の観測-(トランジットより)深い大気をプローブ-

大気圧、温度、表面組成への制限、アルベド-

ターゲット数多マイルストーン✓ biosignaturesの検出✓ 大気圧の推定✓ 二次大気リッチな惑星の同✓ 大気を持つHZ惑星の表面定、大気組成の同定

温度の推定✓ 表面の液体の水の同定✓ 表面組成の同定, …

具体的な疑問
岩石惑星の水の起源•

どのような惑星にどれくらい水があるか？
それは何に依存しているか？
✓

木星型惑星との相関 (←水を持った小惑星が飛来?)✓

質量・軌道長半径依存性 (←散逸? building block?
Nebula gas捕獲?)

Fig. 1. The amount of water on Earth compared with the overall globe. (Note: two of the three droplets are quite small and may
be difficult to see.) The largest droplet represents the volume of the Earth’s oceans, the second largest droplet represents the total
volume of water other than that in the oceans (such as in rivers, lakes, ground water, water vapor and the water in living organisms), and the smallest droplet represents the volume of water that humans can readily utilize. From Howard Perlman, USGS;
globe illustration by Jack Cook, Woods Hole Oceanographic Institution; „ Adam Nieman.

Genda (2017)L22より一般に、揮発性物質の起源 (N, C, O, …)

地球の水~0.02%

all water is vaporized. Conversely, a planet far from its
star will hold only frozen water. The amount of atmospheric greenhouse gases is also important in determining
the stability of liquid water. As an example, if Earth had
no greenhouse gases (that is, no CO2 or water vapor), its
surface temperature could be as low as –15∞C, and therefore it would be fully covered with ice. The adequate distance of Earth from the sun and a suitable amount ofgreenhouse gases in the Earth’s atmosphere have madethis planet habitable.
The water on Earth also plays many important rolesin the solid regions of the planet. In plate tectonics, water acts a lubricant (e.g., Regenauer-Lieb et al., 2001),and water also promotes long-term climate stability
through the carbon cycle between the atmosphere and theplanet (Walker, 1982; Tajika and Matsui, 1992). If, forexample, Earth had ten times its present volume of oceanic water, there would be no dry continents and theEarth’s environment would be quite different (MaruyamaLEE, BERGIN, &Lee+ (2010)28•et al., 2013). Therefore, an adequate amount of liquidwater on the Earth’s surface is also important in terms offorming and preserving the present Earth’s surface environment.
Liquid water is one of the most important compounds
required to support life (at least terrestrial life as we now
know it), and many believe that liquid water played a significant role in the generation of living organisms on theplanet. Indeed, H2O molecule has many unique characteristics. Hydrogen bonding between molecules gives
water its relatively high melting and boiling temperaturescompared to other compounds with comparable molecular weights (Fig. 2). For this reason, liquid water is stable
up to a reasonably high temperature, and so chemical reactions in aqueous solutions can potentially proceed rapidly, which has been advantageous with regard to the birthand evolution of life. The unique properties and high abundance of H2O molecules in the universe suggest that extraterrestrial life will also be water-based.

H. Genda

系外惑星にどのくらい多様性があり、それは何に依存しているか？

rawebfFg2a(o(smFigure 1. Carbon abundances relative to silicon in the solar system. AbundancecF具体的な疑問
HZコンセプトの検証•

HZのinner edgeで水(水蒸気)の有無が分かれているか？

•HZ内の水を持った惑星の表面温度(CO2量)には日射量に応じた傾向があるか？ (←carbon-silicate cycleの検証)•

水(H)を失った惑星はどうなるのか(ref: 金星や火星のCO2)

Kasting+ (1993)

具体的な疑問
惑星大気の時間進化•

マグマオーシャンの検証•

若い地球型惑星の大気組成 (H2, CO2, CH4?)•

バイオマーカーと年齢•602
火成活動（e.g., SO2, H2S）の影響

KALTENEGGER, TRA

Earth’s atmosphere

Kaltenegger+ (2007)

EXOPLANETS

究極的な目標EARTH

SOLAR SYSTEM PLANETS

- どのような惑星が水をどのくらい保持しているか- 大気組成のトレンドはあるか？（質量・年齢・日射量、etc）- どのような惑星が大陸を持つか

究極的な目標- etc…

- 地球生命の起源- 地球の水の起源、大気の起源- 初期の地球・金星・火星の大気？
- 火成活動、磁場、プレートテクト二クス、生命の存在などとの関連

今の観測の主要ターゲットとなる岩石惑星は、基本的にM型星周り＝観測に有利
M型星特有の事情-

pre-main-sequenceの長さ、大きな光度変化-

High-energy radiation

-

潮汐固定

-

アーキテクチャの違い（木星型惑星が少ない, etc.)-…

最終的には、太陽型星周りの惑星にも行きたい( 〜 行かなければいけない )20

Discovery

Bulk Composition(gas/water/mantle/core fraction)

0

Spectroscopy
Details
0204

205

0

Detections

Insights
System architecture
Occurrence rate
Correlation with stellar properties

Mass andRadius
203

太陽型星周りの温暖な岩石惑星

WON
20

Observation Type

M型星周りの温暖な岩石惑星0

ガス惑星 or 熱い惑星

201

まとめこ
AtmosphericProfiles
こ(Surfaceへ Composition)of golden targets
行

Fig.1 Development of Exoplanet Exploration

きCharacterization

たい
Photometric/
SpectroscopicSurvey