Toward Detections and Characterization of
Habitable Transiting Exoplanets
Norio Narita (NAOJ)
This document is provided by JAXA.
Outline
•
Current Status and Next Step to Detect Habitable
Transiting Exoplanets
•
Methodology and Prospects of Characterizing
Habitable Transiting Exoplanets
•
Summary
This document is provided by JAXA.
Various Exoplanet Detection Methods
•
Radial velocity method
–
First detection in 1995, 500+ planets
•
Transit method (this talk)
–
First detection in 2000, 400+ planets, 3000+ candidates
•
Gravitational microlensing method
–
First detection in 2004, 20+ planets
•
Direct imaging method
–
First detection in 2008, 10+ planets/brown dwarfs
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What is Planetary Transit?
primary eclipse
= transit
secondary
eclipse
planetary orbit
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The First Discovery of a Transiting Exoplanet
Charbonneau et al. (2000)
Transits of “hot Jupiter” HD209458b
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Features of Transits
•
Can determine
planetary radius
–
Other methods cannot do this
•
Can determine
planetary true mass and density
when combined with the RV method
–
The density is important information to infer planetary
internal structure (gas, rock, iron, etc)
•
Can characterize
planetary atmosphere and orbit
(later)
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How to Detect Transiting Exoplanets
One can search for periodic dimming from this kind of data
From TrES survey
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Space Mission for Transiting Planet Search
CoRoT
launched 2006/12/27
Kepler
launched 2009/3/6
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Kepler Field of View
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TrES-2
(Kepler-1)
HAT-P-7
(Kepler-2)
HAT-P-11
(Kepler-3)
Pre-Kepler Transiting Planets
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<1.25 R
E
First 4 Month Kepler Planet Candidates
1235
Planet Candidates
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2740 planet candidates (2013/01) -> 3277 candidates (2013/06)
<1.25 R
E
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54 candidates are in
possible habitable zone.
5 are terrestrial size.
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Possible Habitable Planet reported in 2011
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Habitable Super-Earths reported in 2013
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Habitable Super-Earths reported in 2013
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(Sub-)Earth-sized Planets
Earth-sized planet Kepler-20f
Mars-sized planet KOI-961.03 (renamed as Kepler-42d)
This document is provided by JAXA.
Kepler’s Weakness
•
Kepler targets relatively faint and far stars
–
Although over 3000 candidates discovered, RV follow-
ups for all targets are difficult
–
Further characterization studies are also difficult
Kepler is good for statistical studies, but not for
detailed studies for each planet
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Strategy of Future Transit Survey
•
Future transit surveys will target
nearby bright stars
to detect terrestrial planets in habitable zone
•
Ground-based transit survey for nearby M dwarfs
–
MEarth lead by D. Charbonneau at Harvard
–
Other teams all over the world
–
IRD transit group
•
Space-based all-sky transit survey for bright stars
–
TESS (Transiting Exoplanet Survey Satellite) by MIT team
This document is provided by JAXA.
All-Sky Transit Survey: TESS
Led by MIT and approved by NASA in April 2013.
TESS will be launched in 2017.
This document is provided by JAXA.
Outline
•
Current Status and Next Step to Detect Habitable
Transiting Exoplanets
•
Methodology to Characterize Transiting Exoplanets
and Future Prospects
•
Summary
This document is provided by JAXA.
What we would like to study for Habitable Planets?
1. What are components of their atmospheres?
–
Important information to infer habitability
–
Do they have hydrogen atmosphere?
–
Hydrogen is strong green house gas and affect habitability
(Pierrehumbert & Gaidos 2011)
2. How do they form?
–
Uncovering their migration mechanism
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Characterization of their Atmospheres
star
Transit depths depend on lines / wavelength reflecting atmosphere
Transmission Spectroscopy
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Differences of Transmission Spectra
Super-Earths may have hydrogen-rich atmosphere,
which has a large atmospheric scale height
Courtesy of Yui Kawashima
This document is provided by JAXA.
Discriminating Hydrogen-Rich Atmosphere
Miller-Ricci & Fortney (2010)
Solar abandance atmosphere
One can tell whether a planet has hydrogen-rich atmosphere
or not
by multi-color transit photometry
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Other Spectroscopic Features
Benneke & Seager (2012)
Optilal-NIR region has some features of atmospheric compositions
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Transmission Spectroscopy by MOS
•
One can do transmission spectroscopy using
MOS
(multi-object spectrograph) instruments
–
VLT/FORS2, Gemini/GMOS, Magellan/MMIRS already
reported excellent results
•
Simultaneously observe target and reference stars
–
using very wide slit (~10”) to avoid light-loss from slits
–
integrate wavelength to create high precision light curves
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Example by Bean et al. (2010)
•
Instrument: VLT/FORS2
•
Target: GJ1214b (V=14.7)
•
Integration: 20 nm (R ~ 30)
•
Precision: 331-580 ppm
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Recent Example by Gibson et al. (2012)
•
Instrument: Gemini South/GMOS
•
Target: WASP-29b (V=11.3)
•
Integration: about 15 nm (R ~ 40)
•
Precision: ~400 ppm
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Optical MOS is useful to see Rayleigh Slope
One can tell whether the atmosphere is dominated by hydrogen or not
and possible existence of haze particle
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Kepler-22 Properties
•
Planet
–
Period: 289.86 days
–
Radius: 2.4 R
E
(super-Earth), transit depth: 500 ppm
–
gaseous mini-Neptune or large ocean planet?
•
Host Star
–
G5V star
–
B=11.5, R=11.7
, J=10.5, H=10.2
•
TMT’s optical MOS instrument (WFOS) can measure the
Rayleigh slope in optical wavelength
This document is provided by JAXA.
Transmission Spectroscopy with Space Telescopes
H
2
O
CO
2
Simulated ~100hr detections of molecules in atmospheres of habitable
transiting super-Earths (Deming et al. 2009)
JWST/SPICA can characterize NIR-MIR transmission spectra
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What E-ELT’s High Dispersion Spectrographs Can
•
Transmission spectroscopy
–
Can detect atmospheric atomic/molecular absorptions
•
High dispersion instruments can directly detect
planet’s shadow and can measure orbital obliquity
–
Important information to infer ``how do they form?’’
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What is Planet’s Shadow?
planet hides an approaching side
planet hides a receding side
planet
planet
star
Planet removes a part of velocity component of stellar lines
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What happen to Shape of Stellar Lines
Stellar lines of HAT-P-2 taken with Keck/HIRES
Albrecht et al. (2013)
optimal kernel of lines
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Planet’s Shadow in Stellar Lines
transit
This shadow shows a trajectory of the planet in front of the star
This document is provided by JAXA.
What we can learn by planet’s shadow
The obliquity tells us planetary migration mechanisms of exoplanets.
Like our Solar System or experienced dynamical migration.
Planetary Orbital Plane
Planet
Planetary Orbital Axis
Stellar Spin Axis
Star
This document is provided by JAXA.
Capability of E-ELT’s High Dispersion Spectrographs
•
Can detect planet’s shadow and measure orbital
obliquity of smaller planets
–
TMT can reveal migration history for smaller planets
–
which means,
TMT can answer an aspect of “how
planetary systems form”
This document is provided by JAXA.
Summary
•
Ongoing and future transit survey (TESS) will discover
habitable transiting planets in Solar neighborhood
•
Future E-ELTs and space telescopes will work on
characterizing their atmospheres and formation
mechanisms
This document is provided by JAXA.
Document Outline - スライド番号 1
- Outline
- Various Exoplanet Detection Methods
- What is Planetary Transit?
- The First Discovery of a Transiting Exoplanet
- Features of Transits
- How to Detect Transiting Exoplanets
- Space Mission for Transiting Planet Search
- Kepler Field of View
- Pre-Kepler Transiting Planets
- First 4 Month Kepler Planet Candidates
- スライド番号 12
- スライド番号 13
- Possible Habitable Planet reported in 2011
- Habitable Super-Earths reported in 2013
- Habitable Super-Earths reported in 2013
- (Sub-)Earth-sized Planets
- Kepler’s Weakness
- Strategy of Future Transit Survey
- All-Sky Transit Survey: TESS
- Outline
- What we would like to study for Habitable Planets?
- Characterization of their Atmospheres
- Differences of Transmission Spectra
- Discriminating Hydrogen-Rich Atmosphere
- Other Spectroscopic Features
- Transmission Spectroscopy by MOS
- Example by Bean et al. (2010)
- Recent Example by Gibson et al. (2012)
- Optical MOS is useful to see Rayleigh Slope
- Kepler-22 Properties
- Transmission Spectroscopy with Space Telescopes
- What E-ELT’s High Dispersion Spectrographs Can
- What is Planet’s Shadow?
- What happen to Shape of Stellar Lines
- Planet’s Shadow in Stellar Lines
- What we can learn by planet’s shadow
- Capability of E-ELT’s High Dispersion Spectrographs
- Summary
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