Habitable Transiting Exoplanets
Norio Narita (NAOJ)
This document is provided by JAXA.
Current Status and Next Step to Detect Habitable
Methodology and Prospects of Characterizing
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
This document is provided by JAXA.
Charbonneau et al. (2000)
Transits of “hot Jupiter” HD209458b
Other methods cannot do this
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)
One can search for periodic dimming from this kind of data
From TrES survey
Pre-Kepler Transiting Planets
possible habitable zone.
5 are terrestrial size.
Earth-sized planet Kepler-20f
Mars-sized planet KOI-961.03 (renamed as Kepler-42d)
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
Future transit surveys will target
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
Led by MIT and approved by NASA in April 2013.
TESS will be launched in 2017.
Methodology to Characterize Transiting Exoplanets
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
2. How do they form?
Uncovering their migration mechanism
Super-Earths may have hydrogen-rich atmosphere,
which has a large atmospheric scale height
Courtesy of Yui Kawashima
Miller-Ricci & Fortney (2010)
Solar abandance atmosphere
One can tell whether a planet has hydrogen-rich atmosphere
by multi-color transit photometry
Benneke & Seager (2012)
Optilal-NIR region has some features of atmospheric compositions
One can do transmission spectroscopy using
(multi-object spectrograph) instruments
VLT/FORS2, Gemini/GMOS, Magellan/MMIRS already
using very wide slit (~10”) to avoid light-loss from slits
integrate wavelength to create high precision light curves
Target: GJ1214b (V=14.7)
Integration: 20 nm (R ~ 30)
Precision: 331-580 ppm
Instrument: Gemini South/GMOS
Target: WASP-29b (V=11.3)
Integration: about 15 nm (R ~ 40)
Precision: ~400 ppm
One can tell whether the atmosphere is dominated by hydrogen or not
and possible existence of haze particle
Period: 289.86 days
Radius: 2.4 R
(super-Earth), transit depth: 500 ppm
gaseous mini-Neptune or large ocean planet?
, J=10.5, H=10.2
TMT’s optical MOS instrument (WFOS) can measure the
transiting super-Earths (Deming et al. 2009)
JWST/SPICA can characterize NIR-MIR transmission spectra
Can detect atmospheric atomic/molecular absorptions
High dispersion instruments can directly detect
Important information to infer ``how do they form?’’
planet hides an approaching side
planet hides a receding side
Stellar lines of HAT-P-2 taken with Keck/HIRES
Albrecht et al. (2013)
optimal kernel of lines
The obliquity tells us planetary migration mechanisms of exoplanets.
Like our Solar System or experienced dynamical migration.
Planetary Orbital Plane
Planetary Orbital Axis
Can detect planet’s shadow and measure orbital
TMT can reveal migration history for smaller planets
TMT can answer an aspect of “how
planetary systems form”
Ongoing and future transit survey (TESS) will discover
characterizing their atmospheres and formation