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ARIEL
Atmospheric Remote-sensing IR Exoplanet Large-survey
(ESA M4 proposal)
Towards a statistical description
of planets
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre 2014
The Solar System is not representative
There is much more variety than the Sun’s planets
?
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre 2014
Key questions
Why the Solar System is as it is? is it special?
Why are exoplanets as they are?
What are the causes for the observed diversity?
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre 2014
Stars are well behaved….
(Hertzsprung-Russel diagram, 1910)
The breakthrough to understanding stars, was the coherent analysis of a large sample
and the identification of the most “important” parameters
Ariel, La ricerca sui pianeti extrasolari in
Italia, Roma – 5-7 Novembre 2014
Planets are more complex
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre 2014
Planets are more complex
Which are the main properties that determine the
characteristics of a planet and its following evolution?
! Planet mass
! Orbital distance
! Formation site
! Stellar luminosity and color
! temperature
! Proto-planetary disk lifetime
! …..
Is it possible a “population”
description for planets?
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre 2014
How to proceed?
• We may select planets according to planet mass, orbital
distance stellar, radiation properties (a >3-d grid)
•  But these parameters are not sufficient ! initial
conditions and evolution
•  Do we have diagnostics reminiscent of initial conditions
and planet history?
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre 2014
Predicted atmospheric composition of
exoplanets (2014) – main component
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre 2014
Forget & Leconte, 2013
Predicted atmospheric composition of
exoplanets (2014) – main component
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre 2014
Forget & Leconte, 2013
Strategy for low mass (warm-hot)
planets
A >3-d grid to explore
1) planet mass
2) stellar radiation (luminosity & color)
3) Temperature *
Few objects per bin – measurement of main components and of
equilibrium temperature
Minimum requirement #bins 3x3x3=27 bins to explore
" >100 targets
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre 2014
Predicted atmospheric composition of
exoplanets (2014) – main component
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre 2014
Forget & Leconte, 2013
Disks allow planets to migrate
!  Migration stops
when disks
dissipate
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre 2014
Ariel
Carbon/Oxygen
Understanding planet formation/migration (~500/1000 planets)
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1 AU
10 AU
100 AU
Obert et al., 2011; Turrini, Nelson,Barbieri 2014
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre 2014
Massive (warm-hot) planets
!  C/O ratio " formation site
!  After migration the final distance from the star (temperature) is
reached when the disk is dissipated " migration timescale vs
disk dissipation time
!  The distribution of eq. temperature (final distance from star &
chemistry) depends also on the combination of formation site &
disk lifetime.
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre 2014
Main
components
Equilibrium
temperature
C/O
! > 500 targets
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre 2014
Information on
Planet mass
Stellar radiation
Orbital
distance
Ariel observations
Input
Strategy for massive (warm-hot)
planets
Formation site
Initial mass
Disk lifetime
Optimal spectral window (2-8 micron)
Hot & warm planets
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre 2014
Optimal spectral window
Molecular signatures
1 micron
2.5 micron
5 micron
Water vapour
Methane
Carbon dioxide
Carbon monoxide
Ammonia
Hydrogen cyanide
Ozone
Phosphine
Hydrogen Sulfide
Acetylene
Ethane
Sulfur Dioxide
Titanium Oxide
Vanadium Oxide
11 micron H3+
Tinetti,
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre
2014 Encrenaz, Coustenis, 2013
Targets from NASA-TESS
Dedicated mission to detect transiting planets (2017)
Transiting planets expected to
be discovered by TESS
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre 2014Courtesy of the TESS team
Targets from ESA-PLATO
Dedicated mission to detect transiting planets (2024)
Courtesy
of the TESS & PLATO teams
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre
2014
Requirements
!  Bandwidth 2- 8 micron
!  Spectral resolution ~200
!  1m class (70K)
!  Compact instrument (50K, 40K detector)
!  Low noise
!  High throughput ~.35
Initial radiometric model: the case of a warm
Neptune @SNR=10, K ~9
CH4
CO
CO2
NH3
3.3μ
2.3μ
4.6μ
2.8μ
4.3μ
3.0μ
6.1μ
10-7
10-3
10-5
10-6
10-7
10-6
10-6
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre 2014
Current an Ariel observations
Equilibrium chemistry
Non-equilibrium chemistry
~ 10 planets
Today
~ 500-1000 planets
Ariel
Ariel
Ariel
Ariel
Today
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre 2014
Venot et al., 2012
Venot et al 2012
Atmospheric Remote-sensing IR
Exoplanet Large-survey
(ARIEL) proposal
due to 15 January 2015
Ariel, La ricerca sui pianeti extrasolari in Italia, Roma – 5-7 Novembre 2014