Observing How Habitable Conditions Develop (Or Not) in Protoplanetary Disks
Colette SalykNational Optical Astronomy Observatory
Credit: JPL-Caltech/T. Pyle (SSC) Credit: NASA
?
Why studying protoplanetary disks is important for understanding habitability
• Planet formation “laboratory” – ground truth for our ideas about how planets form and habitability develops
Even if you don’t care how planets form…
Milky way diameter: 40 kpc(120,000 light years)
Microlensing planets: 5 kpc
Kepler planets: 2 kpc
Imaged planets: 0.2 kpc
Credit: Exoplanet app
Planet detection remains difficult at large distances, and characterization even more so
Why studying protoplanetary disks is important for understanding habitability
• Planet formation “laboratory” – ground truth for our ideas about how planets form and habitability develops
• Understanding formation process allows us to extrapolate to the rest of the galaxy/universe
• Overview of what we do and don’t know about protoplanetary disks
• Current studies of development of Goldilocks properties:– Location– Planet size and type– Chemistry
Composed of gas and (opaque) dust, Few 100 AU in size
CO velocity in HD 163296 (ALMA)
de Gregorio-Monsalvo et al. 2013
Opaque disks in Orion (Hubble)1800 AU
Small (but evolved) dust, consistent with olivine composition
Spitzer spectra of Si-O stretch
Chondrule from American Museum of Natural History meteorite collection
Kessler-Silacci et al. 2006
Data
Models
Small (but evolved) dust, consistent with olivine composition
Chondrule from American Museum of Natural History meteorite collection
Spitzer spectra of Si-O stretch
Kessler-Silacci et al. 2006
Data
Models
Protoplanetary disks are ubiquitous*
Kraus & Ireland, 2011
*around sun-like stars in nearby star-forming regions
Protoplanetary disks last a few Myr
Kraus & Ireland, 2011
Masses are consistent with Minimum Mass Solar Nebula, or slightly lower
Ophiuchus data from Andrews et al. 2007
Masses are consistent with Minimum Mass Solar Nebula, or slightly lower
Ophiuchus data from Andrews et al. 2007∨
small
• Planet size and location: Snow lines and disk dispersal
• Chemistry: Chemical inventories of planet forming regions
Active research related to habitability
What processes determine planetary size and location?
Gas giantsTerrestrial planets
What processes determine planetary size and location?
Gas giantsTerrestrial planets
The “snow line” – an increase in solid surface density
What is the expected location of the snow line?
What is the expected location of the snow line?
Gas giantsTerrestrial planets
The “snow line”
Habitable zone
Multi-wavelength observations of water vapor measure snow line locations
ice lineK. Pontoppidan
First measured locations of snow lines in disks
Meijerink+ 2009Zhang+ 2013
First measured locations of snow lines in disks
Meijerink+ 2009Zhang+ 2013
See poster by Sandra Blevins for an update!
Gas giantsTerrestrial planets Ice giants (super Earths?)
Planet type affected by disk dispersal
Dispersal of disk gas also affects planet migration
Snapshot of disk surface densitywith planet undergoing migration
P. Armitage
1 10 100
# of planets
Orbital Period [days]
Hot Jupiters
How do disks evolve/disperse?Disk winds
Blandford & Payne 1982Pudritz & Norman 1983Cartoon inspired by Bai et al. 2013
B wind
accretion
Molecular emission lineshapes and images – evidence for disk winds?
Pontoppidan+ 2009; also Bast+ 2011
Flux
Velocity
ALMA CO velocity field
Salyk+ in prepBrown+ 2013
Vibrational CO
How do disks evolve/disperse?Photoevaporative winds wind
FUVEUVX-ray
How do disks evolve/disperse?Photoevaporative winds wind
FUVEUVX-ray
?
Main open question: How quickly do disks dissipate at each disk radius?
Observations of photoevaporation tracers measure location and mass-loss
[Ne II] emission from two disks + models
Pascucci & Sterzik 2009
• Chemistry: Chemical inventories of planet forming regions
Solar data from Grevesse et al. 2010Chondrite data from Allegre et al. 2001
CI chondrite abundances vs. solar abundances(R ~ 4 AU)
Earth abundances vs. solar abundances(R = 1 AU)
Solar data from Grevesse et al. 2010Chondrite data from Allegre et al. 2001
N2, HCN, NH3, organics ?
CO, CO2, organics, graphite?
Earth abundances vs. solar abundances(R = 1 AU)
Solar data from Grevesse et al. 2010Chondrite data from Allegre et al. 2001
What is the correct chemical pathway? Inheritance or reset?
Maximum “reset”
Maximum “Inheritance”
Resemblance between cometary and cloud ice compositions = an inheritance assumption
Data from Mumma & Charnley 2011 (and references therein)
Cometary abundance% relative to water
Cloud abundance% relative to water
Evidence for reset in the solar system: CAIs and chondrules
Chondrule
Calcium Aluminum-rich Inclusion (CAI)
Thin sections from the American Museum of Natural History meteorite collection
Carr & Najita 2008Also, Salyk+ 2008
The study of chemistry in inner disks was enabled by the Spitzer InfraRed Spectrograph (IRS)
O,C,N inventory in inner disks is being measured
Pontoppidan+ 2014
O C N
Fraction
Evidence for reset in disks: O,C,N inventory different from birth cloud
Salyk et al. 2011; Öberg et al. 2011
Evidence for reset in disks: Variability in disk chemistry
Banzatti et al. 2012
See poster by Andrea Banzatti
Current: Partial chemical inventory, evidence for reset
Yet to come: Chemical differences between disks, and as a function of radius
• Basic protoplanetary disk properties have been characterized
• Studies of development of Goldilocks properties ongoing:– Location– Planet size and type– Chemistry
Conclusions
Measuring snow linesObserving disk evolution/dispersal
Chemical inventory in planet-forming regions, evidence for reset, details yet to come
Questions about observing disks?