Challenges and Opportunities in Constraining the Bulk Properties of Super-Earths with Transmission Spectroscopy Eliza Kempton (Formerly: Miller-Ricci) Assistant Professor of Physics Grinnell College, Grinnell, IA Image Credit: Zach Berta
Super-Earths have diverse bulk properties Hadden & Lithwick, ApJ, submitted
Super-Earths have diverse bulk properties H2-He atmospheres Hadden & Lithwick, ApJ, submitted
Super-Earths have diverse bulk properties H2-He atmospheres Hadden & Lithwick, ApJ, submitted
Super-Earths have diverse bulk properties H2-He atmospheres - rocky planet, H2 atmosphere - ice/rock planet, H2O atmosphere - + other volatiles? Hadden & Lithwick, ApJ, submitted
With JWST we anticipate the type of data that are now coming in for hot Jupiters from HST WASP-43b HD 209458b Deming et al., ApJ 2013 Kreidberg et al., ApJ 2014
With JWST we anticipate the type of data that are now coming in for hot Jupiters from HST WASP-43b HD 209458b Deming et al., ApJ 2013 Kreidberg et al., ApJ 2014 Water detections for transiting exoplanets
Measurements of molecular and atomic features in transmission spectra can lead to degenerate interpretations (ΔD) Mean molecular weight Kempton et al., PASP, (2017)
Measurements of molecular and atomic features in transmission spectra can lead to degenerate interpretations (ΔD) Mean molecular weight Kempton et al., PASP, (2017)
Atmospheric observations for low-mass planets reveal the challenges to interpretation HD 97658b GJ 1214b HD 189733b Knutson et al., ApJ, 2014 HAT-P-11b Kreidberg et al., Nature 2013 Fraine et al., Nature, 2014
Many of the recently discovered super-earths most amenable to atmospheric follow-up do not have mass measurements
Many of the recently discovered super-earths most amenable to atmospheric follow-up do not have mass measurements ΔD ΔD ~ 2 H R pl / R * 2 0.5 1 3 10 Scale height: H = kt μg mg Planetary Mass: Mpl = ktrp 2 μgh
Many of the recently discovered super-earths most amenable to atmospheric follow-up do not have mass measurements ΔD ΔD ~ 2 H R pl / R * 2 0.5 1 3 10 Scale height: H = kt mg Planetary Mass: Mpl μg = from Teq ktrp 2 μgh from transit 2.3 for gas giants =?? for super-earths from ΔD
Many of the recently discovered super-earths most amenable to atmospheric follow-up do not have mass measurements ΔD ΔD ~ 2 H R pl / R * 2 0.5 1 3 10 Scale height: H = kt mg Planetary Mass: Mpl μg = from Teq ktrp 2 μgh from transit 2.3 for gas giants =?? for super-earths from ΔD
Parameter space study of super-earths with H2-H2O atmospheres T atm = 400 K R pl = 1.5 R log[h2o/h2] = -0.3 1.0 g = 5 25 m/s 2 (Mpl = 1 5 M ) Batalha, Kempton, & Mbarek, ApJL, 2017
Parameter space study of super-earths with H2-H2O atmospheres T atm = 400 K Degeneracy region R pl = 1.5 R log[h2o/h2] = -0.3 1.0 g = 5 25 m/s 2 (Mpl = 1 5 M ) Batalha, Kempton, & Mbarek, ApJL, 2017
Degenerate spectra as observed with 200 hours of JWST time T obs = 200 hr M4.5 host star (T = 3,000 K, R = 0.2 R ) J = 8 JWST simulations w/ PandExo (Batalha et al. PASP, in press) Batalha, Kempton, & Mbarek, ApJL, 2017
Degenerate spectra as observed with 200 hours of JWST time Volatile-rich water world, water-rich atmosphere Rocky planet, outgassed H2-rich atmosphere T obs = 200 hr M4.5 host star (T = 3,000 K, R = 0.2 R ) J = 8 JWST simulations w/ PandExo (Batalha et al. PASP, in press) Batalha, Kempton, & Mbarek, ApJL, 2017
The degeneracies are further enhanced by the presence of aerosols Batalha, Kempton, & Mbarek, ApJL, 2017
The degeneracies are further enhanced by the presence of aerosols You too can model transmission spectra! Exo-Transmit available publicly on Github https://github.com/elizakempton/exo_transmit Kempton et al., PASP (2017) Batalha, Kempton, & Mbarek, ApJL, 2017
Planet formation N-body simulations predict the existence of water-rich super-earths Raymond et al., Icarus, 2006
Degeneracies in the mass-radius relationship for low-mass planets provide a challenge to diagnosing bulk water abundances GJ 1214b Lissauer et al., Nature, 2011 (modified c/o E. Lopez)
The low bulk density of GJ 1214b informs us of its possible atmospheric composition 1. Mini-Neptune Scenario: Rock / ice interior + hydrogen-dominated atmosphere (mostly H2+ trace H2O, CH4, etc.) 2. Water World Scenario: Mostly H2O - ice interior + steam atmosphere (Rogers & Seager, ApJ, 2010 + Nettelmann et al. 2011)
The low bulk density of GJ 1214b informs us of its possible atmospheric composition 1. Mini-Neptune Scenario: Rock / ice interior + hydrogen-dominated atmosphere (mostly H2+ trace H2O, CH4, etc.) 0.01-5% H2 / He by mass 2. Water World Scenario: Mostly H2O - ice interior + steam atmosphere > 60% H2O by mass (Rogers & Seager, ApJ, 2010 + Nettelmann et al. 2011)
Transit Depth (%) The power of complementary methods: Atmospheric spectroscopy + interior structure modeling Raymond et al., Icarus, 2006 + Wavelength (microns)
Takeaway: 1) Atmospheric studies of small-radius planets should not be undertaken without knowledge of the planet s mass 2) Independent mass measurements (via RVs or TTVs) are necessary in many cases for interpreting the spectra of low-mass exoplanets 3) JWST will provide the first opportunities to unambiguously discover water worlds