Diana Dragomir Hubble Fellow MIT Kavli Institute UNSOLVED PROBLEMS - - PowerPoint PPT Presentation

Diana Dragomir Understanding Super-Earths

Diana Dragomir

Hubble Fellow MIT Kavli Institute

Towards the Nature and Origin

• f Super-Earths

UNSOLVED PROBLEMS Budapest, Hungary July 2, 2018

Diana Dragomir Understanding Super-Earths

Small Exoplanets Are Common

Super-Earths Sub-Neptunes

Fulton et al. (2017)

Diana Dragomir Understanding Super-Earths

Measuring turbulence is hard How to probe vertical structure/interior of disks? Uncertain chemical inventories

Time evolution

Measuring the dust mass is hard

Diana Dragomir Understanding Super-Earths

Exoplanet Atmospheres: Transmission spectroscopy

Can constrain:

• scale height (how puffy the

atmosphere is)

• atmospheric composition
• molecular abundances

Diana Dragomir Understanding Super-Earths

GJ 436b

Knutson et al. (2014) Kreidberg et al. (2014)

GJ 1214b

First Challenge: Small Exoplanet Atmospheres Are Often Cloudy…

Knutson, Dragomir et al. (2014)

HD 97658b GJ 3470b

Ehrenreich et al. (2014)

M dwarf host stars

Diana Dragomir Understanding Super-Earths

… But Not Always

Fraine et al. (2014) HAT-P-11b

H2O H2O H2O CO2, CO H2O Cloud CH4

STIS 750L WFC3 G102 WFC3 G141 IRAC 3.6 IRAC 4.5

.4 .5 .6 .7 .8 .9 1 1.5 2 2.5 3 3.5 4 5 μ

0.066 0.068 0.070 0.072 0.074 0.076 0.078

.4 .5 .6 .7 .8 .9 1 1.5 2 2.5 3 3.5 4 5

0.066 0.068 0.070 0.072 0.074 0.076 0.078

• 4
• 3
• 2
• 1

1 2 3 4 5 6

Scale Height Transit Depth (Rp/R*) Wavelength (µm)

0.4 5.0 4.0 3.0 2.0 1.0 0.6 0.8 0.5 1.5 2.5 3.5

Wakeford et al. (2017)

HAT-P-26b

Wavelength (µm) Wavelength (µm)

K dwarf host stars

Diana Dragomir Understanding Super-Earths

Crossfield & Kreidberg (2017)

Do Clouds/Hazes Correlate With Planet Temperatures?

see also Stevenson (2016)

Diana Dragomir Understanding Super-Earths

Other Challenges for Transmission Spectroscopy

Only probes day-night terminator Partial Clouds vs. Mean Molecular Weight

Global 0.01mbar Cloud Morning Terminator 0.01mbar Cloud

Cloudy Annulus Clear Annulus 10 bar Radius

Line & Parmentier (2015)

Warm Neptune

Clear Solar Global 0.01 mbar Cloud Solar Patchy Cloud Solar Clear High MMW Global 1 mbar Cloud Solar

Degeneracy between molecular abundances and reference pressure

Heng & Kitzmann (2017)

R0 Rp/Rs

?

Diana Dragomir Understanding Super-Earths

Other Paths: Emission Spectroscopy

Can constrain:

• the temperature -

pressure profile, and thus the atmospheric structure

• heat redistribution

efficiency

• atmospheric composition

Diana Dragomir Understanding Super-Earths

The first emission spectrum of a super-Earth

(55 Cnc e)

Dragomir et al. (2018)

Diana Dragomir Understanding Super-Earths 101 102 103 104 105 106

Detections

Earths 70

±9

< 1.25R⊕ Super-Earths 510 486

±22

1.25 − 2R⊕ Sub-Neptunes 3k 1111

±122

2 − 4R⊕ Giants 17k 67

±8

> 4R⊕

Full-Frame Images 2x105 Target Stars

Sullivan et al. (2015)

Launched April 18, 2018

Transiting Exoplanet Survey Satellite (TESS)

Diana Dragomir Understanding Super-Earths

5 10 15 20 Mass [MEarth] 1 2 3 4 Radius [REarth]

100 % water pure rock maximum iron fraction Earth−like

Hydrogen

★ ★

Earth Venus

Other Paths: Small Planet Mass-Radius Diagram

Search for trends as a function of:

• distance from the host

star (orbital period)

• stellar mass
• stellar metallicity

and abundances

Diana Dragomir Understanding Super-Earths

Takeaways

• Connecting super-Earth composition to their formation

is a multi-nuanced challenge

• Transmission spectroscopy is prone to degeneracies

➡ but for now it is the only way to probe the

atmospheres of most (transiting) super-Earths

• Use complementary approaches to enhance the

efficiency of super-Earth characterization

➡ emission spectroscopy and bulk density statistics