Exploring Exoplanetary Atmospheres from Laboratory Simulations

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Exploring Exoplanetary Atmospheres from Laboratory Simulations

C. He, S. M. Horst, N. K. Lewis, J. I. Moses, E. M.-R. Kempton, P. A.

Mcguiggan, M. S. Marley, C. V. Morley, J. A. Valenti, Véronique Vuitton, et al.

To cite this version:

C. He, S. M. Horst, N. K. Lewis, J. I. Moses, E. M.-R. Kempton, et al.. Exploring Exoplanetary Atmospheres from Laboratory Simulations. Exoplanets in Our Backyard: Solar System and Exoplanet Synergies on Planetary Formation, Evolution, and Habitability, Feb 2020, Houston, TX, United States.

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1

Exploring Exoplanetary Atmospheres from Laboratory Simulations

Chao He

, Sarah M. Hörst

, Nikole K. Lewis

, Julianne I. Moses

, Eliza Miller-Ricci Kempton

, Patricia A.

McGuiggan

, Mark S. Marley

, Caroline V. Morley

, Jeff A. Valenti

, Véronique Vuitton

, and Xinting Yu

1

Johns Hopkins University, Baltimore, MD, USA (che13@jhu.edu),

Space Telescope Science Institute, Balti- more, MD, USA,

Cornell University, Ithaca, NY, USA,

Space Science Institute, Boulder, CO, USA,

University of Maryland, College Park, MD, USA,

NASA Ames Research Center, Mountain View, CA, USA,

University of Texas at Austin, Austin, TX, USA,

Université Grenoble Alpes, Grenoble, France,

University of California Santa Cruz, Santa Cruz, CA, USA.

Introduction: The majority of discovered ex- oplanets (over 4,000 by November, 2019) are super- Earths and mini-Neptunes (with size or mass between Earth’s and Neptune’s), and their atmospheres are expected to exhibit a wide variety of atmospheric compositions. Clouds and/or hazes are likely to be present in these atmospheres as they exist in every solar system planetary atmosphere. However, the pho- tochemical processes for haze formation in these ex- oplanet atmospheres remain largely unknown as the atmospheric phase space has not been explored previ- ously. To understand haze formation in these atmos- pheres, we have conducted a series of laboratory ex- periments simulating a range of atmospheric composi- tions at four different temperatures (300, 400, 600, and 800 K) [1,2,3,4].

Figure 1: Schematic of the PHAZER setup.

Experimental Setup: We carried out the experi- ments using the PHAZER setup (Figure 1) at Johns Hopkins University [5], which allows us to conduct simulation experiments over a broad range of atmos- pheric parameters with two different energy sources (AC plasma or FUV photons). Figure 2 shows the initial gas mixtures for our experiments, which is pre- pared from high-purity gases. The gas mixture flows through a heating coil that heats the gas mixture to the required experimental temperature, and then flows into the chamber where the heated gas mixture is ex- posed to AC plasma, or UV photons. The gas flowing out the chamber is monitored with a Residual Gas Analyzer (RGA, a quadrupole mass spectrometer).

We run the experiment for 72 hr, and collect the solid samples in a dry (<0.1 ppm H

O), oxygen free (<0.1 ppm O

) N

glove box.

Figure 2: Initial gas mixtures used in the experiments, which span a range of temperatures (300-800 K) and initial gas mixtures (100 to 10,000x solar metallicity).

Results and Conclusions: The mass spectra of the gas phase show the compositional changes during the experiments, suggesting that distinct chemical pro- cesses happen in the experiments as a function of dif- ferent initial gas mixture and different energy sources (plasma or UV photons). We identified new gas prod- ucts that could be indicative to photochemistry and haze formation in these atmospheres [1]. All simulat- ed atmospheres resulted in haze formation with both energy sources, but the production rates varied sub- stantially with different conditions [2,3,4]. The result- ing haze particles display different properties, such as color, size distribution, particle density, and composi-

Gas Mixture

Heating Coil Pressure

Gauge Mass Flow Controller

AC Plasma

V_AC

UV Lamp

Pressure Gauge

Pumps

Residual Gas Analyzer Reaction

Chamber

2 tion. Our laboratory results indicate that complex at- mospheric photochemistry can happen and produce new gas products and haze particles in diverse ex- oplanet atmospheres, including compounds (O

and organics) that could be falsely identified as biosigna- tures.

References:

[1] He, C. et al. (2019) ACS Earth and Space Chemistry, 3, 39-50,

[2] He, C. et al. (2018) Astronomical Journal, 156, 38.

[3] He, C. et al. (2018) Astrophysical Journal Let- ters, 856:L3.

[4] Hörst, S.M. et al. (2018) Nature Astronomy, 2, 303-306.

[5] He, C. et al. (2017) Astrophysical Journal Let-

ters, 841:L31.