Abstract
Thousands of exoplanets have been discovered in last two decades,
including a sample of rocky worlds in the habitable zones of their host
stars. Assessing their habitability will rely on the observation and
characterization of atmospheres of these distant worlds. Laboratory
simulations can provide critical information for atmospheric
observations of exoplanets. Thus, we conducted a series of laboratory
experiments that simulated a broad range of atmospheres in cooler
(<800 K), smaller (<0.3× Jupiter’s mass) exoplanets.
We investigated three types of atmospheric metallicities, 100× solar
(H2-dominated), 1,000× (H2O-dominated), and 10,000× (CO2-dominated) at
three temperatures, 300, 400, and 600 K using the PHAZER (Planetary Haze
Research) chamber at Johns Hopkins University (He et al. 2017) with one
of two energy sources (AC glow plasma and UV photons). We find that all
simulated atmospheres resulted in haze formation with both energy
sources, but the production rates vary a lot with different conditions
(He et al. 2018a, 2018b; Hörst et al. 2018). The resulting haze
particles can affect the atmospheric and surface temperature of the
exoplanets, and their potential habitability. We monitored the gas phase
compositional changes with a quadrupole mass spectrometry during the
experiments and characterized the resulted haze particles. We find that
the organic molecules are produced in both gas and solid phases, which
could provide a source of organic material to the surface for life to
arise. We identified potential precursors (C2H2, HCN, CH2NH, HCHO, etc.)
for haze formation, among which HCHO and HCN are also important
prebiotic precursors for products of biological significance (sugars,
amino acids, and nucleobases). The laboratory results increase our
understanding the habitability of exoplanets and can help guide and
interpret current and future atmospheric observations of exoplanets.
Ref: He, C., Hörst, S. M., et al. 2017, APJL, 841, L31 He, C., Hörst, S.
M., Lewis, N. K., et al. 2018, ApJL, 856, L3 He, C., Hörst, S. M.,
Lewis, N. K., et al. 2018, AJ, 156, 38 Hörst, S. M., He, C., Lewis, N.
K., et al. 2018, Nat. Astron., 2, 303