Terrestrial planets across space and time

The study of cosmology, galaxy formation and exoplanets has now advanced to a stage where a cosmic inventory of terrestrial planets may be attempted. By coupling semi-analytic models of galaxy formation to a recipe that relates the occurrence of planets to the mass and metallicity of their host stars, we trace the population of terrestrial planets around both solar-mass (FGK type) and lower-mass (M dwarf) stars throughout all of cosmic history. We find that the mean age of terrestrial planets in the local Universe is $7\pm{}1$ Gyr for FGK hosts and $8\pm{}1$ Gyr for M dwarfs. We estimate that hot Jupiters have depleted the population of terrestrial planets around FGK stars by no more than $\approx 10\%$, and that only $\approx 10\%$ of the terrestrial planets at the current epoch are orbiting stars in a metallicity range for which such planets have yet to be confirmed. The typical terrestrial planet in the local Universe is located in a spheroid-dominated galaxy with a total stellar mass comparable to that of the Milky Way. When looking at the inventory of planets throughout the whole observable Universe, we argue for a total of $\approx 1\times 10^{19}$ and $\approx 5\times 10^{20}$ terrestrial planets around FGK and M stars, respectively. Due to light travel time effects, the terrestrial planets on our past light cone exhibit a mean age of just $1.7\pm 0.2$ Gyr. These results are discussed in the context of cosmic habitability, the Copernican principle and searches for extraterrestrial intelligence at cosmological distances.Comment: 11 pages, 8 figures. v.2: Accepted for publication in ApJ. Some changes in quantitative results compared to v.1, mainly due to differences in IMF assumption

Probe for Measuring Soil Specific Heat Using A Heat-Pulse Method

Temperature rise, measured a short distance from a line heat source, can be used to determine the volumetric specific heat of soil and other materials. Volumetric specific heat is linearly related to the inverse of the temperature rise. The purpose of this note is to describe the construction and performance of a device for measuring specific heat using the line source method. The device was constructed from two hypodermic needles, 0.813 mm in diam. and 28 mm long, and spaced 6 mm apart. One needle contained a heater and the other a thermocouple. The temperature rise from heat pulses given to the heater were measured with the thermocouple. The coefficientof variation (CV) of specific heat on replicate samples was around 1%. Since water is the main variable component of the specific heat in nonswelling soil, changes in water content might be resolved to 0.01 or better in nonswelling soil

JWST/NIRCam Coronagraphy of the Young Planet-hosting Debris Disk AU Microscopii

High-contrast imaging of debris disk systems permits us to assess the composition and size distribution of circumstellar dust, to probe recent dynamical histories, and to directly detect and characterize embedded exoplanets. Observations of these systems in the infrared beyond 2--3 $\mu$m promise access to both extremely favorable planet contrasts and numerous scattered-light spectral features -- but have typically been inhibited by the brightness of the sky at these wavelengths. We present coronagraphy of the AU Microscopii (AU Mic) system using JWST's Near Infrared Camera (NIRCam) in two filters spanning 3--5 $\mu$m. These data provide the first images of the system's famous debris disk at these wavelengths and permit additional constraints on its properties and morphology. Conducting a deep search for companions in these data, we do not identify any compelling candidates. However, with sensitivity sufficient to recover planets as small as $\sim 0.1$ Jupiter masses beyond $\sim 2^{\prime\prime}$ ($\sim 20$ au) with $5\sigma$ confidence, these data place significant constraints on any massive companions that might still remain at large separations and provide additional context for the compact, multi-planet system orbiting very close-in. The observations presented here highlight NIRCam's unique capabilities for probing similar disks in this largely unexplored wavelength range, and provide the deepest direct imaging constraints on wide-orbit giant planets in this very well studied benchmark system.Comment: 27 pages, 14 figure

GRB 171010A/SN 2017htp: a GRB-SN at z = 0.33

The number of supernovae known to be connected with long-duration gamma-ray bursts (GRBs) is increasing and the link between these events is no longer exclusively found at low redshift (z ≲ 0.3) but is well established also at larger distances. We present a new case of such a liaison at z = 0.33 between GRB 171010A and SN 2017htp. It is the second closest GRB with an associated supernova of only three events detected by Fermi-LAT. The supernova is one of the few higher redshift cases where spectroscopic observations were possible and shows spectral similarities with the well-studied SN 1998bw, having produced a similar Ni mass (⁠ M Ni =0.33±0.02 M ⊙ MNi=0.33±0.02 M⊙ ⁠) with slightly lower ejected mass (⁠ M ej =4.1±0.7 M ⊙ Mej=4.1±0.7 M⊙ ⁠) and kinetic energy (⁠ E K =8.1±2.5× 10 51 erg EK=8.1±2.5×1051 erg ⁠). The host-galaxy is bigger in size than typical GRB host galaxies, but the analysis of the region hosting the GRB revealed spectral properties typically observed in GRB hosts and showed that the progenitor of this event was located in a very bright H ii region of its face-on host galaxy, at a projected distance of ∼ 10 kpc from its galactic centre. The star-formation rate (SFRGRB ∼ 0.2 M⊙ yr−1) and metallicity (12 + log(O/H) ∼8.15 ± 0.10) of the GRB star-forming region are consistent with those of the host galaxies of previously studied GRB–SN systems

The \textit{JWST} Early Release Science Program for Direct Observations of Exoplanetary Systems III: Aperture Masking Interferometric Observations of the star HIP\,65426 at 3.8 μm\boldsymbol{3.8\,\rm{\mu m}}

We present aperture masking interferometry (AMI) observations of the star HIP 65426 at $3.8\,\rm{\mu m}$ as a part of the \textit{JWST} Direct Imaging Early Release Science (ERS) program obtained using the Near Infrared Imager and Slitless Spectrograph (NIRISS) instrument. This mode provides access to very small inner working angles (even separations slightly below the Michelson limit of ${}0.5\lambda/D$ for an interferometer), which are inaccessible with the classical inner working angles of the \textit{JWST} coronagraphs. When combined with \textit{JWST}'s unprecedented infrared sensitivity, this mode has the potential to probe a new portion of parameter space across a wide array of astronomical observations. Using this mode, we are able to achieve a contrast of $\Delta m_{F380M}{\sim }7.8$\,mag relative to the host star at a separation of {\sim}0.07\arcsec but detect no additional companions interior to the known companion HIP\,65426\,b. Our observations thus rule out companions more massive than 10{-}12\,\rm{M\textsubscript{Jup}} at separations ${\sim}10{-}20\,\rm{au}$ from HIP\,65426, a region out of reach of ground or space-based coronagraphic imaging. These observations confirm that the AMI mode on \textit{JWST} is sensitive to planetary mass companions orbiting at the water frost line, even for more distant stars at $\sim$100\,pc. This result will allow the planning and successful execution of future observations to probe the inner regions of nearby stellar systems, opening essentially unexplored parameter space.Comment: 15 pages, 9 figures, submitted to ApJ Letter

The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems II: A 1 to 20 Micron Spectrum of the Planetary-Mass Companion VHS 1256-1257 b

We present the highest fidelity spectrum to date of a planetary-mass object. VHS 1256 b is a $<$20 M$_\mathrm{Jup}$ widely separated ($\sim$8\arcsec, a = 150 au), young, planetary-mass companion that shares photometric colors and spectroscopic features with the directly imaged exoplanets HR 8799 c, d, and e. As an L-to-T transition object, VHS 1256 b exists along the region of the color-magnitude diagram where substellar atmospheres transition from cloudy to clear. We observed VHS 1256~b with \textit{JWST}'s NIRSpec IFU and MIRI MRS modes for coverage from 1 $\mu$m to 20 $\mu$m at resolutions of $\sim$1,000 - 3,700. Water, methane, carbon monoxide, carbon dioxide, sodium, and potassium are observed in several portions of the \textit{JWST} spectrum based on comparisons from template brown dwarf spectra, molecular opacities, and atmospheric models. The spectral shape of VHS 1256 b is influenced by disequilibrium chemistry and clouds. We directly detect silicate clouds, the first such detection reported for a planetary-mass companion.Comment: Accepted ApJL Iterations of spectra reduced by the ERS team are hosted at this link: https://github.com/bemiles/JWST_VHS1256b_Reduction/tree/main/reduced_spectr