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In this study, LED based mini-lidar to install into Mars rover has been developed. Its aim is to capture the dynamics of dust twister called “Dust Devil”. For Mars rover installation, there are large restrictions of 10cm3 optics size, 1kg weight, 1W power consumption, etc. We have developed its concept model, and conducted the demonstration experiment. The LED mini-lidar is equipped with a high speed photon counter, of which data sampling interval is 1ns, corresponding to a range bin of 0.15m, and a high repetition pulsed LED beam, of which repetition frequency is greater than 500kHz. Transmitting optical pulse power was

著者人数: 16名, Accepted: 2019-04-12, 資料番号: SA1190014000

著者人数: 13名, Accepted: 2018-11-28, 資料番号: SA1180242000

The existence of liquid water within an oxidized environment on early Mars has been inferred by the Mn-rich rocks found during recent explorations on Mars. The oxidized atmosphere implied by the Mn-rich rocks would basically be comprised of CO$_2$ and H$_2$O without any reduced greenhouse gases such as H$_2$ and CH$_4$. So far, however, it has been thought that early Mars could not have been warm enough to sustain water in liquid form without the presence of reduced greenhouse gases. Here, we propose that H$_2$O$_2$ could have been the gas responsible for warming the surface of the oxidized early Mars. Our one-dimensional atmospheric model shows that only 1 ppm of H$_2$O$_2$ is enough to warm the planetary surface because of its strong absorption at far-infrared wavelengths, in which the surface temperature could have reached over 273~K for a CO$_2$ atmosphere with a pressure of 3~bar. A wet and oxidized atmosphere is expected to maintain sufficient quantities of H$_2$O$_2$ gas in its upper atmosphere due to its rapid photochemical production in slow condensation conditions. Our results demonstrate that a warm and wet environment could have been maintained on an oxidized early Mars, thereby suggesting that there may be connections between its ancient atmospheric redox state and possible aqueous environment., Comment: 8 pages, 7 figures, published in ApJ

Accepted: 2017-06-04, 資料番号: SA1170203000

著者人数: 19名, Accepted: 2016-12-08, 資料番号: SA1160259000

In order to investigate a possible variety of atmospheric states realized on a synchronously rotating aquaplanet, an experiment studying the impact of planetary rotation rate is performed using an atmospheric general circulation model (GCM) with simplified hydrological and radiative processes. The entire planetary surface is covered with a swamp ocean. The value of planetary rotation rate is varied from zero to the Earth’s, while other parameters such as planetary radius, mean molecular weight and total mass of atmospheric dry components, and solar constant are set to the present Earth’s values. The integration results show that the atmosphere reaches statistically equilibrium states for all runs; none of the calculated cases exemplifies the runaway greenhouse state. The circulation patterns obtained are classified into four types: Type-I characterized by the dominance of a day-night thermally direct circulation, Type-II characterized by a zonal wave number one resonant Rossby wave over a meridionally broad westerly jet on the equator, Type-III characterized by a long time scale north-south asymmetric variation, and Type-IV characterized by a pair of mid-latitude westerly jets. With the increase of planetary rotation rate, the circulation evolves from Type-I to Type-II and then to Type-III gradually and smoothly, whereas the change from Type-III to Type-IV is abrupt and discontinuous. Over a finite range of planetary rotation rate, both Types-III and -IV emerge as statistically steady states, constituting multiple equilibria. In spite of the substantial changes in circulation, the net energy transport from the day side to the night side remains almost insensitive to planetary rotation rate, although the partition into dry static energy and latent heat energy transports changes. The reason for this notable insensitivity is that the outgoing longwave radiation over the broad area of the day side is constrained by the radiation limit of a moist atmosphere, so that the transport to the night side, which is determined as the difference between the incoming solar radiation and the radiation limit, cannot change greatly.

Direct-imaging techniques of exoplanets have made significant progress recently, and will eventually enable to monitor photometric and spectroscopic signals of earth-like habitable planets in the future. The presence of clouds, however, would remain as one of the most uncertain components in deciphering such direct-imaged signals of planets. We attempt to examine how the planetary obliquity produce different cloud patterns by performing a series of GCM (General Circulation Model) simulation runs using a set of parameters relevant for our Earth. Then we use the simulated photometric lightcurves to compute their frequency modulation due to the planetary spin-orbit coupling over an entire orbital period, and attempt to see to what extent one can estimate the obliquity of an Earth-twin. We find that it is possible to estimate the obliquity of an Earth-twin within the uncertainty of several degrees with a dedicated 4 m space telescope at 10 pc away from the system if the stellar flux is completely blocked. While our conclusion is based on several idealized assumptions, a frequency modulation of a directly-imaged earth-like planet offers a unique methodology to determine its obliquity., Comment: 29 pages, 18 figures, accepted for publication in ApJ

We describe the dayside cloud top structure of Venus as retrieved from 93 images acquired at a wide variety of solar phase angles (0–120°) using the 2.02-μm channel of the 2-μm camera (IR2) onboard the Venus orbiter, Akatsuki, from April 4 to May 25, 2016. Since the 2.02-μm channel is located in a CO2 absorption band, the sunlight reflected from Venus allowed us to determine the cloud top altitude corresponding to unit aerosol optical depth at 2.02 μm. First, the observed solar phase angle dependence and the center-to-limb variation of the reflected sunlight in the region equatorward of 30° were used to construct a spatially averaged cloud top structure characterized by cloud top altitude zc, Mode 2 modal radius rg,2, and cloud scale height H, which were 70.4 km, 1.06 μm, and 5.3 km, respectively. Second, cloud top altitudes at individual locations were retrieved on a pixel-by-pixel basis with an assumption that rg,2 and H were uniform for the entire planet. The latitudinal structure of the cloud top altitude was symmetric with respect to the equator. The average cloud top altitude was 70.5 km in the equatorial region and showed a gradual decrease of ~2 km by the 45° latitude. It rapidly dropped at latitudes of 50–60° and reached 61 km in latitudes of 70–75°. The average cloud top altitude in the region equatorward of 30° showed negligible local time dependence, with changes up to 1 km at most. Local variations in cloud top altitude, including stationary gravity wave features, occurred within several hundreds of meters. Although long zonal or tilted streaky features poleward of ~45° were clearly identifiable, features in the low and middle latitudes were usually subtle. These did not necessarily appear as local variations at the cloud top level, where mottled and patchy UV patterns were observed, suggestive of convection and turbulence at the cloud top level.

We report observations of a stellar occultation by Pluto on 2019 July 17. A single-chord high-speed (time resolution $= 2\,$s) photometry dataset was obtained with a CMOS camera mounted on the Tohoku University 60 cm telescope (Haleakala, Hawaii). The occultation light curve is satisfactorily fitted to an existing Pluto's atmospheric model. We find the lowest pressure value at a reference radius of $r = 1215~{\rm km}$ among those reported after 2012, indicating a possible rapid (approximately $21^{+4}_{-5} \%$ of the previous value) pressure drop between 2016 (the latest reported estimate) and 2019. However, this drop is detected at a $2.4\sigma$ level only and still requires confirmation from future observations. If real, this trend is opposite to the monotonic increase of Pluto's atmospheric pressure reported by previous studies. The observed decrease trend is possibly caused by ongoing ${\rm N_2}$ condensation processes in the Sputnik Planitia glacier associated with an orbitally driven decline of solar insolation, as predicted by previous theoretical models. However, the observed amplitude of the pressure decrease is larger than the model predictions., Comment: 7 pages, 3 figures, accepted for publication in Astronomy and Astrophysics

A compact LED lidar was constructed and fieldtested with the aim to observe the Mars’ dust devils. To be able to fit it on the Mars rover, a specialized Cassegrain telescope was designed to be within a 10 cm-cube, with a field of view of 3mrad. The transmitter has 385 nm LED light source with 3 cmϕ opening, 70mrad divergence, 0.75W (7.5nJ/10ns) pulse power, and 500 kHz repetition frequency. The configuration of the optical system is biaxial to easily configure the overlap between their optical axes.

The oxygen isotope ratios 17O/16O and 18O/16O in Venus׳s atmosphere were measured simultaneously by ground-based IR spectroscopy. The CO2 absorption lines in the 2648 cm−1 (for 17O/18O) and 4582 cm−1 (for 18O/16O) regions were observed using the IRTF/CSHELL spectrometer. The deviations of the isotope fractions are found to be δ17O=+92±158‰ and δ18O=−42±85‰ as compared to the terrestrial standard (HITRAN 2012) where the uncertainties include both random and systematic errors. Such combination agrees with the Earth–Moon fractionation line within the errors. This is consistent to the fact that the proto-Venus matter was also well mixed with the proto-Earth–Moon matter.

著者人数: 15名, Accepted: 2014-10-19, 資料番号: SA1004980000

著者人数: 22名, Accepted: 2013-07-13, 資料番号: SA1004507000

A mini-lidar to observe the activity of Martian atmosphere is developed. The 10cm-cube LED mini-lidar was designed to be onboard a Mars rover. The light source of the mini-lidar is a high powered LED of 385nm. LED was adopted as light source because of its toughness against circumference change and physical shock for launch. The pulsed power and the pulse repetition frequency of LED beam were designed as 0.75W (=7.5nJ/10ns) and 500kHz, respectively. Lidar echoes were caught by the specially designed Cassegrain telescope, which has the shorter telescope tube than the usual to meet the 10cm-cube size limit. The high-speed photon counter was developed to pursue to the pulse repetition frequency of the LED light. The measurement range is no shorter than 30m depending back-ground condition. Its spatial resolution was improved as 0.15m (=1ns) by this photon counter. The demonstrative experiment was conducted at large wind tunnel facility of Japan Meteorological Agency. The measurement target was smoke of glycerin particles. The smoke was flowed in the wind tunnel with wind speed of 0 – 5m. Smoke diffusion and its propagation due to the wind flow were observed by the LED mini-lidar. This result suggests that the developed lidar can pursue the structure and the motion of dust devil of >2m.

著者人数: 11名, Accepted: 2012-01-30, 資料番号: SA1003638000

The abundance of HDO above the clouds in the dayside atmosphere of Venus was measured by ground-based 2.3 μm spectroscopy over 4 days. This is the first HDO observation above the clouds in this wavelength region corresponding to a new height region. The latitudinal distributions found show no clearly defined structure. The disk-averaged mixing ratio is 0.22 ± 0.03 ppm for a representative height region of 62–67 km. This is consistent with measurements found in previous studies. Based on previous H2O measurements, the HDO/H2O ratio is found to be 140 ± 20 times larger than the telluric ratio. This lies between the ratios of 120 ± 40 and 240 ± 25, respectively, reported for the 30–40 km region by ground-based nightside spectroscopy and for the 80–100 km region by solar occultation measurement on board the Venus Express.

著者人数: 14名, Accepted: 2011-06-09, 資料番号: SA1003050000

The abundance of carbon monoxide in the Venus’ dayside atmosphere above the clouds was measured by ground-based 2.3 μm spectroscopy for 4 days. The hemispherical distributions found show no significant latitudinal or longitudinal structure. The disc-averaged mixing ratio of 58 ± 17 ppm found at a representative height of 62–67 km is consistent with previous measurements. Such a flat distribution of CO abundance above the clouds seems to be controlled by an efficient horizontal eddy diffusion with a time scale of 30 days or shorter although the CO distribution below the clouds seems to be controlled by the meridional circulation. The pole-ward wind speed of the meridional circulation above the clouds is estimated to be 0.2 m s −1 or less based on the difference between the CO mixing ratios above and below the clouds.

The abundance of hydrogen chloride (HCl) in the Venus atmosphere was measured by ground-based IR spectroscopy. The dayside measurements were performed in May 2007 with a resolution of 40,000, and the nightside measurements in October 1999 with a resolution of 1000. The hemispheric distributions of the HCl mixing ratio measured above the Venus’ clouds show no significant structure with a disc-averaged value of 0.74±0.06 ppm which is in the similar range as the previous report of 0.6±0.2 ppm. The representative height for the dayside measurements is estimated to be 60–66 km. Recent results by Venus Express/SPICAV/SOIR show much smaller values of 0.1–0.2 ppm at 64–94 km; however the direct comparison is difficult due to the different spatial conditions. The hemispheric distributions of the 35Cl/37Cl isotope ratio are also found to show no significant structure with a disc-averaged value of 3.1±0.4 which coincides with the terrestrial value of 3.1. The HCl mixing ratios below the clouds are also found to show no significant structure with a disc-averaged value of 0.40±0.05 ppm, which is similar to the previous reports of 0.4–0.5 ppm. The larger HCl mixing ratio above the clouds than below suggests the production of HCl in the cloud region or above. Also, a uniform hemispherical distribution of H2O is found below the clouds with a disc-averaged mixing ratio of 25±5 ppm; this is in the same range as the previous measurements. Those uniform distributions of HCl and H2O support the fact that their chemical lifetimes are much longer than that of mixing as has been discussed so far.

著者人数：21名, Accepted: 2006-04-10, 資料番号: SA1000187000

Accepted: 2007-03-30, 資料番号: SA1000233000

We review two models describing the Venus climate system: the carbonate and pyrite models. It has been argued carbonate and pyrite are potentially important minerals controlling the climate of Venus, though existence of either minerals has not been confirmed. Although it used to be proposed that carbonation reaction might explain the Venus’ atmospheric CO 2 abundance, it is unlikely Venus’ surface is reactive enough to control the Venus’ massive CO 2 atmosphere. Venus’ surface carbonate is also able to affect the climate through the reaction with atmospheric SO 2 to form anhydrite. Under the carbonate model the climate state is not in equilibrium and would be unstable due to the reaction between carbonate and SO 2 . On the other hand, pyrite–magnetite reaction is proposed to explain the Venus’ atmospheric SO 2 abundance. Under pyrite–magnetite reaction, however, the climate would be stabilized such that the existing climate state is maintained over a geological timescale, while some observational facts such as atmospheric abundance of SO 2 and surface temperature could also be reasonably explained.

A two-dimensional model study revealed that the meridional circulation can have a large influence on the distributions of the cloud and condensable gases on Venus. In our model, the generally observed depression of near-infrared optical thickness at midlatitude is reproduced as a result of the enhancement of cloud thickness at low and high latitudes. At high latitudes, the modeled poleward transport of H2SO4-H2O droplets in the upper atmosphere makes a thick cloud, since most of the H2SO4-H2O droplets photochemically produced are transported poleward by the meridional circulation. At low latitudes, the modeled large-scale ascent of the concentrated H2SO4 vapor forms a dense lower cloud in accord with observations by entry probes. The equatorward transport of H2SO4 vapor below the cloud by the modeled meridional circulation and the sedimentation of droplets in the lower cloud leads to the accumulation of H2SO4 vapor around the cloud base at low latitudes. The calculated H2SO4 vapor distribution agrees with radio occultation observations. The middle cloud appears to be caused by the condensation of H2SO4 vapor transported upward from below by convective mixing.

Accepted: 2008-12-10, 資料番号: SA1000963000

Received 2 March 2008; revised 29 July 2008; accepted 18 September 2008; published 31 December 2008. [1] We evaluated the spatial variation of Venusian surface emissivity at 1.18 mm wavelength and that of near-surface atmospheric temperature using multispectral images obtained by the Near-Infrared Mapping Spectrometer (NIMS) on board the Galileo spacecraft. The Galileo NIMS observed the nightside thermal emission from the surface and the deep atmosphere of Venus, which is attenuated by scattering from the overlying clouds. To analyze the NIMS data, we used a radiative transfer model based on the adding method. Although there is still an uncertainty in the results owing to the not well known parameters of the atmosphere, our analysis revealed that the horizontal temperature variation in the near-surface atmosphere is no more than ±2 K on the Venusian nightside and also suggests that the majority of lowlands likely has higher emissivity compared to the majority of highlands. One interpretation for the latter result is that highland materials are generally composed of felsic rocks. Since formation of a large body of granitic magmas requires water, the presence of granitic terrains would imply that Venus may have had an ocean and a mechanism to recycle water into the mantle in the past.

International audience; The Venus Express spacecraft images the nightside thermal emissions using the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS). At 1.02, 1.10, and 1.18 mum, thermal emission from the surface is observed. The signal is attenuated by scattering and absorption in the dense atmosphere. The measured flux at the top of the atmosphere is positively correlated with surface temperature and surface emissivity. The surface temperature of Venus is relatively well constrained as being mainly a function of altitude with a gradient lesser or equal to the adiabatic lapse rate. This study examines the correlation of VIRTIS images showing a signal of the surface at 1.02 mum with viewing geometry, stray sunlight, cloud opacity, and topography and applies semiempirical relations to remove their influence. The remaining contrast can be either ascribed to surface emissivity or unexpected temperature variations. Temperature variations due to active volcanism are unlikely to be persistent over the time of observations; therefore, the mosaic of all processed images is here interpreted in terms of surface emissivity variation. The emissivity variation found is correlated with geomorphological features established from Magellan synthetic aperture radar images. It is generally lower at tessera terrain. Some, but not all, volcanic edifices show increased emissivity. Large lava flows in the Lada terra-Lavinia planitia region also show an increased thermal emission. This might indicate a more felsic surface composition of tessera highlands and large-scale extrusive volcanism of ultramafic composition.

Accepted: 2007-02-02, 資料番号: SA1000161000

We present the thermal evolution and emergent spectra of solidifying terrestrial planets along with the formation of steam atmospheres. The lifetime of a magma ocean and its spectra through a steam atmosphere depends on the orbital distance of the planet from the host star. For a type-I planet, which is formed beyond a certain critical distance from the host star, the thermal emission declines on a timescale shorter than approximately $10^6$ years. Therefore, young stars should be targets when searching for molten planets in this orbital region. In contrast, a type-II planet, which is formed inside the critical distance, will emit significant thermal radiation from near-infrared atmospheric windows during the entire lifetime of the magma ocean. The Ks and L bands will be favorable for future direct imaging because the planet-to-star contrasts of these bands are higher than approximately 10$^{-7}$-10$^{-8}$. Our model predicts that, in the type-II orbital region, molten planets would be present over the main sequence of the G-type host star if the initial bulk content of water exceeds approximately 1 wt%. In visible atmospheric windows, the contrasts of the thermal emission drop below $10^{-10}$ in less than $10^5$ years, whereas those of the reflected light remain $10^{-10}$ for both types of planets. Since the contrast level is comparable to those of reflected light from Earth-sized planets in the habitable zone, the visible reflected light from molten planets also provides a promising target for direct imaging with future ground- and space-based telescopes., 17 pages, 12 figures, 1 table, accepted for publication in ApJ

Accepted: 2011-03-20, 資料番号: SA1002864000

著者人数: 31名, Accepted: 2011-02-15, 資料番号: SA1002853000

In response to public concerns, 165 Meo Laotians had stools screened for intestinal parasites by the Illinois Department of Public Health. One hundred twenty-nine had at least one pathogenic parasite detected. Hookworm was detected most frequently, followed by Giardia lamblia, Trichuris trichiura , and Ascaris lumbricoides . Hookworm and overall infection were more frequent in persons 4 years of age and older, while giardiasis, ascariasis, and trichuriasis were most common in the 4- to 14-year age group. Most infections were helminthic and of no public health consequence in the United States. However, giardiasis was seven times as prevalent in refugee children as in the general US population, posing a potential public health risk in child-care settings. ( JAMA 1980;244:2543-2544)