Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

The planetary missions including the Venus Climate Orbiter ‘Akatsuki’ provide new information on various atmospheric phenomena. Nevertheless, it is difficult to elucidate their three-dimensional structures globally and continuously only from observations because satellite observations are considerably limited in time and space. We constructed the first ‘objective analysis’ of Venus’ atmosphere by assimilating cloud-top horizontal winds on the dayside from the equator to mid-latitudes, which is frequently obtained from Akatsuki's Ultraviolet Imager (UVI). The three-dimensional structures of thermal tides, found recently to play a crucial role in maintaining the super rotation, are greatly improved by the data assimilation. This result is confirmed by comparison with Akatsuki's temperature observations. The momentum transport caused by the thermal tides and other disturbances are also modified by the wind assimilation and agrees well with those estimated from the UVI observations. The assimilated dataset is reliable and will be open to the public along with the Akatsuki observations for further investigation of Venus’ atmospheric phenomena.

DOI： 10.1038/s41598-022-18634-6

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Other Link： https://www.nature.com/articles/s41598-022-18634-6

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

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 10cm(3) 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 <10nJ/10ns (= 1W). For summation time of greater than 0.2s, surface atmosphere activity in the order of seconds can be visualized with this high resolution. The dynamics measurement of an artificial twister was successfully conducted with this mini-lidar.In this report, the quantitative measurement method to distinguish dust samples in relation to Zirconia beads measurements is proposed. The relationship between the shaking off dust weight and its scattering cross section is obtained. The dust chamber experiment was conducted with several kinds of dust particles, too. These lidar echo results were compared with transmissometer, and they were well coincided due to the concentration change. The nature fog observation was conducted with this mini-lidar, too. The liquid water content was estimated under the consideration of the result of the quantitative measurement.

DOI： 10.1117/12.2604237

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1051/0004-6361/202037762

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.3847/1538-4357/ab7db4

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/ab7db4

Language：Japanese   Publisher：The Japanese Society for Planetary Sciences  

DOI： 10.14909/yuseijin.27.4_314

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Other Link： https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-16H02225/

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Berlin Heidelberg  

The ultraviolet imager (UVI) has been developed for the Akatsuki spacecraft (Venus Climate Orbiter mission). The UVI takes ultraviolet (UV) images of the solar radiation reflected by the Venusian clouds with narrow bandpass filters centered at the 283 and 365 nm wavelengths. There are absorption bands of SO2 and unknown absorbers in these wavelength regions. The UV images provide the spatial distribution of SO2 and the unknown absorber around cloud top altitudes. The images also allow us to understand the cloud top morphologies and haze properties. Nominal sequential images with 2-h intervals are used to understand the dynamics of the Venusian atmosphere by estimating the wind vectors at the cloud top altitude, as well as the mass transportation of UV absorbers. The UVI is equipped with off-axial catadioptric optics, two bandpass filters, a diffuser installed in a filter wheel moving with a step motor, and a high sensitivity charge-coupled device with UV coating. The UVI images have spatial resolutions ranging from 200 m to 86 km at sub-spacecraft points. The UVI has been kept in good condition during the extended interplanetary cruise by carefully designed operations that have maintained its temperature maintenance and avoided solar radiation damage. The images have signal-to-noise ratios of over 100 after onboard desmear processing. [Figure not available: see fulltext.].

DOI： 10.1186/s40623-017-0772-6

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Berlin Heidelberg  

The existence of lightning discharges in the Venus atmosphere has been controversial for more than 30 years, with many positive and negative reports published. The lightning and airglow camera (LAC) onboard the Venus orbiter, Akatsuki, was designed to observe the light curve of possible flashes at a sufficiently high sampling rate to discriminate lightning from other sources and can thereby perform a more definitive search for optical emissions. Akatsuki arrived at Venus during December 2016, 5 years following its launch. The initial operations of LAC through November 2016 have included a progressive increase in the high voltage applied to the avalanche photodiode detector. LAC began lightning survey observations in December 2016. It was confirmed that the operational high voltage was achieved and that the triggering system functions correctly. LAC lightning search observations are planned to continue for several years.

DOI： 10.1186/s40623-018-0836-2

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：EDP Sciences  

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 cm 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.

DOI： 10.1051/epjconf/201817602013

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Language：Japanese  

DOI： 10.11440/rssj.38.317

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGEROPEN  

The status and initial products of the 1-mu m camera onboard the Akatsuki mission to Venus are presented. After the successful retrial of Venus' orbit insertion on Dec. 2015 (5 years after the failure in Dec. 2010), and after a long cruise under intense radiation, damage in the detector seems small and fortunately insignificant in the final quality of the images. More than 600 dayside images have been obtained since the beginning of regular operation on Apr. 2016 although nightside images are less numerous (about 150 in total at three wavelengths) due to the light scattered from the bright dayside. However, data acquisition stopped after December 07, 2016, due to malfunction of the electronics and has not been resumed since then. The 0.90-mu m dayside images are of sufficient quality for the cloud-tracking procedure to retrieve wind field in the cloud region. The results appear to be similar to those reported by previous 1-mu m imaging by Galileo and Venus Express. The representative altitude sampled for such dayside images is estimated to be 51-55 km. Also, the quality of the nightside 1.01-mu m images is sufficient for a search for active volcanism, since interference due to cloud inhomogeneity appears to be insignificant. The quality of the 0.97-mu m images may be insufficient to achieve the expected spatial resolution for the near-surface H2O mixing ratio retrievals.

DOI： 10.1186/s40623-017-0773-5

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40623-018-0789-5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

We provide an overview of data products from observations by the Japanese Venus Climate Orbiter, Akatsuki, and describe the definition and content of each data-processing level. Levels 1 and 2 consist of non-calibrated and calibrated radiance (or brightness temperature), respectively, as well as geometry information (e.g., illumination angles). Level 3 data are global-grid data in the regular longitude-latitude coordinate system, produced from the contents of Level 2. Non-negligible errors in navigational data and instrumental alignment can result in serious errors in the geometry calculations. Such errors cause mismapping of the data and lead to inconsistencies between radiances and illumination angles, along with errors in cloud-motion vectors. Thus, we carefully correct the boresight pointing of each camera by fitting an ellipse to the observed Venusian limb to provide improved longitude-latitude maps for Level 3 products, if possible. The accuracy of the pointing correction is also estimated statistically by simulating observed limb distributions. The results show that our algorithm successfully corrects instrumental pointing and will enable a variety of studies on the Venusian atmosphere using Akatsuki data.

DOI： 10.1186/s40623-017-0749-5

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3847/1538-3881/aa78a5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

The planet Venus is covered by thick clouds of sulfuric acid that move westwards because the entire upper atmosphere rotates much faster than the planet itself. At the cloud tops, about 65 km in altitude, small-scale features are predominantly carried by the background wind at speeds of approximately 100 ms(-1). In contrast, planetary-scale atmospheric features have been observed to move slightly faster or slower than the background wind, a phenomenon that has been interpreted to reflect the propagation of planetary-scale waves. Here we report the detection of an interhemispheric bow-shaped structure stretching 10,000 km across at the cloud-top level of Venus in middle infrared and ultraviolet images from the Japanese orbiter Akatsuki. Over several days of observation, the bow-shaped structure remained relatively fixed in position above the highland on the slowly rotating surface, despite the background atmospheric super rotation. We suggest that the bow-shaped structure is the result of an atmospheric gravity wave generated in the lower atmosphere by mountain topography that then propagated upwards. Numerical simulations provide preliminary support for this interpretation, but the formation and propagation of a mountain gravity wave remain difficult to reconcile with assumed near-surface conditions on Venus. We suggest that winds in the deep atmosphere may be spatially or temporally more variable than previously thought.

DOI： 10.1038/NGEO2873

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Language：Japanese   Publisher：The Japanese Society for Planetary Sciences  

DOI： 10.14909/yuseijin.26.3_92

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.14909/yuseijin.25.2_68

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

AKATSUKI is the Japanese Venus Climate Orbiter that was designed to investigate the climate system of Venus. The orbiter was launched on May 21, 2010, and it reached Venus on December 7, 2010. Thrust was applied by the orbital maneuver engine in an attempt to put AKATSUKI into a westward equatorial orbit around Venus with a 30-h orbital period. However, this operation failed because of a malfunction in the propulsion system. After this failure, the spacecraft orbited the Sun for 5 years. On December 7, 2015, AKATSUKI once again approached Venus and the Venus orbit insertion was successful, whereby a westward equatorial orbit with apoapsis of similar to 440,000 km and orbital period of 14 days was initiated. Now that AKATSUKI's long journey to Venus has ended, it will provide scientific data on the Venusian climate system for two or more years. For the purpose of both decreasing the apoapsis altitude and avoiding a long eclipse during the orbit, a trim maneuver was performed at the first periapsis. The apoapsis altitude is now similar to 360,000 km with a periapsis altitude of 1000-8000 km, and the period is 10 days and 12 h. In this paper, we describe the details of the Venus orbit insertion-revenge 1 (VOI-R1) and the new orbit, the expected scientific information to be obtained at this orbit, and the Venus images captured by the onboard 1-mu m infrared camera, ultraviolet imager, and long-wave infrared camera 2 h after the successful initiation of the VOI-R1.

DOI： 10.1186/s40623-016-0457-6

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

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/l0ns) 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 (=ins) 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 &gt;2m.

DOI： 10.1117/12.2241976

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.pss.2014.10.004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

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 nearinfrared 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.

DOI： 10.1088/0004-637X/806/2/216

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

We present phase curves for Venus in the 1-2 mu m wavelength region, acquired with IR1 and IR2 on board Akatsuki (February-March 2011). A substantial discrepancy with the previously-published curves was found in the small phase angle range (0-30 degrees). Through analysis by radiative-transfer computation, it was found that the visibility of larger (similar to 1 mu m or larger) cloud particles was significantly higher than in the standard cloud model. Although the cause is unknown, this may be related to the recently reported increase in the abundance of SO2 in the upper atmosphere. It was also found that the cloud top is located at similar to 75 km and that 1-mu m particles exist above the cloud, both of these results being consistent with recent studies based on the Venus Express observations in 2006-2008. Further monitoring, including photometry for phase curves, polarimetry for aerosol properties, spectroscopy for SO2 abundance, and cloud opacity measurements in the near-infrared windows, is required in order to understand the mechanism of this large-scale change. (C) 2014 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.icarus.2014.10.030

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Japanese Venus Climate Orbiter/AKATSUKI was proposed in 2001 with strong support by international Venus science community and approved as an ISAS (The Institute of Space and Astronautical Science) mission soon after the proposal. The mission life we expected was more than two Earth years in Venus orbit. AKATSUKI was successfully launched at 06:58:22JST on May 21, 2010, by H-IIA F17. After the separation from H-IIA, the telemetry from AKATSUKI was normally detected by DSN Goldstone station (10:00JST) and the solar cell paddles' deployment was confirmed. After a successful cruise, the malfunction happened on the propulsion system during the Venus orbit insertion (VOI) on Dec. 7, 2010. The engine shut down before the planned reduction in speed to achieve. The spacecraft did not enter the Venus orbit but entered an orbit around the Sun with a period of 203 days. Most of the fuel still had remained, but the orbital maneuvering engine was found to be broken and unusable. However, we have found an alternate way of achieving orbit by using only the reaction control system (RSC). We had adopted the alternate way for orbital maneuver and three minor maneuvers in Nov. 2011 were successfully done so that AKATSUKI would meet Venus in 2015. We are considering several scenarios for VOI using only RCS. (C) 2013 IAA. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actaastro.2013.07.027

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

Mid-infrared images of almost the entire Venus nightside hemisphere obtained by the Longwave Infrared Camera (LIR) onboard Akatsuki on December 9 and 10, 2010 reveal that the brightness temperature of the cloud-top ranges from 237 K in the cold polar collars to 243 K in the equatorial region, significantly higher than the values obtained by Venera 15. Other characteristic features of the temperature distributions observed are zonal belt structures seen in the middle and low latitudes and patchy temperature structures or quasi-periodic streaks extending in a north-south direction in the northern middle latitudes and southern low latitudes. (c) 2012 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.icarus.2012.01.024

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.icarus.2011.07.026

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Language：English   Publishing type：Research paper (other academic)  

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Publishing type：Research paper (international conference proceedings)  

Japanese Venus Climate Orbiter/AKATSUKI was proposed in 2001 with strong support by international Venus science community and approved as an ISAS (Institute of Space and Astronautical Science) mission soon after the proposal. The mission life we expected was more than two Earth years in Venus orbit. AKATSUKI was successfully launched at 06:58:22JST on May 21, 2010, by H-IIA F17. After the separation from H-IIA, the telemetry from AKATSUKI was normally detected by DSN Goldstone station (10:00JST) and the solar cell paddles' expansion was confirmed. The malfunction happened on the propulsion system during the Venus orbit insertion (VOI) on Dec 7, 2010. We failed to make the spacecraft become a Venus orbiter, and the spacecraft entered an orbit around the Sun with a period of 203 days. Most of the fuel still had remained, but the orbital maneuvering engine was found to be broken. We decided to use only the reaction control system (RCS) for orbital maneuver and three minor maneuvers in Nov 2011 were successfully done so that AKATSUKI will meet Venus in 2015. We are considering several scenarios for VOI using only RCS. Copyright © (2012) by the International Astronautical Federation.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.5047/eps.2011.02.009

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

The Longwave Infrared Camera (LIR) is one of a suite of cameras onboard the Venus orbiter Akatsuki. It will take images of thermal radiation in the wavelength range of 8-12 mu m emitted by the Venus cloud tops. The use of an uncooled micro-bolometer array as an infrared image sensor makes LIR a lightweight, small and low-power consumption instrument with a required noise equivalent temperature difference of 0.3 K. Temperature and horizontal wind fields at the cloud-top will be retrieved for both dayside and nightside with equal quality. This will provide key observations to understand the mechanism of super rotation and the thermal budget of the planet. LIR will also monitor variations of the polar dipole and collar which are characteristic thermal features in the Venusian atmosphere. Mechanisms of the upper-cloud formation will be investigated using sequences of close-up images. The morphology of the nightside upper cloud will be studied in detail for the first time.

DOI： 10.5047/eps.2011.06.019

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TERRA SCIENTIFIC PUBL CO  

The 1 mu m camera onboard the Japanese Venus Mission/Akatsuki scheduled to arrive at Venus in 2015 or 2016 is described. In addition to its scientific goals, the optical and mechanical designs, the calibration procedures, and some results of feasibility studies are presented. Those studies are about the source of the contrast in the dayside image, the resolution of the H(2)O detection on the nightside surface, and a possibility of finding an active volcano.

DOI： 10.5047/eps.2011.03.007

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.icarus.2009.12.019

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CiNii Article

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Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2008je003184

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Language：Japanese   Publisher：日本天文学会  

CiNii Article

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Language：Japanese   Publisher：The Japanese Society for Planetary Sciences  

CiNii Article

CiNii Books

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DOI： 10.1029/2008JE003134

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

We evaluated the spatial variation of Venusian surface emissivity at 1.18 mu m 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.

DOI： 10.1029/2008JE003134

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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 Cl-35/Cl-31 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. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.pss.2008.05.009

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Other Link： http://orcid.org/0000-0002-8160-3553

Language：English   Publishing type：Research paper (international conference proceedings)  

The Longwave Infrared Camera (LIR), which mounts an uncooled micro-bolometer array (UMBA), is under development for the Japanese Venus orbiter mission, PLANET-C. LIR detects thermal emission from the top of the sulfur dioxide cloud in a wavelength region 8-12 μm to map the cloud-top temperature which is typically as low as 230 K. The requirement for the noise equivalent temperature difference (NETD) is 0.3 K. Images of blackbody targets in room temperature (∼300 K) and low temperature (∼230 K) have been acquired in a vacuum environment using a prototype model of LIR, showing that the NETD of 0.2 K and 0.8 K are achieved in ∼300 K and ∼230 K, respectively. We expect that the requirement of NETD &lt
0.3 K for ∼230 K targets will be achieved by averaging several tens of images which are acquired within a few minutes. The vibration test for the UMBA was also carried out and the result showed the UMBA survived without any pixel defects or malfunctions. The tolerance to high-energy protons was tested and verified using a commercial camera in which a same type of UMBA is mounted. Based on these results, a flight model is now being manufactured with minor modifications from the prototype.

DOI： 10.1117/12.784932

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The Venus Climate Orbiter mission (PLANET-C), one of the future planetary missions of Japan, aims at understanding the atmospheric circulation of Venus. Meteorological information will be obtained by globally mapping clouds and minor constituents successively with four cameras at ultraviolet and infrared wavelengths, detecting lightning with a high-speed imager, and observing the vertical structure of the atmosphere with radio science technique. The equatorial elongated orbit with westward revolution fits the observation of the movement and temporal variation of the atmosphere which as a whole rotates westward. The systematic, continuous imaging observations will provide us with an unprecedented large data set of the Venusian atmospheric dynamics. Additional targets of the mission are the exploration of the ground surface and the observation of zodiacal light. The mission will complement the ESA's Venus Express, which also explores the Venusian environment with different approaches. (C) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.pss.2007.01.009

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The Longwave Infrared Camera (LIR) onboard the first Japanese Venus mission, PLANET-C, or the Venus Climate Orbiter, operates in the middle infrared region with a single bandpass filter of 8-12 μm, measuring thermal radiation emitted from the cloud tops of the Venusian atmosphere. A horizontal wind vector field at the cloud-top height will be retrieved by means of a cloud tracking method. In addition, absolute temperature will be determined with an accuracy of 3 K. Since solar irradiation scattered by the atmosphere is much weaker than the atmospheric thermal radiation, LIR can continuously monitor a hemispheric wind field independent of the local time of the apocenter throughout the mission life. Wind and temperature fields obtained by LIR will provide key parameters to solve climatological issues related to the Venusian atmosphere. The use of an uncooled micro-bolometer array (UMBA), which requires no cryogenic apparatus, as an image sensor contributes to the reduction of power consumption and the weight of the LIR imager. An instrumental field-of-view of 12° is equal to the angle subtended by Venus when observed from a height of 9.5 Rv. The pixel field-of-view corresponds to a spatial resolution of 70 km viewed from the apocenter. A mechanical shutter functions not only as an optical shutter but also as a reference blackbody. The temperature stability of the sensor is especially important, because fluctuation of thermal radiation from the internal environment of the sensor itself causes background noise. Therefore, the temperature of the UMBA package is stabilized at 313 ± 0.1 K with a feedback controlled Peltier cooler/heater, and a NETD of 0.3 K, which is required for this infrared imager, will be achieved. Flat field images are taken with the shutter closed several seconds before and after 1 s exposure for a Venus thermal image. After a Venus image is taken, the LIR imager takes a cold calibration image of deep space. This measurement sequence is repeated every two hours when the spacecraft is orbiting at apocenter. Image data are transmitted down to the Earth after onboard calibration and data compression by common digital electronics. © 2007 COSPAR.

DOI： 10.1016/j.asr.2007.05.085

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

[1] The chemical composition of Earth&apos;s early atmosphere is likely to have played an important role in the origin of life. In particular, the redox state of Earth&apos;s early atmosphere may have controlled greatly the efficiency of abiotic synthesis of biologically important organic compounds. However, the chemical composition of the Earth&apos;s early atmosphere has not been studied extensively before. In this study, we theoretically estimate the chemical composition of an atmosphere near the end of the completion of planetesimal accretion of the Earth. Our calculation results show that the Earth&apos;s early atmosphere is very reducing, rich in H(2) and/or CH(4), regardless of which meteoritic materials accrete and regardless of which chemical reactions control the molecular abundance in the atmosphere. In other words, impact-degassed origin of Earth&apos;s atmosphere leads inevitably to a reducing chemical composition, which is very favorable to efficient prebiotic synthesis of organic matter on Earth.

DOI： 10.1029/2006JE002844

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A one-dimensional microphysical model study revealed that vertical winds govern the H2SO4 cycle in the equatorial cloud system of Venus. In the upper cloud region, photochemical production of H2SO4 vapor leads to the formation of small droplets, which are blown off by the upward/poleward branch of the Hadley circulation. In the middle and lower cloud regions, H2SO4 vapor is supplied from below by dynamical processes and condenses into large droplets, which fall against the up-welling of the Hadley circulation. The local circulation of H2SO4 near the cloud base explains the observed accumulation of H2SO4 vapor beneath the equatorial cloud. It was also revealed that the transient strong vertical winds associated with transient eddies can explain the contradictory results for the particle size distribution observed by entry probes: the adiabatic cooling in an updraft forces H2SO4 vapor to condense onto condensation nuclei, thereby producing a large number of middle-size droplets. (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

Lava eruptions can be observed remotely on Venus' nightside using a near-infrared window at a 1.0-micrometer wavelength, i.e., radiation at this wavelength emitted from the planetary surface traverses through the thick Venus atmosphere and clouds. Due to the strong dependence of the intensity of thermal emission on temperature, a hot surface produced by a lava eruption emits intense radiation, with the intensity of the excess radiation depending on the surface area and temperature of the lava flow. The excess emission from the hot surface is blurred by clouds, yet a 1-km(2) 1500-K basaltic lava lake and a 50-km(2) 1000-K lava flow are readily detected using this technique. Rapid cooling of exposed lava results in excess surface radiation that is detectable for just one Earth day after the end of an eruption; hence short-term eruptions are only detectable on the side of the planet where night is occurring. Eruptions lasting more than half a Venus day (i.e., more than about 60 Earth days), however, are detectable across the globe as nighttime occurs sometime during this period for every such event. Due to limited observational geometries, a complete global survey of active volcanos cannot be achieved from Earth, and in fact, only about 10% of short-lived major volcanic eruptions are observable. Alternatively, a satellite orbiting high above Venus (similar to6 Venus radii) could detect virtually all short-lived nighttime volcanic events, or about half the events expected to occur across the globe. (C) 2001 Elsevier Science (USA).

DOI： 10.1006/icar.2001.6713

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

We developed a simple physical model of Venus' cloud to understand the influence of cloud on the evolution of the surface environment and the climate on Venus. For a given atmospheric structure and composition, the cloud structure and its albedo are calculated through our model. We successfully reproduced the present Venus albedo: the calculated value is 0.87 for 550-nm wavelength, while the observed one is 0.85. The variability of cloud albedo caused by the change of H2O abundance in the Venus atmosphere is examined. Although H2O is merely a minor component of the atmosphere, its influence on the surface environment is found to be quite large. Increase in H2O abundance raises the albedo and cools the surface environment. When H2O abundance is smaller than a critical value of about 0.5 ppmv, complete evaporation of cloud occurs owing to a warming of the atmosphere. When H2O abundance is increased, the H2O abundance in the upper atmosphere is reduced owing to a lower atmospheric temperature produced by high albedo of thick clouds. The cooling of the atmosphere will affect the escape flux of hydrogen from the Venus atmosphere into space.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER METEOROLOGICAL SOC  

As the global distribution of Venusian H2SO4-H2O clouds is strongly related to the global circulation of H2SO4 governed by wind transport and sedimentation of droplets, the circulation of H2SO4 in the Tropics was studied by simultaneously solving advection and cloud microphysics equations using a one-dimensional model that includes a weak upwelling representing the rising branch of Hadley circulation near the equator. H2SO4 vapor in the upper cloud region is supplied by photochemical production and condenses into cloud droplets that are removed from the tropical atmosphere by Hadley circulation, whereas in middle and lower cloud regions, dynamical processes supply H2SO4 vapor from below such that resultant droplets are large and fall against the upwelling. The combination of the mean upward advection of vapor and the sedimentation of droplets leads to accumulation of H2SO4 and H2O vapor near the cloud base: an observed phenomenon. A separate model run was performed to investigate the effect of transient strong winds on condensational growth, with results indicating that transient winds produce a variety of size distributions similar to those observed. Variation in cloud thickness associated with such events is thought to explain large opacity variations in near-infrared observations.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TERRA SCIENTIFIC PUBL CO  

It has been suggested that the atmospheric concentration of SO2 observed on Venus coincides with the equilibrium concentration over pyrite-magnetite assemblage (pyrite-magnetite buffer). If the atmospheric SO2 abundance is controlled by the chemical reaction at the planetary surface, we expect coupling between the atmospheric SO2 abundance and the surface temperature. Here, we propose that the pyrite-magnetite buffer combined with cloud albedo feedback controls the surface temperature on Venus. We show that this mechanism keeps the surface temperature in a rather narrow range around the presently observed value against large variations of solar luminosity and total atmospheric mass.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON PRESS LTD  

The meridional circulation can have a large influence on the cloud formation on Venus. In our model, the observed depression of near-infrared optical thickness at mid-latitude is reproduced as a result of the enhancement of cloud thickness at low and high latitudes. At high latitudes, the 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 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 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 H2SO4 vapor distribution agrees with the radio occultation observations. The middle cloud can be caused by the condensation of H2SO4 vapor carried aloft by convective mixing. (C) 1999 COSPAR. Published by Elsevier Science Ltd.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

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 blow by convective mixing.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Which mechanism determines the planetary atmospheric inventories of various gases is an important problem. It has been suggested that Venus' atmospheric CO2 abundance is controlled or buffered by carbonation reaction on the surface (carbonate buffer). According to this hypothesis, the formation or decomposition of carbonate stabilizes atmospheric CO2 concentration. However, the amount of carbonate existing on the Venus' surface is not established yet. Using a stability analysis that combines the greenhouse effect, carbonation reaction, and topography, we place an upper limit to carbonate on Venus. This upper limit of carbonate is only about 4 bar of CO2 and is much smaller than the amount of CO2 in the atmosphere. This suggests that the present CO2 concentration in Venus' atmosphere is not controlled by the carbonation reaction but by the total abundance of CO2 in near surface layers.

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Publisher：Springer Science and Business Media LLC  

© 2017 The Author(s). The first year (December 2015 to November 2016) of IR2 after Akatsuki&#039;s successful insertion to an elongated elliptical orbit around Venus is reported with performance evaluation and results of data acquisition. The single-stage Stirling-cycle cryo-cooler of IR2 has been operated with various driving voltages to achieve the best possible cooling under the given thermal environment. A total of 3091 images of Venus (1420 dayside images at 2.02 μm and 1671 night-side images at 1.735, 2.26, and 2.32 μm) were acquired in this period. Additionally, 159 images, including images of stars for calibration and dark images for the evaluation of noise levels, were captured. Low-frequency flat images (not available in pre-launch calibration data) have been constructed using the images of Venus acquired from near the pericenter to establish the procedure to correct for the IR2 flat-field response. It was noticed that multiple reflections of infrared light in the PtSi detector caused a weak but extended tail of the point-spread function (PSF), contaminating the night-side disk of Venus with light from the much brighter dayside crescent. This necessitated the construction of an empirical PSF to remove this contamination and also to improve the dayside data by deconvolution, and this work is also discussed. Detailed astrometry is performed on star-field images in the H-band (1.65 μm), hereby confirming that the geometrical distortion of IR2 images is negligible.

DOI： 10.1186/s40623-017-0736-x

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Publisher：Springer Science and Business Media LLC  

© 2017 The Author(s). The Venus Climate Orbiter Akatsuki arrived at Venus in December 2015, and the Longwave Infrared Camera (LIR) onboard the spacecraft started making observations. LIR has acquired more than 8000 images during the first two Venusian years since orbit insertion without any serious faults. However, brightness temperature derived from LIR images contained an unexpected bias that related not to natural phenomena but to a thermal condition of the instrument. The bias could be partially eliminated by keeping the power supply unit for LIR always active, while the residual bias was simply correlated with the baffle temperature. Therefore, deep-space images were acquired at different baffle temperatures on orbit, and a reference table for eliminating the bias from images was prepared. In the corrected images, the brightness temperature was ~ 230 K at the center of the Venus disk, where the effect of limb darkening is negligible. The result is independent of the baffle temperature and consistent with the results of previous studies. Later, a laboratory experiment with the proto model of LIR showed that when the germanium (Ge) lens was heated, its actual temperature was slightly higher than the temperature measured by a thermal sensor attached to the lens holder. The experiment confirmed that transitory baffle heating accounted for the background bias found in the brightness temperature observed by LIR.[Figure not available: see fulltext.]

DOI： 10.1186/s40623-017-0727-y

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Language：Japanese   Publisher：Center for Earth Information Science and Technology, Japan Agency for Marine-Earth Science and Technology  

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第29回大気圏シンポジウム（2016年3月7日-8日. 宇宙航空研究開発機構宇宙科学研究所（JAXA)(ISAS)）, 相模原市, 神奈川県資料番号: SA6000051002レポート番号: I-2

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Copyright © 2016 by the International Astronautical Federation (IAF). All rights reserved. Japan&#039;s Venus Climate Orbiter Akatsuki was proposed to ISAS (Institute of Space and Astronautical Science) in 2001 as an interplanetary mission. We made 5 cameras with narrow-band filters to image Venus at different wavelengths to track the cloud and minor components distribution at different heights to study the Venusian atmospheric dynamics in 3 dimension. It was launched on May 21st, 2010 and reached Venus on December 7th, 2010. With the thrust by the orbital maneuver engine, Akatsuki tried to go into the westward equatorial orbit around Venus with the 30 hours&#039; orbital period, however it failed by the malfunction of the propulsion system. Later the spacecraft has been orbiting the sun for 5 years. On December 7th, 2015 Akatsuki met Venus again after the orbit control and Akatsuki was put into the westward equatorial orbit whose apoapsis is about 0.44 million km and orbital period of 14 days. Its main target is to shed light on the mechanism of the fast atmospheric circulation of Venus. The systematic imaging sequence by Akatsuki is advantageous for detecting meteorological phenomena with various temporal and spatial scales. We have five photometric sensors as mission instruments for imaging, which are 1 m-infrared camera (IR1), 2 m-infrared camera (IR2), ultra-violet imager (UVI), long-wave infrared camera (LIR), and lightning and airglow camera (LAC). These photometers except LIR have changeable filters in the optics to image in certain wavelengths. Akatsuki&#039;s long elliptical orbit around Venus is suitable for obtaining cloud-tracked wind vectors over a wide area continuously from high altitudes. With the observation, the characterizations of the meridional circulation, mid-latitude jets, and various wave activities are anticipated. The technical issues of Venus orbit insertion in 2015 and the scientific new results will be given in this paper.

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第47回月・惑星シンポジウム (2014年8月4日-6日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県
47th ISAS Lunar and Planetary Symposium (August 4-6, 2014. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan
形態: カラー図版あり
資料番号: SA6000033005

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Language：Japanese   Publisher：日本惑星科学会  

2013年9月17日から20日まで,北海道ニセコ町で惑星科学フロンティアセミナー2013(主催・惑星科学フロンティアセミナー実行委員会)が開催されました.この中で,講師に迎えた独立行政法人宇宙航空研究開発機構(JAXA)の宇宙科学研究所(ISAS)名誉教授で科学雑誌Newton編集長の水谷仁氏を囲んで,ISAS在任中の思い出を語り合う座談会が企画されました.月探査機LUNAR-A計画の狙いに始まり,宇宙科学研究をどのように展開すればよいのか研究手法にも話題が及び,さらには惑星科学コミュニティーが中心となって次なる惑星科学の研究テーマをどう見出すべきなのかといった内容が話し合われました.以下,座談会で行われた主なやり取りを紹介します.(敬称略)

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DOI： 10.14909/yuseijin.22.1_44

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DOI： 10.14909/yuseijin.21.2_175

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Language：English   Publisher：Terra Scientific Pub. Co  

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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 CO2 abundance, it is unlikely Venus' surface is reactive enough to control the Venus' massive CO2 atmosphere. Venus' surface carbonate is also able to affect the climate through the reaction with atmospheric SO2 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 SO2. On the other hand, pyrite-magnetite reaction is proposed to explain the Venus' atmospheric SO2 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 SO2 and surface temperature could also be reasonably explained. © 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.pss.2005.01.005

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Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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 CO2 abundance, it is unlikely Venus' surface is reactive enough to control the Venus' massive CO2 atmosphere. Venus' surface carbonate is also able to affect the climate through the reaction with atmospheric SO2 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 SO2. On the other hand, pyrite-magnetite reaction is proposed to explain the Venus' atmospheric SO2 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 SO2 and surface temperature could also be reasonably explained. (c) 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.pss.2005.01.005

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DOI： 10.1016/j.pss.2005.01.005

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Other Link： http://id.nii.ac.jp/1141/00105931/

DOI： 10.14909/jsps.2004f.0.1.0

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The purpose of the Longwave IR camera onboard Planet-C is to observe the horizontal distribution of cloud top temperature. In this paper, the science objectives, the selection criteria of observation wavelengths and the required specifications are summarized.

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Event date： 2007.3.23

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：La Thuile, Italy  

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Venue：京都  

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