2020.10.01 (Thu) C領域セミナ（西田）
2020.10.02 (Fri) 研究室セミナ（中村/塚田）
2020.10.08 (Thu) C領域セミナ（宮本）
2020.10.15 (Thu) C領域セミナ（小山）
The Martian thermosphere-ionosphere is a source for atmospheric escape, which is affected by both the lower-middle atmosphere and external forces. Recent studies suggest a significant impact of the lower-middle atmosphere on the upper atmosphere. However, its effect on ionospheric compositions and compositions of escape ions is not well understood.
Seasonal variations of atmospheric compositions in the dayside thermosphere and ionosphere have been investigated using data from December 2014 to March 2018 obtained by Neutral Gas and Ion Mass Spectrometer (NGIMS) on Mars Atmosphere and Volatile EvolutioN (MAVEN). We have investigated the effect of variations of homopause altitude (Jakosky et al., 2017; Slipski et al., 2018; Yoshida et al., under review) on atmospheric composition in the upper atmosphere using CO2 and N2 densities. Additionally, the coupling between neutral and ion species in the upper atmosphere has observationally confirmed among CO2, O, CO2+, O2+, and O+ densities, as well as N2 and N+ densities below the photochemical equilibrium region below ~200 km. We find that seasonal variations of CO2+, O2+, and O+density, during solar minimum activity, are by ~6, ~3, and ~1.5 at 180 km, respectively, which are mainly controlled by the seasonal variation of CO2 density in the upper atmosphere. It suggests that inflation and contraction of the atmosphere have more impacts on atmospheric compositions in the upper atmosphere (cf. Fox, 2009; Krasnopolsky, 2002).
A depletion of O, O+, and O2+ densities between 150 and 250 km altitude are simultaneously found during Ls = 342-346 in MY 33. A regional dust storm event was found during the same period (Liu et al., 2018). A decrease of O density in the thermosphere can qualitatively explain the depletion of O+ and O2+ density in the ionosphere. Our result suggests that there would be a different behavior of ionospheric species during the dust storm event.
2020.10.19 (Mon) 4年生研究発表会
2020.10.22 (Thu) C領域セミナ（学会リハ）
heavy ions in the energy range between a few tens of keV and GeV,
which are originated from solar flares in the low corona, shock waves
driven by coronal mass ejections (CME), planetary magnetospheres, and
bow shock. SEPs are well known to damage not only spacecraft and
detectors but also human body. For future international space
explorations in the 2020s, the human activity is going to expand to
the Moon and Mars. Thus, the impact of SEP on future explorations on
Mars needs to be addressed. However, the effect of SEP on the Martian
atmosphere and surface environment is not well understood. In
addition, SEP penetrates into Earth’s atmosphere down to tens of
kilometers at high geomagnetic latitudes, which affects the
composition in the middle atmosphere. During the large solar flare in
October 2003, SEP caused NO2 enhancement of several hundred percent
and tens of percent ozone depletion between 36 and 60 km altitudes
(e.g., Seppälä et al., 2004; Rohen et al., 2005). In contrast, the
vertical distribution of ozone on Mars was extensively observed by
SPICAM onboard Mars Express from 2004 to 2014. Results of previous
studies show that the ozone layer was located around 50 km altitude in
the southern polar winter, and around 30-40 km altitude in low to
middle latitudes in both hemispheres at aphelion season (Montmessin et
al., 2013, Maattanen et al., 2019). Mars has a thin atmosphere, less than 1% of that on Earth. The surface and atmosphere are heavily affected by energetic photons and particles that easily penetrate it owing to insufficient magnetospheric and atmospheric shielding. The Imaging UltraViolet Spectrograph (IUVS) spectroscopy onboard Mars Atmosphere and Volatile EvolutioN(MAVEN) detected diffuse aurora, suggesting widespread occurrences with increased SEPs (Schneider et al., 2015; Schneider et al., 2018). Schneider et al. (2018) reported the low-altitude, “diffuse” aurora spanning across Mars’ nightside hemisphere, coincident with a SEP outburst. The emission extended down to an altitude of ~60 km. Deep precipitation in the middle atmosphere requires extremely energetic
electron fluxes up to 100 keV. This fact suggests that SEP may have
additional effects on global atmospheric structures in the Martian
atmosphere. Incident particles ionize and dissociate atmospheric
species deeply, as well as heat the target atmosphere.
The purpose of this study is to investigate the effects of SEP on the
Martian atmosphere, especially on ozone, which will help us to
understand the study of astrobiology and the greenhouse effect of the
early Martian atmosphere. In this study, we use vertical profiles of ozone, carbon dioxide, and oxygen number densities observed by stellar occultation measurements by Imaging UltraViolet Spectrograph (IUVS) on board Mars Atmosphere and Volatile EvolutioN (MAVEN), and the energy fluxes of electrons and ions by Solar Energetic Particles onboard MAVEN (MAVEN/SEP). Since March 2015, MAVEN/IUVS has generally conducted stellar occultation campaign for 1-2 days on average for every 2-3 months. MAVEN/IUVS observations cover whole longitudinal area, and wide range of latitudes from 80°S to 75°N. MAVEN/SEP detects an energy spectrum of
electrons from 30 keV to 1 MeV and ions from 30 keV to 12 MeV up to
10-10^6 eV/[cm^2 s sr eV]. The distribution of ozone observed by MAVEN/IUVS confirms the seasonal, latitudinal and altitudinal characteristics of the ozone distribution observed by MEX/SPICAM. MAVEN/IUVS observations show the peak number density of ozone to be the order of 10^8 /cc at the southern polar winter and the order of 10^9 /cc for both hemispheres at aphelion season. These peak number densities are generally well in agreement with the SPICAM observation, but some data are not quantitatively consistent in detail. Using the MAVEN/SEP, we analyzed the energy fluxes of solar energetic particles observed between March 2014 and January 2020 in order to identify the periods of strong solar energetic particle arrival events, related to the IUVS observations. Here, we focus on the events; Occurred in 3-4th November 2015 for 27 hours after the arrival of electrons to the arrival of ions, with 34 profiles. The effect of SEP on the atmosphere is addressed by comparing with 26 profiles in 8-9 October 2017 during the quiet period.
immigration for business in a decade or two, next to Moon. In the
human activities on Mars, water and oxygen would be main resources as
they may be the materials of hydrogen energy and life-support, so the
exploration and securement of them would be important. In this
context, making the frequent opportunities to send spacecrafts to Mars
to get the information of their distributions is indispensable, and
the use of low-cost micro-satellites would extremely help that.
We are developing micro-satellite Mars spacecrafts with a terahertz
spectrometer onboard, named TEREX (TERahertz EXplorer). A terahertz
spectrometer can be made very small and lightweight (several
kilograms) with a high-frequency heterodyne spectroscopic system,
covering the wavelength range in which the simultaneous detection of
H2O, O2, H2O2 and O3 are possible with high sensitivities. TEREX-1 is
planned to be launched as a piggyback payload in 2022 at the earliest,
costing 10-20M US-dollars which is less than 1/10 of previous Mars
missions. We are also planning the following TEREX-2 as a Mars
orbiter, intended TEREX to be a micro-satellite mission series.
In addition, O2 on Mars is a hot target also in the astrobiological
aspect, as new findings about the mixing ratios and their variability
near the surface have been reported (Hartogh et al., 2010, A&A;
Trainer et al., 2019, JGR Planets). We discuss the mission and
observational plans of TEREX for both the economic and scientific
2020.10.25 – 30 Division for Planetary Science 2020 52nd Annual meeting (online)
2020.10.29 (Thu) C領域セミナ（田邊）
2020.11.01 (Sun) – 04 (Wed) 第148回地球電磁気・地球惑星圏学会総会・講演会 (online)
2020.11.05 (Thu) 地球物理学専攻合同セミナ
2020.11.05 – 06 Outer planet moon-magnetosphere interaction workshop (online)
Vertical profiles of ozone were retrieved from ground-based infrared
spectra observed with FTIR at Tsukuba. The profiles were retrieved from
the spectra between 1000.0 and 1005.0 cm-1 with SFIT4 spectral fitting
program using the recommended parameters by NDACC/IRWG. There are many absorption lines of ozone in this spectral window and we can achieve a high degrees of freedom for signal (DOFS) of 5. This means that we can get information for 5 independent layers. The instrumental line shape (ILS) is important for profile retrieval. As for the Bruker IFS125HR
which is used at Tsukuba, the alignment of the optics is very good and
the ILS derived from HBr cell measurements are nearly perfect.
Therefore, we don’t need to correct the spectra.
The derived ozone profiles were validated using ozonesonde and Brewer
data observed at Tateno. Tateno is located very close to our site and we
can consider them as the same location. Total columns derived from FTIR
are 5 % higher than the Brewer in average for 2019. This difference
agree with the results of Vigouroux, et al. and may be due to the
bias of the line intensity. The profiles between 17 and 35 km agree with
ozonsonde within 15 % for two case. More comparison results will be
presented in the seminar.
Exoplanets with substantial Hydrogen/Helium atmospheres have been discovered in abundance, many residing extremely close to their parent stars. The extreme irradiation levels these atmospheres experience causes them to undergo hydrodynamic atmospheric escape. Ongoing atmospheric escape has been observed to be occurring in a few nearby exoplanet systems through transit spectroscopy both for hot Jupiters and lower-mass super-Earths/mini-Neptunes. Detailed hydrodynamic calculations that incorporate radiative transfer and ionization chemistry are now common in one-dimensional models, and multi-dimensional calculations that incorporate magnetic-fields and interactions with the interstellar environment are cutting edge. However, there remains very limited comparison between simulations and observations. While hot Jupiters experience atmospheric escape, the mass-loss rates are not high enough to affect their evolution. However, for lower mass planets atmospheric escape drives and controls their evolution, sculpting the exoplanet population we observe today.
2020.11.12 (Thu) – 14 (Sat) 日本惑星科学会秋季講演会 (online)
2020.11.19 (Thu) C領域セミナ
Previous studies have calculated orbit that take into account the co-rotation of the Martian atmosphere and have shown that the lifetime of the captured asteroid is relatively long when the atmosphere rotates at the angular velocity of Mars near geostationary orbit. However, in order to follow the orbital evolution of captured asteroid after its capture, we need to consider the evolution of the Martian atmosphere. When the Martian atmosphere was expanded significantly beyond the geostationary orbit, it is possible that the atmosphere rotated at an angular velocity relatively close to the rotation of Mars. However, considering the process of shrinkage of the expanded atmosphere, it deviates from co-rotation for various reasons. In this study, we calculate the orbit of Phobos, taking into account the deviation from the co-rotation of the atmosphere, and estimate the change in the lifetime of the captured asteroid.
In recent years, the coupling of atmospheric regions on Mars has been actively studied. Due to its thin atmosphere and lack of strong magnetic field, Mars has a much more intense solar radiation and intense convection activity than Earth, atmospheric waves excited by the intense solar radiation, the dynamic circulation and mass transport associated with the Hadley cells that extend to the middle atmosphere, and the disappearance of the cold trap (hygropause) due to the dust heating. Characteristic features, such as vertical water vapor transport, have been reported by the latest observations. In this presentation, we will review our recent activities and try to look forward to the future..
2020.11.26 (Thu) C領域セミナ
The ionospheric electron temperature is important for determining the neutral/photochemical escape rate from the Martian atmosphere via the dissociative recombination of O2+. The Langmuir Probe and Waves instrument onboard MAVEN (Mars Atmosphere and Volatile EvolutioN) measures electron temperatures in the ionosphere. Overall, the electron temperature is lower in the crustal-field regions, namely, the strong magnetic field region, which is due to a transport of cold electrons along magnetic field lines from the lower to upper atmosphere. The electron temperature is also greater for high solar extreme ultraviolet (EUV) conditions, which is associated with the local EUV energy deposition. The current models can explain the electron temperature in the draped-field region, while underestimating the electron temperature above 250 km altitude in the crustal-field region. Electron heat conduction associated with a photoelectron transport in the crustal-field regions is altered due to kinetic effects, such the magnetic mirror and/or ambipolar electric field because the electron mean free path exceeds the relevant length scale for electron temperature. The mirror force can affect the electron and heat transport between low altitudes, where the neutral density and related electron cooling rates are the greatest, and high altitudes, while the ambipolar electric field decelerates the electron’s upward motion. These effects have not been included in current models of the electron energetics, and consideration of such effects on the electron temperature in the crustal-field region should be considered for future numerical simulations. In this presentation, I will summarize the previous studies on the electron temperature in the Martian ionosphere, and discuss our plans for the upcoming year, including a coupling of the electron temperature model with the Monte Carlo method, which enable us to deal with kinetic effects.
2020.12.01 – 17 AGU Fall Meeting 2020 (online)
2020.12.04 (Fri) 研究室セミナ（吉田/塚田）
spectrometer using hollow fibers
The mid-IR laser heterodyne spectroscopy provides high spectral
resolution > 106 by combining an IR source from the observing target
and an IR laser, such as a quantum cascade laser (QCL) and/or a CO2
gas laser, as the local oscillator (LO). We have developed the
mid-infrared laser heterodyne spectrometer MILAHI (Mid Infrared LAser
Heterodyne Instrument) mounted on our dedicated Tohoku 60 cm telescope
(T60) at the summit of Mt. Haleakala, Hawaii, which has successfully
operated for measurements of Venusian and Martian atmosphere (Nakagawa
et al., 2016, Takami et al., 2020).
The two beams are combined at the ZnSe beam splitter and then focused
onto a HgCdTe photomixer. A precise optical alignment is required to
combine two beams. In this study, we aim to simplify the optics by
applying mid-IR transmissive hollow fibers.
There is few optical fiber which has a high transmittance at the
wavelengths longer than 2 μm. Recently mid-IR (5-20 μm) transmissive
hollow fibers has been developed by Tohoku University (e.g. Matsuura
et al., 2002). The fibers are made of glass tubing whose inner
diameter are 1 mm and have a metallic layer of Ag on the inside of
glass tubing and then a dielectric layer of AgI over the metallic
layer. Transmittance of 95 %/m at 10.6 μm was reported in previous
studies (e.g. George and Harrington, 2004), meanwhile we have achieved
about 70% transmittance with a 600 mm hollow fiber at 10.4 μm from our
laboratory measurements. Transmittance of hollow fibers strongly
depends on its incident angle of the light. Better transmittance might
be possible by improving the alignment.
In this study, we made a fiber system which guides two beams by 300mm
hollow fibers and combines them by a conventional beam splitter to
evaluate the efficiency of the heterodyne signal using hollow fibers.
A CO2 gas laser which emits IR at 10.3 μm was used as a LO and a small
blackbody furnace and a QCL were used as IR sources. I will report
the result of this experiment.
In addition, I will introduce the technology related to the fiber
coupler and divider for the hollow fibers. (Tamura et al., 2017) The
fiber coupler can provide downsizing, weight saving, high
stabilization of the instrument, which are essential to develop the
instrument for space-born missions.
2020.12.13 – 18 SPIE Astronomical Telescopes + Instrumentation 2020 (online)
2020.12.25 (Fri) 研究室セミナ（田邊/晝場）
2021.01.08 (Fri) 研究室セミナ（B4リハ）
2021.01.15 (Fri) 研究室セミナ（片田/藤田）
2021.01.19 (Tue) 4年生研究発表会
2021.01.22 (Fri) 修士論文提出締め切り
2021.01.28 (Thu) 研究室セミナ（修論審査リハ小山）
2021.01.29 (Thu) 研究室セミナ（修論審査リハ田邊、宮本）
2021.01.28 – 02.04 43rd COSPAR Scientific Assembly
2021.02.01 – 04 修士・博士学位論文審査会
2020.02.22 – 24 惑星圏シンポジウム (TBD)