First ENA observations at Mars: ENA emissions from the martian upper atmosphere     

Y. Futaana  S. Barabash  M. Holmström  E. Kallio  H. Gunell  R. Lundin  M. Yamauchi  J.D. Winningham  J.R. Sharber  A.J. Coates  D.O. Kataria  P. Riihelä  H. Koskinen  J. Luhmann  D. Williams  C.C. Curtis  B.R. Sandel  M. Carter  A. Fedorov  S. Orsini  M. Maggi  P. Bochsler  N. Krupp  M. Fränz  C. Dierker 《Icarus》2006,182(2):424-430

The neutral particle detector (NPD) on board Mars Express has observed energetic neutral atoms (ENAs) from a broad region on the dayside of the martian upper atmosphere. We show one such example for which the observation was conducted at an altitude of 570 km, just above the induced magnetosphere boundary (IMB). The time of flight spectra of these ENAs show that they had energies of 0.2-2 keV/amu, with an average energy of ∼1.1 keV/amu. Both the spatial distribution and the energy of these ENAs are consistent with the backscattered ENAs, produced by an ENA albedo process. This is the first observation of backscattered ENAs from the martian upper atmosphere. The origin of these ENAs is considered to be the solar wind ENAs that are scattered back by collision processes in the martian upper atmosphere. The particle flux and energy flux of the backscattered ENAs are and , respectively.  相似文献   

What makes a planet habitable?     

H. Lammer  J. H. Bredehöft  A. Coustenis  M. L. Khodachenko  L. Kaltenegger  O. Grasset  D. Prieur  F. Raulin  P. Ehrenfreund  M. Yamauchi  J.-E. Wahlund  J.-M. Grießmeier  G. Stangl  C. S. Cockell  Yu. N. Kulikov  J. L. Grenfell  H. Rauer 《Astronomy and Astrophysics Review》2009,17(2):181-249

This work reviews factors which are important for the evolution of habitable Earth-like planets such as the effects of the host star dependent radiation and particle fluxes on the evolution of atmospheres and initial water inventories. We discuss the geodynamical and geophysical environments which are necessary for planets where plate tectonics remain active over geological time scales and for planets which evolve to one-plate planets. The discoveries of methane–ethane surface lakes on Saturn’s large moon Titan, subsurface water oceans or reservoirs inside the moons of Solar System gas giants such as Europa, Ganymede, Titan and Enceladus and more than 335 exoplanets, indicate that the classical definition of the habitable zone concept neglects more exotic habitats and may fail to be adequate for stars which are different from our Sun. A classification of four habitat types is proposed. Class I habitats represent bodies on which stellar and geophysical conditions allow Earth-analog planets to evolve so that complex multi-cellular life forms may originate. Class II habitats includes bodies on which life may evolve but due to stellar and geophysical conditions that are different from the class I habitats, the planets rather evolve toward Venus- or Mars-type worlds where complex life-forms may not develop. Class III habitats are planetary bodies where subsurface water oceans exist which interact directly with a silicate-rich core, while class IV habitats have liquid water layers between two ice layers, or liquids above ice. Furthermore, we discuss from the present viewpoint how life may have originated on early Earth, the possibilities that life may evolve on such Earth-like bodies and how future space missions may discover manifestations of extraterrestrial life.  相似文献   

Discovery of a New Pulsating X-Ray Source with a 1549.1 Second Period, AX J183220-0840     

Sugizaki M  Kinugasa K  Matsuzaki K  Terada Y  Yamauchi S  Yokogawa J 《The Astrophysical journal》2000,534(2):L181-L184

A new pulsating X-ray source, AX J183220-0840, with a 1549.1 s period was discovered at R.A.=18h32m20s and decl.=-8&j0;40'30" (J2000, with an uncertainty of 0&farcm;6) during an ASCA observation on the Galactic plane. The source was observed two times, in 1997 and in 1999. A phase-averaged X-ray flux of 1.1x10-11 ergs cm-2 s-1 and a pulsation period of 1549.1+/-0.4 s were consistently obtained from these two observations. The X-ray spectrum was represented by a flat, absorbed power law with a photon index of Gamma approximately 0.8 and an absorption column density of NH approximately 1.3x1022 cm-2. Also, a signature of iron K-shell line emission with a centroid of 6.7 keV and an equivalent width of approximately 450 eV was detected. From the pulsation period and the iron-line feature, AX J183220-0840 is likely to be a magnetic white dwarf binary with a complexly absorbed thermal spectrum with a temperature of about 10 keV.  相似文献   

The Impact of the Winter Monsoon on Marine Surface-Layer Turbulence     

Tomoya Nishida  Takuji Waseda 《Boundary-Layer Meteorology》2015,157(1):141-156

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Propagating tsunami wave and subsequent resonant response signals detected by HF radar in the Kii Channel,Japan     

Hirofumi Hinata  Satoshi Fujii  Keita Furukawa  Tomoya Kataoka  Masafumi Miyata  Takashi Kobayashi  Masahiro Mizutani  Takahiro Kokai  Nobuyoshi Kanatsu 《Estuarine, Coastal and Shelf Science》2011

Signals from the tsunami waves induced by the March 11, 2011 moment magnitude (M_w) 9.0 Tohoku-Oki earthquake and from subsequent resonances were detected as radial velocity variability by a high-frequency ocean surface radar (HF radar) installed on the eastern coast of the Kii Channel, at a range of about 1000 km from the epicenter along the eastern to southern coasts of Honshu Island. A time–distance diagram of band-passed (9–200 min) radial velocity along the beam reveals that the tsunami waves propagated from the continental shelf slope to the inner channel as progressive waves for the first three waves, and then natural oscillations were excited by the waves; and that the direction of the tsunami wave propagation and the axis of the natural oscillations differed from that of the radar beam. In addition, spectral analyses of the radial velocities and sea surface heights obtained in the channel and on the continental shelf slope suggest complex natural oscillation modes excited by the tsunami waves.  相似文献   

Structure of the martian wake     

A. Fedorov  E. Budnik  C. Mazelle  R. Lundin  M. Holmström  M. Yamauchi  J.-J. Thocaven  R. Frahm  J. Scherrer  D.R. Linder  E. Kallio  T. Säles  W. Schmidt  J. Luhmann  D. Williams  C.C. Curtis  B.R. Sandel  M. Carter  S. Orsini  M. Maggi  P. Bochsler  J. Woch  K. Asamura 《Icarus》2006,182(2):329-336

We present the first results from the ion mass analyzer IMA of the ASPERA-3 instrument on-board of Mars Express. More than 200 orbits for May 2004-September 2004 time interval have been selected for the statistical study of the distribution of the atmospheric origin ions in the planetary wake. This study shows that the martian magnetotail consists of two different ion regimes. Planetary origin ions of the first regime form the layer adjacent to the magnetic pile-up boundary. These ions are accelerated to energy greater than 2000 eV and exhibit a gradual decreasing of energy down to the planetary tail. The second plasma regime is observed in the planetary shadow. The heavy ions (considered as planetary ones) are accelerated to the energy of the solar wind protons. Obviously the acceleration mechanism is different for the different plasma regimes. Study of two plasma regimes in the frame referred to the interplanetary magnetic field (IMF) direction (we used MGS magnetometer data to obtain the IMF clock angle) clearly shows their spatial anisotropy. The monoenergetic plasma in the planetary shadow is observed only in the narrow angular sector around the positive direction of the interplanetary electric field.  相似文献   

First ENA observations at Mars: Subsolar ENA jet     

Y. Futaana  S. Barabash  M. Holmström  E. Kallio  H. Gunell  R. Lundin  M. Yamauchi  J.D. Winningham  J.R. Sharber  A.J. Coates  D.O. Kataria  P. Riihelä  H. Koskinen  J. Luhmann  D. Williams  C.C. Curtis  B.R. Sandel  M. Carter  A. Fedorov  S. Orsini  M. Maggi  P. Bochsler  J. Woch  K. Asamura 《Icarus》2006,182(2):413-423

The Neutral Particle Detector (NPD), an Energetic Neutral Atom (ENA) sensor of the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) on board Mars Express, detected intense fluxes of ENAs emitted from the subsolar region of Mars. The typical ENA fluxes are (4-7) × 10⁵ cm⁻² sr⁻¹ s⁻¹ in the energy range 0.3-3 keV. These ENAs are likely to be generated in the subsolar region of the martian exosphere. As the satellite moved away from Mars, the ENA flux decreased while the field of view of the NPD pointed toward the subsolar region. These decreases occurred very quickly with a time scale of a few tens of seconds in two thirds of the orbits. Such a behavior can be explained by the spacecraft crossing a spatially constrained ENA jet, i.e., a highly directional ENA emission from a compact region of the subsolar exosphere. This ENA jet is highly possible to be emitted conically from the subsolar region. Such directional ENAs can result from the anisotropic solar wind flow around the subsolar region, but this can not be explained in the frame of MHD models.  相似文献   

Erratum: Are passive spiral galaxies truly 'passive' and 'spiral'? A near-infrared perspective     

Chisato Yamauchi  Tomotsugu Goto 《Monthly notices of the Royal Astronomical Society》2004,354(4):1280-1280

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First ENA observations at Mars: Solar-wind ENAs on the nightside     

K. Brinkfeldt  H. Gunell  P. C:son Brandt  R.A. Frahm  E. Kallio  Y. Futaana  R. Lundin  M. Yamauchi  J.R. Sharber  A.J. Coates  D.O. Kataria  T. Säles  W. Schmidt  J. Luhmann  D. Williams  C.C. Curtis  B.R. Sandel  M. Carter  A. Fedorov  S. McKenna-Lawler  R. Cerulli-Irelli  P. Wurz  N. Krupp  M. Fränz  C. Dierker 《Icarus》2006,182(2):439-447

We present measurements with an Energetic Neutral Atom (ENA) imager on board Mars Express when the spacecraft moves into Mars eclipse. Solar wind ions charge exchange with the extended Mars exosphere to produce ENAs that can spread into the eclipse of Mars due to the ions' thermal spread. Our measurements show a lingering signal from the Sun direction for several minutes as the spacecraft moves into the eclipse. However, our ENA imager is also sensitive to UV photons and we compare the measurements to ENA simulations and a simplified model of UV scattering in the exosphere. Simulations and further comparisons with an electron spectrometer sensitive to photoelectrons generated when UV photons interact with the spacecraft suggest that what we are seeing in Mars' eclipse are ENAs from upstream of the bow shock produced in charge exchange with solar wind ions with a non-zero temperature. The measurements are a precursor to a new technique called ENA sounding to measure solar wind and planetary exosphere properties in the future.  相似文献   

Ion escape at Mars: Comparison of a 3-D hybrid simulation with Mars Express IMA/ASPERA-3 measurements     

E. Kallio  A. Fedorov  T. Säles  W. Schmidt  P. Riihelä  R. Lundin  H. Gunell  Y. Futaana  M. Yamauchi  J.-A. Sauvaud  J.D. Winningham  J.R. Sharber  A.J. Coates  D.O. Kataria  J.G. Luhmann  D. Williams  C.C. Curtis  B.R. Sandel  M. Carter  S. Orsini  M. Maggi  P. Bochsler  J. Woch  K. Asamura 《Icarus》2006,182(2):350-359

We have analysed ion escape at Mars by comparing ASPERA-3/Mars Express ion measurements and a 3-D quasi-neutral hybrid model. As Mars Express does not have a magnetometer onboard, the analysed IMA data are from an orbit when the IMF clock angle was possible to determine from the magnetic field measurements of Mars Global Surveyor. We found that fast escaping planetary ions were observed at the place which, according to the 3-D model, is anticipated to contain accelerated heavy ions originating from the martian ionosphere. The direction of the interplanetary magnetic field was found to affect noticeably which regions can be magnetically connected to Mars Express and to the overall 3-D Mars-solar wind interaction.  相似文献