Akatsuki at Venus: The First Year of Scientific Operation A.Ikeshita Editorial Board (March 2020) Editor-in-Chief Yasuo Ogawa, Tokyo Institute of Technology, Japan Vice Editors-in-Chief Masato Furuya, Hokkaido University, Japan Nozomu Nishitani, Nagoya University, Japan Solid Earth Science Space Science Editors Valerio Acocella Tomokazu Kobayashi David Shelly Ryosuke Ando Alexey Kuvshinov Hisayoshi Shimizu Kimiyuki Asano Juanjo Ledo Hiroko Sugioka Joseph B.H. Baker Huixin Liu Sunny Tam Nanan Balan Yohei Miyake Yoshiyuki Tanaka Paul Bedrosian Haruhisa Nakamichi Yanbin Wang Stephan Buchert Yasuhito Narita Yih-Min Wu Phil Cummins Takuya Nishimura Chuang Xuan Hao Dong Takaaki Noguchi Takuji Yamada Aditya Gusman Masahito Nose Mare Yamamoto Shin-Chan Han Makiko Ohtake Takahiro Yamamoto James Hickey Keiji Ohtsuki Yuhji Yamamoto Thomas Hobiger Kyoko Okino Tadashi Yamasaki Hauke Hussmann Duggirala Pallamraju Tatsuhiro Yokoyama Takeo Ito Severine Rosat Kazunori Yoshizawa Art Jolly Akinori Saito Shunichi Kamata Tatsuhiko Saito Advisory Board Benjamin Fong Chao Hiroo Kanamori Toshitaka Tsuda Bernard Chouet Jun'ichiro Kawaguchi Zhongliang Wu Yoshimori Honkura Takafumi Matsui Kiyoshi Yomogida Toshihiko Iyemori Hitoshi Mizutani Journal Scope Earth, Planets and Space (EPS) is the official journal of the Society of Geomagnetism and Earth, Planetary and Space Sciences, The Seismological Society of Japan, The Volcanological Society of Japan, The Geodetic Society of Japan, and The Japanese Society for Planetary Sciences. EPS is a peer-reviewed, open-access journal published under SpringerOpen. It is an international journal covering scientific articles in the entire field of earth and planetary sciences, particularly geomagnetism, aeronomy, space science, seismology, volcanology, geodesy, and planetary science. EPS also welcomes articles in new and interdisciplinary subjects, and technical reports on instrumentation and software. The journal was launched in 1998 and has since published over 3000 articles. All of them are available for free on SpringerLink: https://link.springer.com/journal/40623 More information about the journal, its article collections, and the submission process is available on the journal homepage: https://earth-planets-space.springeropen.com Submit your next research article to Earth, Planets and Space via: https://www.editorialmanager.com/epsp Yours sincerely, Prof. Yasuo Ogawa Editor-in-Chief, Earth, Planets and Space [email protected] Earth, Planets and Space Nakamura et al. Earth, Planets and Space (2018) 70:144 https://doi.org/10.1186/s40623-018-0916-3 PREFACE Open Access Special issue “Akatsuki at Venus: The First Year of Scientific Operation” Masato Nakamura1*, Dmitri Titov2, Kevin McGouldrick3, Pierre Drossart4, Jean‑Loup Bertaux5,6 and Huixin Liu7 The JAXA Venus explorer, which had been developed in of instruments can monitor the dynamics of the whole Japan since 2001, was launched in 2010. The spacecraft atmosphere in three dimensions. was named “Akatsuki” after the Japanese word meaning The second attempt of the orbit insertion using atti- dawn. Akatsuki was inserted into the Venus orbit and tude control thrusters in 2015 was perfectly successful. began its observation program in 2015, after 5 years wan- The first scientific discovery was made just 3 h after the dering around the sun due to the failure of orbit insertion arrival: the longwave infrared camera captured a plane- in 2010. Nakamura et al. (2016) described the orbit inser- tary-scale atmospheric gravity wave that was stationary tion as well as some initial results from the IR1, UVI, and with respect to the surface topography. Starting with LIR cameras. this discovery, many other scientific results have been In the twentieth century, well before the start of Akat- accomplished. suki mission, the former Soviet Union and the USA had This issue presents initial results of the Akatsuki mis- explored Venus and elucidated basic characteristics such sion. Iwagami et al. (2018) reported the initial results as atmospheric temperature, pressure, composition, wind from Akatsuki/1-μm camera (IR1). More than 600 day- speed, surface topography and the plasma environment. side and 150 night-side images have been obtained However, the physical processes leading to the present since the beginning of regular operation on April 2016. state were still unclear. Among them, the Akatsuki mis- The night-side images are less numerous due to limita- sion focused on the study of atmospheric dynamics as a tions related to the light scattered from the bright day- major goal of Venus exploration in the early twenty-first side. Satoh et al. (2017) reported the performance of century. The Venusian atmosphere encircles the planet Akatsuki/2-μm camera (IR2), and the results obtained from east to west at all latitudes at a speed much faster with IR2 camera from December 2015 through Novem- than the solid planet. This wind system, called the super- ber 2016. A total of 3091 images of Venus (1420 dayside rotation, is one of the biggest mysteries of planetary images at 2.02 μm and 1671 night-side images at 1.735, meteorology and should have a major effect on Venus’ 2.26, and 2.32 μm) were acquired in this period. Addi- environment. Akatsuki is aimed at a comprehensive tionally, 159 images, including those of stars for calibra- survey of the meteorological processes and a quantita- tion and dark images for the evaluation of dark levels, tive evaluation of the momentum transport sustaining were obtained. Yamazaki et al. (2018) described the ini- the super-rotation. For this purpose, five cameras imag- tial results from Akatsuki/Ultraviolet Imager (UVI) at ing the planet at different wavelengths are installed on 283 nm and 365 nm. The UV images provide the spatial the spacecraft to visualize atmospheric motions at dif- distribution of SO2 and the unknown absorber at the ferent altitudes. Combined with a radio occultation cloud tops and characterize the cloud-top morpholo- instrument that probes the vertical structure, this suite gies and haze properties. Nominal sequential images with 2-h intervals are used to understand the dynamics of the Venusian atmosphere by deriving the wind velocity field from measured motion vectors at the cloud tops, as *Correspondence: [email protected] 1 Institute of Space and Astronautical Science, Japan Aerospace well as the mass transportation of UV absorbers. Fuku- Exploration Agency, Sagamihara, Japan hara et al. (2017) described the calibration of the Akat- Full list of author information is available at the end of the article suki/longwave infrared camera (LIR). The brightness © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat iveco mmons .org/licen ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. 1 Akatsuki at Venus: The First Year of Scientific Operation Nakamura et al. Earth, Planets and Space (2018) 70:144 Page 2 of 3 temperature derived from LIR images contained an unex- the atmosphere and are thus a key diagnostic tool when pected bias related not to natural phenomena but to a quantitative dynamical analysis is not feasible due to thermal condition of the instrument. Deep-space images insufficient information. were acquired at different baffle temperatures, and a ref- In this special issue, you will find the history of the erence table for eliminating the bias from images was spacecraft development, the design of the observation prepared. Takahashi et al. (2018) described the lightning instruments, the data processing procedure and the ini- search using the Akatsuki/lightning and airglow camera tial scientific results. We hope this special issue will (LAC). LAC was designed to observe the light curve of familiarize readers with the outline of the JAXA Akatsuki possible flashes at a sufficiently high sampling rate to dis- mission that opened up a new era of Venus exploration. criminate lightning from other sources and thereby per- Akatsuki follow-up Venus missions are planned by some form a more definitive search for optical emissions. It was space agencies and are discussed by Glaze et al. (2018). confirmed that the operational high voltage was achieved Authors’ contributions and that the triggering system functions correctly. LAC All authors read and approved the final manuscript. lightning search observations are planned to continue for Author details several years. 1 Institute of Space and Astronautical Science, Japan Aerospace Exploration Imamura et al. (2017) reported the initial results of Agency, Sagamihara, Japan. 2 ESA/ESTEC, Keplerlaan 1, 2200 AG Noordwijk, the radio occultation experiments revealing the Venus The Netherlands. 3 Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, 3665 Discovery Dr., Boulder, CO 80303, USA. 4 LESIA, atmosphere structure. The physical quantities retrieved Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris include the pressure, the temperature, the H2SO4 vapor Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France. density, and the ionospheric electron density and their 5 LATMOS/UVSQ, Guyancourt, France. 6 IKI/RAS, Moscow, Russia. 7 Department of Earth and Planetary Science, Faculty of Science, Kyushu University, Fukuoka,