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Cloud Worlds: from Venus to Exoplanet

Periodic Reporting for period 1 - CLOUDWORLDS (Cloud Worlds: from Venus to Exoplanet)

Reporting period: 2019-06-10 to 2021-06-09

Venus is a unique terrestrial planet in the Solar System. It is Earth-sized and covered by clouds completely. The sulfuric acid cloud is highly reflective, so remote observations can measure reflected solar light by the clouds. In this project (CLOUDWORDLS) we characterized properties of Venus clouds using such reflected light. Similar techniques will be applicable for future direct imaging analysis of exoplanets. We also can better understand the radiative and dynamical process in the atmosphere of Venus near the cloud top level.
We showed that Venus albedo varies over a decadal period using data acquired by four spacecraft. This study was published at the beginning of the project and received considerable attention from media and research community (dissemination: invited talk at a planetary conference EPSC-DPS 2019, press briefing at JAXA headquarter in Japan, many internet articles, and selected as Highlight of Year 2019 of American Astronomy Society journals). We then examined whether high mountains on the surface would affect the albedo distributions near the cloud top level (70 km altitude) and confirmed that temporal variations of the clouds is much stronger than possible influences by the surface (dissemination: publication in the Journal of Geophysical Research – Planets). We analyzed disk-integrated brightness of Venus and found considerable brightness modulations. Such light modulations should be a way to detect the existence of atmospheres on exoplanets using future direct imaging (dissemination: publication in Nature Communications, German newspaper, Featured image of the journal: the attached image, Top 50 physics article of year 2020 of the journal, and invited talks/seminars). We investigated the observed scattering behavior of Venus at ultraviolet wavelength using radiative transfer model calculations and found that an unknown absorber should be abundant right below the cloud top level (dissemination: publication in Geophysical Research Letter and talks in conferences and workshops). The researcher (Yeon Joo Lee) actively participated in new Venus data acquisition by spacecraft. She continued working with the Japanese Venus orbiter (Akatsuki) and was selected as a Guest Investigator of ESA-JAXA’s BepiColombo mission. She coordinated Venus observations by the two spacecraft (dissemination: press briefing at a planetary conference EPSC-DPS 2019, several internet news articles, publication in Space Science Review, webpage contents preparations). The researcher also worked actively in international collaboration in the Venus community, and participated in many colleagues’ studies about Venus atmosphere (dissemination: publications in Geophysical Research Letter, Journal of Geophysical Research – Planets, Astronomy and Astrophysics journal, and Astrobiology journal). During the project period, the researcher communicated actively in the Venus and exoplanet research communities. Such activities can be summarized in numbers: 18 international workshops, 6 international conferences, 5 press release in Japan, Germany, USA and an international conference, 2 social media. The researcher performed public outreach activities, such as science class for Korean children over the world (dissemination: 3 times of science classes for children).
All results of the CLOUDWORLDS project contributed to better understand about Venusian atmosphere, especially near the cloud top level. We analyzed Venus as an exoplanet and propose a way to compare with future observational data analysis of exoplanets. Our results will help future Venus missions, ESA/EnVision, NASA/VERITAS and DAVINCI+, which will be operative in 2030s, in terms of scientific observational strategy.
Featured image of Nature Communications. Brightness modulations of Venus in false color