Press release | 7 December 2020 | pp

Hot Winds on Venus

New models for analyzing observation data on exoplanets

The search for a “second Earth” in space, for a habitable planet, preoccupies astrophysicists around the world. Until now, there has only been indirect proof of exoplanets, in other words heavenly bodies orbiting a sun light years away from our solar system. Currently, science assumes that time-series measurements of brightness or reflected starlight provide information concerning the possible nature of the surface of a planet, the presence of an atmosphere, or its rotational period. TU scientist Dr. Yeon Joo Lee and her colleague Dr. Antonio García Muñoz, who is also a member of the Institute of Planetary Research at the German Aerospace Center (DLR), have now analyzed observation and measurement data provided by the Japanese Akatsuki orbiter. Their findings demonstrate that, contrary to what was previously thought, variations in brightness do not enable conclusions to be drawn about the atmosphere of planets. The study was conducted together with colleagues form Japan, including researchers at JAXA, the Japanese aerospace agency. The findings of the study have now been published in “Nature Communications”.

“Until now, we had assumed that frequently modulating levels of brightness indicated the rotational speed of the planet as well as the diameter of its atmosphere. Our precise measurements and calculations show that this is not necessarily the case,” explains Yeon Joo Lee of the Zentrum für Astronomie und Astrophysik at TU Berlin (ZAA). Their observations have revealed that the different brightness modulations are in no way an indication of the rotational speed of the solid body of Venus and have much more to do with the active winds in the atmosphere. As such, data relating to Venus are not reliable for the interpretation of brightness modulations of other terrestrial exoplanets. The scientists therefore propose calculation models that could indicate the existence of an atmosphere, but not its diameter. These models could also be used for a more precise analysis of data from future observation missions.

TU scientists are also contributing to BepiColombo, the largest European space mission to date

Researchers are eagerly awaiting the latest data from the four-part European-Japanese BepiColombo space probe, which was launched two years ago from the Kouro spaceport in French Guiana. In October 2020, it passed close to Venus – just 10,000 kilometers from the planet – as part of its seven-year journey to Mercury. BepiColombi is a joint mission of ESA and JAXA, the Japanese aerospace exploration agency. Astrophysicists at TU Berlin have already contributed a number of experiments to this, Europe’s largest planetary mission to date. “We are expecting the data to provide information on the complexity of the atmosphere of Venus,” explains Yeon Joo Lee. The planet’s atmosphere is particularly dense. It consists of more than 90 percent carbon dioxide, with its surface concealed by a 20-kilometer-thick layer of cloud with a high content of sulphuric acid. A thermal infrared spectrometer and radiometer on board BepiColombo provide information on the density, temperature and chemical composition of the central atmosphere of Venus. A UV spectrometer measures reflections and emissions from the upper atmospheric layers, while a magnetometer charts the magnetic environment. Further instruments are used to study the interaction between the sun and the upper atmosphere of Venus. “The surface temperature of Venus measures 470 degrees Celsius, largely the result of a powerful greenhouse effect, ruling out the existence of water on its surface and placing it outside the habitable zone,” explains Yeon Joo Lee. “It is possible however that it was habitable in the past, with conditions similar to those on Earth. We are unable to say exactly when it drifted away from this situation.”

The Japanese members of the team research at the University of Tokyo, the Planetary Exploration Research Center (PERC), the Institute of Space and Astronautical Science (ISAS/JAXA), and the Hokkaido Information University.

Y. J. Lee, A. García Muñoz, T. Imamura, M. Yamada, T. Satoh, A. Yamazaki, and S. Watanabe
Brightness modulations of our nearest terrestrial planet Venus reveal atmospheric super-rotation rather than surface features
in: Nature Communications 11 (2020), DOI: 10.1038/s41467-020-19385-6