A new camera from Sevilla in Calar Alto to study Venus’ clouds

The planet Venus has always fascinated human beings. Right after the Sun and the Moon, it is the third brightest object in the sky. Such a “lighthouse” of an immaculate white color had already focused the attention of our ancestors. It was venerated as a divinity by the peoples of antiquity, like the well-known goddess of love of the Romans. The calendar of the Mayan culture (people who lived in what is now the Yucatan Peninsula, Mexico) was partly based on the visibility of Venus.

Being an inner planet, Venus only appears high in the twilight sky a few hours after sunset or a few hours before sunrise. Moreover, it has phases, as Galileo saw when he first pointed his telescope (spyglass) at the planet in December 1610: it looked very much like the Moon, with its phase increasing (and its size decreasing) until it appears almost like a disk when it is on the other side of the Sun, what we call the superior conjunction. That observation was an additional decisive argument for the great Tuscan physicist to defend the heliocentric theory, which sooner than later caused him many problems.

Nowadays, we know that the planet Venus is both very similar in size and mass to our own, but also very different because of its thick atmosphere with a tremendous greenhouse effect, which makes it toxic and very hot at the surface, where the temperature would melt lead. Studying Venus and its atmosphere is crucial to understand what happens to a terrestrial-type planet when it experiences an extreme greenhouse effect, and this can give us clues as to when we might reach a point of no return in our climate emergency.

However, studying its atmosphere is no simple task, and while we have spent nearly a century studying in detail the clouds on its day side that can be seen in ultraviolet and visible images, its night side remained a mystery until the 1980s and 1990s when astronomers discovered between 1 and 2 microns (our eyes only see between 0. 4 to 0.7 microns) several spectral windows in which its dense atmosphere lets infrared radiation escape, therefore allowing us to see the deepest clouds and even its unknown surface (this is the main objective of EnVision, the new space mission to Venus of the European Space Agency).

In this context, the researcher at the University of Seville Javier Peralta leads a project funded by the program EMERGIA of the Regional Government of Andalusia and entitled DUVAC (Discovering the Unknown in Venus' Atmospheric Circulation), which has allowed firm progress in the study of Venus' clouds and surface thanks to the installation at the Calar Alto Observatory 1.23 meter telescope of a FirstLight C-RED 2 ER, a new generation SWIR infrared camera.

The use of  this “SWIR” camera at Calar Alto is the result of a Collaboration Agreement between CAHA and the Universidad de Sevilla signed in February 2025, in the framework of a previous larger agreement.

Among the scientific goals of DUVAC we can highlight the study of the temporal evolution of the deep clouds, winds and aerosols of Venus in search for evidence of an ongoing climate change on this planet, and to obtain high-precision measurements of the Venusian winds, exploring regions where the atmospheric circulation is not entirely clear.

According to Javier Peralta, "This new infrared camera has unique features, as it is sensitive to several spectral windows that will allow us to observe the deep clouds of Venus, the nightglow of its upper atmosphere, and the thermal emission of its surface which could provide evidence of recent volcanic activity. These observations not only warrant the continuity of the studies initiated with the previous Venus Express (ESA) and Akatsuki (JAXA) space missions, but they will also help us to better plan the future EnVision space mission of the European Space Agency."

Using the SWIR camera along with filters specially designed for the scientific objectives of the DUVAC project, researchers Javier Peralta (US) and Itziar Garate-Lopez (UPV/EHU) obtained in February 2025 the first images of the deep clouds of Venus, making Calar Alto Observatory the only place along with the NASA’s IRTF telescope at Mauna Kea (Hawaii) where such images of Venus are being taken. These first images reveal cloud patterns never seen before, whose movements will be studied by combining the images obtained by both observatories in Almeria and Hawaii.

Jesús Aceituno, CAHA Director, adds "Although still in the commissioning phase, this close collaboration between Calar Alto and the Universidad de Sevilla is already proving fruitful. And the future is very promising since the sensitivity and speed of this camera also makes it perfect for the study of impacts on other Solar System bodies, stellar occultations by bodies beyond Neptune, and for transits of exoplanets, among others".

CONTACT

Universidad de Sevilla

Javier Peralta This email address is being protected from spambots. You need JavaScript enabled to view it.

Observatorio de Calar Alto

Gilles Bergond This email address is being protected from spambots. You need JavaScript enabled to view it.

The Calar Alto Observatory is one of the infrastructures that belong to the national map of Unique Scientific and Technical Infrastructures (Spanish acronym: ICTS), approved on March 11th, 2022, by the Science, Technology and Innovation Policy Council (CPCTI).

COMUNICATION – CALAR ALTO OBSERVATORY

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