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Venus transit

BIRA-IASB and the SOIR team

The Belgian Institute for Space Aeronomy is a federal scientific research institute created in 1964. Its activities are related to the study of atmospheres in a general way. This implies instrument conception as analysis of scientific data recorded by those instruments.

One of the teams, composed of researchers and engineers, is interested in planetary atmospheres, like those of Mars and Venus (in fact all atmospheres except that of the Earth). The team is responsible for the SOIR instrument on-board Venus express.


The researchers of the SOIR team hold all a PhD diploma in sciences (physics and chemistry) or in applied sciences (physics, mechanics).

A engineering team, together with technicians, is also working on this project. They have been responsible for the technical development (YouTube video) of the instrument. They now are in charge of:



Main results of the SOIR instrument

The SOIR instrument is an infrared spectrometer. It's actually onboard Venus Express, a spacecraft orbiting around Venus since april 2006.

This instrument has been conceived in Belgium in collaboration with LATMOS in France and IKI in Russia. It performs solar occultations, which means it uses the Sun as light source.

Thanks to this technique, SOIR, which probes the Venus atmosphere in function of altitude in between 70 and 170 km, can measure the concentration of molecules like:

  • carbon dioxide (CO2), the main component of the Venus atmosphere
  • carbon monoxide (CO)
  • water (H2O)
  • deuterated water (HDO)
  • hydrogen halides (HCl et HF)

A thick cloud layer is found at 70 km and absorbs entirely the sunlight preventing us of analysing the lower atmosphere. However SOIR enables us to detect and characterize the haze present just above the clouds, between 70 and 90 km of altitude.


Planned measurements during the Venus transit

The Venus transit will be a special moment for the scientific community. SOIR will be the only instrument onboard Venus Express to be on.

The commands that will be sent to the instrument will enable us to record spectra of CO2 on the whole altitude range available to the SOIR instrument. These measurements will give us indirect information about the temperature. Absorption due to aerosols will also be investigated.

Thanks to our collaborations with astronoms and ground-based observers, simultaneous measurements have been planned, namely with Pr. T. Widemann (Observatoire de Paris, France) and Dr. B. Sandor (Space Science Institute, Boulder, Colorado, USA). Dr. B. Sandor will, for instance, observe the Venus transit from Mauna Kea, Hawaï, using the James Clerk Maxwell (JCMT) telescope.

The data obtained with SOIR and the telescopes will be compared. This will enable exoplanet scientists to test their instruments.


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