Herschel Mars observations: First results

The Herschel Space Observatory is providing the first exciting results on Mars, from its guaranteed-time key program 'Water and related chemistry in the Solar System'. An accurate globally-averaged temperature profile of the Martian atmosphere may cause scientists to revise their models about atmospheric circulation on Mars. The first sub-millimetre observation of molecular oxygen on the planet may lead to a completely new picture of the oxygen distribution in the Martian atmosphere. These are only a few of the new discoveries that will be presented by Dr Paul Hartogh at the European Planetary Science Congress in Rome, on Monday 20th September.

The Herschel Space Observatory (HSO) is a space-borne far-infrared observation facility of the European Space Agency, launched on 14 May 2009. The 'Water and related chemistry in the Solar System' project, was conceived with the sole aim to determine the origin, evolution, and distribution of water in Mars, the outer planets, Titan, Enceladus and the comets.

'Water vapour plays a key role in the Martian atmospheric chemistry and physics,' says Dr Hartogh of the Max Planck Institute for Solar System Research in Germany. Herschel has observed Mars with its three instruments, the Heterodyne Instrument for the Far Infrared (HIFI), the Photodetector Array Camera and Spectrometer, and the Spectral and Photometric Imaging Receiver (SPIRE).

SPIRE has provided the first continuous spectrum of the Martian atmosphere in the spectral range in the far-IR/sub-mm, as well as, the first complete set of water vapour and carbon monoxide (CO) content in this range. 'SPIRE was designed for very faint sources, however unexpectedly it could even provide high quality data from the brightest far infrared object Herschel observed in the solar system,' says Dr Hartogh.

HIFI has observed Mars between 11-16 April 2010. Only a small part of the data has been analysed up to now, but it already provided some interesting results: A globally averaged temperature profile has been retrieved from the first simultaneous observations of two carbon monoxide isotopes. 'The best fit of the Martian atmospheric model to these observations shows important differences compared to what we were predicting: between 40 and 80 km from the ground, the atmosphere appears to be more than 10 K colder than predicted,' says Dr Hartogh.

Scientists also report on the first sub-mm detection of O2 on Mars, with an observational accuracy at least 10 times better than was done before. 'Our sub-mm observations provide for the first time a vertical profile of molecular oxygen in the Martian atmosphere. We found that, contrary to the general assumption of a constant O2 content independently of altitude, the Martian atmosphere is richer in oxygen near the ground and then O2 decreases rapidly with altitude,' says Dr Hartogh. If this profile is confirmed it may imply different oxygen production and loss processes not considered before, leading to new insights about the Martian atmosphere. 'Obviously, much work still needs to be done on the vertical profile of O2 before we draw such conclusions,' he adds cautiously.

Herschel will continue exploring our solar system in the next 2 - 3 years of its planned mission duration. 'We hope that surprises and major breakthroughs in our knowledge will keep coming in, and that at the end we will have gained a unified picture of the origin and evolution of water in the Solar System objects,' says Dr Hartogh.