Two windows on ozone: extending our view of the Martian atmosphere
16 February 2010New measurements of ozone in the atmosphere of Mars are being obtained in a coordinated observation campaign with Mars Express and a Hawaiian-based telescope. The combined observation set covers a longer time period and broader range of regions on Mars than previous campaigns, thereby improving the ability to verify and refine detailed models of the Martian atmosphere.
Ozone is an important tracer of photochemical processes in the atmosphere of Mars. Its abundance, which can be derived from the molecule's characteristic absorption features in spectra of the atmosphere, is intricately linked to that of other constituents and it is an important indicator of atmospheric chemistry. To test predictions by current models of photochemical processes and general atmospheric circulation patterns, observations of spatial and temporal ozone variations are required.
Coordinated campaign - two windows on ozone
These measurements can be complemented by ground-based observations taken at different times and probing different sites on Mars, thereby extending the spatial and temporal coverage of the SPICAM measurements. To quantitatively link the ground-based observations with those by Mars Express, coordinated campaigns are set up to obtain simultaneous measurements.
Infrared heterodyne spectroscopy, such as that provided by the Heterodyne Instrument for Planetary Wind and Composition (HIPWAC), provides the only direct access to ozone on Mars with ground-based telescopes; the very high spectral resolving power (λ/Δλ >106) allows Martian ozone spectral features to be resolved when they are Doppler shifted away from ozone lines of terrestrial origin.
The observations had been coordinated in advance with the Mars Express science operations team, to ensure overlap with ozone measurements made in this same period with SPICAM.
The main goal of the December 2009 campaign was to confirm that observations made with SPICAM (which measures the broad ozone absorption feature centred at around 250 nm) and HIPWAC (which detects and measures ozone absorption features at 9.7 µm) retrieve the same total ozone abundances, despite being performed at two different parts of the electromagnetic spectrum and having different sensitivities to the ozone profile. A similar campaign in 2008, had largely validated the consistency of the ozone measurement results obtained with SPICAM and the HIPWAC instrument (see related publication by Fast, K.E. et al. ).
Results from a successful campaign
The weather conditions and the seeing were very good at the IRTF site during the December 2009 campaign, which allowed for good quality spectra to be obtained with the HIPWAC instrument.
Kelly and her colleagues gathered ozone measurements for a number of locations on Mars, both in the planet's northern and southern hemisphere. During this four-day campaign the SPICAM observations were limited to the northern hemisphere. Several HIPWAC measurements were simultaneous with observations by SPICAM allowing a direct comparison. Other HIPWAC measurements were made close in time to SPICAM orbital passes that occurred outside of the ground-based telescope observations and will also be used for comparison.
The team also performed measurements of the ozone abundance over the Syrtis Major region, which will help to constrain photochemical models in this region.
Linking datasets for a broader perspective
Analysis of the data from this recent campaign is ongoing, with another follow-up campaign of coordinated HIPWAC and SPICAM observations already scheduled for March this year.
Putting the compatibility of the data from these two instruments on a firm base will support combining the ground-based infrared measurements with the SPICAM ultraviolet measurements in testing the photochemical models of the Martian atmosphere. The extended coverage obtained by combining these datasets helps to more accurately test predictions by atmospheric models.
It will also quantitatively link the SPICAM observations to longer-term measurements made with the HIPWAC instrument and its predecessor IRHS (the Infrared Heterodyne Spectrometer) that go back to 1988. This will support the study of the long-term behaviour of ozone and associated chemistry in the atmosphere of Mars on a timescale longer than the current missions to Mars.
Fast, K.E. et al. (2009), "Comparison of HIPWAC and Mars Express SPICAM observations of ozone on Mars 2006–2008 and variation from 1993 IRHS observations", Icarus, volume 203, issue 1, pages 20-27, DOI:10.1016/j.icarus.2009.05.005
Notes for editors
The Infrared Telescope Facility (IRTF) is a 3.0 meter telescope, optimized for infrared observations, and located at the summit of Mauna Kea, Hawai'i. The observatory is operated and managed for NASA by the University of Hawai'i Institute for Astronomy, located in Honolulu.
The NASA Goddard Heterodyne Instrument for Planetary Wind And Composition (HIPWAC) is a heterodyne spectrometer observing in the mid-infrared between 9-12 micrometers.
Olivier Witasse, ESA Mars Express project scientist
Kelly Fast, Principal investigator, Mars ozone program, NASA/GSFC
Franck Montmessin, Principal Investigator, SPICAM experiment aboard Mars Express, Laboratoire Atmosphères, Milieux, Observations Spatiales