Much has happened since the last news update! The first aerobraking phase of the Mars Global Surveyor mission concluded at the end of March. MGS is now orbiting Mars once every 11.6 hours and will continue to do so until aerobraking begins again in September. The closest approach to Mars on each orbit is now at an altitude of approximately 107 miles. At that altitude, there is almost no atmospheric drag on the spacecraft. MGS has completed over 250 orbits around the red planet since its orbit insertion in September, 1997.
MGS is now in what is being called a science phasing orbit. The MGS instruments will gather whatever data they can in the phasing orbit until aerobraking begins again in September to take MGS into its ultimate mapping orbit in early 1999. All spacecraft activities will cease for a period of a few weeks in May when Mars passes the Sun in the sky. That event is called solar conjunction, and spacecraft activities are halted because reliable radio communication with the spacecraft is impossible when the angle between Mars and the Sun (as viewed from Earth) is small.
One of the major objectives of the early part of the science phasing orbit was to use the MGS camera to take photographs of the so-called Face on Mars in the Cydonia region. That objective was successfully accomplished, and the announement that there was not actually an artificial Face or any other artificial remnant made headlines around the world!
The MGS Radio Science Team began to acquire raw data and generate temperature and pressure profiles of the martian atmosphere at the end of January, 1998. The profiles illustrate the vertical structure of the atmosphere, and some of them are now posted on this Web site. All of the data which the MGS Radio Science Team has made available to participants in this education outreach program have been derived from the atmospheric profiles. The Team halted its acquisition of raw atmospheric data on April 17. Due to technical and geometrical constraints, no new atmospheric data will be collected by the Radio Science Team until at least November of this year. The Team is still planning to acquire the bulk of its martian meteorological data during the mapping phase of the MGS mission which begins in March, 1999. The duration of the mapping phase of the mission will be 687 days (one martian year).
It took a short while to iron out the data processing procedures and software, but the Team did reach a point where it was able to generate atmospheric profiles from raw data and make martian surface temperature and pressure information available to participants in the outreach program on the same day which the raw data were actually acquired. Considering that the raw data are collected at NASA Deep Space Network complexes in Spain, Australia and the Mojave Desert of California, that is quite an achievement! Due to a change in the daily spacecraft operations which took place when the first aerobraking phase of the mission was terminated, there are still nearly two weeks worth of atmospheric data which have not yet been processed. When the Team receives the detailed information about the spacecraft trajectory which it requires to process the remaining data, the results will be added to the martian meteorological data already available to participants in the outreach program.
The martian atmospheric data from the first aerobraking sequence are very impressive. There are nearly 100 sets of atmospheric profiles from Mars, beginning with measurements in the early fall in the Northern hemisphere and ending with measurements in the middle of summer in the Southern hemisphere. The range of surface temperatures measured between January and April of this year was approximately 100 Fahrenheit degrees! The transfer of carbon dioxide from the martian atmosphere to the Northern polar cap was clearly in evidence in the pressure measurements. The transfer occurred as carbon dioxide froze out of the atmosphere and was deposited at the pole during the Northern winter. Unfortunately, we will not be able to observe the carbon dioxide sublime back into the atmosphere during the Northern spring. That will have to wait for the main MGS mapping sequence!
Educators are welcome to register classes for this program at any time. The program will continue through the end of the MGS mapping mission in the year 2000. Interested teachers should contact joe@nova.stanford.edu.