The MGS Radio Science Team acquired new data from the martian atmosphere between November 21 and December 31, 1998. It was late Spring in the northern hemisphere of Mars and late Fall in the southern hemisphere during this time period. The Team has not yet completed the processing of all of the raw data, but atmospheric profiles have been retrieved for all of the data acquired through December 25. Results through that date are available on this web site to participants in the Team's education outreach program. The remainder of the data will be processed in the next week or two, and results will be made available to outreach program participants at the same time.
The Team made nearly 200 good observations of the martian atmosphere in November and December. A map showing the locations of the atmospheric observations is available on this site, and it is possible to see the weather record associated with each observation by clicking on the corresponding occultation point.
The Team will be collecting new weather data from Mars in the next couple of months when the opportunity to do so arises. The mapping phase of the MGS mission will officially begin in late March or early April. The Radio Science Team will be making the bulk of their martian atmospheric observations during this phase of the mission which will continue for one complete martian year (687 days).
MGS has nearly completed the two aerobraking phases of its mission. As of January 27, 1999, aerobraking had reduced the period of the MGS orbit around Mars to 2 hours and 10 minutes. This reduction from the original orbit period of approximately 45 hours was accomplished with 800 passes through the upper martian atmosphere! The orbit period is currently being reduced by about 20 seconds each time the spacecraft encounters the upper atmosphere during its closest approach to Mars. On January 27, the altitude of the closest approach to Mars on each orbit was 64 miles. The altitude of the apoapse (most distant point from Mars) on each orbit was 773 miles.
Aerobraking will be terminated on February 3, 1999, at which point the MGS orbit will be nearly circular at an altitude of approximately 250 miles. The period of the orbit will be two hours, and the orbit will be synchronized to the Sun so that MGS will cross the equator of Mars at the same local time on every orbit. Synchronization to the Sun provides consistent experimental conditions for the MGS instruments and investigations. The specific timing of the equator crossings was arrived at through compromises by the MGS science teams.
There will be a number of instrument calibration periods between the end of aerobraking and the beginning of the mapping phase of the MGS mission. There will also be a short data collection period by all of the instruments before the MGS high-gain (dish) antenna is deployed. Earlier in this mission there was some concern in the project about the deployment of the MGS antenna. The concerns have been for the most part alleviated, and the antenna will be deployed at the beginning of the mapping phase of the mission.
The meteorological data acquired by the MGS Radio Science Team during the second MGS aerobraking phase have been very interesting! The Team was able to acquire data in both the northern and southern martian hemispheres on most of the MGS orbits. Many of the observations in the southern hemisphere were made near the south polar cap of Mars in late Fall when the Sun was either just above or below the horizon.
The atmospheric temperatures were so cold for most of these observations that the martian atmosphere was either fully saturated or nearly saturated with carbon dioxide. The saturated region of the atmosphere was variable; some of the time the atmosphere was saturated near the martian surface and some of the time it was saturated at higher altitude. It was likely snowing frozen carbon dioxide when the atmosphere was saturated. The surface temperatures for these southern observations were typically about 195 degrees below zero Fahrenheit. On the other hand, surface temperatures in the late Spring high in the northern hemisphere were approximately 75 degrees below zero Fahrenheit in the early morning hours.
The outreach program web site recently made a long-awaited move to a new web server. The transition from a Digital Equipment Corporation server to a Sun Microsystems server was accomplished with only a short down time, much to the relief of the MGS Radio Science Team and their webmaster. Hopefully, nothing will stand in the way now of making all of the Team's mapping data available to participants in the outreach program!