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By Jonathan AmosScience correspondent, BBC News
Maven will execute a number of "deep dips" to directly sample thicker parts of the atmosphere
The Maven orbiter will study the planet's high atmosphere, to try to understand the processes that have robbed the world of most of its air.
Evidence suggests Mars was once shrouded in a thick blanket of gases that supported the presence of liquid water at its surface. Air pressure is now so low, this is no longer possible.
The probe will be sent up on Monday from Florida by an Atlas V rocket.
Controllers at the Cape Canaveral Air Force Station have set aside a two-hour launch window that extends from 11:28 to 13:28 local time (16:28-18:28 GMT).
They will, however, endeavour to get the mission off the ground at the earliest opportunity.
The rocket's upper-stage will release Maven about 53 minutes into the flight. The probe will then have a 10-month cruise to its destination.
"Maven will open up its solar arrays and then slew so that they are pointed at the Sun," explained Guy Beutelschies, the spacecraft operations manager at manufacturer Lockheed Martin
"During cruise, we perform four planned trajectory correction manoeuvres where we fire thrusters to tweak the trajectory so that we arrive at the right place and time to go into orbit around Mars. At that point, we will fire a set of thrusters to slow down the spacecraft and get captured into orbit," he told BBC News.
Maven also carries equipment to relay data from the Curiosity and other rovers to Earth
Mars atmosphere, composed mostly of carbon dioxide, is today extremely thin.
Atmospheric pressure at the surface is only about 0.6% of the Earth's surface pressure, meaning any open liquid water would rapidly boil away.
The Martian landscape though retains channels that were evidently cut by abundant, flowing water - proof that the planet had a much denser atmosphere in the past.
Some of the air would certainly have reacted with, and been incorporated into, minerals at the surface.
But the most likely explanation for its loss is that the solar wind - the great outflow of energetic particles from the Sun - has simply eroded it through time.
This has been possible because, unlike Earth, the Red Planet lacks a protective global magnetic field, which is capable of deflecting the abrasive assault from our star.
The Mars Atmosphere and Volatile EvolutioN spacecraft will measure the rates at which different air molecules are being lost today, distinguishing between the various processes responsible.
Scientists will use this information to get some insights into the history of Mars' climate - from the time billions of years ago when it was warmer and wetter, and potentially habitable to life, to the present environment which is cold and desiccated.
The 2.4-tonne probe carries eight instruments for the purpose: some to study the Sun's influence at Mars; others to investigate the planet's atmosphere itself.
Arrival at Mars is timed for 22 September next year.
"Maven will be in an elliptical orbit that ranges as far away as 6,220km and as close as 150km," said Mr Beutelschies.
"We will also execute a set of operations to dip down into the tenuous upper reaches of the atmosphere to do some direct sampling for approximately a week at a time. These are called "deep dips" and we do five of them during the primary mission."
That primary mission lasts one Earth year (half a Mars year), after which the science team will need additional funding to continue their investigations.
Nasa, though, fully intends to keep operating Maven long into the future as a data-relay platform for surface rovers like Curiosity.
"If things go nominally, we should have fuel left onboard to keep the vehicle flying for years beyond its design life. As a reference, Mars Odyssey was launched in 2001 and is still operating."
India launched its Mangalyaan mission to Mars on 5 November but is taking a less direct trajectory to the Red Planet than Maven, which means the US mission should get into orbit just a few days before the other orbiter
BBC News - Nasa's Maven Mars mission set for launch
Maven will execute a number of "deep dips" to directly sample thicker parts of the atmosphere
The Maven orbiter will study the planet's high atmosphere, to try to understand the processes that have robbed the world of most of its air.
Evidence suggests Mars was once shrouded in a thick blanket of gases that supported the presence of liquid water at its surface. Air pressure is now so low, this is no longer possible.
The probe will be sent up on Monday from Florida by an Atlas V rocket.
Controllers at the Cape Canaveral Air Force Station have set aside a two-hour launch window that extends from 11:28 to 13:28 local time (16:28-18:28 GMT).
They will, however, endeavour to get the mission off the ground at the earliest opportunity.
The rocket's upper-stage will release Maven about 53 minutes into the flight. The probe will then have a 10-month cruise to its destination.
"Maven will open up its solar arrays and then slew so that they are pointed at the Sun," explained Guy Beutelschies, the spacecraft operations manager at manufacturer Lockheed Martin
"During cruise, we perform four planned trajectory correction manoeuvres where we fire thrusters to tweak the trajectory so that we arrive at the right place and time to go into orbit around Mars. At that point, we will fire a set of thrusters to slow down the spacecraft and get captured into orbit," he told BBC News.
Mars atmosphere, composed mostly of carbon dioxide, is today extremely thin.
Atmospheric pressure at the surface is only about 0.6% of the Earth's surface pressure, meaning any open liquid water would rapidly boil away.
The Martian landscape though retains channels that were evidently cut by abundant, flowing water - proof that the planet had a much denser atmosphere in the past.
Some of the air would certainly have reacted with, and been incorporated into, minerals at the surface.
But the most likely explanation for its loss is that the solar wind - the great outflow of energetic particles from the Sun - has simply eroded it through time.
This has been possible because, unlike Earth, the Red Planet lacks a protective global magnetic field, which is capable of deflecting the abrasive assault from our star.
The Mars Atmosphere and Volatile EvolutioN spacecraft will measure the rates at which different air molecules are being lost today, distinguishing between the various processes responsible.
Scientists will use this information to get some insights into the history of Mars' climate - from the time billions of years ago when it was warmer and wetter, and potentially habitable to life, to the present environment which is cold and desiccated.
The 2.4-tonne probe carries eight instruments for the purpose: some to study the Sun's influence at Mars; others to investigate the planet's atmosphere itself.
Arrival at Mars is timed for 22 September next year.
"Maven will be in an elliptical orbit that ranges as far away as 6,220km and as close as 150km," said Mr Beutelschies.
"We will also execute a set of operations to dip down into the tenuous upper reaches of the atmosphere to do some direct sampling for approximately a week at a time. These are called "deep dips" and we do five of them during the primary mission."
That primary mission lasts one Earth year (half a Mars year), after which the science team will need additional funding to continue their investigations.
Nasa, though, fully intends to keep operating Maven long into the future as a data-relay platform for surface rovers like Curiosity.
"If things go nominally, we should have fuel left onboard to keep the vehicle flying for years beyond its design life. As a reference, Mars Odyssey was launched in 2001 and is still operating."
India launched its Mangalyaan mission to Mars on 5 November but is taking a less direct trajectory to the Red Planet than Maven, which means the US mission should get into orbit just a few days before the other orbiter
BBC News - Nasa's Maven Mars mission set for launch
