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What Happened to Mars?
A Planetary Mystery presented by Science@NASA
Billions of years ago
when the planets of our solar system were still young,
Mars was a very different world.
Liquid water flowed in long rivers
that emptied into lakes and shallow seas.
A thick atmosphere blanketed the planet
and kept it warm.
In this cozy environment,
living microbes might have found a home,
starting Mars down the path toward becoming a second
life-filled planet next door to our own.
But that's not how things turned out.
Today, Mars is bitter cold and desiccated.
The planet's thin,
wispy atmosphere provides scant cover
for a surface marked by dry riverbeds and empty lakes.
If Martian microbes still exist,
they're probably eking out a meager existence
somewhere beneath the dusty Martian soil.
What happened?
This haunting question has long puzzled scientists.
To find the answer,
NASA is sending a new orbiter to Mars
called MAVEN [ Mars Atmosphere and Volatile Evolution ]
'The goal of MAVEN is to figure out what processes were responsible
for those changes in Martian climate,'
says Bruce Jakosky, Principal Investigator for MAVEN
at the University of Colorado at Boulder.
Scheduled for launch in Nov. 2013,
and due to arrive in Sept. 2014,
MAVEN is bristling with instruments to study Mars' upper atmosphere.
That's where many researchers believe the answer lies.
The only way Mars could have been wet and warm 4 billion years ago,
is if it also had a thick atmosphere.
CO2 in the Martian atmosphere is a greenhouse gas,
just as it is in our own atmosphere.
A thick blanket of CO2 and other greenhouse gases
would have provided the warmer temperatures
and greater atmospheric pressure required
to keep liquid water from freezing solid
or boiling away.
Somehow, Mars lost most of that blanket.
One possibility is the solar wind.
Unlike Earth, Mars is not protected by a global magnetic field.
Instead, it has 'magnetic umbrellas'
scattered around the planet that shelter only part of the atmosphere.
Erosion of exposed areas by solar wind
might have slowly stripped the atmosphere away
over billions of years.
Recent measurements of isotopes in the Martian atmosphere
by the Mars rover Curiosity support this idea-
light isotopes of hydrogen and argon are depleted
compared to their heavier counterparts,
suggesting that they have been lost to space.
Scientists have also speculated that the planet's surface
might have absorbed the CO2
and locked it up in minerals such as carbonate.
However, while carbonates have been found on the surface,
they aren't present in enough abundance
to account for an early, thick atmosphere.
MAVEN will be the first mission to Mars
specifically designed to help scientists
understand the ongoing escape of CO2
and other gases into space.
The probe will orbit Mars for at least one Earth-year.
At the elliptical orbit's low point,
MAVEN will be 125 km above the surface;
its high point will take it more than 6000 km out into space.
MAVEN's instruments will track ions and molecules
in this broad cross-section of the Martian atmosphere,
thoroughly documenting the flow of CO2
and other molecules into space for the first time.
MAVEN's instruments
also will measure the solar energetic inputs
into the Martian upper atmosphere
and the atmospheric response;
this will allow us to determine the processes
that are responsible for that loss to space.
Once Jakosky and his colleagues know how quickly Mars is losing CO2
right now
and what might be causing that loss,
they can extrapolate backward in time
to estimate the total amount lost
during the last four billion years.
'MAVEN will determine if loss to space
was the most important player in driving Martian climate change,'
Jakosky says.
In the grand scheme of the Solar System,
Earth orbits alongside a world
that began with as much promise for life as our own ...
yet turned out so differently.
After all these years,
MAVEN could write the final chapter
in a haunting planetary mystery.
For more clues to the mysteries of Mars,
visit science.nasa.gov