Life on Mars
Among our discoveries about Mars, one stands out above all
others: the possible presence of liquid water on Mars, either in its ancient
past or preserved in the subsurface today. Water is key because almost
everywhere we find water on Earth, we find life. If Mars once had liquid water,
or still does today, it's compelling to ask whether any microscopic life forms
could have developed on its surface. Is there any evidence of life in the
planet's past? If so, could any of these tiny living creatures still exist
today? Imagine how exciting it would be to answer, "Yes!!"
Even if Mars is devoid of past or present life, however,
there's still much excitement on the horizon. We ourselves might become the
"life on Mars" should humans choose to travel there one day. Meanwhile,
we still have a lot to learn about this amazing planet and its extreme
environments. Since our first close-up picture of Mars in 1965, spacecraft
voyages to the Red Planet have revealed a world strangely familiar, yet
different enough to challenge our perceptions of what makes a planet work.
Every time we feel close to understanding Mars, new discoveries send us
straight back to the drawing board to revise existing theories. You'd think
Mars would be easier to understand. Like Earth, Mars has polar ice caps and
clouds in its atmosphere, seasonal weather patterns, volcanoes, canyons and
other recognizable features. However, conditions on Mars vary wildly from what
we know on our own planet. Over the past three decades, spacecraft have shown
us that Mars is rocky, cold, and dry beneath its hazy, pink sky. We've
discovered that today's Martian wasteland hints at a formerly volatile world
where volcanoes once raged, meteors plowed deep craters, and flash floods
rushed over the land. And Mars continues to throw out new enticements with each
landing or orbital pass made by our spacecraft.
Seek
Signs of Life on Mars
To discover the possibilities for past or present life on
Mars, NASA's Mars Exploration Program is currently following an exploration
strategy known as "Seek Signs of Life."
This science theme marks a transition in Mars exploration.
It reflects a long-term process of discovery on the red planet, built on
strategies to understand Mars' potential as a habitat for past or present
microbial life. Searching for this answer means delving into the planet's
geologic and climate history to find out how, when and why Mars underwent
dramatic changes to become the forbidding, yet promising, planet we observe
today.
About 3.8-3.5 billion years ago, Mars and Earth were much
more similar. Evidence from Mars missions suggest Mars may have been much
warmer and wetter than we observe it to be today. In this ancient timeframe,
scientists find the first evidence of microbial life on Earth. Did Mars provide
similar environmental conditions for life long ago? If microbes were present on
Mars in the planet's ancient past, could it exist in special regions today?
And, even if microbial life never existed, might Mars provide a future habitat
for human explorers someday in the future?
Because water is key to life as we know it, earlier Mars
missions (2001 Mars Odyssey, Mars Exploration Rovers, Mars Reconnaissance
Orbiter, Mars Phoenix Lander) were designed to make discoveries under the
previous Mars Exploration Program science theme of "Follow the
Water." Progressive discoveries related to evidence of past and present
water in the geologic record make it possible to take the next steps toward
finding evidence of life itself.
The Mars Science Laboratory mission and its Curiosity rover
mark a transition between the themes of "Follow the Water" and
"Seek Signs of Life." In addition to landing in a place with past
evidence of water, Curiosity is seeking evidence of organics, the chemical building
blocks of life. Places with water and the chemistry needed for life potentially
provide habitable conditions. Future Mars missions would likely be designed to
search for life itself in places identified as potential past or present
habitats. Like all Mars Exploration Program missions, future missions will be
driven by rigorous scientific questions that continually evolve from
discoveries by prior missions. New and previously developed technologies will
enable us to explore Mars in ways we never have before, resulting in
higher-resolution images, precision landings, longer-ranging surface mobility
and even the return of Martian soil and rock samples for studies in
laboratories here on Earth.