Big Questions for Planets
Channels on Mars scoured by ancient outbursts of flood waters are seen in this orbital view from Odyssey's Thermal Emission Imaging System. The channels are billions of years old and have likely been affected by multiple processes over time. Here, two channels, Tiu Vallis on the left and Ares Vallis on the right, flow northward from the highlands of the southern hemisphere of Mars.
The stark difference between today's cold, dry Mars and the evidence of flood waters in the past tells scientists that the Martian climate has seen great changes. Unraveling the workings of that climate history is one of the major challenges in Mars science.
Credit: NASA/JPL-Caltech/ASU
Solar system exploration is a grand human enterprise that seeks to discover the nature and origin of the celestial bodies among which we live and to explore whether life exists beyond Earth. The scientific foundation for this enterprise is described in the NRC’s Decadal Survey in Planetary Science, New Frontiers in the Solar System: An Integrated Exploration Strategy (NRC, 2003). The quest to understand our origins is universal. How did we get here? Are we alone? What does the future hold? Modern science, and especially space science, provides extraordinary opportunities to pursue these questions. The tools that are available and that will become available in the coming years will enable us to develop an astoundingly vast range of mission opportunities. We are at the leading edge of a journey of exploration that will yield a profound new understanding of our home, the Earth, and of ourselves. Robotic exploration is the key precursor for the expansion of humanity into our solar system.
These grand themes are captured in five fundamental science questions in the planetary science community’s 2006 Solar System Exploration Roadmap that form the basis for NASA’s approach to the exploration of the solar system:
- How did the sun's family of planets and minor bodies originate?
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For the first time in human history we know of planets around other stars and many of those other planetary systems look quite different from our own. Many have a planet like Jupiter, or even bigger, nearest to the Sun. If we are to understand why this is the case, and how likely it is that there are Earth-like planets elsewhere, we need to better understand how planets form.
- How did the solar system evolve to its current diverse state?
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Many of the other solar systems have massive Jupiter like planets close to their Sun, closer even than Mercury. Many scientists now believe that these gas giants could not have formed there. Rather, they must have began out where our Jupiter is, and moved inwards, scattering the smaller planets with their powerful gravity as they went. Why is it that our Jupiter and Saturn did not migrate inward? We are trying to learn more about our outer solar system by sending probes there. We sent Galileo to Jupiter, Cassini is at Saturn right now, and New Horizons is on its way to Pluto even as you read this.
- How did life begin and evolve on Earth, and has it evolved elsewhere in the Solar System?
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Microbial life forms have been discovered on Earth that can survive and even thrive at extremes of high and low temperature and pressure, and in conditions of acidity, salinity, alkalinity, and concentrations of heavy metals that would have been regarded as lethal just a few years ago. These discoveries include the wide diversity of life near sea–floor hydrothermal vent systems, where some organisms live essentially on chemical energy in the absence of sunlight. Similar environments may be present elsewhere in the Solar System.
- What are the characteristics of the Solar System that lead to the origins of life?
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The possibility of finding life elsewhere is for many people the most compelling reason for humankind to explore beyond the Earth. We believe that liquid water and carbon are required for life to arise and thrive, as well as a source of energy. Many places in the Solar System provide these, at least for a time; not only planets, but also some moons and even certain comets. But for life to arise we presume that a hospitable environment must be more than just transient.