On Earth, a fast runner takes a few hours to complete a marathon. On Mars, it's taken 11 years. NASA's Opportunity rover crossed that finish line in 2015.
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Planets: New Worlds, New Discoveries
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.
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.
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.
The small bodies in the solar system include comets, asteroids, the objects in the Kuiper Belt and the Oort cloud, small planetary satellites, Triton, Pluto, Charon, and interplanetary dust. As some of these objects are believed to be minimally altered from their state in the young solar nebula from which the planets formed, they may provide insight into planet Earth and the formation and evolution of the solar system.
NASA’s Planetary Science missions to the outer planets help reveal secrets about the solar system by observing those outer distant worlds up close. Jupiter’s moon Europa and Saturn’s moon Enceladus are now thought to hide liquid water beneath their frozen surfaces and are high priority targets for NASA. Unlocking their secrets and those of the outer planets will help scientists understand more about planet Earth and the formation and evolution of the solar system.
Planetary Science missions, past, current, in planning or in development, extend mankind’s presence to the solar system’s inner rocky worlds, helping to unlock the secrets of the solar systems’ composition, history and evolution, and how life established itself on Earth.