Ours is the first generation to discover solar systems beyond our own. Understanding how and where these exoplanets (planets around other stars) form and what they are like, and understanding how life survives under extreme conditions, are key steps in the search for life beyond Earth.
The Kepler Mission is specifically designed to survey our region of the Milky Way galaxy to discover hundreds of Earth-size and smaller planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets. Results from this mission will allow us to place our solar system within the continuum of planetary systems in the Galaxy.
The quest for Earth-like planets, habitable environments and signs of life outside the solar system is emerging as a vigorous, quantitative science that within our lifetimes may answer the question: Are we alone?
To understand how planetary systems form and evolve, we must probe planet formation, try to detect the youngest planets, and understand the creation and delivery of organics to planets.
As we explore the diversity of other worlds, we look to giant planets as the signposts of a planetary system around another star. Continued searches will help us understand the frequency of Earth sized planets. As we search for habitable planets, and possible life, we need to characterize both giant and terrestrial planets around other stars, including their mass, composition, etc.
The challenge now is to find terrestrial planets (i.e., those one half to twice the size of the Earth), especially those in the habitable zone of their stars where liquid water and possibly life might exist. Searching for life beyond the solar system requires us to understand the conditions under which life might be found, identify what biomarkers might be in place, and find the means to detect them from far away.
Planets form out of swirling disks of gas and dust. Spitzer observed infrared light coming from one such disk around a young star, called LRLL 31, over a period of five months. One theory of planet formation suggests that planets start out as dusty grains swirling around a star in a disk. They slowly bulk up in size, collecting more and more mass like sticky snow. As the planets get bigger and bigger, they carve out gaps in the dust, until a so-called transitional disk takes shape with a large doughnut-like hole at its center. Over time, this disk fades and a new type of disk emerges, made up of debris from collisions between planets, asteroids and comets. Ultimately, a more settled, mature solar system like our own forms.
Astrobiology is devoted to the scientific study of life in the universe - its origin, evolution, distribution, and future. This multidisciplinary field brings together the physical and biological sciences to address some of the most fundamental questions of the natural world: How do living systems emerge? How do habitable worlds form and how do they evolve? Does life exist on worlds other than Earth? How could terrestrial life potentially survive and adapt beyond our home planet?
The habitable zone is the distance from a star where one can have liquid water on the surface of a planet. If a planet is too close to its parent star, it will be too hot and water would have evaporated. If a planet is too far from a star it is too cold and water is frozen. Stars come in a wide variety of sizes, masses and temperatures. Stars that are smaller, cooler and lower mass than the Sun (M-dwarfs) have their habitable zone much closer to the star than the Sun (G-dwarf). Stars that are larger, hotter and more massive than the Sun (A-dwarfs) have their habitable zone much farther out from the star.
Contributions to this story were made by the Smithsonian Astrophysical Observatory and the Space Telescope Science Institute
National Aeronautics and Space Administration, Science Mission Directorate. (2009). A Quest For Exoplanets?. Retrieved , from Mission:Science website:
Science Mission Directorate. "A Quest For Exoplanets?" Mission:Science. 2009. National Aeronautics and Space Administration.