EPOXI
Two intriguing investigations -- One flight-proven spacecraft
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EPOCh Observations:
EPOXI's Spacecraft Observes Earth's Polar Regions
EPOXI's spacecraft is en route to an encounter with Comet Hartley 2 in early November of 2010. EPOXI uses the Earth's gravity as a slingshot to propel it to the comet. Hence the spacecraft orbit is close to Earth's orbit around the Sun, but is tilted with respect to the plane of the Earth's orbit. Consequently, when the spacecraft comes closest to Earth it is either above the Earth (north), or below the Earth (south). The EPOCh science team exploited this viewing geometry to image the Earth from both the North and South polar view, over a full rotation. The spacecraft was about 11 million miles from Earth in both cases. The team is using these data to understand how planets orbiting other stars (so-called extrasolar planets) will appear when imaged by advanced missions of the future. The polar views of Earth are especially important in this study, because extrasolar planets are as likely to be seen from a polar view as from an equatorial view.
The EPOCh team worked with Don Lindler (Sigma Space Corporation) to assemble the data into color-composite videos. Unlike normal color composites, the EPOXI videos use a near-infrared wavelength (850 nm), in lieu of visible red light. Using the infrared wavelength makes the Earth's continents more prominent, and this will be an important wavelength for potentially detecting land and vegetation of Earth-like extrasolar planets. Notice that the continents appear reddish in the EPOXI videos! Seeing the Earth from the South polar view is unusual, so the EPOCh team added the outlines of the continents on the South video. Another interesting phenomenon - that could potentially indicate the presence of liquid oceans or lakes on extrasolar planets - is the presence of polarized specular reflections of starlight. Look for this specular reflection of sunlight in the circled region of the EPOXI videos! Sometimes it brightens very noticeably, for reasons that are not yet completely understood. The properties of this variable specular reflection are now an active topic of research by the EPOCh team.
North Pole
Video Credit: Don J. Lindler, Sigma Space Corporation and NASA/JPL-Caltech/GSFC/UMD
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South Pole
Video Credit: Don J. Lindler, Sigma Space Corporation and NASA/JPL-Caltech/GSFC/UMD
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Press Release: Sun Glints Seen from Space Signal Oceans and Lakes
Just for fun: Why is the Earth spinning in 'different' directions? What continents are or are not visible in each animation?
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