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Deep impact sticks around like EPOXI.

The spacecraft 'Deep Impact' that analysed the light when an object was slammed into comet Tempel 1 in July 2005, still lives on doing good science, now in the guise of the EPOXI mission (Extrasolar Planet Observation and Deep Impact Extended Investigation). EPOXI is a combination of the names for the two extended mission components: a search for extrasolar planets during its cruise phase to comet Hartley 2, called Extrasolar Planet Observations and Characterization (EPOCh), and the eventual flyby of the comet, called the Deep Impact eXtended Investigation (DIXI).

By looking back at the spectrum of Earth from tens of millions of kilometers away, EPOXI has been used to practice techniques for detecting oceans on extrasolar planets. A method has been developed to indicate the presence of oceans by analyzing how Earth's light changes as the planet rotates. Extrasolar ocean-bearing Earths may be found by looking at the changing spectrum of the light these planets give off as they rotate.

Our planet looks blue because of Rayleigh scattering of sunlight by the atmosphere. This is the same reason the sky appears blue from the surface. What was studied was how that blue colour changes with time. Oceans are bluer than continents, which appear red or orange because land is most reflective at red and near-infrared wavelengths. The oceans mainly reflect at the shorter, blue wavelengths. Other things besides water can make a planet appear blue. For example, Neptune is blue due (in part) to the presence of methane in its upper atmosphere. A Neptune-like world however would appear as an unchanging blue using this technique.

To confirm the existence of oceans in an exoplanet, spectroscopy, typically by future large space telescopes, is needed to reveal the presence of water. Finding the water molecule in the spectrum of an extrasolar planet would indicate that there is water vapour in its atmosphere, making it likely that any blue patches seen as it rotates were indeed oceans of liquid water.

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Title Annotation:news notes; Extrasolar Planet Observation and Deep Impact Extended Investigation
Publication:Monthly Notes of the Astronomical Society of Southern Africa
Geographic Code:6SOUT
Date:Aug 1, 2009
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