You must see new video from EPOXI, whose effect can only be suggested by the photo montage below (click the link below for the movie). EPOXI is the combined extended mission of the Deep Impact spacecraft. As we discussed in an earlier story here, EPOXI turned its cameras on the Earth to view the moon transiting the planet’s disk from a vantage point of 31 million miles. Think in terms of viewing the Earth the way we will eventually view terrestrial worlds around other stars. The idea is to build insights into how these worlds can be observed and characterized.
Image: The moon crossing the Earth, as viewed by EPOXI. Video credit: Donald J. Lindler, Sigma Space Corporation/GSFC; EPOCh/DIXI Science Teams.
Drake Deming (NASA GSFC), deputy principal investigator for EPOXI and leader of the extrasolar planet component of the mission (called EPOCh), points out how the information can be helpful:
“Our video shows some specific features that are important for observations of Earth-like planets orbiting other stars. A ‘sun glint’ can be seen in the movie, caused by light reflected from Earth’s oceans, and similar glints to be observed from extrasolar planets could indicate alien oceans. Also, we used infrared light instead of the normal red light to make the color composite images, and that makes the land masses much more visible.”
None of our current or projected planet hunter missions will be able to see a terrestrial world as close up as this, but we will be able to see such a planet as a point of light that can be studied to observe changes in its total brightness. Such changes could be telling us about continents on a planet affecting the light signature as, interspersed with water, they rotate in and out of view. So taking views of a known living world helps us understand how these light changes occur, and we’ll want to keep taking pictures of Earth at ever greater distances to continue that effort. The moon transit occurring in these frames is a priceless bonus.
Now take a look at the second movie. Whereas the first was made using a red-green-blue filter, the second was made using infrared-green-blue. With plants reflecting more strongly in the near-infrared, the land masses become more readily visible. We’re thus looking at the possibility of detecting vegetation on extrasolar planets whose marker will be changes in near-infrared light as the planet rotates. All this in the future from a tiny point of light whose properties we’re learning to parse thanks to a mission that once set out to drive an impactor into a comet.