Deep Impact, however, is presently on another mission while waiting for its 2010 date with comet Hartley 2. The EPOXI mission, or Extrasolar Planet Observations and Characterization (EPOCh) and Deep Impact eXtended Investigation (DIXI), is presently returning a wealth of information about how astronomers might identify Earth-like extrasolar planets.

As it lounges around in space waiting for Hartley 2, Deep Impact will make observations of five extrasolar systems previously detected by other means. Each of these systems has at least one transitory planet, or a planet that orbits in such a way to pass between its star and Earth's point of view. By using several observations of these planets, astronomers can subtract the local star's light from combined views and get a good idea of what a planet's atmosphere might be composed of by analyzing the leftover data. Different atmospheric compositions reflect light differently, and by using this data, they can infer what elements and chemicals are present.

But this is not the only type of data that will help discover new Earths. Recently, NASA published a video taken by Deep Impact at a distance of 31 million miles from Big Blue. The video is the first of its kind, clearly showing the moon, with a good amount of detail, transitioning Earth. While the video is interesting for just this sight, it also gives clues of what to look for in visible and near-visible light from nearby planets that might have a similar ecosystem or geological makeup.

Clearly visible in the video is the sun's light, glinting off the oceans as Earth spins in view. Where a continent passes, the glint momentarily vanishes. Should a telescope view an extrasolar planet from a similar angle, the same telltale flickering glint could easily indicate the presence of dry land mass and liquid or ice oceans of some kind.

Another sign of a life-bearing planet becomes more visible in near-infrared. Foliage reflects light more strongly in this span of the electromagnetic spectrum, thus a similar pattern of reflections could be the hallmark of Earth-like vegetation.

These ideas are similar to ones published in a paper by University of Florida researchers, which was covered by DailyTech last December. Though many of the ideas are similar, this is the first time hard data has been available to bolster the brain spills. The videos themselves are available at NASA's website in .mov format and can be viewed with either red-green-blue visible light filtering, or infrared-green-blue filtering.

Deep Impact will continue to relay data on the five systems its mission planners have assigned to it as it lingers patiently, waiting for comet Hartley 2 to come calling. In this time it may return more valuable data and further foster ideas on how to identify alien Earths that are not much more than a pixel in images taken by modern telescopes. At worst, the data collected on its target star systems will help astronomers learn about solar systems unlike our own and how their planets interact with their stars and each other.