When you have assets in space, the thing to do is redeploy them as needed. That creates what’s called an ‘extended mission,’ and the latest spacecraft to get one is Deep Impact, the vehicle whose impactor made such a splash when it was driven into comet Tempel 1 in the summer of 2005. That July 4 explosion was memorable enough, but under the name EPOXI the doughty craft leaves its vaporized impactor behind and moves on to two other missions, one of which has direct extrasolar applications.

For one of EPOXI’s twin goals is to observe five nearby stars known to have transiting exoplanets. Observations began on January 22. The ‘hot Jupiters’ around the five stars have been confirmed previously, but EPOXI’s mission is to see whether any of these transiting gas giants is accompanied by other worlds in the same stellar system. Perhaps the most intriguing aspect of the investigation is summed up by Drake Deming (NASA GSFC): “We’re on the hunt for planets down to the size of Earth, orbiting some of our closest neighboring stars” (italics mine).

Such worlds might be making transits of their own, but transit timing of the known gas giants will tell the tale, the gravity of the unseen world perturbing the transit of the larger. Deep Impact may not have been designed for this work, but the prospects are exciting. What stands out about recent exoplanet findings from space is the success of COROT, once thought to be a relatively modest mission compared to efforts like Kepler and the much more ambitious Darwin, yet a spacecraft that is producing results far beyond what many of us had expected. Can Deep Impact, under its new name, make a successful transition and surprise us again?

Nor is exoplanet hunting the only goal of the extended mission. EPOXI is actually a conflation of two missons: Extrasolar Planet Observation and Characterization, as just discussed, and the Deep Impact Extended Investigation, aimed at taking a close look at comet Hartley 2 with a flyby on October 11, 2010. So the cometary challenge remains, but wouldn’t it be extraordinary if we turn what had been Deep Impact into the platform that flags the first Earth-sized exoplanet? We’ll also learn much about those hot Jupiters, including information about their atmospheres and the possibility that one or more may have moons or rings.

Keep your own eyes on EPOXI’s blurry vision. As discussed in these pages back in July, the Deep Impact telescope is out of focus, which actually makes for better photometry, allowing the system’s CCD to collect more photons before it becomes saturated. Drake Deming explained this puzzling point to Emily Lakdawalla last summer: “With a defocused image, we have about 75 pixels collecting light for us, so we can collect lots of photons in each exposure without saturating, and that gives us the high signal-to-noise ratio that we need.”

A blurry view, then, may be just the ticket as we go hunting for planets of Earth size and above. A final EPOXI aim: To observe the Earth in visible and infrared wavelengths. Looking back at our own terrestrial world provides useful data points when we begin to collect information about such worlds around other stars. All this from a mission that’s clearly a long way from exhausting its useful life, making the case that if you build the hardware right, the mission possibilities continue to grow.