Dr. Deming, Principal Investigator (PI) for the EPOCh portion of the mission
EPOCh observations resumed on May 4, as the spacecraft telecom anomaly has disappeared at greater Sun range. EPOCH is now observing transits of the Neptune-sized planet orbiting the nearby (d=10 pc) red dwarf star GJ436. The orbit of this planet is known to have a significant eccentricity (e=0.15), and this eccentricity is believed to be forced by the gravitational perturbations from a second planet. The second planet may have a mass comparable to Earth, and the EPOCh team believes it has an orbital period in the range from 20 to 30 days. Because this star is small and much less luminous than the Sun, the second planet may be close to or within the habitable zone. So searching for this "exo-Earth" is a high priority for EPOCh. EPOCh has two ways to find it. First, it may lie in the same orbital plane as the Neptune-sized planet, and may therefore transit the star while EPOCh is watching. In that case EPOCh can measure its radius, and we will be sensitive to planets nearly as small as our own Earth! A second method EPOCH is using involves looking for changes in the transit characteristics of the Neptune-sized planet, produced by the gravitational perturbations of the exo-Earth. In this case too, EPOCh has excellent sensitivity. So this is an exciting time for EPOCh, as we search for an exo-Earth orbiting a stellar neighbor of our Sun!
On May 29 and June 5, EPOCh will again turn the EPOXI telescope toward our own Earth, and observe it in the visible and infrared for a full rotation. These data will be used to characterize the "Earth as an exoplanet," essentially to calibrate the properties of possible "pale blue dots" that may eventually be imaged by advanced missions such as the Terrestrial Planet Finder. The May 29 observations will be especially interesting because the Moon will "transit" the Earth while EPOCh is watching, and this is a view of the Earth-Moon system that has seldom if ever been seen before.