Although we have no direct observations of objects in the Oort Cloud, we may be able to change that with space missions like Kepler and CoRoT. So argue Eran Ofek (Caltech) and Ehud Nakar (Tel-Aviv University) in a recent paper. If they’re right, we’ll improve our understanding of the Solar System’s planetary accretion disk and get a better feel for the dynamics of planet formation. Right now even the largest telescopes can’t find Oort Cloud objects. Where do Kepler and CoRoT fit in?
The answer is that they may be able to observe occultations of background stars, a method that has been put to use for Kuiper Belt Objects already, although to date there is only one reported occultation by a KBO. Ofek and Nakar look at the rate of occultation events, creating an estimate that shows the possibility of Kepler detections of Oort objects and presenting statistical methods that can be used to verify that any occultations are real events and not simply noise in the data. Moreover, they think we should be able to differentiate between Oort objects and KBOs using these methods.
The odds of detection favor Kepler more than CoRoT, but searching the data may surprise us. From the paper:
Considering Kepler capabilities and reasonable Oort Cloud parameters, we find that Kepler may detect 0 to ~ 102 stellar occultations by Oort Cloud objects. We find that Kepler is unlikely to detect Kuiper Belt objects (mainly because of its high ecliptic latitude pointing). Moreover, CoRoT is unlikely to detect Kuiper Belt or Oort Cloud objects. However, the exact properties of the Oort Cloud and the Kuiper Belt are not known. Therefore, such searches are warranted.
True enough, especially when you consider that the occultation rate depends on many things we don’t know, including the mass of the Oort Cloud, the distance to its ‘inner edge’ (now thought to be between 1000 and 3000 AU), and the size distribution of the objects within it. Whether or not we do get Oort object detections from Kepler, these results could be helpful for future space-based exoplanet detection missions, which could add useful observations of events in the outer reaches of our own system to their primary purpose.
The paper is Ofek and Nakar, “Detectability of Oort cloud objects using Kepler,” submitted to Astrophysical Journal Letters and available as a preprint.