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.
Interesting. Can it detect giant planets?m Something the size of Jupiter or Saturn should occult stars even more. It might be an easier method than looking for infrared signatures.
So… a star blinks on and off. Then what? Given that the the Oort cloud is supposedly spherical and that therefore, orbits are arbitrariy inclined, we would need a follow-up observation of another star blinking on and off (probably at least 3, before any conclusion could be drawn). Don’t want to be a wet blanket here, but…
arbitrarily, I mean…
djlactin writes:
The paper argues that as many as 100 occultations could be expected, or as few as zero. One wouldn’t be terribly useful, perhaps, but 50 might be.
Kepler is to observe sun-like stars for terrestrial-sized bodies. Might occultations of stars of lower luminosity, such as M dwarfs, yield useful data?
Were Oort object occultations detected by Kepler, they might be characterized. At the least, a preliminary census of objects could come of this part of the sky. And Kepler has potential for serendipitous discoveries…
Wouldn’t the characteristics of the occultation differ enough from transits or stellar variations to allow them to be identified as occultations by solar system objects? Say the timing and shape of the light curve?
Speaking of Kepler those safe mode events are giving me grey hairs.
Lets hope they don’t become a major problem for the mission.
Off-topic but important enough, two news items:
Report about planets orbiting binary stars, confirming that a (lasting) protoplanetary disc around such binaries, and hence planets, is well possible (didn’t we know that already?).
http://www.universetoday.com/2009/12/10/forming-planets-around-binary-stars/
And a much more fascinating article (the official publication isn’t out yet) about the discovery of two very solar system like (sets of) exoplanet. One of these discoveries consists of 3 planets orbiting 61 Virginis at almost 28 light years. It seems that the system is reminiscent of a quite solar system like situation (quote: ‘planets’ masses ranging from 5.3 to 24.9 Earth masses’), but, annoyingly, the article, or any that I could find on this news topic, does not mention any orbital radius (AU), nor eccentricity. The extrasolar planets encyclopedia does not even mention it yet, it’s that fresh.
http://www.telegraph.co.uk/science/space/6808239/Discovery-of-new-planets-raises-hopes-of-other-life-in-universe.html
Not an Oort Cloud object, but quite relevant to the subject: the discovery of the smallest known Kuiper Belt object by detecting it passing in front of a background star, using the Fine Guidance Sensors on Hubble.