Pan-STARRS and the OOC

Normally astronomy discovers new Outer Solar System objects pretty slowly – a telescope stares at a patch of sky for a while, a few days in a row, and anything that moves relative to the “fixed” stars is further analysed. Is it something we already know? is the first question. Then its orbit is further refined… and the telescope has to move on to other things. If what you’ve spotted is something really excited, then you might be able to book some time on the Keck or the HST, but that’s really expensive.

But now something different is watching the sky – ALL of it. At least the bit that can be watched from Hawaii. A large, dedicated telescope is taking all-sky images and monitoring the whole sky over several years. They’re hoping to spot all sorts of odd things, as well as Earth-threatening comets and asteroids. The observation program is called Pan-STARRS and it will, by 2012, have 4 1.8 metre telescopes ganged together to form a single 3.6 metre aperture. From its Hawaiian locale Pan-STARRS will observe about 30,000 square degrees of sky. (there’s 41,253 square degrees total, thus Pan-STARRS covers ~73% of the total sky.) Because it uses a specially designed CCD, of 4800×4800 pixels, it is able to record a relatively large patch of sky down to about magnitude 24, and a whole-sky observation can be made in about 40 hours observing time (typically 4 nights.) The astronomers are hoping to make whole sky observations about 4 times a month.

Here’s the homepage… Pan-STARRS

A consortium of Universities and the like will run the first scope… PS1 Science Consortium …but we’ll have to wait until 2012 for all four to be up and running to full strength.

Being such a new kind of high magnitude observing there’s the potential for a whole bunch of new phenomena to be observed – variables of new varieties, optical transients of all sorts, and who knows what else. From an Outer Solar System perspective the system will discover thousands upon thousands of Trojans, comets, KBOs, Plutoids, Centaurs and various odds and ends. The catalogues of such objects will swell enormously.

But what else? Just how far out is Pan-STARRS going to let us see at a limiting magnitude of 24?

Well “New Scientist” asks “Is there a Planet X?” Pan-STARRS might track it down.

Ian O’Neill asks a similar question at astroENGINE… Where is Planet X? Where is Nemesis?

Ian pointed out a paper by uber-Kuiper Belt guru, Dave Jewitt, from 2004 which gives limits for Pan-STARRS observations of various objects. Interestingly Plutos will be detected down to the M = 24 limit out to 300 AU.

V (1 AU) is the apparent magnitude of the object as seen at 1 AU; R(M=24) is the radius at which the object is seen at magnitude 24; and Rgrav is the radius at which the objects gravity would already be noticed by its perturbations. As you can see Pan-STARRS will cover a huge volume around the Sun, picking up any Jupiter-sized body out to 0.034 light-years.

Lorenzo Iorio has updated the gravitational minimum distance limits based on the motions of the Inner Planets, for which we have the best orbital data. Mars-mass, Earth-mass, Jupiter-mass and Sun-mass objects can orbit around the Sun at radii of 62 AU, 430 AU, 886 AU and 8995 AU respectively, without being noticed in current orbital data. Of course we would SEE a Sun-like star at 8,995 AU as a -1 magnitude star, so it’s definitely ruled out, but red-dwarfs or brown-dwarfs would be much harder to see.

Of course that’s just the Inner Opik-Oort Cloud (Inner OOC) covered for large bodies. Any Earths or Plutos in the OOC will be missed if they’re too dark – Earth and Pluto reflect about 30% and 60% of the incident light, but if they were as dark as some KBOs, down to albedos of just 0.1-0.06, then they’ll be largely invisible. However once Pan-STARRS proves the technology of combining the images from 4 scopes, then virtual apertures of arbitarily large sizes will be possible for anyone who wants to fund such a large scale search in the future. A similar set-up on the Farside of the Moon, or the moons of Jupiter, will eventually allow a very comprehensive survey out into the depths of OOC. Nothing of decent size will be able to hide from prying eyes…