Pan-STARRS

Pan-STARRS (an acronym for Panoramic Survey Telescope And Rapid Response System) is a planned astronomical survey that will conduct astrometry and photometry of much of the entire sky on a continuous basis. By detecting any differences from previous observations of the same areas of the sky, it is expected to discover a very large number of new asteroids, comets, variable stars and other celestial objects. Its primary mission is to detect near-Earth objects that threaten to cause impact events. It is expected to create a database of all objects visible from Hawaii (three-quarters of the entire sky) down to apparent magnitude 24.

The Pan-STARRS is a collaboration between the University of Hawaii Institute for Astronomy, MIT Lincoln Laboratory, Maui High Performance Computing Center and Science Applications International Corporation. Telescope construction is funded by the US Air Force. Once PS1 reaches the milestone of passing its Operational Readiness Review, expected Fall 2008, the Pan-STARRS Project will focus on building PS4.

The operations for the first Pan-STARRS telescope (PS1) are funded by The PS1 Science Consortium or PS1SC a consortium including the Max Planck Society in Germany, National Central University in Taiwan, Edinburgh, Durham and Queen's, Belfast Universities in the UK, and Johns Hopkins and Harvard Universities in the USA and the Las Cumbres Observatory Global Telescope Network.

Instruments

Pan-STARRS will use four 1.8 m telescopes that will be located either at Mauna Kea or Haleakala in Hawaii. All four telescopes in the final 'PS4' system will point in the same direction: data will be compared to remove CCD artifacts due to chip defects and bad pixels and cosmic rays, and then the light input will be summed to give the equivalent of a single 3.6 m telescope. Funding has been obtained to construct all four telescopes.

A prototype telescope 'PS1' has been constructed, and saw first light using a low-resolution camera in June 2006. The telescope has a 3° field of view, which is extremely large for telescopes of this size, and is equipped with the largest digital camera ever built, recording 1.4 billion pixels per image. A 64 × 64 array of orthogonal transfer CCDs (OTCCDs) is used in the camera, with each component CCD being roughly 600 × 600 pixels. This gigapixel camera or 'GPC' saw first light on August 22, 2007, imaging the Andromeda Galaxy.

Each image requires about 2 gigabytes of storage and exposure times will be 30 to 60 seconds (good enough to record objects down to apparent magnitude 24), with an additional minute or so used for computer processing. Since images will be taken on a continuous basis, it is expected that 10 Terabytes of data will be acquired by 'PS4' every night. Because of this very large volume of data, the computer processing will record the positions and magnitudes of all objects in the image after which the image itself will be discarded. Comparing against a database of known unvarying objects compiled from earlier observations will yield objects of interest: anything that has changed brightness and/or position for any reason.

The very large field of view of the telescopes and the short exposure times will enable approximately 6000 square degrees of sky to be imaged every night. The entire sky is 4π steradians, or 4π × (180/π)² ≈ 41,253.0 square degrees, of which about 30,000 square degrees are visible from Hawaii, which means that the entire sky can be imaged in a period of 40 hours (or about 10 hours per night on four days). Given the need to avoid times when the Moon is bright, this means that an area equivalent to the entire sky will be surveyed four times a month, which is entirely unprecedented.

The project is believed to be achievable with existing technology, although on a larger scale than anything previously attempted.

Science

Systematically surveying the entire sky on a continuous basis is an unprecedented project and is expected to produce a dramatically larger number of discoveries of various types of celestial objects. For instance, the current leading asteroid discovery project LINEAR only goes down to apparent magnitude 19 and concentrates its searches mostly near the ecliptic; Pan-STARRS will go five magnitudes fainter and cover the entire sky visible from Hawaii.

Solar system

In addition to large number of expected discoveries in the main asteroid belt, Pan-STARRS is expected to detect at least 100,000 Jupiter Trojan asteroids (compared to 1800 known as of mid-2005); at least 20,000 Kuiper belt objects (compared to 800 known as of mid-2005); thousands of Trojan asteroids of Saturn, Uranus and Neptune (currently only four Neptune Trojans are known, and none for the other planets excluding Mars and Jupiter); and large numbers of Centaurs and comets.

Apart from drastically adding to the number of known solar system objects, Pan-STARRS will remove or mitigate the observational bias inherent in many current surveys. For instance, among currently known objects there is a bias favoring low orbital inclination, and thus an object such as escaped detection until recently despite its bright apparent magnitude of 17, which is not much fainter than Pluto. Also, among currently known comets there is a bias favoring those with short perihelion distances. Reducing the effects of this observational bias will enable a more complete picture of solar system dynamics. For instance it is expected that the number of Jupiter Trojans larger than 1 km may in fact roughly match the number of main asteroid belt objects, although the currently known population of the latter is several orders of magnitude larger.

One intriguing possibility is that Pan-STARRS may detect "interstellar debris" or "interstellar interlopers" flying through the solar system. During the formation of a planetary system it is thought that a very large number of objects are ejected due to gravitational interactions with planets (as many as 10¹³ such objects in the case of our solar system). Objects ejected by planetary systems around other stars might plausibly be flying throughout the galaxy and some may pass through our solar system.

Another intriguing possibility is that Pan-STARRS may actually detect collisions involving small asteroids. These are quite rare and none have yet been observed, but with the drastically larger number of asteroids that will be discovered it is expected from statistical considerations that some collision events may be observed.

Pan-STARRS will also likely detect a number of Kuiper belt objects the size of Pluto or larger, similar to Eris.

Beyond the solar system

It is anticipated that Pan-STARRS will discover an extremely large number of variable stars, including such stars in other nearby galaxies; in fact, this may lead to the discovery of hitherto unknown dwarf galaxies. In discovering a large number of Cepheid variables and eclipsing binary stars, it will help determine distances to nearby galaxies with greater precision. It is expected to discover a large number of Type Ia supernovae in other galaxies, which are important in studying the effects of dark energy, and also optical afterglows of gamma ray bursts.

Because very young stars (such as T Tauri stars) are usually variable, Pan-STARRS should discover a large number of these and improve our understanding of them. It is also expected that Pan-STARRS may discover a large number of extrasolar planets by observing their transits across their parent stars, as well as gravitational microlensing events.

Pan-STARRS will also measure proper motion and parallax and should thereby discover a large number of brown dwarfs and white dwarfs and other nearby faint objects, and it should be able to conduct a complete census of all stars within 100 parsecs of the Sun. Prior proper motion and parallax surveys often did not detect faint objects such as the recently-discovered Teegarden's star, which are too faint for projects such as Hipparcos.

Also, by identifying stars with large parallax but very small proper motion for followup radial velocity measurements, Pan-STARRS may even be able to permit the detection of hypothetical Nemesis-type objects if these actually exist.