2008 TC3 final trajectory 2008 TC3 final trajectory Explosion of 2008 TC3 from above 2008 TC3 was car- sized rock (2 - 5 meters across) that hit the Earth's atmosphere and exploded over Sudan on October 7, 2008. Rocks this size hit the Earth several times a year- what was special about this rock is that it the *first* natural space object that was observed out in space and predicted to hit the Earth. The explosion had an energy of about 2 kilotons (or 0.002 MT) of TNT (about 1/10 the yield of the WWII A-bombs). The airburst explosion was imaged from above by a Europen weather satellite (2nd picture).
From intensive observations over the time from discovery until collision (only about 20 hours!) we know that 2008 TC3 had been orbiting the sun every 1.50 years, with a semimajor axis of 1.31 AU, an orbital eccentricity of 0.31 and an inclination of 2.5 degrees. The speed in its orbit was not too different from the Earth's speed and it hit the Earth at a relatively low speed (about 12 km/sec), which is not much above Earths escape speed.
NEA discoveries last 15 years Histogram of discovery observatories of NEAs (Near Earth asteroids) since 1994. (This graph uses a pretty loose definition of NEAs). How things have changed since the pioneering days of the Shoemakers! Note that, prior to about 1998, only a handful of NEAs were found each year. In 1998 the LINEAR survey (blue bars) (see below) started up and found the majority of the NEAs until about 2005. Around 2004, the Catalina Sky Survey (purple) ( see below) started and it has found the most NEAs for the past few years.
A quick glance shows that several thousand NEOs have been found in the last 15 years. Many of these are smaller than the 1 km size usually taken as objects with "global" impact.
LINEAR site The LINEAR (LIncoln labs Near Earth Asteroid Research) operates several meter-class telescopes near White Sands New Mexico. It is an Air Force / NASA /MIT project to find NEAs and, as shown in previous histogram, dominated the search from about 1998 to 2004.
Catalina Sky Survey 1.5meter (Arizona) Catalina Sky Survey 0.5meter (Australia) There are several telescopes that together have found the bulk of the NEAs so far known. One survey, known as the Catalina Sky Survey (CSS) associated with the U. of Arizona (on of the powerhouse universities in the astronomy world, and the place where drbill got his PhD) operates a 1.5 meter telescope near Tucson (first image- the streak of light behind dome is the International Space Station) and an associated 0.5 meter telescope in Australia (second image). By modern research telescope standards, these are modest, if not downright TINY, telescopes. The success of these modest telescopes in finding NEAs comes partially from their relatively wide fields, but mostly from the sophisticated software that is used to process the images, usually in near real time, to find moving objects. Telescopes of this size can image about a billion different stars- finding a few moving dots of light amongst these is a real tour de force of programming and image processing!
Pan-STARRS -- the Panoramic Survey Telescope & Rapid Response System The next "big thing" in NEA work will be Pan-STARRS. This is a set of 4 1.8 meter telescopes located on Haleakala, Maui HI. Each scope will have a 1.4 billion pixel camera. The first telescope, PS1, and camera are now being tested.
Large Synoptic Survey Telescope (LSST) Perhaps by the middle of the next decade, the LSST will be working. The proposed LSST will have a mirror roughly equal in size (8.4 meters) to the mirrors in the largest telescopes now operating, but will operate quite differently from other large telescopes. Current large telescopes can only look at a very small part of the sky at once. The LSST will be able to look at a much larger piece of sky. The LSST will take very detailed pictures covering the ENTIRE SKY every few nights. Current big telescopes would require years or decades to take pictures covering the entire sky. The LSST will allow astronomers to do many types of projects, including searching for asteroids that might someday hit the Earth. If the $300 million can be found to build the telescope, it could be operating around 2016. The data will be made public immediately. This will allow astronomers from anywhere to do their own research using the data. Although there are current astronomical data archives that allow public access to vast amounts of data, such as the HST archives, this telescope should mark a new way to obtain and deal with optical images from large groundbased telescopes. There is, of course, a website: www.lsst.org.
Large Synoptic Survey Telescope optics To make a large telescope that can cover a 3 degree wide field of view, LSST designers invented a radical optical system. The main mirror has a unique "mirror within a mirror" configuration.
Large Synoptic Survey Telescope optical path The light comes from the top, hits mirror M1, bounces up to mirror M2, then down to M3 (which is physicaly part of M1), then up through several lenses to come to a focus above the set of 3 lenses. The bottom of the 3 lenses will be 1.5 meter across, the largest precision lens ever made.
Large Synoptic Survey Telescope mirror blank The LSST main mirror is 8.4 meters across - thats about 9.2 yards, so, as I tell undergrads in intro astronomy "its almost a first down".
The mirror is not a solid disk of glass (it would be VERY heavy and impossible to cool downto night time temperature, inducing optical turbulence). Instead it is a solid thin disk on top supported by a honycomb glass structure, which can be seen through the top sheet of glass and along the sides. These mirrors are made by first making a mold of "cores" which define where the glass isn't, filling up the mold with chunks of glass, then melting the glass in a giant rotating oven (located under the football stadium at the University of Arizona). The melted rotating glass mass forms a concave shaped surface (meaning there is much less glass to figure away when the mirror is being ground and polished) and is cooled slowly to preserve that shape. This process, invented by UA professor Roger Angel (in red shirt at far side of mirror) has been used for many of the largest telescope mirrors.
Model of detector for LSST camera The camera for the LSST will use a large number of individual CCDs (electronic "film") arranged in a big array. This is an "actual size" model of the array. Each little square is a CCD bigger and more sensitive than the best digital camera chip. All together, the camera will have about 3.2 Billion pixels, or individual "dots" in the image. In terms of digital camera advertising, this is a "3200 megapixel" camera!! The camera will produce a staggering amount of digital data each clear nite, and the guys from Google are planning to help deal with the tremendous data flow. Each clear *nite*, the camera is expected to generate about 10 TeraBytes of digital images!!
Comparison of existing and proposed sky surveys One quick figure of merit for sky surveys is the "etendue", which is derived by multiplying the collecting area of a telescope (in square meters) by its field of view (in square degrees). Current productive NEA surveys (CSS and LINEAR) have etendue around 1. The LSST will have an etendue of 300, so that, roughly speaking, the LSST will be able to do in a single night what LINEAR does in a year!!
NEO orbit types These are names given to subtypes of asteroid orbits that are considered at "Near Earth Objects" (NEOs).
NEO number vs size Essentially an updated version of plot as that shown the other day from Shoemaker (1982). This is from a 2007 NASA report to Congress on the NEO situation. Congress has asked NASA to study how we can find 90% of NEOs bigger than 140 meters by the year 2025. Objects 140 meters (about size of OU football stadium) hit the Earth every few millennia, with the impact energy of hundreds of megatons of TNT (that is, energies multiple times the largest H-bombs ever detonated). As you can see from this plot, the current estimate is that there are 100,000 such objects!!