07/02/06

Because this question gets to the heart of what we do at Francisquito Observatory, it deserves its own page rather than a short slot on the FAQ list.  We'll address the question on two levels: the big picture - why scientists and policymakers  have an interest in finding out as much as they can about NEAs; and at the small observatory level - why we do what we do at Francisquito.

THE BIG PICTURE ON NEAs

Within the last 50 years or so, scientists have come to understand that at least two mass extinctions of life have occurred on our planet in the distant past: one about 65 million years ago, and another about 250 million years ago.  There is a fairly general consensus among these scientists that the extinction of the dinosaurs 65 million years ago came about as the result of a dramatic change in the Earth's climate, which itself was precipitated in the aftermath of an asteroid or comet impact at the Earth's surface.  Some believe they have identified the remnants of the actual impact crater that was left behind after this cataclysmic event, off the Yucatan Peninsula in the Caribbean Sea.  The link between the mass extinction that occurred 250 million years ago and the impact of an interplanetary object is a current topic of debate among geologists, paleontologists, and astronomers.

Our solar system contains millions of small bodies composed of rock and ice, in addition to the larger planets which we see arcing across the night sky.  These smaller bodies are simply cosmic leftovers from the formation of the Sun and planets.  There is a well-studied, well-understood band of asteroids which orbit the Sun between the orbits of Mars and Jupiter.  These are for the most part harmless as far as we are concerned, as their orbital paths would not normally take them in close proximity to the earth.  There is another class of asteroids, however, which do have orbits that could potentially cross paths with our own planet at some time in the future.  These are categorized as Near Earth Asteroids.  And among these, there is a smaller sub-class, which based on projected orbits for 200 years or so into the future, could present a calculable risk of Earth impact; these are known as Potentially Hazardous Asteroids or PHAs.  Based on some broad assumptions and rough calculations, it is believed that an Earth impact of an asteroid approximately one kilometer in diameter or greater, could produce the kind of effects that would lead to catastrophic, planet-wide disruption of the Earth's ecosystems.

Even if we knew of an imminent threat of impact from a large - say 1km diameter - asteroid, what could be done about it?  There is no simple answer to this question.  If we discovered a 1km diameter asteroid tomorrow on a trajectory that indicated an Earth impact in 3 months, there is little if anything that could be done to divert it or mitigate the devastating effects of an impact.  If we had 20 or 30 years advance warning, then our options for taking effective action are greatly multiplied, and the chance of a successful intervention rises to a realistic level.  And having a 20-year forewarning of an Earth-crossing orbit for an NEA is entirely possible, and in fact quite likely for a larger-sized object.  One rough calculation done recently indicated that a 1km diameter asteroid that was 20 years away from a projected collision with the Earth could have its momentum vector modified by just a few fractions of a percent with the amount of energy available in the Space Shuttle main engine/booster combination, and that this extremely small change in momentum would be sufficient to avoid an Earth impact 20 years later.

The total number of NEAs which may fall into this critical size classification - 1km in diameter or larger - is also being debated among scientists.  Right now the estimated number seems to range between 1,100 and 2,500.  As of early 2004, just over 700 NEAs believed to be larger than 1km in diameter have been identified and have reasonably precise orbits calculated for them.  The good news is that none of these are believed to pose a significant risk of Earth impact within the next 200 years.  The bad news is that there are many NEAs which have yet to be discovered and their orbits calculated.  Five years ago NASA initiated a program now referred to as the Spaceguard Survey.  The stated goal of the survey has been to discover at least 90% of all NEAs over 1km in diameter during a 10-year period.  NASA believes they are on track to achieve this objective. The survey operates a number of large telescopes located in Arizona and New Mexico, which scan the sky from dusk to dawn, looking for moving objects with orbits that would be characteristic of an NEA.  These telescopes can each cover their visible sky within a 1- to 2-week period of time, and then repeat the process week after week, month after month.  Other research telescopes at places like Mt. Palomar, California and  Haleakala, Hawaii contribute to the NEA search on a part-time basis.  Some interesting insights into the significance and progress of the search for NEOs/NEAs is found in testimony given by Dr. Lindley Johnson, program manager of NASA's NEO observation program, at a U.S. Senate hearing on April 7,2004.  A transcript of Dr. Johnson's testimony is reproduced here.  Dr. Johnson also makes a couple of references to the importance of work done by observatories such as Francisquito.  Which leads us into the next topic.

WHY NEA OBSERVATIONS AT FRANCISQUITO?

When a suspected NEA is first discovered - say by one of the large research telescopes involved in the Spaceguard Survey, the Minor Planet Center immediately posts a worldwide call for confirmation observations.  The survey telescopes need to continue their broad survey of the sky and generally cannot afford the time to go back and make repeat observations of prospective NEA discoveries.  The Minor Planet Center depends on other observatories, both professional and non-professional to make the critical confirmation and follow-up observations.  The initial discovery observations define a very short arc through the sky, and there are a large number of possible orbital paths that could be fit to the same set of observations.  With each successive set of observations, the number of possible orbital solutions decreases, until eventually a single 3-dimensional orbital path is uniquely defined.  This process usually takes a few days of observations to a few weeks, until hopefully the NEA's orbit is well enough defined to be able to predict its return after its next trip around the Sun.  And on any given night, there may only be 10 to 15 observatories worldwide that meet the following criteria: 1) are sufficiently equipped and experienced for precision astrometry of fast moving NEAs; 2) are enjoying good enough weather to conduct observations at their particular location; and, 3) are operationally available to take on a new NEA astrometry assignment that night.  Thus, each observatory involved in NEA astrometry is extremely important to the overall effort.

When establishment of the Francisquito Observatory was first being contemplated, there was thought to make it a purely recreational facility, with an emphasis on astrophotography.  However, after accidentally stumbling onto the Camarillo Observatory's web site, there was no doubt as to which path Francisquito would take.  Here was an opportunity to explore the cosmos in a very "hands-on" fashion, and to make a significant and valued contribution to science at the same time.  And that's how, and why, we got into the NEA astrometry biz.