NASA’s workshop on identifying objectives for missions to near-Earth objects will be held next week, August 10-11 at the Renaissance Mayflower Hotel in Washington, DC. We can hope that this gathering of NASA leaders, academics, and space experts from across the international community will help keep the public’s attention on the need for such missions. Part of the reason for having the workshop is to communicate NASA’s preliminary plans for a human mission to an NEO, a useful step as we build expertise about these objects and ponder strategies to handle any future impact scenarios. You can follow the video stream at the appropriate time here.

Meanwhile, the continuing survey of near-Earth objects has produced another one, asteroid 101955 1999 RQ36, with a slight impact possibility in 2182. We can call this object a Potentially Hazardous Asteroid (PHA) based on the results from the two mathematical models — Monte Carlo Method and line of variations sampling — being used to study it. The object was discovered in 1999 and is about 560 meters in diameter. You would think that after 290 optical observations and thirteen radar measurements, the orbit of this asteroid would be well understood, but complicating the matter is the so-called Yarkovsky effect.

Russian civil engineer Ivan Yarkovsky (1844-1902) noted the eponymous effect by studying how rotating objects in space experience thermal changes over time. He realized that their orbits can be modified because a rotating small object heats unevenly. The Estonian astronomer Ernst Öpik applied Yarkovsky’s ideas to small objects like meteoroids in the Solar System, and the effect was first measured (1991-2003) on the asteroid 6489 Golevka, which was observed to have moved 15 kilometers from its predicted position over twelve years of observations. Because the effect depends on size, it can be significant on smaller asteroids and negligible on larger ones.

Even so, over the course of time, asteroids can be perturbed enough to move out of the main belt and into the inner system. The problem is that the Yarkovsky effect on a particular asteroid can be hard to predict because of variables like the asteroid’s shape and albedo. Moreover, a close approach to the Earth can modify the orbit so that, in the words of the paper on this work, “…the problem becomes like that of a newly discovered asteroid with a weakly determined orbit.” A close pass, in other words, can confound what had been a precisely determined orbit.

María Eugenia Sansaturio (University of Valladolid), co-author of a paper on 1999 RQ36 that ran last year, explains that the object’s projected movement can only be measured in probabilities:

“The total impact probability of asteroid ‘(101955) 1999 RQ36’ can be estimated in 0.00092 – approximately one-in-a-thousand chance-, but what is most surprising is that over half of this chance (0.00054) corresponds to 2182.”

But what is more telling is the scientist’s take on our chances of deflecting such an asteroid. The research, published in Icarus, notes that the object approaches the Earth between 2060 and 2080, making another approach in 2162 and another in 2182, deemed the most likely year for a collision if one is going to occur. If moving an asteroid is the objective, the longer the lead time, the better:

“The consequence of this complex dynamic is not just the likelihood of a comparatively large impact, but also that a realistic deflection procedure (path deviation) could only be made before the impact in 2080, and more easily, before 2060… If this object had been discovered after 2080, the deflection would require a technology that is not currently available. Therefore, this example suggests that impact monitoring, which up to date does not cover more than 80 or 100 years, may need to encompass more than one century. Thus, the efforts to deviate this type of objects could be conducted with moderate resources, from a technological and financial point of view.”

I take that last sentence to mean that it will be cheaper and more within the range of our near-term technology to deflect an object whose orbit is determined to be dangerous if we have a century or more to prepare. The necessary refinements of orbital calculations continue during this period, allowing us to rule out the impact possibity altogether or to study the object further if the odds on a strike increase. Continued attention to maintaining facilities like Arecibo, whose planetary radar can help us track such objects, should be a paramount part of our overall space policy.

The paper is Sansaturio et al., “Long term impact risk for (101955) 1999 RQ36,” published online in Icarus, Vol. 203, Issue 2 (October, 2009), pp. 460-471 (abstract / preprint).