Subj: Fwd: 1999 RM45: A potential impactor in need of follow up Date: 10/4/99 9:56:57 AM Pacific Daylight Time From: DFranck To: Phikent For your info.... - Don Franck Don Franck's Astronomy Page ----------------- Forwarded Message: Subj: 1999 RM45: A potential impactor in need of follow up Date: 10/4/99 3:20:29 AM Pacific Daylight Time From: chesley@dm.unipi.it (Steve Chesley) Sender: chesley@newton.dm.unipi.it To: mplist@bitnik.com (Minor Planet Mailing List) Dear MPMLers, I have added another potential impactor to the NEODyS Risk Page and it is in critical need of follow up. We have identified potential collision solutions for 1999 RM45 in 2042 and 2050, each with very low probabilities (less than 10^-8). Such a very low probability of impact means that the risk posed by RM45 is not of serious concern to the public at large; however, I think it is very important for the NEO community to take all reasonable and practical steps to ensure that this PHA is not lost, or at least to improve the orbit as much as possible before it does become lost. 1999 RM45 was discovered by LINEAR on September 14th, and observed 38 times over the next six days. It has not been observed since September 20th. The following table provides a crude summary of its brightness and 3-sigma uncertainty on the sky in the coming weeks. Date Magnitude Uncertainty(arcmin) ------------------------------------------------- Now 19.3 +/- 0.5 Mid-Oct. 20 +/- 2 Late-Oct. 21 +/- 5 Mid-Nov. 22 +/- 8 A detailed ephemeris can be obtained from the usual suspects, including NEODyS. One note of caution, the estimate of the brightness has a formal uncertainty of +/- 0.7 magnitudes. It is clear that this is a difficult target, and is already out of reach of many amateur setups, but I expect that it still is a reasonable target for numerous observers during the present dark run. In November it will probably limited to very large (read professional) observatories. An ephemeris based on the nominal orbit indicates that this object will not be observable at brighter than 23rd magnitude until 2008, at which point it will already be lost by a full revolution around the sun. However, the orbit is so uncertain at the present time that it may be observable much sooner than 2008, and orbital improvements now could facilitate a recovery much earlier. Moreover, the two collision solutions we have found are quite far from nominal, thus it is very reasonable to expect that these impacts may be ruled out simply by extending the arc at this apparition. I should be clear that I am not suggesting that we need to devote an inordinate amount of follow up resources to this target; there is obviously a point of diminishing returns. But on the other hand, the fact that this object may not be observable for a very long time, and that it is a PHA with a nonzero probability of collision tells me that this object deserves special attention. Typically it is most efficient to simply extend the arc as long as possible with sparse observations, but in this case that may not be enough. In such a situation, it is valuable to have a more dense set of observations along the available arc to minimize the effect of random errors, and from several observatories to minimize the effect of systematic errors. Steve Chesley University of Pisa