Re: Smart 1 will crash on the moon

From: Richard Clark (rclark@lpl.arizona.edu)
Date: Sun Jan 29 2006 - 04:52:00 EST

  • Next message: Peter Wakelin: "SATOBS 2006 January 28-29"

    Hello Tristan,
    
    Have you heard much response from this request?
    
    Observations of lunar impacts have been made in the past few years.
    The Leonid meteors have a particularly high relative velocity when
    they intersect the Earth and Moon. Their impact flashes on the lunar
    nightside have been observed. Most meteors do not produce visible impact
    flashes-- at velocities under ~40km/sec (not sure what the lower threshold
    is) the specific energy is too low to efficiently produce light in the
    visible range.
    
    An impact "fireball" was observed when the Japanese Hiten probe hit
    the lunar surface in the mid 90s. However, what was sseen then was
    the ejecta plume. The moon was ~3 days past new and the impact was
    in the unlit region, but fairly near the teminator so much of the
    ejecta was thrown up into sunlight. It was visible for close to a
    minute before falling back into shadow.
    
    This also is very likely the explanation for an event observed and
    photographed back in the 50s. The impact/illumination circumstances
    were similar to Hiten. It was discussed in the correspondence pages
    of Sky & Telescope about 2 years ago. Attempts to analyze the impact
    based on the false assumption that what was observed was the initial
    impact flash yielded a prediction of a sizeable crater which, of course,
    was not detected on high resolution images of the impact area. What was
    seen was the ejecta plume, just as with Hiten.
    
    At its low impact velocity the most useful observations of the Smart-1
    impact will likely be in studies of ejecta dynamics and crater
    morphology. The latter will require high resolution imaging from lunar
    orbit.  Have any decisions been made regarding the exact timing and
    targeting?
    
    Richard Clark
    Global Oscillation Network Group
    National Solar Observatory
    Tucson, AZ.
    
    
    On Wed, 18 Jan 2006, Tristan Cools wrote:
    
    > Hello,
    >
    > Hopefully this is 'on topic'...
    >
    > I've got this from a Belgian Astronomical mailing list but this must
    > have been posted somewhere before.
    > Can someone tell us if the impact of Smart 1 will show us something ?
    >
    > Some results of remaining impact craters of SIVB's and Rangers are
    > known but these are the only ones I've ever found:
    > http://www.hq.nasa.gov/office/pao/History/SP-362/ch5.2.htm
    >
    > I believe a previous impact observation attempt resulted in zero
    > observations, although it crashed into the polar regions.(can't
    > recall its name however)
    >
    >
    > With the SMART-1 end of mission impact due in August
    > || > > 2006, we are looking at
    > || > > the possibility of using our last hydrazine fuel, to
    > || > > adjust the impact date
    > || > > and move the impact to the near side, and allow to
    > || > > perform an impact
    > || > > experiment, involving ground based observers.
    > || > >
    > || > > The impact of the 290 kg spacecraft will take place
    > || > > at a speed of 2 km/s in a
    > || > > very grazing trajectory in a latitude of around -37
    > || > > deg.
    > || > >
    > || > > I wish to call on the expert community to make as
    > || > > early as possible
    > || > > predictions of the impact flash (in visible and
    > || > > infrared), ejecta dynamics,
    > || > > dust and exospheric effects and to look at
    > || > > possibility of coordinated ground
    > || > > based observations.
    > || > >
    > || > > I would appreciate if you could contact me ASAP to
    > || > > indicate your interest to
    > || > > participate to the impact prediction exercise or to
    > || > > the observations
    > || > > campaign.
    > || > >
    > || > > We call also the community to collaborate in
    > || > > coordinated lunar observations,
    > || > > especially when SMART-1 perilune will be at
    > || > > altitude below 300 km from June
    > || > > until impact.
    > || > >
    > || > > Best regards,
    > || > > Bernard H. Foing
    >
    >
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