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  • Bruce Kamiat
    A list for asteroid and comet researcher ... From: mpml@yahoogroups.com To: mpml@yahoogroups.com Sent: Friday, November 04, 2011 12:07 PM Subject: {MPML}
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      A list for asteroid and comet researcher



      ----- Original Message -----
      From: mpml@yahoogroups.com
      To: mpml@yahoogroups.com
      Sent: Friday, November 04, 2011 12:07 PM
      Subject: {MPML} Digest Number 3967


      A list for asteroid and comet researcher

      1. Dawn Journal - October 31, 2011 From: Ron Baalke
      2. EPOXI Mission Status Report - October 20, 2011 From: Ron Baalke
      3. EPOXI Mission Status Report - November 1, 2011 From: Ron Baalke

      1. Dawn Journal - October 31, 2011
      Posted by: "Ron Baalke" baalke@...
      Thu Nov 3, 2011 10:30 am (PDT)

      http://dawn.jpl.nasa.gov/mission/journal_10_31_11.asp

      Dawn Journal
      Dr. Marc Rayman
      October 31, 2011

      Dear Dawnderfuls,

      Dawn has completed another wonderfully successful phase of its
      exploration of Vesta, studying it in unprecedented detail during the
      past month. From the time of its discovery more than two centuries ago
      until just a few months ago, this protoplanet appeared as hardly more
      than a fuzzy blob, an indistinct fleck in the sky. Now Dawn has mapped
      it with exquisite clarity, revealing a fascinatingly complex alien world.

      The high altitude mapping orbit (HAMO) includes the most intensive and
      thorough imaging of the entire year Dawn will reside at Vesta.
      Spectacular as the results from survey orbit were, the observations from
      HAMO are significantly better. From four times closer to the surface,
      Dawn's sensors provided much better views
      of the extraordinary surface of craters large and small, tremendous
      mountains, valleys, towering cliffs, ridges, smooth and flat regions,
      gently rolling plains, systems of extensive troughs, many clusters of
      smaller grooves, immense landslides, enormous boulders, materials that
      are unusually bright and others that are unusually dark (sometimes
      adjacent to each other), and myriad other dramatic and intriguing
      features. There is no reason to try to capture in words what visual
      creatures like humans can best appreciate in pictures. To see the sites,
      which literally are out of this world, either go to Vesta or go here
      <http://dawn.jpl.nasa.gov/multimedia/imageoftheday/archives.asp>.

      Circling the colossus 680 kilometers (420 miles) beneath it in HAMO, the
      probe has spent most of its time over the illuminated side taking
      pictures and other scientific measurements and most of the time over the
      dark side beaming its precious findings back to eager Earthlings.

      Dawn revolves in a polar orbit around Vesta, passing above the north
      pole, then traveling over the day side to the south pole, and then
      soaring north over the night side. Each circuit takes 12.3 hours.
      Meanwhile, Vesta completes a rotation on its axis every 5.3 hours.
      Mission planners choreographed this beautiful cosmic pas de deux by
      choosing the orbital parameters so that in 10 orbits, nearly every part
      of the lit surface would come within the camera's field of view.
      (Because it is northern hemisphere winter on that world, a region around
      the north pole is hidden in the deep dark of night. Its appearance in
      Dawn's pictures will have to wait for HAMO2.) A set of 10 orbits is known
      to Dawn team members (and now to you) as a mapping cycle.

      Although the HAMO phase was extremely complex, it was executed almost
      flawlessly, following remarkably well the intricate plan worked out in
      great detail last year. It consisted
      of six mapping cycles, and they were conducted in order of their overall
      importance. In the first cycle, Dawn aimed its camera straight down and
      took pictures with all of the instrument's color filters.
      In addition to showing the startling
      diversity of exotic features, the color images provide scientists some
      information about the composition of the surface materials, which
      display an impressive variation on this mysterious protoplanet. Cycle 1
      yielded more than 2500 photos of Vesta, nearly as many as were acquired
      in the entire survey orbit phase. These
      observations were deemed so important that not only were they first, but
      cycle 6 was designed to acquire nearly the same data. This strategy was
      formulated so that if problems precluded the successful mapping in cycle
      1, there would be a second chance without requiring the small and busy
      operations team to make new plans. As it turned out, there were only
      minor glitches that interfered with some of the pictures in cycle 1, but
      the losses were not important. Nevertheless, cycle 6 did fill in most of
      the missing views.

      Cycles 2 through 5 were devoted to acquiring images needed to develop a
      topographical map. Instead of flying over the sunlit side with its
      camera pointed straight down, the spacecraft looked at an angle. Each
      direction was chosen to provide scientists the best combination of
      perspective and illumination to build up a three dimensional picture of
      the surface. Knowing the elevations of different features and the angles
      of slopes is essential to understanding the geological processes that
      shaped them.

      In cycle 2, the camera constantly was directed at the terrain ahead and
      a little to the left of the point directly below the spacecraft. Cycle
      3, in contrast, looked back and slightly to the left. Cycle 4 pointed
      straight ahead but by a smaller angle than in cycle 2. Cycle 5 did not
      look forward or backwards; it only observed the surface to the right.
      With the extensive stereo coverage in each of these 10-orbit mapping
      cycles, most of the terrain now has been photographed from enough
      different directions that the detailed shape of the alien landscape can
      be determined.

      The HAMO observations constitute the most comprehensive visible mapping
      of Vesta for the mission. The survey orbit images were obtained from a
      higher altitude and so do not show as much detail. When Dawn flies down
      to its low altitude mapping orbit (LAMO), its primary objectives will be
      to measure the atomic constituents with the gamma ray and neutron detector
      (GRaND) and to map the gravitational field. While some images will be
      acquired,
      they will be a secondary objective. The principal resources, both for
      the spacecraft and for the operations team, will be devoted to the
      higher priority science. In addition, the probe will be too close in
      LAMO for its camera to collect enough pictures for a global map. The
      subsequent observations in HAMO2 will be designed mostly to glimpse some
      of the northern latitudes that are currently too dark to see.

      The more than 7000 images Dawn acquired in HAMO will form a very firm
      basis for years of productive study. Combined with the other data the
      explorer returns from Vesta, we will follow the global maps to find
      exciting new insights about the solar system. What better destination
      could the maps guide us to?

      Included in the "other data" is a collection of fabulous new
      observations with the visible and infrared mapping spectrometer (VIR).
      A spectrum is the intensity of light at
      different wavelengths. When you enjoy the sight of light dispersed
      through a prism, which decomposes white light into its constituent
      colors, you have a similar view. The material on Vesta leaves its
      signature in the spectrum of light it reflects from the sun. Each VIR
      snapshot produces a "frame,' which consists of a full spectrum, from a
      portion of ultraviolet through the entire visible range into infrared,
      at 256 distinct locations on the surface. Every frame contains a
      richness of information.

      The direction in which Dawn pointed its instruments in HAMO was dictated
      by the plan for thoroughly mapping Vesta with the camera. Nevertheless,
      VIR was used to acquire a sumptuous set of spectra which are the
      principal means by which scientists will determine the nature of the
      minerals on its surface. The spectra extend far enough into the infrared
      that they also measure the meager heat radiated from the surface,
      thereby acting as a thermometer.

      As with the pictures from the camera, the VIR frames in HAMO benefit
      from the lower altitude by showing more detail than those acquired in
      survey orbit. VIR acquired 15 thousand frames in HAMO, yielding full
      spectra on nearly four million regions over Vesta's vast surface.

      The spectra from VIR provide greater chromatic detail than the seven
      color filters in the camera. The camera is able to cover larger areas
      with finer resolution in a single image. The two instruments are
      complementary, and together they contribute to developing a detailed
      picture of the geology of Vesta.

      Although the main gravity and GRaND measurements will be made in LAMO,
      they have already begun. The gravity investigation is revealing hints of
      the interior structure even before the probe travels to its lowest
      altitude. The nuclear radiation GRaND will measure is so weak
      that Dawn will need to go closer to allow that instrument to do its primary
      work. Nevertheless, even in HAMO it has been detecting neutrons emitted by
      Vesta.

      After GRaND was reactivated at the end of September as part of the
      recovery from safe mode, scientists
      observed that one of its sophisticated gamma ray detectors showed an
      increase in noise. Scientists and engineers worked together in analyzing
      the telemetry from the instrument and establishing the best way to
      remedy it. They proceeded carefully and gradually over the course of
      about 10 days, first powering selected internal components off, then
      deactivating the entire instrument, rebooting it, and reconfiguring it.
      They were rewarded by seeing GRaND back to its normal performance, once
      again ready to contribute fully to this grand mission of exploration.

      Dawn collected slightly more data during most of its transits over the
      lit side of Vesta than it could transmit over the subsequent dark side
      passes. Therefore, by the end of HAMO, it still had precious information
      that had accumulated in its memory. Following the completion of mapping
      cycle 6 early this morning, the spacecraft is spending another two days
      beaming the last of its findings back to the distant planet it left more
      than four years ago.

      Engineers are taking advantage of this time with the main antenna
      pointed to Earth to perform some reconfigurations of the spacecraft.
      They are preparing it for operating closer to Vesta, where more
      reflected light from the surface will reach some of the sensors that
      keep track of the location of the sun and the vast rocky body will cause
      fewer stars to be visible to the star trackers. Other changes are scheduled
      to occur at lower altitudes.

      With a truly amazingly productive HAMO phase complete and the spacecraft
      ready to venture on, plans are all in place for what may be the most
      arduous phase of the mission. On November 2 at 5:20 a.m. PDT, the ship will
      set sail again with its ion propulsion system to push down to its lowest
      orbit.
      It will take more than five weeks to reach LAMO. In the next log we will
      check
      in on the probe's progress and consider some of the obstacles to be overcome
      in
      dipping so low.

      In the meantime, your correspondent was inspired by the splendid results
      from HAMO to devise his best Halloween costume in a long time. This year, he
      pretended to be someone who is unmoved by the stunning views of Vesta and
      the
      extraordinary accomplishments of the indefatigable spacecraft that
      acquired them. He appeared not to feel the deep gratification of being a
      member of a species that works together to extend beyond our limitations
      to undertake bold adventures in search of some of the greatest rewards
      of all: new knowledge and new perspectives on the cosmos. He disguised
      himself as one who does not feel the powerful longing to share in the
      unveiling of an alien world. He acted as if he has not hungered for the
      wonderful feast Dawn is now serving. He was not only unrecognizable, but
      in this costume he surely would not be mistaken for any of the
      dawnderful readers of these logs.

      Dawn is 680 kilometers (420 miles) from Vesta. It is also 2.03 AU (303
      million kilometers or 184 million miles) from Earth, or 795 times as far
      as the moon and 2.04 times as far as the sun today. Radio signals,
      traveling at the universal limit of the speed of light, take 34 minutes
      to make the round trip.


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      2. EPOXI Mission Status Report - October 20, 2011
      Posted by: "Ron Baalke" baalke@...
      Thu Nov 3, 2011 11:07 am (PDT)

      http://epoxi.umd.edu/1mission/status.shtml

      EPOXI Mission Status Report
      Michael A'Hearn
      October 20, 2011

      The spacecraft went through a cool-down period at the end of
      September to optimize the capabilities of the near-IR spectrometer and
      to carry out a Trajectory Correction Maneuver (TCM). This maneuver
      changed our target point based on our improved knowledge of the position
      of the comet relative to the spacecraft. We think that the new target
      point will be within 100-200 km of the desired flyby point (which is 700
      km from the nucleus). We expect our next and final TCM to be on October
      27. We have a contingency plan for a TCM on November 2 in case the
      previous TCM does not perform as expected.

      We have been receiving Hartley 2 data from a variety of other spacecraft
      and collaborators. The WISE mission released data acquired in May.
      Those data will be useful in understanding the onset of activity by the
      comet
      as it approaches the sun in its orbit. Weaver et al. released
      Hubble Space Telescope images acquired on September 25. The HST images
      are particularly valuable because they allowed us to confirm that the
      cometary nucleus is separable from the coma. Eventually, we will be able
      to separate the nucleus from the coma within our own data. For now, HST
      has a huge advantage over our own cameras in this respect due to the
      much larger aperture of HST coupled with the fact that Earth and HST
      were much closer to the comet than was our spacecraft. These data are
      consistent with earlier determinations of the size of the nucleus.

      We have also been receiving widespread reports of jets in the coma of
      the comet. The first such report was from Matthew Knight and colleagues
      <http://www.lowell.edu/rsch/content/comets/hartley2/hartley2.html> at
      Lowell Observatory who found jets in the gas (the unstable radical CN)
      but not in the dust during an August observing run . Since then, we have
      had more recent reports of jets from both professional and amateur
      observers.

      Since the Deep Impact spacecraft has its cameras dedicated to monitoring
      Hartley 2 during this phase of the mission, we now have an advantage
      over other observatories and telescopes because we have nearly
      continuous coverage (16 out of every 24 hours). We too see fluctuations
      and jet-like structures in our data that are presumed to be due to
      variations in the release of dust and gas as the nucleus rotates. More
      excitingly, we have discovered a new cometary phenomenon!
      In September, outgassing from CN, as
      detected by the MRI, increased slowly by a factor of 5 and then slowly
      decreased while the dust showed no dramatic change. This activity took
      place over the course of 16 days. We are unaware of any other instances
      of this type of activity in any other comets and it is very different
      from the dust outbursts observed with the same instrument at Tempel 1.
      (Reported in CBET 2512
      <http://www.cbat.eps.harvard.edu/cbet/RecentCBETs.html>, which requires
      a subscription to view.)


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      3. EPOXI Mission Status Report - November 1, 2011
      Posted by: "Ron Baalke" baalke@...
      Thu Nov 3, 2011 11:10 am (PDT)

      http://epoxi.umd.edu/1mission/status.shtml

      EPOXI Mission Status Report
      Michael A'Hern
      November 1, 2011

      As we approach the anniversary of the EPOXI flyby of Hartley 2,
      it is time to look at what we have learned about comets from this
      mission. In the first week of October, a special session of the annual
      DPS meeting <http://meetings.copernicus.org/epsc-dps2011/>, jointly held
      with the European Planetary Science Congress, highlighted recent mission
      results in an all-day session
      <http://meetingorganizer.copernicus.org/EPSC-DPS2011/session/8405>. Key
      results from EPOXI included:

      * new evidence that the two lobes of Hartley 2 are different in
      composition,
      * separation of the icy grains from the refractory grains
      quantitatively improved statistics on the motion of the large
      chunks in the coma,
      * the correlation of surface ice with topography on the nucleus,
      * an analysis of spectra showing that the thermal inertia of the
      nucleus is very small (highest surface temperature at noon rather
      than in the afternoon).

      The results for the abundances of carbon monoxide (CO) and carbon
      dioxide (CO_2 ) relative to water mesh nicely with results from the
      Akari satellite on these abundances in other comets and the results on
      deuterium in Hartley 2 suggest that the origin of comets needs to be
      rethought.

      Meanwhile, NASA has decided that there will be a senior review of all
      operating planetary exploration missions. That will likely include a
      review of the status of the Deep Impact Flyby spacecraft to determine
      whether an additional extended mission should be approved. Decisions
      will not occur until early 2012.
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