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Re: [talk-about-sy] OT but interesting: Rendezvous with Comet Tempel 1

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  • miguel de castro henriques
    Well, I met a friend of a friend, and he has a telescope and a bunch of friends all aith telescopes going out to farfetched places to spend all the night
    Message 1 of 2 , Jul 1, 2005
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      Well, I met a friend of a friend, and he has a telescope and a bunch of friends all aith telescopes going out to farfetched places to spend all the night watching the skies. They spend more money in telescopes than in new cars, so they have updated equipment.
      I was invited to participate in one of these scouting skies nights. I'm thrilled. Plus there is a moment for a grill and beers.
      He told me that the area I'm currently living is one of the best in Europe for night sky watching, due to the low densitiy of artificial luminosity. The best area is in the Baleares Islands, Spanish Islands, where there are several observatories. They have strict legislation regulating illumination. Let's say if Las Vegas, USA,  is perhaps the most illuminated spot in the whole world, Baleares Island are its antipodes.
      This expedition will be in July. But he and his group of friends are currently circuiting the whole country watching sky events.
      Giahn as you're the astronomer freak of this forum... do you have a telescope?
      Giahn <nutmeg2323@...> wrote:

      Cosmic Crash Won't Destroy Comet or Earth nutmeg2323

      Here's an update on the forthcoming "tangle" with Comet Tempel 1 on
      July 4th. Anyone gonna watch the fireworks?



      By Leonard David
      Senior Space Writer
      posted: 28 June 2005
      2:00 a.m. ET

      BOULDER, Colorado – Late Sunday and early Monday, skywatchers might
      be treated to celestial fireworks unlike anything witnessed before.

      Like some Space Age equivalent of WrestleMania, NASA's Deep Impact
      spacecraft is double-billed to tangle with Comet Tempel 1 on July 4.
      The mission is a two-part project: A "Flyby" vehicle will unleash
      an "Impactor" probe that will slam into the fast-moving comet.

      The comet and Impactor will collide at about 23,000 mph.

      Deep Impact is the first mission to make contact with a comet's
      surface. The hope is to produce a crater in the large comet and
      reveal what is underneath the surface.

      The event could be visible from backyards. But for some, the novel
      space shot conjures visions of comet chunks careening into Earth. Is
      there any chance that Deep Impact will result in icy lumps of the
      comet splitting off, placing our planet in danger?

      Put your crash helmets back in the closest and get some sleep.

      Comet kamikaze mission

      "We're sending a bug onto the windshield of a train," said Monte
      Henderson, Deputy Director of Programs in Civil Space Systems for
      Ball Aerospace & Technologies Corporation here.

      Ball Aerospace, in association with the University of Maryland and
      NASA's Jet Propulsion Laboratory (JPL), developed and integrated the
      Flyby spacecraft, the Impactor spacecraft, and science instruments,
      including three telescopes, three cameras and a spectrometer for
      analyzing the interior of the comet – as revealed by the high-speed

      Comet Temple 1 is moving at a brisk 66,000 miles per hour. The
      ejected Impactor is slated to be speeding at roughly 43,000 miles per
      hour. Deep Impact won't have a head-on crash with the comet, like the
      old anti-ballistic missile defense adage of "hitting a bullet with a

      "We're being overrun from behind," Henderson told SPACE.com. "The
      speeds are just mind-boggling."

      Telescopes onboard the Flyby vehicle will be trained on the Impactor
      as it is overtaken by the comet. The intent is to see crater
      formation as it's occurring, Henderson said. Scientists expect to see
      a crater shaped that's a 100 yards long, and between seven to twelve
      stories deep, "with nice vertical walls," he said.

      In the event that the Impactor isn't successfully ejected by the
      Flyby spacecraft, then the entire vehicle is on a true comet kamikaze
      mission. It is to pile-drive itself into the comet, Henderson
      said. "It's important to the science community that we create a

      "This is a one-time exciting event," Henderson explained.

      Simulation of a natural event

      The excavation of the comet by Deep Impact may create a cloud of
      meteoroids, objects larger than the gas and dust that NASA predicts.
      And that possibility might not be so unnatural, contends Peter
      Jenniskens, an astronomer with the SETI Institute in Mountain View,

      In a paper accepted for publication in the September issue of the
      Astronomical Journal, Jenniskens and co-author Esko Lyytinen, an
      amateur astronomer and meter shower expert from Finland, report that
      as a result of Tempel 1 breaking, a meteoroid stream will be
      created "in much the same manner as the mechanism that causes most of
      our meteor showers."

      Jenniskens has been studying the formations of meteoroid streams by
      the disintegration of comets. He points to the idea that many
      meteoroid streams are caused by wholesale disintegration of comets,
      which are loose assemblages of cometesimals and are known to
      frequently break apart.

      There are several possible causes of such fragmentations. But the
      idea that collisions between comets and large meteoroids spark such
      fragmentation is on the table, Jenniskens said. Furthermore, the Deep
      Impact mission acts as a simulation of such a natural event.

      "Depending on how the kinetic energy of the impact will be
      distributed, there is a real possibility that sufficient internal gas
      pressure builds up to break the comet apart. At that time, we can
      study the peculiarities of dust generation in the way that led to our
      main meteor showers," Jenniskens and Lyytinen conclude. They also
      predict that the dust production will be moderate.

      Risk to Earth?

      There is a "way outside chance" that Deep Impact will promote an
      explosive release of built-up, sub-surface gas pressure, said Donald
      Yeomans, Supervisor of the Solar System Dynamics Group at the Jet
      Propulsion Laboratory (JPL) in Pasadena, California.

      Yeomans said in the event that any meteoroid material is released, it
      will be modest and come no where near the Earth. (Meteor showers on
      Earth develop when Earth passes through a stream of comet debris.)

      "So a modest meteoroid stream might be created that would follow the
      parent comet but no visible meteors would result of course," Yeomans
      said. "Perhaps an enhanced meteoroid stream following the comet might
      be discernable in pre- and post-impact infrared images. It would be
      unlikely, but not out of the question," he explained.

      But given that the Impactor and Tempel 1 will bang into each other at
      a force of four-and-a-half tons of TNT, why wouldn't that explosive
      energy toss out huge bits of comet…splinters that could head toward

      "The bottom line is that we have an object the size of a washing
      machine colliding with a comet the size of Manhattan Island. No
      contest," Yeomans said.

      If Comet Tempel 1 happened to be smaller, say roughly 500 feet (150
      meters) across as opposed to its true average diameter of 4 miles (6
      kilometers), the Deep Impact crash would be sufficient to adjust the
      comet's course by an amount equal to Earth's radius ten years after
      the spacecraft impact, Yeomans told SPACE.com.

      Mitigation techniques

      Yeomans and his colleagues have done some calculations, just to help
      put worries about the risk to Earth to rest. They assumed a 98-foot
      (30-meter) chunk was broken off as a result of the impact. That size
      was selected as the smallest chunk that might cause some ground
      damage at Earth.

      But for that chunk to be propelled into a new Earth-crossing
      trajectory, Deep Impact would need to impart a wallop that must be,
      well, simply astronomical. Furthermore, for the same impact velocity
      as Deep Impact, the impacting spacecraft mass would then have to
      about 5,900 times the mass of the actual Impactor.

      "On a number of levels, it would be impossible for Deep Impact to
      deliver a comet chunk to Earth," Yeomans concluded.

      While the primary science goals for Deep Impact do not include a
      demonstration of possible mitigation techniques, Yeomans said that
      the rather sophisticated autonomous navigation process used to impact
      the comet would be similar to those necessary to mitigate a
      threatening near-Earth object in the years to come.

      Comets: devilishly difficult to pin down

      But while Deep Impact is an impressive science mission, it won't be
      all that helpful in learning how to fend off troublemaking asteroids.

      That's the view of former NASA Apollo astronaut Russell Schweickart.
      He is chairman of the B612 Foundation, a group of experts dedicated
      to significantly alter the orbit of an asteroid in a controlled
      manner by 2015.

      "It will not tell us very much about the issue of asteroid
      deflection," Schweickart said, "even though kinetic impact is a
      possible option for a small sub-set of asteroids that we might need
      to deflect." For one, the surface structural characteristics are
      quite likely very different given the high water component of comets,
      he added.

      "The relative velocity in the Deep Impact case is considerably higher
      than we would be able to achieve with most asteroids," Schweickart
      noted. "And finally, the change in the comet's trajectory will be so
      small that measurement and attribution will be very challenging."

      Comets are "devilishly difficult to pin down accurately due to their
      outgassing," Schweickart suggested. After the impact it will be
      difficult -- if not impossible -- to separate the effects of the
      impact itself from any changes brought about by post-impact
      outgassing - expected to rise dramatically due to the impact, he said.

      "Still, it is an interesting experiment to watch. The cratering
      process, the ejecta pattern and other observations will surely give
      us some clues," Schweickart observed. Those involved with Deep
      Impact "are clever folk and there are doubtless some lessons to be

      Balance of the solar system

      The Deep Impact mission is designed to alter the comet so that
      scientists can see beneath the surface, said Lucy McFadden, a member
      of Deep Impact's science team. She is an Associate Research Scientist
      for the University of Maryland's Astronomy Department in College
      Park, Maryland.

      As for altering the comet's path, "the answer is no, not measurably,"
      McFadden told SPACE.com. "This event is happening in space, and space
      is huge, even when we are operating within our solar system."

      McFadden notes that objects moving in space are not like billiard
      balls on a pool table.

      "We won't knock the comet off its orbit and into a collision course
      with Earth. The comet has tremendous orbital energy that is orders of
      magnitude greater than that of the spacecraft," McFadden explained.

      The experiment mimics impacts in the Solar System that have occurred
      since its formation, McFadden added. "It will not upset the balance
      of the solar system."


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