Deep Impact Imminent

NASA announced on June 9th 2005 that it’s mission to collide a 1 metre wide, 372 kilogram impact probe – deployed by the "Deep Impact" spacecraft – into the nucleus of Comet 9P/Tempel 1, is expected to occur at 5.52am +/- 3mins GMT on July 4th 2005 (10.52pm PST on July 3rd).  Two or three days prior to impact they will know the exact time of impact within 30 secs.

Unfortunately, the strike will occur at approximately 3.52pm for Australian (Brisbane) observers, but was timed to allow for full coverage by NASA’s Deep Space Network complexes in both Australia and California, and for observations by the Hubble Telescope during a 10-15 minute window before it moves behind the Earth on it’s 90 minute orbit.  Several other ground-based observatories will be monitoring the event, including Keck1 and Keck2 – the two largest telescopes in the world, which are located atop Hawaii’s Mauna Kea.  Following dispatch of the probe, the "Deep Impact" spacecraft will maneuver to a safe distance and become a fly-by observer in the sky, along with numerous other "space-based" devices, including the Chandra X-Ray Observatory and the European Space Agency’s "Rosetta" spacecraft.

The probe will be literally "run over" by the comet at a velocity of 10.3 kilometres per second, with the release of kinetic energy carving a crater approximately 2 to 14 stories deep, and ranging from the size of a large house up to a football stadium in diameter.  Occuring when the comet is nearing it’s perihelion (closest point to the sun in it’s orbit), the collision will decrease the comet’s perihelion distance by 10 metres, slow it’s velocity by 0.0001 millimetres p/sec, and reduce orbital period by far less than 1 second – "the astronomical equivalent of a mosquito running into a 767 airliner."  Comparing this to when Comet 9P/Tempel 1 passes Jupiter in 2024, where perihelion distance will alter by 34 million kilometres, the orbital changes to perihelion distance caused by "Deep Impact" will be negligible.

This information possibly came about as a result of concerns that the mission could cause the Near Earth Object to change course, inducing a potential threat to our planet in the future.  Another, was the curious report of Russian astrologist, Marina Bai, filing a lawsuit against NASA and asking for 8.7 billion rubles (US$311 million) in compensation for moral damages.  She claimed the mission, which is operating under the 1967 United Nations treaty on "Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies" (also known as the "Outer Space Treaty") and has a Category 2 status under NASA’s Planetary Protection policy, interfered with the natural life and balance of the Universe.  The Russian high court ruled on May 6th 2005 that NASA’s US embassy office in Moscow fell under it’s jurisdiction and Ms Bai could sue the space agency.  Russian scientists backed the case, claiming the project was an act of "vandalism that cannot be justified."

The "Deep Impact" spacecraft was successfully launched on January 12th 2005 from Cape Canaveral Airforce Station in Florida.  The comet will be 133.6 million kilometres from Earth when the impact occurs.  The "Deep Impact" craft will have travelled a total distance of 431 million kilometres when it reaches the target.  The aim of the mission is to study the interior material composition of a typical comet, amoungst other objectives, which include answering some basic questions which relate to the formation of the solar system.  The nucleus of Comet 9P/Tempel 1 is an irregular elongated shape, estimated to be 14 x 4.6 x 4.6 kilometres, about half the size of Manhatten Island NY.  It is traveling through space at approximately 29.9 kilometres p/second.  At this speed it would take 6.5 minutes to travel from east to west across North America.

Amateur observation of the comet from Earth requires large binoculars or a small telescope, and will be best from June 24th 2005.  It brightens as it continues it’s approach towards the Sun and will appear in the constellation of Virgo in the evening sky.  The impact itself could make the comet 15 to 40 times brighter than normal (which is about magnitude 9.5) – possibly making it viewable by the unaided human eye at magnitude 6 (larger numbers connote dimmer objects).  The impactor probe is carrying a mini-compact disc containing the names of more than half a million space-enthusiasts from around the world, collected by the "Send Your Name to a Comet" internet campaign.  The mini-CD and impactor will be totally obliterated on collision with Comet 9P/Tempel 1 on July 4th – America’s Independence Day.

For more information visit NASA’s Jet Propulsion Laboratory "Deep Impact" website, and the NASA "Deep Impact" site.

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