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ஆசிரியர்:வ.ந.கிரிதரன்                                    Editor: V.N.Giritharan
மே 2009 இதழ் 113  -மாத இதழ்
 பதிவுகள் 
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பதிவுகள் சஞ்சிகை உலகின் பல்வேறு நாடுகள் பலவற்றில் வாழும் தமிழ் மக்களால் வாசிக்கப்பட்டு வருகிறது. உங்கள் வியாபாரத்தை  சர்வதேசமயமாக்க பதிவுகளில் விளம்பரம் செய்யுங்கள். நியாயமான விளம்பரக் கட்டணம். விபரங்களுக்கு ngiri2704@rogers.com 
என்னும் மின்னஞ்சல் முகவரிக்கு எழுதுங்கள்.

பதிவுகளில் வெளியாகும் விளம்பரங்களுக்கு விளம்பரதாரர்களே பொறுப்பு. பதிவுகள் எந்த வகையிலும் பொறுப்பு அல்ல. வெளியாகும் ஆக்கங்களை அனைத்துக்கும் அவற்றை ஆக்கியவர்களே பொறுப்பு. பதிவுகளல்ல. அவற்றில் தெரிவிக்கப்படும் கருத்துகள் பதிவுகளின்கருத்துகளாக இருக்க வேண்டுமென்பதில்லை.

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அன்பான இணைய வாசகர்களே! 'பதிவுகள்' பற்றிய உங்கள் கருத்துகளை வரவேற்கின்றோம். தாராளமாக எழுதி அனுப்புங்கள். 'பதிவுகளின் வெற்றி உங்கள் ஆதரவிலேயே தங்கியுள்ளது. உங்கள் கருத்துகள் ­ப் பகுதியில் இணைய வாசகர்கள் நன்மை கருதி பிரசுரிக்கப்படும்.  பதிவுகளிற்கு ஆக்கங்கள் அனுப்ப விரும்புவர்கள் யூனிகோட் தமிழ் எழுத்தைப் பாவித்து மின்னஞ்சல் editor@pathivukal.com மூலம் அனுப்பி வைக்கவும். தபால் மூலம் வரும் ஆக்கங்கள் ஏற்றுக் கொள்ளப் படமாட்டாதென்பதை வருத்தத்துடன் தெரிவித்துக் கொள்கின்றோம். மேலும் பதிவுக'ளிற்கு ஆக்கங்கள் அனுப்புவோர் தங்களது சரியான மின்னஞ்சல் முகவரியினைக் குறிப்பிட்டு அனுப்ப வேண்டும். முகவரி பிழையாகவிருக்கும் பட்சத்தில் ஆக்கங்கள் பிரசுரத்திற்கு ஏற்றுக் கொள்ளப் படமாட்டாதென்பதை அறியத் தருகின்றோம். 'பதிவுக'ளின் நோக்கங்களிலொன்று இணையத்தமிழை வளர்ப்பது. தமிழ் எழுத்துகளைப் பாவித்துப் படைப்புகளை பதிவு செய்து மின்னஞ்சல் மூலம் அனுப்புவது அதற்கு முதற்படிதான். அதே சமயம் அவ்வாறு அனுப்புவதன் மூலம் கணிணியின் பயனை, இணையத்தின் பயனை அனுப்புவர் மட்டுமல்ல ஆசிரியரும் அடைந்து கொள்ள முடிகின்றது.  'பதிவுக'ளின் நிகழ்வுகள் பகுதியில் தங்களது அமைப்புகள் அல்லது சங்கங்களின் விழாக்கள் போன்ற விபரங்களைப் பதிவு செய்து கொள்ள விரும்புகின்றவர்கள் மின்னஞ்சல் மூலம் அல்லது மேற்குறிப்பிடப்பட்ட முகவரிக்குக் கடிதங்கள் எழுதுவதன் மூலம் பதிவு செய்து கொள்ளலாம்.
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Science

VOYAGER 2

By Thamayanthi Giritharan

IMAGE OF SATURN TAKEN BY VOYAGER In the midst of the Cold War, space enthusiasts were shrewd to take advantage of the competitive panic during the Space Race. With space exploration as a new curiosity to several, many astronomers were eager to collect more data. During the 1970s, the major outer planets of Jupiter, Saturn, Uranus and Neptune were still relatively unknown objects. As a result, NASA (National Aeronautics and Space Administration) sent two, unmanned spacecrafts to study these planets, Voyager 2 and Voyager 1, as part of the Voyager program. Voyager 2, however, is probably one of the most productive spacecrafts to date. The purpose of this paper is to inform the reader of the general outline of, key data and conclusions gathered from the gas giants of the Solar System, and other current and future events from Voyager 2.

Voyager 2 was launched before its sister probe, Voyager 1, on August 20, 1977.  It was launched by Titan IIIE (space booster rocket) in Cape Canaveral, Florida.  Like its twin, it is comprised of 65,000 individual parts, including powerful cameras.  It was at a fraction of the cost when compared to future probes, such as Cassini-Huygens.  Unlike its twin, it followed a slower flight path in order to be kept in the solar system’s plane, otherwise known as the ecliptic.  This allowed Voyager 2 to travel to Uranus and Neptune with a gravity assist from Saturn.  The completion of the Planetary Grand Tour was made possible through Voyager 2.  NASA sought to send probes to the outer planets via gravitational assist during the alignment of all the outer planets (a phenomenon that would take place in the late 1970s and not again for another 176 years).  Hitherto, it is the only spacecraft to travel to Uranus and Neptune (also being the first).  Voyager 2 has had flybys of Jupiter, Saturn, Uranus and Neptune.

Its flyby of Jupiter occurred on July 9, 1979.  It reached within 570,000 kilometres of Jupiter’s cloud tops.  Voyager 1 already visited the planet earlier, having taken 19,000 images and Voyager 2 took another 14,000.  With the two probes, important comparisons could be made to reveal different characteristics of not only Jupiter, but its major moons and ring system as well.  Through Voyager 2’s journey between Jupiter and Saturn, it found that Jupiter’s magnetotail extended to at least Saturn’s orbit around 650 million kilometres away.  The magnetotail is the part of the magnetosphere (the area around a planet where its magnetic field is present) facing away from the Sun because of its interaction with solar winds.           

Through Voyager 2’s images, a small satellite, Adrastea, was discovered orbiting just outside the main ring of Jupiter.  Due to its similar composition to the rings of Jupiter, it is thought to be the main contributor to the ring system (as debris from the moon when meteorites bombard its surface).  However, it was another moon that probably brought more revelation.  Volcanic activity was detected on Io, making it the first time active volcanoes to be seen on any other object in the solar system.  Sulphur, oxygen and sodium are believed to spew from the volcanoes.  When Voyager 2 made its flyby, eight of the nine volcanoes were active, with the ninth one shutting down during the interval between Voyager 1’s departure and Voyager 2’s arrival.  Ionian activity is thought to be a possible factor of “changes” seen in Jupiter and its surrounding region.  For example, the sulphuric concentrations detected in the magnetosphere by both Voyagers were not detected by the Pioneers five years earlier. 

Voyager 2’s flyby of Saturn took place on August 26, 1981.  It searched Saturn’s upper atmosphere.  Winds were found to be about 500 meters per second, most to be blowing easterly and strongest at the equator.  Moreover, symmetry between north and south winds were measured through Voyager 2.  This symmetry led some to conclude that the winds may stretch from north to south through the core of Saturn.

Voyager 2 showed that Saturn seemingly plunged into Jupiter’s magnetotail.  There were areas where Saturn’s radio emissions could not be detected.  Areas where the Jovian magnetotail appeared to exist were believed to be where the radio emissions were undetectable.  This suggests that the Jovian magnetotail exists to this point, but there is no explicit evidence.

Along with Voyager 1, Voyager 2 aided in the mapping of Saturn and its satellites, including its superlative rings.  For example, the satellite, Phoebe, was probed by Voyager 2 and found to orbit Saturn in retrograde motion (opposite to the other satellites).  Six new satellites were found, including three found by Voyager 2.  Titan was found to be the most captivating satellite with chemistry in the atmosphere to be that of an Earth’s atmosphere several billion years ago.

Voyager 2 was closest to Uranus on January 24, 1986 within 81,500 kilometres of its cloud tops.  It made many important observations, such as discovering 10 moons, studied its ring system (including a discovery of two new rings) and its unique axial tilt of about 97.8°.  Uranus’ magnetotail is believed to continue to at least 10 million kilometres behind it.  Due to its axial tilt, some wondered whether a magnetic field existed.  Voyager 2 abolished those doubts by showing Uranus had an intense, yet skewed magnetic field that was tilted to a 60° angle to its rotational axis.  Its intensity is similar to Earth’s, but it varies from points because of its offset from the centre.  However, the source of the magnetic field is unknown.  Theories of water and ammonia pressurized within the core seem to have been eradicated with Voyager’s findings, making the source of the magnetic field still a mystery.   

Voyager 2 found that Uranus’ radiation belt’s intensity was comparable to Saturn’s, but it was of a different constitution.  The belt is believed to be mainly made of hydrogen ions.  The intensity is great, and because of this, irradiation would darken any methane in the surfaces of the inner moons or ring particles within 100,000 years.  This is thought to be the explanation of the darkened surfaces of Uranus’ satellites.    

One of the innermost moons of Uranus, Miranda, had some grand peculiarities.  Images from Voyager 2 shows fault canyons as deep as 20 kilometres and an amalgamation of young and old surfaces.  From this, some have inferred that Miranda may be a remoulding of material from a previous time when it was shattered by a violent collision. 

IMAGE TAKEN 3 DAYS AFTER FLYBY; TRITON IS THE SMALLER CRESCENT BELOW NEPTUNE.

The closest approach to Neptune by Voyager 2 occurred on August 25, 1989.  Neptune was the last gas giant and last planetary target on Voyager 2’s mission.  As a result, Neptune’s largest moon, Triton, was taken into further study.  It was found that geyser-like activity occurred on Triton.  Eruptions would emit nitrogen and dark particles 2 to 8 kilometres upward before falling down.   In addition to two already known moons (one being Triton), six new moons and a ring system were found through Voyager 2.  It made its closest approach to any planet since its launch, passing 4,950 kilometres above Neptune’s North Pole.

The probe photographed the Great Dark Spot on Neptune, similar to that of Jupiter, but relatively cloud-free.  Around the region, the retrograde winds were measured to be 2,400 kilometres per hour – among the fastest in our Solar System.  The Great Dark Spot is thought to be a hole in the methane deck, similar to holes in Earth’s ozone layer.  Large white clouds have also been found swirling about Neptune.  They were akin to Earth’s cirrus clouds, but instead of being made of crystals of ice, they were made of crystals of frozen methane.  The Great Dark Spot has since disappeared (as seen through images from the Hubble Space Telescope).

Voyager 2’s expedition of Neptune also led to the now demoted status of Pluto. Predicted and observed positions of Uranus and Neptune differed, leading many to believe that the gravity of a “Planet X” influenced these discrepancies.  However, with Voyager 2’s findings, it was found that Neptune’s mass was 0.5% less than that of what was predicted earlier.  (This difference is about the mass of Mars)  Therefore, it was the mistaken mass number and not the gravity of “Planet X” (Pluto) to be causing these incongruities.  Nevertheless, it took another 17 years to officially downgrade Pluto from planet to “dwarf planet.”

Thirty-one years later, Voyager 2 continues to explore beyond what the eye cannot see.   It has definitely been one of the most productive probes to date, visiting all four gas giants and their satellites.  After the Neptune mission, it has entered its Interstellar Mission Phase, having escaped the solar system’s trajectory.  It is journeying into a space beyond the heliosphere (the bubble in space that is pushed into the interstellar medium by the solar wind; almost all material here is from the Sun).  The most recent conjecture (published in July 2008) from the data was that the heliosphere is not perfectly round, but squashed.  Voyager 2 crossed the boundary between the heliosphere and the rest of interstellar space closer to the Sun than expected.  This led to the theory that the heliosphere in this region is pushed closer to the Sun (inward) by an interstellar magnetic field.  This helps us learn how the Sun relates with the encompassing interstellar medium. 

The future is, as it always is, uncertain.  As of May 2008, Voyager 2 is about 85.84 AU from the Sun and continues to travel at about 3.28 AUs per year.  By 2016, it is expected to terminate its gyro operations.  Voyager 2 is expected to cease transmission 48 years after its launch, in 2025.  In around 296 millennia, it is anticipated to pass by Sirius, the brightest star in the northern sky.  The probe has already surpassed many of the wildest dreams.  We will just have to wait for what happens next.

SOURCES
I. http://www.nasa.gov/mission_pages/voyager/voyager-20080703.html
II. http://nssdc.gsfc.nasa.gov/planetary/voyager.html
III. http://video.google.com/videoplay?docid=1825648771198195435
IV. http://voyager.jpl.nasa.gov/science/thirty.html
V. http://voyager.jpl.nasa.gov/
VI. http://voyager.jpl.nasa.gov/spacecraft/spacecraftlife.html
VII. http://pds.jpl.nasa.gov/planets/welcome/voyager.htm


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