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Дата: 14 февраля 1998 (1998-02-14) От: Alexander Bondugin Тема: Overview of Comet Hale-Bopp meeting at Tenerife, Feb. 2-5, 1998 [1/3] Привет всем! Вот, свалилось из Internet... ESO Education and Public Relations Dept. Text with all links is available on the ESO Website at URL: http://www.eso.org/outreach/info-events/hale-bopp/report-rw-hbitp98.html This is a provisional overview of some of the discussions that took place at the First International Hale-Bopp Conference at Tenerife in February 1998. It was prepared by R. M. West (ESO, email: rwest@eso.org). I. Introduction Ten months after the perihelion passage, the First International Meeting about Comet Hale-Bopp was held at the Conference Centre in Puerto de la Cruz (Tenerife, Canary Islands, Spain) on February 2-5, 1998. Nearly 150 specialists from all major comet research groups in the world participated. During 4 days of intensive debates and with the presentation of approximately 150 papers, the participants surveyed the current status of the many research programmes related to this most unusual comet. The Local Organising Committee, headed by Mark Kidger and Monica Murphy (IAC) had done a great job and the frame was excellent. The conference provided a good opportunity for a discussion about some of the fundamental issues connected to this spectacular astronomical event. For instance: why was this comet so bright and in which respect(s) did it differ from other comets observed with modern equipment? Although many new results were presented and some main lines can be perceived, those present were left with the impression that there are still many open questions. There is no doubt that the associated research will continue for some time. It is also obvious that further meetings on these subjects will be held in due time. The Hale-Bopp event provided observers with a long lead time, thanks to the early discovery in July 1995 by Alan Hale and Tom Bopp who were both at the conference. Thus, it was possible for the scientists to obtain a substantial amount of observing time at the world's major observational facilities and to prepare their runs well. Moreover, the Comet was visible in the sky for an extremely long period. It was very bright and in the end, a large number of telescopes and instruments were used at all wavelengths from X-ray to radio. It is therefore no surprise that all the work by so many scientists during the past months has resulted in important new knowledge, as exposed at this meeting. In what follows, some of the highlights of the conference will be reviewed. They are arranged roughly in the order they were presented at the meeting. Kindly note that not all contributions mentioned here are attributed to individual speakers and various information by others has been left out in order to keep this survey within a reasonable size. However, a complete version of the conference summary, with full references and more details, will ultimately appear in the Conference Proceedings. II. Motion and Early Observations The meeting began with some basic information about the comet. The Orbit Based on more than 2600 astrometric observations from 1993-98, Brian Marsden has calculated a new and improved orbit, now taking into account non-gravitational forces arising from the jet effect associated with the Comet's vigorous activity. He found that the original period was 4211 years and that the future period will be 2392 years with a formal uncertainty of a few months only. However, the limited knowledge about the future development of the Comet's activity may still change this period somewhat. Had it arrived about four months earlier this time, it would have passed the Earth nearly as close as did Comet Hyakutake one year earlier. In that case it would have been an incredible view. Interestingly, it appears that Comet Hale-Bopp may have passed very close to Jupiter on June 7, 2216 BC. In view of the rather unstable orbit, it is unlikely that there have been more than a few earlier, close perihelion passages. Early Observations Alan Fitzsimmons reviewed the various signs of very early activity which are typical for this comet. In particular, investigations of early images of the dust tail by Hermann Boehnhardt and Marco Fulle have shown that the Comet most probably was active already 4-5 years before discovery, that is at pre-perihelion distance 18-20 AU. In addition to a UK Schmidt pre-discovery image obtained in April 1993, an image of the Comet may possibly be present on another photographic plate taken with the same telescope in September 1991; this will now be investigated. III. The Nucleus Size Harold Weaver and Philippe Lamy surveyed 7 different methods which have led to reasonably consistent estimates of the size of Comet Hale-Bopp's nucleus. Most of these lie in the interval between 20 and 40 km radius (i.e., 40 and 80 km diameter), but a few are somewhat larger. There is also a possible indication that the nucleus may have elongated shape. Particularly impressive among these observations were those performed at radio wavelengths with the VLA in New Mexico and which lasted more than 6 days -- they pointed towards a diameter of approximately 50 km. Interestingly, there may be more than one component of the nucleus. By very careful analysis of high-resolution HST images obtained in 1996, Zdenek Sekanina believes that the primary nucleus may have a lesser companion of approximately half the size. This issue is still somewhat controversial, but observations with the Adonis adaptive optics camera at the ESO 3.6 m telescope in November 1997 and January 1998 by three ESO astronomers also appear to show a double nucleus. More observations with this facility in the coming months and/or with the HST scheduled for later this month are expected to clarify this issue. Rotation In a review talk on this subject, Dave Jewitt listed the observational possibilities for measuring the rotation period of Comet Hale-Bopp's nucleus. With the nucleus hidden inside the coma already at the moment of discovery, they include periodic fluctuations of that part of the light at the centre of the coma which supposedly comes from the nucleus itself, and also periodic changes in the coma structure (orientation of jets, outward motion of shells, etc.). Many such observations are available; the longest series was apparently obtained by Mark Kidger and his group at the Teide Observatory on Tenerife, right above the site of the conference. At this moment, there is good agreement among the values published by 8 different groups and the true rotation period of the nucleus must be close to 11.34 +/- 0.03 hours. Although there were originally some signs of precession (wobbling of the rotation axis), this is now less sure. The direction of the polar axis has also not been unambiguously determined yet, but this may become possible after further analyses. Hа сегодня все, пока! =SANA=

Дата: 14 февраля 1998 (1998-02-14) От: Alexander Bondugin Тема: Overview of Comet Hale-Bopp meeting at Tenerife, Feb. 2-5, 1998 [2/3] Привет всем! Вот, свалилось из Internet... Composition and Structure Dominique Bockelee-Morvan and Hans Rickman surveyed the many new observations which will ultimately allow a better `look' into the still unknown interior of a cometary nucleus. This is first of all due to the very extensive observations which were made of the production rates of various molecules, as the comet came closer to the Sun. These observations show that not all of these species emerge in parallel and there seem to be certain `transitory' periods during which changes in the production rates can be observed. They are indicative of the composition and structure of the upper layers of the nucleus. For instance, a slowing down of the rate of increase of CO production was observed at about the time when the water production started at a heliocentric distance of approximately 3.5 AU. The production rates of some, less abundant molecules, showed a very steep dependence on heliocentric distance. All in all, the observed behaviour seems to follow quite well what is predicted by the models which have been put forward and which were described at the meeting by Dina Prialnik -- they include in particular heat release by sub-surface cristallization of amorphous ice in the nucleus. It is also well established that the unusually great activity of Hale-Bopp which was observed while it was still far from the Sun is mostly caused by the outgassing of CO from its interior; this process pushed large amounts of dust into space. The more dust there is around the nucleus, the more sunlight is reflected and the brighter will the comet appear. IV. The Gas Phase Many gaseous molecules and atoms were observed in the coma. Some of these are electrically uncharged (neutrals), others have lost one or more electrons (ions). Sodium, a neutral atom observed extensively in Hale-Bopp, plays a particular role and was discussed in a special session. Neutrals Didier Despois reviewed extensive radio observations which have led to the discovery of a total of 8 new molecules never seen before in a comet (SO, SO2, H2CS, HC3N, HNCO, NH2CHO, HCOOH, CH3OCHO). Observations of isotopes (now also including DCN, HC15N and C34S for the first time) indicate that this comet is similar to Comet Halley and that it was formed in the solar system. In particular, the HDO/H2O ratio was found to be twice that measured in the Earth's oceans, and 10 times larger than the protosolar value. Thanks to great technological advances, it has now become possible to produce detailed maps of the distribution of individual molecules in the coma. This has led to very interesting research which will ultimately help to understand the extremely complex chemistry of a cometary coma. In particular, this may allow to determine which of the molecules observed really come from the nucleus itself (as parents) and which are secondary products (daughters). Jacques Crovisier reported equally exciting new observations in the infrared spectral region, from the ground with several of the largest infrared telescopes and from space (ISO). This includes hydrocarbons (organic molecules) and also water for which the ortho-to-para ratio was equal to that measured at Halley and indicates the very low spin temperature of 25 K. It is not clear whether this is also the temperature of formation. Unfortunately, at least for this type of research, the very large dust-to-gas ratio observed in Comet Hale-Bopp made observations of spectral emission lines difficult since they were recorded on top of a very strong continuum spectrum of solar light reflected from the dust in the coma. Partly for this reason, it appears that it has not been possible to gain new knowledge about the interesting emission lines from organic molecules seen in the 3.2 - 3.6 micron band. Nevertheless, many new mineral bands were seen in the infrared region (see below). Many spectral observations in the optical region were reported by Claude Arpigny. They generally show that Hale-Bopp is similar to other long-period comets. Several groups have reported detailed, very high-resolution spectroscopic monitoring of the various emission lines in this wavelength region. There is obviously still much work to be done on all of these high-dispersion spectra. In the ultraviolet spectral region observations were made with a number of spacecraft and also with several sounding rockets. Paul Feldman described the spectra obtained with HST and the IUE Space Observatories which include many atomic lines. Further towards shorter wavelengths, a line of singly ionized oxygen (O+) has been detected by the EUVE satellite at 538 A, but unexpectedly, neon (Ne) was not etected in the same spectral region. This points to a very low neon-to-oxygen ratio in this comet, at least 25 times less than the solar value. An enormous Lyman-alpha halo of hydrogen, about 150 million km diameter, that is the distance from the Sun to the Earth, was observed by the SOHO Observatory when the comet was near perihelion. It was also possible to view the comet in the ultraviolet light of various atoms; when compared to images obtained at other spectral wavelengths, they will contribute to the understanding of the processes in the coma. Ions Heike Rauer reported that most of the ions known in earlier comets have also been observed in Comet Hale-Bopp. Strangely, emission from CO+ was first detected quite late (at a heliocentric distance of 3.6 AU); the reason for this is still unclear. Very complex coma and tail structures were observed by Steve Larson and others in the light of CO+ and other selected ions, indicating an exceedingly complex interaction between the solar wind and the cometary ions (streamers, sunward arcs, etc.). In this respect, the detailed mapping of the spatial distribution in the coma and the corresponding velocity field of HCO+ by groups in Europe and the USA provided very valuable observational information. There has clearly been tremendous progress in the modelling of the solar wind/comet interaction in recent years. Tamas Gombosi showed that new and very complex computer software running on the fastest machines available now make it possible to reproduce in quite some detail the observed structure (distribution of ions, magnetic field lines, cavities, sheets, etc.). In this context, the discovery by the Ulysses Spacecraft that the solar wind moves faster at high ecliptic latitudes and therefore interacts stronger with the comet when it is far from the ecliptic plane, has provided an important breakthrough in this field. Sodium While sodium has been seen since 1910 in comets that come close to the Sun, the first signs of a sodium tail was reported in 1957 from an objective prism spectrum obtained of the unusual Comet Mrkos. However, it was in mid-April 1997 that the now famous third cometary tail of neutral sodium atoms and measuring more than 50 million km was discovered by Gabriele Cremonese and his colleagues of the European Comet Hale-Bopp Team. Already at that time, the correct interpretation was brought forward, that is fluorescence acceleration of sodium atoms released in the coma. Meanwhile, this and other groups have also reported the presence of neutral sodium in the normal dust tail, demonstrating that these atoms are also released from the dust in this tail. It is still unclear, however, from where the sodium in the inner coma comes. Interestingly, no NaOH (soda) or NaCl (salt) was found in gaseous form in the coma (but may still be present in the dust grains). Hа сегодня все, пока! =SANA=

Дата: 14 февраля 1998 (1998-02-14) От: Alexander Bondugin Тема: Mars Global Surveyor Update - February 12, 1998 Привет всем! Вот, свалилось из Internet... MEDIA RELATIONS OFFICE JET PROPULSION LABORATORY CALIFORNIA INSTITUTE OF TECHNOLOGY NATIONAL AERONAUTICS AND SPACE ADMINISTRATION PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011 http://www. jpl.nasa.gov Mars Global Surveyor Mission Status February 12, 1998 Mars Global Surveyor is currently in its 128th orbit around Mars. Aerobraking continues to go normally and is being aided by the relatively calm state of the Martian atmosphere. Atmospheric stability allows the spacecraft to dip lower into the Martian atmosphere, experience more air resistance and lower its orbit at a faster rate. The spacecraft's closest approach to Mars is currently bringing it to within 117 kilometers (about 73 miles) of the surface and has reduced the time it takes to complete one orbit around the red planet to 17 hours. The flight team reported that there have been no additional issues with the slightly damaged attachment structure on one of the spacecraft's two solar panels. Global Surveyor's science instruments are scheduled to be turned off on Wednesday, Feb. 18 and remain off until late March. The payload is being shut off because of Surveyor's much- diminished orbital period, which no longer allows enough time to both send aerobraking commands to the spacecraft and to transmit to Earth the scientific data stored onboard. The flight team has begun commands to rotate the spacecraft twice per orbit so that different parts of Global Surveyor are better exposed to the Sun. Normally, Surveyor spends the majority of its time with its high-gain antenna pointed directly at the Earth. The new commands are necessary to keep the temperatures onboard the laser altimeter from falling below 10 degrees Celsius (50 degrees Fahrenheit). Current analysis suggests that the rotations will be necessary until September. After 462 days in flight, Mars Global Surveyor is currently about 340 million kilometers (211 million miles) from Earth, circling Mars about once every 17 hours. The spacecraft's current elliptical orbit takes it about 117 kilometers (73 miles) above the surface of Mars at the closest point and about 25,000 kilometers (15,500 miles) from the planet at the farthest point in the orbit. At present, one-way light time from Global Surveyor to Earth is 18 minutes, 9 seconds. Real-time orbital information about Mars Global Surveyor is available on the Internet at http://marsnt3.jpl.nasa.gov/mgs/realtime/orbit.html. The information is automatically updated every 30 seconds. ##### Hа сегодня все, пока! =SANA=

Дата: 14 февраля 1998 (1998-02-14) От: Alexander Bondugin Тема: NASA Radar Reveals Hidden Remains At Ancient Angkor Привет всем! Вот, свалилось из Internet... MEDIA RELATIONS OFFICE JET PROPULSION LABORATORY CALIFORNIA INSTITUTE OF TECHNOLOGY NATIONAL AERONAUTICS AND SPACE ADMINISTRATION PASADENA, CALIFORNIA 91109. TELEPHONE (818) 354-5011 http://www.jpl.nasa.gov Contact: Mary A. Hardin (818) 354-0344 FOR IMMEDIATE RELEASE February 12, 1998 NASA RADAR REVEALS HIDDEN REMAINS AT ANCIENT ANGKOR New evidence of a prehistoric civilization and remnants of ancient temples in Angkor, Cambodia have been discovered by researchers using highly detailed maps produced with data from an airborne imaging radar instrument created by NASA. Experts say the findings, made possible by the Airborne Synthetic Aperture Radar (AIRSAR) developed by NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA, may revolutionize the way archaeologists view the ancient city's development. Angkor is a vast complex of some 1,000 temples covering more than 160 square kilometers (about 100 square miles) of northern Cambodia. Little is known of the prehistoric occupation of this fertile flood plain, but at its height the city housed an estimated population of 1 million people. The famous temples were built from the 8th to 13th century AD and were accompanied by a massive hydrological system of reservoirs and canals. Today, much of the civilization of Angkor is hidden beneath a dense forest canopy and is inaccessible due to poor roads, land mines and political instability. "The radar data have enabled us to detect a distribution of circular 'prehistoric' mounds and undocumented temples far to the northwest of Angkor," said Dr. Elizabeth Moore, Head of the Department of Art & Archaeology at the School of Oriental and African Studies at the University of London. "The site's topography is highlighted by the radar, focusing our attention on previously neglected features, some at the very heart of the city. "The radar maps not only bring into question traditional concepts of the urban evolution of Angkor, but reveal evidence of temples and earlier civilization either absent or incorrect on modern topographic maps and in early 20th century archaeological reports," she said. "The radar images make apparent many features that are not readily identifiable on the ground," said Dr. Anthony Freeman, a radar scientist at JPL who has collaborated with Moore for the past three years studying the use of radar on the Angkor site. "We can see differences in vegetation structure and some features that are obscured by vegetation cover." In December 1997, Moore surveyed a small mound on the perimeter of the famous 12th century AD temple, Angkor Wat, that Freeman had first noticed in the radar image. "Previous archaeological accounts from 1904 and 1911 note only two temples and make no mention of the distinct circular form of the mound. We found four to six temple remains, including pre-Angkorean structures," Moore said. "This suggests occupation of the 12th century site some 300 years earlier, radically changing accepted chronologies of Angkor." Angkor's beauty is seen its in temples, but the greatness of the Khmer city lies in the multitude of water-related constructions, according to Moore. The Khmer kings nominally dedicated temples to Hindu and Buddhist deities, but the underlying significance was veneration of ancestral spirits, ensuring fertility of the land. Management of water was essential, both for control during the monsoon rains and conservation during the dry season and involved the construction of moats, dikes, canals, tanks, and reservoirs. The largest of these reservoirs, dated to the 12th century AD, is eight kilometers (five miles) long and its function remains a matter of archaeological debate. "These new detailed topographic maps have shown us many more hydrological features and highlighted how they function in the rituals and daily life of the Khmer people," Moore explained. "Using a technique known as radar interferometry, which combines two images to create a three-dimensional topographic map, we can construct a map of the area surrounding Angkor that is more accurate than most maps we have of the United States," said Dr. Scott Hensley, a radar engineer at JPL. "This map lets us see both natural and human-made water management features at the site with great clarity." "Angkor is situated on the edge of the Tonle Sap lake, a unique body of water that doubles in size during the rainy season. These maps give us new insights into the human impact on this ecosystem, from the ancient Khmer to the present day, and are of importance in the study of our changing Earth," Freeman continued. The Angkor radar images were taken in late 1996 as part of the AIRSAR Pacific Rim Deployment and were a follow-up to the 1994 study of Angkor with data collected by the Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar (SIR-C/X-SAR) that flew on NASA's Space Shuttle Endeavour. Like SIR-C/X-SAR, AIRSAR transmits and receives three radar frequencies in both horizontal and vertical polarizations. While both systems use C-band and L-band wavelengths, AIRSAR has the added benefit of P-band, a longer wavelength that can penetrate below the forest canopy. In addition, AIRSAR can be flown in a mode called TOPSAR that allows it to measure topography and create three-dimensional images of the surface. AIRSAR images of the Angkor region will be posted to the Internet at this address: http://www.jpl.nasa.gov/news/ AIRSAR flies on a NASA DC-8 aircraft that is managed at NASA's Dryden Flight Research Center, Edwards, CA. The AIRSAR instrument is managed by JPL, a division of the California Institute of Technology for NASA's Office of Earth Sciences, Washington, DC. This office manages NASA's Earth Science enterprise, an internationally coordinated effort to study natural and human-induced changes in the Earth's land, oceans, atmosphere, ice and life. The AIRSAR flight over Cambodia was funded by the Government of Thailand. Ground verification has been made possible by Vann Molyvann, Minister of State for Culture and Fine Arts, Territorial Management, Urban Planning and Construction; and Dr. Ang Choulйan of the Cambodian Authority for the Protection and Management of Angkor and the Region of Siem Reap. ##### Hа сегодня все, пока! =SANA=

Дата: 14 февраля 1998 (1998-02-14) От: Alexander Bondugin Тема: NASA Selects 335 Innovative Small Business Projects Привет всем! Вот, свалилось из Internet... Donald Nolan Headquarters, Washington, DC February 12, 1998 (Phone: 202/358-1983) RELEASE: 98-25 NASA SELECTS 335 INNOVATIVE SMALL BUSINESS PROJECTS NASA has selected 335 research proposals for negotiation of Phase I contract awards for NASA's Small Business Innovation Research (SBIR) Program. SBIR goals are to stimulate technological innovation, increase the use of small business (including women-owned and disadvantaged firms) in meeting federal research and development needs, and increase private sector commercialization of results of federally funded research. The 1997 solicitation closed on Oct. 14, 1997. NASA received 2,665 proposals submitted by small, high technology businesses from across the Un