Беннет кометинің 1970 жылғы Жерге жақын өтуі

Icy small Solar System body; passed closest to Earth in 1970

Comet Bennett, formally known as C/1969 Y1 (old style 1970 II and 1969i), was one of the two bright comets observed in the 1970s, along with Comet West and is considered a great comet. The name is also borne by an altogether different comet, C/1974 V2. Discovered by John Caister Bennett on December 28, 1969, while still almost two AUs from the Sun, it reached perihelion on March 20, passing closest to Earth on March 26, 1970, as it receded, peaking at magnitude 0. It was last observed on February 27, 1971. At that time the comet was about 1.7 AU both from the Sun and the Earth. The comet continued to brighten during March, as it approached both the Sun and Earth. By the middle of the month it was a first magnitude object with a prominent curved tail about 10 degrees long. On 26 March was the perigee of the comet, when it approached Earth at a distance of 0.69 AU. Numerous research projects were therefore initiated, so that Comet Bennett became the most photographed and most thoroughly researched comet at the time of its appearance. From the photometric data obtained with OAO 2, the production rates of OH and H and their dependence on the comet's distance from the sun could be derived. The results confirmed the assumption that the gas production of comets at small solar distances is determined by the evaporation of water from the nucleus. The total loss of water during its passage through the inner solar system has been estimated at 200 million tonnes. The comet was also observed for the first time by the Orbiting Geophysical Observatory (OGO 5) on April 1 and 2. With a more sensitive photometer than with OAO 2, emissions from hydrogen atoms could be detected up to a distance of several million km from the comet's nucleus. From the measurements, the mass of this hydrogen could be derived at about 2 million tones. After these first successful measurements, it was decided to continue observing the comet with the instruments on board OGO 5 and thus a total of twelve intensity maps of the comet's Lyman α emission were obtained by April 30. The maps show the evolution of the hydrogen envelope over the course of a month. On April 1, when the comet was about 0.6 AU from the Sun, the hydrogen envelope was 20 million km × 15 million km in size, after which it slowly began to shrink. The derived hydrogen atom production rate was comparable to the value obtained from the OAO 2 observations. In further investigations, attempts were then made to theoretically underpin the measurement results with greater agreement and to provide refined models for the formation of the hydrogen shells.

At the Goddard Space Flight Center in Maryland, images of the comet were taken from March 28 to April 18, 1970, with interference filters at different wavelengths in the violet, blue, green, and yellow regions of the spectrum. In particular, the emission lines of CN, C2, CO+ and Na were evaluated. Maps of the comet's coma with lines of the same brightness (isophotes) up to a distance of 150,000 km from the nucleus were created from these and other images taken on April 8 and 9 at the Hamburg Observatory in white light. Similar surveys were also conducted from March 31 to April 27 at the University of Western Ontario's Hume Cronyn Memorial Observatory in Canada. There, too, images of the comet were taken with interference filters at different wavelengths in the violet, blue and green regions of the spectrum. In particular, the emission lines of CN and C2 were measured and their intensity profiles evaluated in parallel and perpendicular directions to the comet's tail and presented in the form of isophotes. From March 30 to May 7, 1970, spectrographic studies of the comet were made at the Observatory of the University of Toledo in Ohio. In this way, brightness profiles of the emission lines of C2 and CN were obtained up to a distance of 100,000 km from the comet's nucleus. A brightness profile of the "forbidden" emission line of the oxygen atom at 630 nm was also created from images from April 18. It has been suggested that these atoms result from the decay of and that comet Bennett contained in excess of water. The same images were also used to create a brightness profile of the + ion up to a distance of about 100,000 km from the nucleus and to determine its production rate. The results could later be revised through improved processing of the data. From March 7 to 18, images of the comet were taken at the Cerro Tololo Inter American Observatory in Chile. The comet's tail showed no noticeable disturbances, only pronounced side rays could be observed. This indicates that relatively quiet interactions between the solar wind and associated magnetic fields and the comet were occurring during this period. Images taken from late March to late May at the Osservatorio Astrofisico di Asiago in Italy were evaluated for the distribution of gas and dust in Comet Bennett's tail. On the 3/4 April, it was observed that the comet's gas tail had been torn off the coma. Spectra of the neutral gas envelope showed the emission lines of CN, C2, , CH, |NH2 and Na. The gas tail showed a diurnal variation in intensity and structure, indicating a very erratic production of CO+. In particular, attempts were also made to correlate a prominent kink observed in the comet's gas tail on April 4 with simultaneous measurements of solar activity and solar wind. This was done using measurement data provided around the same time by the OGO 5, Vela 5, HEOS 1 and Pioneer 8 spacecraft, as well as by the ALSEP experiment installed on the lunar surface by Apollo 12. In a first investigation, no events were found in the measured dynamics of the solar wind that could explain the deformations of the comet's tail. However, further investigation concluded that, first, the dynamics of the solar wind measured near Earth were probably different from those near the comet, and second, the monitoring of the solar wind was patchy in terms of location and time, so that the deformations of the comet's tail can probably still be traced back to events in the solar wind. Three images of the comet in red light, taken May 5–8 at the Thuringian State Observatory in Tautenburg, when the Earth was almost in the comet's orbital plane, showed two anomalous structures in the comet's tail: a radial structure and a short sunward spikes, probably caused by the comet's dust. The later evaluation of these observations provided evidence for the peculiarity of a "neckline structure" (NLS) in the dust tail of a comet, which was only theoretically derived in 1977.

Observations of the comet's brightness evolution in the infrared were made in late March to mid April 1970 at the Lunar and Planetary Laboratory in Arizona. In addition, on March 31, 1970, observations were made with an infrared telescope on board a Learjet. On April 4, 1970, Comet Bennett was photometrically measured at the O'Brien Observatory of the University of Minnesota in the near and mid infrared at 2 20 μm wavelength. In addition to the continuum of a black body of about 500 K at short wavelengths, an emission line could also be detected at 10 μm, which was traced back to silicate grains in the dust of the comet. The measurement result was confirmed by another measurement on April 21 at Kitt Peak National Observatory in Arizona.

With the radio telescope of the Green Bank Observatory in West Virginia, an attempt was made over six days in mid March 1970 to detect the emission of formaldehyde at 4.83 GHz. Likewise, the radio telescope at the United States Naval Research Laboratory in Maryland attempted to detect the emission of water molecules at 22.2 GHz over four days at the end of March 1970. In both cases, no such emissions could be detected.

Comet Bennett was intended to be photographed by the crew of Apollo 13 during their journey to the Moon. Their first attempt on April 13, 1970, was unsuccessful. On April 14, 1970, after completing the maneuver to orient the spacecraft for a second attempt, Odysseys service module ruptured, forcing the cancellation of the mission's scientific objectives and touchdown on the lunar surface.