Soon after the first orbital elements could be calculated, it was suggested that the comet would become "a bright object, that could be observed with
unaided eye." It was found to combine three favorable characteristics that made it an exceptional comet for observation: a short perihelion distance, a short distance from Earth, and high intrinsic brightness. 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.
Ultraviolet observations A few years earlier it had been suggested that comets are surrounded by a shell of
hydrogen gas, which could be detected by observing in the
ultraviolet the
Lyman α line at 121.5 nm. However, this observation is not possible from the ground because the ultraviolet light does not penetrate the atmosphere. The first observation of a comet in the ultraviolet came in January 1970 when the
Orbiting Astronomical Observatory 2 (OAO-2) acquired the spectrum of comet
C/1969 T1 (Tago–Sato–Kosaka) and verified the predicted hydrogen envelope. In February of the same year, Comet Bennett reached a favorable observation position for observation from space and was systematically observed with OAO-2 and OGO-5 on the basis of this discovery from mid-March to mid-April in order to track the temporal and spatial changes in the comet's coma. 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.
Visible light 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, diatomic carbon|,
CO+ and
Na were evaluated. Maps of the comet's coma with lines of the same brightness (
isophotes) up to a distance of 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 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 and CN were obtained up to a distance of 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, , triatomic carbon|,
CH, amino radical| 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.
Infrared 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 4 April 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.
Microwaves 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.
Apollo 13 attempted photograph 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. == References ==