29. Unusual Chemical Compositions of Noctilucent-Cloud Particle Nuclei

PRECEDING PAGE PLAN'K NOT FI fl D

CURTIS L. HEMENWAY Dudley Observatory and State University of New York at Albany Albany, New York

On August 8, 1970, two Pandora sounding rocket payloads were launched from the ESRO range in Kiruna, Sweden during a noctilucent cloud display. Large numbers of sub-micron particles were collected, most of which appear to be made up of a high- density material coated with a low-density material. Typical electron micrographs are shown. Particle chemical compositions have been measured by use of dispersive x-ray analysis equipment attached to a Phitips EM 300 electron microscope and hat, e re- vealed that most of the high-density particle nuclei have atomic weights greater than iron.

Sundsvall, 600 km south of Esrange. Figure 1 N AUGUST 8, 1970 at 1:48 and at 3:54 local time, two Nike Apache sounding rockets shows a photograph of the noctilucent cloud over containing Pandora micrometeorite collectors Esrange into which the rockets were launched as were launched into a noctilucent cloud display seen from SundsvalI. above Esrange in Kiruna, Sweden. The visual The sampling surfaces as in past Pandora observation of the noctilucent clouds was carried flights (Hemenway and Hallgren, 1970; Hallgren out by Nathan Wilhe]m of Meteorological In- and Hemenway, 1970) consisted of thin nitro- stitute of Stockholm University and P_h cellulose films supported on copper grids. Since Carnevale (AFCRL) who were stationer at in-flight shadowing was used, the grids were

FmVRE I.--Photograph of the noctilucent cloud sampled. 287 288 EVOLUTIONARY AND PHYSICAL PROPERTIES OF METEOROIDS

_eded with tungsten oxide particles to act as a Pandora N, the first payload launched, the monitor of the quality of the shadows. altitudes sampled were 82 to 94 km and 94 to All payload functions performed as planned 124 km and for Pandora M the altitudes were but unfortunately the trajectory of each payload 85 to 96 km and 97 to 133 km. was about 10 km lower than planned, with the Figure 2 shows examples of an unusual type of result that the shadowing for the first two sam- particle found in large numbers on Pandora N pling increments from each payload took place and to a lesser extent on Pandora M. The parti- at an altitude where the ambient pressure was cles generally consist of high-density material sur- too high for producing sharp shadows. For rounded by a round-to-elliptical, droplet-like

FmuR_ 2.--Electron micrographs of noctilucent cloud particles collected. UNUSUAL CHEMICAL COMPOSITIONS OF NOCTILUCENT-CLOUD PARTICLE NUCLEI 289

coating of low electron optical density. Appro.,d- are noted on the left sides of the spectra. Figure 4 mately 70 percent of the collected particles were shows an additional example of x-ray spectra of a of this unusual type. Somewhat similar two- particle and nearby background in which a component particles were collected during a silicon peak at 42.0 ° associated with the particle noctilucent cloud display in 1962 (Hemenway et and other peaks of uncertain origin can clearly al., 1962). be seen. By using an x-ray spectrometer attached to The presence of high atomic number elements our Phillips 300 electron microscope, it has is consistent wkh the high electron-optical been possible to obtain qualitative chemical density of the nuclei of the coated particles. analyses from a study of the characteristic x-ray Tentatively, the following elements have been emission from some of the collected particles. identified as associated with the haloed particles: Figure 3 shows an example of x-ray spectra of a lanthanum, silicon, thulium, praseodymium, os- particle and the nearby background in which mium, ytterbium, and tantalum. There are a the lanthanum lines located at 47.2 ° and 48.5 ° number of weak lines which have not been associated with a noctilueent cloud particle are identified and other marginal identifications clear. The remaining lines of tungsten and gold which have not been included even though they

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Fmvag 3.--X-ray spectra of a particle and nearby back- FIGURE 4,--Xoray _pectra of a particle and nearby beck- ground, ground. _J

290 EVOLUTIONARY AND PHYSICAL PROPERTIES OF METEOROIDS seem to be mostly high z elements. The one ob- of fissioned material and a high efficiency mecha- servation which is clear is that the observed nism for concentrating particles into the Polar x-ray lines from these particles appear for the regions. most part to be restricted to elements of atomic The possibility that supernova particulate number greater than iron. remnants have been encountered has also been The possibility that the particles are fallout suggested and appears to have even more severe from atomic bomb testing has been considered difficulties although Greenberg (1969) has sug- and has difficulties. For example, if atomic gested that an interstellar component of dust bomb debris can be carried upward through the might exist in the solar system. Additional meas- stratosphere to an altitude of 85 km then the wide urements and flight collections will be necessary variety of terrestrial spores, salt particles, bits of before the origin of these intriguing and unex- mica, etc., found in the troposphere should also pected particles can be identified. be elevated. Such is not the case. Furthermore, The author expresses his thanks to Douglas Rauser and Fecht ig (1972) have shown that noctilu- Hallgren, Anthony Laudate, David Wachtcl, cent cloud particles measured at Kiruna, Sweden Helga Sehroedcr, Gall Heylmun, Richard Schwarz and William Radigan for many hours of sample two days after our collection flight were entering scanning and analysis. My thanks go also to the mesopause from above and falling downward James Lease of Goddard Space Flight Center. I through it. In addition, it has been many years wish to thank George Witt and Nathan Wilhelm since any kno_al space tests of atomic devices of 5.IISU and Ralph Carnevale of AFCRL and have been carried out and furthermore such an the Swedish Space Technology groups for their origin would appear to require too large a mass support in Sweden.

REFERENCES

GREENBERG, J. M., 1969. A possible inter-relation between interstellar and interplanetary cosmic dust, Space Research IX, 111-115. HALLGREN, D. S., AND HEMENWAY, C. L., 1970. Sounding rocket samplings of cosmic dust, Space Research X7, 377-381.

HEMENWAY, C. L., AND HALLGREIq, D. S., 1970. Time variation of the altitude distribution of the cosmic dust layer in the upper atmosphere, Space Research X, 272-280. HEMENWAY, C. L., SOBERMAN, R. K., AND WITT, G., 1964. Sampling of noctilucent cloud particles, Tellers, 16, 84-88.

RAUSER, P.j AND FECIITI(], H., 1972. Combined dust collection and detection experiment during a noctilueent cloud display above Kiruna, Sweden, Space Research XII, 391-402.