Stefano Verani

POSSIBLE DETECTION OF METEOR STREAM EFFECTS ON THE LUNAR SODIUM ATMOSPHERE

Abstract We report two sets of observations of sodium emission from the lunar atmosphere. The spectra were taken on two nights having very similar lunar phases, at various distances from the limb. Using Chamberlains model of the exosphere, we obtained values of the temperature, scale height and number density at the surface. These values differ significantly between the two nights. The spectra of the first night were taken when the Earth–Moon system was entering the Leonid meteor stream and show a marked increase in intensity, temperature and scale height relative to those of the second night, and relative to data for similar lunar phases published in the literature. We believe that this increase is related to an enhanced flux of micrometeoroids associated with the Leonid and possible with the Taurid meteor streams. The micrometeoroid component is generally considered the least important contribution to the sodium flux, and its distribution is assumed to be isotropic. We have previously suggested that an anisotropic and enhanced micrometeor component could be associated with meteor streams. The results reported below support this suggestion.

The 1999 Quadrantids and the lunar Na atmosphere

Enhancements of the Na emission and temperature from the lunar atmosphere were reported during the Leonid meteor showers of 1995, 1997 and 1998. Here we report a search for similar enhancement during the 1999 Quadrantids, which have the highest mass flux of any of the major streams. No enhancements were detected. We suggest that different chemical–physical properties of the Leonid and Quadrantid streams may be responsible for the difference.

Meteor Showers On The Lunar Atmosphere

To investigate the role of impacts as a source of gas in the Moon’s atmosphere, we review a series of observations of the lunar limb made during interaction with the Leonids (1995 and 1997), Quadrantids (1999) and Geminids (1999). Using Chamberlain’s model for the exosphere, with an appropriately adjusted partition function, we calculated the scale height (and thus the kinematic temperature) and the emission of the Na atmosphere, and compared the results with observations published in the literature. We found evidence of small enhancements of temperature and emission of Na during the 1995 and 1997 Leonids, while no enhancements were detected during the 1999 Quadrantids and Geminids. Possible explanations of the different behaviour are presented.

Preliminary calibration results of the wide angle camera of the imaging instrument OSIRIS for the Rosetta mission

Rosetta is one of the cornerstone missions of the European Space Agency for having a rendezvous with the comet 67P/Churyumov-Gerasimenko in 2014. The imaging instrument on board the satellite is OSIRIS (Optical, Spectroscopic and Infrared Remote Imaging System), a cooperation among several European institutes, which consists of two cameras: a Narrow (NAC) and a Wide Angle Camera (WAC). The WAC optical design is an innovative one: it adopts an all reflecting, unvignetted and unobstructed two mirror configuration which allows to cover a 12° × 12° field of view with an F/5.6 aperture and gives a nominal contrast ratio of about 10–4. The flight model of this camera has been successfully integrated and tested in our laboratories, and finally has been integrated on the satellite which is now waiting to be launched in February 2004. In this paper we are going to describe the optical characteristics of the camera, and to summarize the results so far obtained with the preliminary calibration data. The analysis of the optical performance of this model shows a good agreement between theoretical performance and experimental results.

PLEXISS: a coronograph for imaging the lunar atmosphere from the International Space Station

PLEXISS (Planetary Exospheres from the International Space Station) is a proposed small instrument dedicated to the coronagraphic imaging in the Na yellow doublet (5890 and 5896 A) and in the K red doublet (7665 and 7699) A of the transient lunar atmosphere from the International Space Station (ISS). The scientific return of PLEXISS can give important information for the understanding of the transient atmospheres of several other bodies of the Solar System; in particular, the European cornerstone mission Bepi-Colombo to planet Mercury can greatly benefit from PLEXISS. This paper describes the two concepts of coronagraphic telescope design (one totally reflecting and one totally refractive) we have developed for this very challenging application, that requires occulting the lunar disk and providing a clear field of approximately ± 2° around it, with a resolution of about 30 arcsec per pixel.

Lunam 2000 (Lunar Atmosphere Mission)

LUNAM 2000 is a small mission dedicated to the coronagraphic imagingin the Na yellow doublet and to UV spectroscopy in the range2800–3400 A of the lunar atmosphere. These studies are possible only from Space. The scientific return of LUNAM 2000 has a wider appeal for the studyof transient atmospheres of other celestial bodies, in particular ofMercury. The mission is in low Earth-orbit (about 350 km); asun-synchronous or other orbits are under investigation. The payload has very small weight, dimensions and power requests, and is essentially made withoff-the-shelf components. It can be built and launched in less than 3years from the approval. This time frame nicely overlaps that of theEuropean technological Mission SMART 1 and can greatly add to itsscientific return. Furthermore, LUNAM 2000 can give very importantinformation to define a mission to Mercury such as Bepi Colombo.