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(meteorobs) Re: NRL Instrument Makes First UV Observation of Meteor in Space

http://www.pao.nrl.navy.mil/rel-00/images/gimi-flyer.pdf

--- Ron Baalke <BAALKE@kelvin.jpl.nasadot gov> wrote:
> Public Affairs Office
> Naval Research Laboratory
> Washington, D.C.
> 
> February 9, 2000
> 
> NRL Press Release 9-00r
> 
> NRL Instrument Makes First UV Observation of Meteor
> in Space
> 
> Scientists from the Naval Research Laboratory (NRL)
> report that the first
> ever far-ultraviolet (UV) image of a meteor has been
> obtained by the
> Global Imaging Monitor of the Ionosphere (GIMI)
> instrument on board the
> DoD Space Test Program's Advanced Research and
> Global Observation
> Satellite (ARGOS). The image was taken on November
> 18, 1999, during the
> annual Leonid maximum, which in 1999, lasted from
> November 16 - 18.
> 
> At the time of the exposure, the ARGOS spacecraft
> was about 20 deg south
> of the equator, over the south Pacific Ocean;
> however, the viewing direction
> (and the ARGOS altitude of 833 km) was such that the
> meteor itself was
> much closer to the equator.
> 
> Dr. George Carruthers, NRL's GIMI principal
> investigator, reports the
> scientific significance of the observation, saying,
> "To our knowledge, this
> is the first observation of a meteor entry to the
> atmosphere in the far-UV
> spectral range. Such an entry cannot be observed
> from Earth's surface or
> from aircraft because of its absorption by the lower
> atmosphere. Ground-
> based observations of meteors cannot detect many of
> the important
> elements and compounds expected to be present in
> meteoroids."
> 
> "The first observation from space of a meteor, by
> GIMI in UV light, adds
> another dimension to the handful of previous space
> observations of
> meteors," notes Dr. Noah Brosch of the Wise
> Observatory and the
> Department of Astronomy and Astrophysics at Tel Aviv
> University in
> Israel. Dr. Brosch explains, "Satellites view the
> Earth continuously and
> rarely detect extremely bright fireballs. These
> detections are mostly in
> the visible or near-infrared spectral domains. The
> GIMI observation is
> the first such space experiment to be done in the
> UV."
> 
> Commenting on the practical application of this
> discovery, Brigadier
> General (sel) S. Pete Worden, USAF Deputy Director
> for Command and
> Control says, "As our civil, commercial and national
> security use of
> space continues to increase, natural phenomena that
> can disrupt satellite
> operations cause growing concern. The Leonid meteor
> storm is such a
> phenomenon. NRL's impressive data promises to
> provide a unique new tool
> to understand the true composition and structure of
> these meteors. This
> is vital information if we are to predict and
> mitigate future
> meteor-induced problems to our space operations."
> 
> Abundances of various elements and compounds found
> in meteors are known
> to be highly variable among the types of meteorites
> which have been
> recovered on the ground, but the latter are not
> representative of the
> range of meteoroids as expected to be present in the
> solar system, since
> only the most refractory and/or massive meteoroids
> survive entry to the
> atmosphere. Once we have an opportunity to analyze
> our data and examine
> other images for events of this type, says
> Carruthers, we may establish
> the feasibility of using far-UV spectroscopic
> instruments to more
> accurately measure the compositions of incoming
> meteoroids.
> 
> Because Earth's lower atmosphere strongly absorbs
> far-UV radiation in the
> wavelength range observed by GIMI (131-200
> nanometers, or 1310-2000
> Angstroms), the scientific team estimates that in
> order to be observable,
> the meteor had to have been at an altitude well
> above 100 kilometers. Since
> its entry velocity was probably in excess of 60
> km/sec (i.e. much higher
> than Earth escape velocity of 11.2 km/sec), the
> energy was probably
> available for producing emission in the far-UV at
> relatively high altitudes,
> due to excitation of the atmosphere and/or meteoric
> constituents.
> 
> The most likely emission source, Dr. Carruthers
> says, is nitric oxide (NO)
> which is produced and excited by dissociation of
> molecular nitrogen and
> its subsequent reaction with atomic oxygen,
> producing emission in the
> 190-200 nm wavelength range. However, if the meteor
> is of carbonaceous
> composition, far-UV emissions of carbon monoxide
> (CO) and atomic carbon
> may be produced as well.
> 
> GIMI is one of nine primary experiments on the ARGOS
> mission, which
> launched into a polar orbit on February 23, 1999 to
> study space weather.
> GIMI's principal objective is to obtain simultaneous
> wide-field FUV/EUV
> images of ionospheric and upper atmospheric
> emissions, covering large
> areas of the earth from a low-earth orbit. The GIMI
> images will be used
> to determine chemical densities [O+, nighttime O2,
> NO and N2] on a global
> basis and to detect disturbances in the ionosphere
> that are caused by
> auroral activity, gravity waves and foreign
> materials from meteors,
> suspected "ice comets," rocket exhausts and chemical
> releases. In between
> the atmospheric observations, GIMI is gathering data
> for an all-sky survey
> of stars and data on celestial diffuse sources at
> far-ultraviolet wavelengths.
> 
> The GIMI instrument has two cameras for simultaneous
> observations of
> selected targets. Camera 1, which is sensitive in
> the 75-110 nm ranges is
> primarily being used for observations of the dayside
> ionosphere, auroras,
> and stellar occultations, and for star field
> surveys. Camera 2 is sensitive
> in the 131-160 and 131-200 nm far-UV wavelength
> ranges and is used for
> observations of the nightside ionosphere, airglow,
> stellar occultations,
> star field surveys, and also gas releases and rocket
> plumes at night.
> 
>                                     -30-
> 
> Meteor image and caption,
>
http://www.pao.nrl.navy.mil/rel-00/images/gimi-flyer.pdf
> (99KB)

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