Broad science objectives of Leonid MAC missions. See also: Leonid
science news.
Astrobiology:
Leonid MAC is NASA's first Astrobiology mission.
It's mission is to learn how extraterrestrial
materials may have been brought to Earth at the time of the origin of life.
In addition, the interaction of meteoroids with the atmosphere generates molecules
that may have played a role in the origin of life on Earth. Our objectives are:
- Determine fate of organic matter during ablation
- differential ablation (117 km)
- conditions in meteor wake plasma
- atmospheric chemistry
- formation of solid debris containing organic matter
- aerothermochemistry, synthesis of molecules
EXAMPLE: LIFE's PRECURSORS CAN SURVIVE PLUNGE IN ATMOSPHERE
Not all meteoric matter is atomized during the plunge in Earth's
atmosphere. Organic matter remained mysteriously undedected during last
year's Leonid MAC. In a recent paper, Jenniskens et al. postulated that
the organic matter may be lost in the form of large complex molecules that can
readily emit the heat deposited by the violent collisions with air
molecules before falling appart altogether. Such large molecules are not
easily detected, except by their heat emission. Indeed, Ray Russell et al. discovered the fingerprint of organic matter in
what may be meteoric debris in the path of a bright Leonid fireball.
Pointing the mid-IR telescope onboard FISTA to the persistent train of the fireball,
emission at 3.4 micron was detected that resembles the signature
of complex organic matter observed in cometary dust. However, at
present it can not be excluded that trace air compounds are responsible.
Read more: Nov. 13 - Organic fingerprint
Nov. 20 - A bacterial fingerprint?
Review paper.
Read more here.
Comet dust trails:
The rate of meteors, when provided in near-real time, is practical
information for satellite operators. It also provides a cross section of the dust
density in the stream, which is a signature of processes of dust ejection. Individual meteors
observed stereoscopically yield orbits in space. Remote sensing of the light and the
breakup in colors called spectroscopy, yields information on meteoroid composition.
Hence, meteor observations are a poor man's comet mission to probe otherwise
invisible phenomena
close to the comet nucleus. Hence for planetary astronomy our objective is:
- Determine how comets loose bulk of mass
- dust trail formation
- dust ejection velocities
- dust grain density
- dust grain main element composition
- dust morphology changes over time
EXAMPLE: URSIDS: DUST FROM TIME OF COLUMBUS ABOUT TO HIT
EARTH ON DECEMBER 22, 2000
Dec. 18 - Dec 22 Ursid outburst
Dec. 23 - Ursid outburst confirmed
Dec. 24 - Ursid shows early release of sodium
Dec. 25 - Ursid shower circular IMO
DURING 1999 METEOR STORM, COMET DUST CRUMBLED LESS FINE
Ian Murray et al. discovered from imaging onboard Leonid MAC that Leonids in
the 1999 encounter fell appart in relatively larger fragments than did
Leonids during the 1998 encounter. Both the 1998 and 1999 Leonid light curves
were flat-topped, implying that the meteoroids quickly fell appart in
fragments upon entry in the Earth's atmosphere, but the 1998 light curves
tended to peak early in the trajectory followed by a gradual fading,
while the 1999 light curves gradually ramped up to a late peak. The cause
of this unexpected behaviour is not understood. Both encounters were with
dust ejected in 1899. We now look forward to an encounter with the dust
trail of 1932 on November 16/17, 2000.
read more: Oct. 30 - Comet dust crumbled less fine
Read more here.
Satellite Impact Hazard:
The Leonid meteoroids are an impact hazard. They represent a collimated beam of
very fast (71 km/s) meteoroids that generate a relatively large and unusually highly
charged vapor cloud when hitting a solar panel. Such cloud can penetrate important
electronics and cause a short-out. Our objective is:
-
Prevent damage to satellites
- Improve prediction models
- Provide near-real time flux information
Near real time flux measurments were reported during the 1999, 2000, 2001, and 2002 Leonid MAC missions. The technique of visually counting the meteors on intensified cameras positioned at the aircraft windows provided a very accurate count in small time intervals. Satellite operators were able to follow the rate of the shower while the storms unfolded.
Read more here.
Earth's upper atmosphere:
The molecules and debris left behind affect the atmospheric chemistry and
physical conditions in the region
between 80 and 120 km altitude, where airglow is normally observed.
Persistent trains probe the atmosphere winds, molecular and turbulent diffusion,
and gravity waves. Persistent trains enable telescopes to
be pointed at the path of a meteor and probe airglow chemistry under unusual conditions.
Much remains ununderstood about these striking phenomena. Also,
during the 1999 Leonid storm, an unsual rate of elves and sprites were observed above
cloud-to-ground lightning. A possible link between meteor activity and lightning phenomena
is studied.
Our objectives are:
- Follow response to dust influx anomaly
- variations in trace air compounds in upper atmosphere
- variations in airglow
- occurrence of sprites/elves
- persistent train chemistry
Different types of airglow trace different altitudes in the atmosphere:
Source Wavelength Height of emitting layer Intensity
H 656.3 nm geocorona 4-6 R (night)
[OI] 630.0 nm 250 - 300 km 60 R
[OI] 636.4 nm 250 - 300 km 20 R
Na D 589.0 nm, 589.6 nm 92 km 30-100 R
O2 (Herzberg bands) 300 nm - 400 nm 90 km 0.8 R/A
[OI] 557.7 nm 90 km 250 R
pseudocontinuum 400 nm - 700 nm 90 km 0.3 R/A
OH 600 nm - 4.5 micron 85 km 4.5 MR(all bands)
O2 864.5 nm 80 km 1 kR
EXAMPLE: ATMOSPHERE GETS A JOLT FROM LEONID STORM
Joe Kristl et al. report an increase in OH airglow emission during the peak
of the Leonid shower. No such change was observed for sodium emission and
O2 airglow emissions. It is not clear yet how the enhanced influx of meteoric
matter caused the change in airglow chemistry.
Despois et al. observed a decline of HCN molecules in the upper atmosphere
one day after the Leonid storm.
Read more: Nov. 07 - Meteors affect atmospheric chemistry
Nov. 15 - HCN disappears mysteriously
Read more here.
A multi-disciplinary approach:
Leonid MAC will utilize a wide range of innovative observing techniques to study the physical
properties of meteors as they interact with the atmosphere.
Each wavelength regime gives a different type of information:
- The ultraviolet and visible wavelenghts reveal electronic transitions in atoms ablated
from the meteors, such as Na, Mg, Fe, and in such molecules as CN, C2 and FeO.
- The interaction with the atmosphere are best studied in the near-infrared, where
molecules such as OH, N2 and O2 radiate.
- The
mid-infrared yields thermal emission and vibrational signatures of molecular materials,
such as the molecule CO and complex organic compounds.
- Sub-millimeter radio observations provide measurements of rotational transitions
in specific molecules such as HCN.
Figure: Observing targets (top) and spectral coverage of instruments (bottom).
The observing targets include dust in space, meteors, meteor persistent trains,
airglow and elves/sprites. The coverage of instruments show the different regimes
of wavelength that are examined by different imagers and spectrographs.
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