NASA Scientific and Technical Aerospace Reports

20040068145 Tokyo Univ., Japan
Contemporaneous Formation of Chondrules in the Al-26-MG-26 System for Ordinary and CO Chondrites
Kurahashi, E.; Kita, N. T.; Nagahara, H.; Morishita, Y.; Lunar and Planetary Science XXXV: Chondrules: The Never-Ending
Story; 2004; 2 pp.; In English; Copyright; Avail: CASI; C01, CD-ROM; A01, Hardcopy
Chronometer using the short-lived extinct-nuclide (26)Al has been applied to chondrules in order to obtain of their
formation ages. Previous studies were mostly performed on Al-rich chondrules, which constitute only 1% of all chondrules,
because of their high Al/Mg ratios. Recently, (26)Al ages of major ferromagnesian chondrules in least equilibrated ordinary
chondrites (OC) have been obtained. However, (26)Al ages of ferromagnesian chondrules in least equilibrated carbonaceous
chondrites (CC) are very limited. Particularly, age data of FeO-poor (Type I) chondrules in CC have been scarcely obtained,
because of their fine textures and lack of phases with high Al/Mg (>100) ratios. In order to clarify the origin and formation
processes of chondrules, we started systematic investigations on Type I chondrules in the most pristine CC (CO3.0
Yamato-81020), by examining textures, bulk chemical compositions, (26)Al ages and oxygen isotopic compositions. We find
Type I chondrules in CC formed contemporaneously with ferromagnesian chondrules in OC.
Author
Chondrule; Chronology; Chondrites; Meteoritic Composition; Aluminum; Magnesium
20040068159 Tokyo Univ., Hongo, Japan
Evaporation and Accompanying Isotopic Fractionation of Sulfur from FE-S Melt During Shock Wave Heating
Tachibana, S.; Huss, G. R.; Miura, H.; Nakamoto, T.; Lunar and Planetary Science XXXV: Chondrules: The Never-Ending
Story; 2004; 2 pp.; In English; Copyright; Avail: CASI; C01, CD-ROM; A01, Hardcopy
Chondrules probably formed by melting and subsequent cooling of solid precursors. Evaporation during chondrule
melting may have resulted in depletion of volatile elements in chondrules. It is known that kinetic evaporation, especially
evaporation from a melt, often leads to enrichment of heavy isotopes in an evaporation residue. However, no evidence for a
large degree of heavy-isotope enrichment has been reported in chondrules for K, Mg, Si, and Fe (as FeO). The lack of isotopic
fractionation has also been found for sulfur in troilites (FeS) within Bishunpur (LL3.1) and Semarkona (LL3.0) chondrules
by an ion microprobe study. The largest fractionation, found in only one grain, was 2.7 +/- 1.4 %/amu, while all other troilite
grains showed isotopic fractionations of <1 %/amu. The suppressed isotopic fractionation has been interpreted as results of
(i) rapid heating of precursors at temperatures below the silicate solidus and (ii) diffusion-controlled evaporation through a
surrounding silicate melt at temperatures above the silicate solidus. The kinetic evaporation model suggests that a rapid heating
rate of >10(exp 4)-10(exp 6) K/h for a temperature range of 1000-1300 C is required to explain observed isotopic
fractionations. Such a rapid heating rate seems to be difficult to be achieved in the X-wind model, but can be achieved in shock
wave heating models. In this study, we have applied the sulfur evaporation model to the shock wave heating conditions of to
evaluate evaporation of sulfur and accompanying isotopic fractionation during shock wave heating at temperatures below the
silicate solidus.
Author
Chondrule; Meteoritic Composition; Chemical Fractionation; Sulfur; Impact Melts
20040068205 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Upcoming and Future Missions in the Area of Infrared Astronomy: Spacecraft and Ground-based Observations
Sittler, E. C., Jr.; International Thermal Detectors Workshop (TDW 2003); February 2004, pp. 1-1 - 1-11; In English; See also
20040068186; No Copyright; Avail: CASI; A03, Hardcopy
The IRIS instrument on the Voyager spacecrafts made major discoveries with regard to the giant planets, their moons and
rings and paved the way for future infrared observations for planetary missions within our solar system. The CIRS instrument
of Cassini with much greater spectral-spatial resolution and sensitivity than that provided by IRIS is now rapidly approaching
the Saturnian system with orbit insertion on July 1, 2004, for which CIRS is expected to provide an order of magnitude
advance beyond that provided by IRIS. The Mars program is also presently dominated by infrared observations in the near
to mid-infrared spectral bands for missions such as Mars Global Surveyor and its TES instrument and Odyssey with its
THEMIS instrument. In the case of Earth science we have such missions as TIMED, which makes infrared observations of
the thermosphere using the SABER instrument. With the newly formed New Frontiers Program we have the opportunity for
$650M missions such as Kuiper Belt-Pluto Explorer and Jupiter Polar Orbiter with Probes. Under the Flagship line, once per
decade, we have the opportunity for $1B missions for which Europa is presently being considered; for this mission infrared
measurements could look for hot spots within the maze of cracks and faults on Europa s surface. On Kuiper Belt- Pluto there
is an imaging near-IR spectrometer called LEISA. Another mission on the horizon is Titan Orbiter Aerorover Mission (TOAM)
for which there is planned a state-of-art version of CIRS called TIRS on the orbiter that will map out the atmospheric
324