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(meteorobs) Excerpts from "CCNet DIGEST, 19 January 1999"


------- Forwarded Message

From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet DIGEST, 19/01/99
Date: Tue, 19 Jan 1999 10:57:39 -0500 (EST)

CCNet DIGEST, 19 January 1999
-----------------------------

(1) NEAR UPDATE
    Ron Baalke <BAALKE@kelvin.jpl.nasadot gov>=20
...

(6) THE SOLAR GAS RECORD IN LUNAR SAMPLES AND METEORITES
    R. Wieler, ETH ZURICH
...

--------------------------------------------------------------------
(1) NEAR UPDATE

>From Ron Baalke <BAALKE@kelvin.jpl.nasadot gov>=20

NEAR Clean-Up Hydrazine Engine Burn Scheduled for Jan. 20
http://near.jhuapldot edu/news/flash/99jan15_1.html

A small hydrazine engine burn is scheduled for Jan. 20 at noon, EST.=20
This burn is intended to fine-tune the spacecraft's trajectory by=20
approximately one degree and to increase its speed by 31 miles per hour =
(14 meters/second), allowing NEAR to gain on the faster-moving Eros=20
asteroid. This trajectory correction maneuver was planned following the =
successful completion of the large bipropellant engine burn on Jan. 3.

--------------------------------------------------------------------
(6) THE SOLAR GAS RECORD IN LUNAR SAMPLES AND METEORITES

R. Wieler: The solar noble gas record in lunar samples and meteorites.
SPACE SCIENCE REVIEWS, 1998, Vol.85, No.1-2, pp.303-314

ETH ZURICH, ISOTOPE GEOL, NO C61, CH-8092 ZURICH, SWITZERLAND

Lunar soil and certain meteorites contain noble gases trapped from the
solar wind at various times in the past. The progress in the last=20
decade to decipher these precious archives of solar history is=20
reviewed. The samples appear to contain two solar noble gas components=20
with different isotopic composition. The solar wind component resides=20
very close to grain surfaces and its isotopic composition is identical=20
to that of present-day solar wind. Experimental evidence seems by now=20
overwhelming that somewhat deeper inside the grains there exists a=20
second, isotopically heavier component. To explain the origin of this=20
component remains a challenge, because it is much too abundant to be
readily reconciled with the known present day flux of solar particles=20
with energies above those of the solar wind. The isotopic composition=20
of solar wind noble gases may have changed slightly over the past few=20
Ga, but such a change is not firmly established. The upper limit of=20
similar to 5% per Ga for a secular increase of the He-3/He-4 ratio sets =
stringent limits on the amount of He that may have been brought from=20
the solar interior to the surface (cf. Bochsler, 1992). Relative=20
abundances of He, Ne, and Ar in present-day solar wind are the
same as the long term average recorded in metallic Fe grains in
meteorites within error limits of some 15-20%. Xe, and to a lesser=20
extent Kr, are enriched in the solar wind similar to elements with a=20
first ionisation potential < 10 eV, although Kr and Xe have higher=20
FIPs. This can be explained if the ionisation time governs the FIP=20
effect (Geiss and Bochsler,  1986). Copyright 1999, Institute for=20
Scientific Information Inc.

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