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------------------------------------------------------------------------

There are 6 messages in this issue.

Topics in this digest:

      1. Arecibo radar observations of 22771 (1999 CU3)
           From: Lance Benner <lance@reason.jpl.nasa.gov>
      2. Arecibo and Goldstone radar observations
           From: Lance Benner <lance@reason.jpl.nasa.gov>
      3. Re: Arecibo and Goldstone radar observations
           From: Petr Pravec <ppravec@asu.cas.cz>
      4. Re: Arecibo and Goldstone radar observations
           From: Petr Pravec <ppravec@asu.cas.cz>
      5. Asteroid first, Mars and Moon Later
           From: "albertajacksoniv" <albertajacksoniv@yahoo.com>
      6. Optical Detection of Anomalous Nitrogen in Comets
           From: Ron Baalke <baalke@zagami.jpl.nasa.gov>


________________________________________________________________________
________________________________________________________________________

Message: 1
   Date: Thu, 11 Sep 2003 16:24:44 -0700
   From: Lance Benner <lance@reason.jpl.nasa.gov>
Subject: Arecibo radar observations of 22771 (1999 CU3)

Greetings everyone,

Arecibo radar observations of near-Earth asteroid 22771 (1999 CU3)
started on September 10 and are going well.  The images reveal that 1999
CU3 is highly elongated, somewhat angular, and that it has a rotation
period of roughly several hours (the actual rotation period is unknown,
to the best of my knowledge).  The images are available at:

http://www.naic.edu/~radarusr/1999CU3/1999cu3.2003sep10.collage.gif
http://www.naic.edu/~radarusr/1999CU3/1999cu3.2003sep11.collage.gif
 
We observed 1999 CU3 at Arecibo two years ago and also saw evidence for
elongation and relatively rapid rotation, but the images this time are
much stronger due to the asteroid's closer approach to Earth.  Arecibo
observations will conclude on September 12 shortly before the asteroid
moves too far north for Arecibo to track.  We also plan to observe 1999
CU3 at Goldstone next week on dates that straddle the closest approach.  

Best wishes,

Lance (on behalf of the radar team)

----------------------------------------------------------------- 
Dr. Lance A. M. Benner		phone:  818-354-7412 
Mail Stop 300-233		fax:           -9476
Jet Propulsion Laboratory	e-mail: lance@reason.jpl.nasa.gov 
4800 Oak Grove Drive		http://echo.jpl.nasa.gov/ 
Pasadena, CA 91109-8099
-----------------------------------------------------------------


________________________________________________________________________
________________________________________________________________________

Message: 2
   Date: Thu, 11 Sep 2003 16:34:40 -0700
   From: Lance Benner <lance@reason.jpl.nasa.gov>
Subject: Arecibo and Goldstone radar observations

Greetings,

To follow up on my previous email regarding radar observations of 1999
CU3, I'd like to mention that radar observations are planned for at
least three other near-Earth asteroids during September and October:
1998 RO1, 2003 KP2, and 2001 KZ66, all at Arecibo.  We are also trying
to schedule observations of 1998 FG2 at Goldstone in October but it's
not clear yet if we will get telescope time.  Photometry for all of
these objects would be useful.

The Arecibo and Goldstone asteroid radar schedules are available on the
web at:

http://www.naic.edu/~pradar/sched.shtml
http://echo.jpl.nasa.gov/asteroids/goldstone_asteroid_schedule.html

These websites also indicate whether optical astrometry is necessary to
support the radar observations and whether physical observations such as
lightcurves and spectroscopy would be useful (usually the answer to the
latter question is YES).  

For those of you who are interested in lightcurves, we recently
established two other websites that list 

1) all the near-Earth asteroids previously detected by radar, their
rotation periods (if known), and when the objects might be visible at
solar elongations greater than 90 degrees and at visual magnitudes
brighter than 20; 

and 

2) similar information for _future_ NEA radar targets scheduled into the
summer of 2004.  

Those websites are available at:

http://echo.jpl.nasa.gov/~lance/radar.nea.periods.html
http://echo.jpl.nasa.gov/~lance/future.radar.nea.periods.html

The main reason we created these two websites is to identify
radar-detected asteroids in need of photometry and when they might be
observable in the future.  It turns out that the rotation periods of
many near-Earth asteroids observed by radar are unknown.  If the
rotation periods became available, they would greatly increase the value
of the radar observations, and, in some cases, enable us to estimate
three-dimensional shapes that we would not be able to obtain otherwise.  

Best wishes,

Lance
 
----------------------------------------------------------------- 
Dr. Lance A. M. Benner		phone:  818-354-7412 
Mail Stop 300-233		fax:           -9476
Jet Propulsion Laboratory	e-mail: lance@reason.jpl.nasa.gov 
4800 Oak Grove Drive		http://echo.jpl.nasa.gov/ 
Pasadena, CA 91109-8099
-----------------------------------------------------------------


________________________________________________________________________
________________________________________________________________________

Message: 3
   Date: Fri, 12 Sep 2003 10:15:26 +0200 (MET DST)
   From: Petr Pravec <ppravec@asu.cas.cz>
Subject: Re: Arecibo and Goldstone radar observations


> Greetings,
> 
> To follow up on my previous email regarding radar observations of 1999
> CU3, I'd like to mention that radar observations are planned for at
> least three other near-Earth asteroids during September and October:
> 1998 RO1, 2003 KP2, and 2001 KZ66, all at Arecibo.  We are also trying

1998 RO1 and 2003 KP2 have been observed both from here in Ondrejov
and by the Peter Brown's group at the Univ. of Western Ontario
in September 2002 and October 2003, respectively.  

1998 RO1 is the binary NEA suspect. We were not able to get a unique
solution for their periods and to decomposite its lightcurve components
due to insufficient data, so, unlike in other cases, we were not able
to reveal if its complex lightcurve really has the characterstics 
features of asynchronous eclisping/occulting binaries, namely
the two additive LC components with the occultation one having
discontinuities in the first derivation.  For this NEA, we need more
data (or radar observations, as planned) to confirm if it really is
a binary. Some preliminary and tentative estimates can be found on
http://www.asu.cas.cz/~ppravec/98ro1.htm
set to assist planning of observations to confirm the suspicion.

2003 KP2 has been found by the both teams to be a relatively slow rotaror
(>~12 h, possibly much longer) with a large amplitude.  Accurate
period determination is pending until we get full linkage data.

Best regards,

Petr Pravec
Ondrejov Observatory


________________________________________________________________________
________________________________________________________________________

Message: 4
   Date: Fri, 12 Sep 2003 10:18:13 +0200 (MET DST)
   From: Petr Pravec <ppravec@asu.cas.cz>
Subject: Re: Arecibo and Goldstone radar observations


I wrote:

> 1998 RO1 and 2003 KP2 have been observed both from here in Ondrejov
> and by the Peter Brown's group at the Univ. of Western Ontario
> in September 2002 and October 2003, respectively.  
    
please read: "in September-October 2002 and August-September 2003."

Sorry for the confusion.

Petr Pravec


________________________________________________________________________
________________________________________________________________________

Message: 5
   Date: Fri, 12 Sep 2003 10:52:31 -0000
   From: "albertajacksoniv" <albertajacksoniv@yahoo.com>
Subject: Asteroid first, Mars and Moon Later

I probably should not post this , since its over on Usenet, but there 
has been question about manned space flight recently, and I feel that 
a manned exploration of an asteroid is important.
(The letter below has probably been posted here too, but am new to 
the group.)

As much as I would love to go back to the moon or go to Mars, my two 
cents is the next manned expedition to an extraterrestrial body 
should be an asteroid.
Mainly because we need an examination of one of those dudes!
Why ? Because the data is needed for mitigation (asteroid deflection )
planning. I can remember reading the University of Arizona book
'Hazards Due to Comets and Asteroids (1995)' and finding out that even
tho a lot of people have deflection ideas... some crucial data about
the material composition of asteroids is needed to know what the
response to the deflection method will be. Short time warnings will 
probably warrant thermonuclear device deployment.
 
Also , just how costly could an international manned (robot augmented)
mission to an asteroid be? You ain't burning all that delta V and
using the associated structure to go in and out of a potential well.
(No matter how modest the Moon's is.)
The future of civilization may just depend on such an expedition.
 
Al Jackson
 
See the letter below:
 
 Mr. Gary L. Martin
 NASA Space Architect
 Room 9F44
 NASA Headquarters
 Washington, D.C., 20546-0001
 
 April 4, 2003 
 
 Dear Mr. Martin, 
 
 The Columbia tragedy has triggered a public discussion of the future
of the space station, space station science, and the utilization of
humans in
space. The outcome that we expect from this activity is an endorsement
of a program of human space flight at NASA - perhaps returning to the
goal enunciated by President Reagan in 1988: "To expand human presence
and activity beyond Earth-orbit into the solar system" -
accompanied by a prolonged and, possibly, divisive debate on the
utility of the space  station for science. As space scientists, we
believe the latter can be avoided by adding a new, exciting, and
affordable goal for human spaceflight and theuse of the space station.
This is the inclusion of  "mitigation" or "NEO deflectionstudies"
(i.e., how to prepare for a comet or asteroid that is found on an
Earth-threatening path), as one of
 NASA's primary goals.  This goal, which we believe can combine the
best of robotic and human space capabilities, can also be thought of
as a precursor to another future endeavor  (e.g., see the discussion
in Scientific Requirements for Human Exploration, Space Studies Board,
1993) - that of a manned mission to explore Mars. Also, such a goal
can be thought of as logical extension of the congressionally mandated
survey, currently being conducted in the Office of Space Science, to
find any potentially hazardous near-Earth objects (NEOs) larger than
one kilometer.
 
 In a recent workshop for NASA's Office of Space Science, we developed
a roadmap for  attaining the "Scientific Requirements for Mitigation
of Hazardous Comets and Asteroids"
(www.noao.edu/meetings/mitigation/report.html). This roadmap shows
that to gain the basic knowledge needed for some future mitigation
technology, a new NASA program is needed consisting of many novel
robotic missions to acquire detailed geophysical information on the
physical diversity, the subsurface, and the deep interiors of a
variety of near-Earth objects. In addition, NASA and DoD will need to
work together to "learn"
 how to apply deflection technologies including the application of low
thrust devices, the  application of novel in-space power sources,
and/or the rapid
application of large amounts of energy on small solar system bodies.
We expect that a mix of both human and robotic missions to objects in
near-Earth space and new uses for the space station  will be required
to test these technologies. The Space Science Board has already noted
that there is a need for an optimal mix of human and robotic
activities in such endeavors
 in their Scientific Opportunities in the Human Exploration of Space
(Space Studies Board, 1993).  
 
 All of this leads us to propose a new goal for human and robotic
space flight: Show how  humans and robots can work together on small
objects in near-Earth interplanetary space to: 1) accomplish new
fundamental science on planetary objects;2) aspire to previously
unimaginable technical achievements on objects ininterplanetary space;
and, 3) protect the Earth from the future possibility of a
catastrophic collision with a hazardous object from space.  Since
these activities would allow human spaceflight to cross the threshold
into interplanetary space, they could also be thought of as a
precursor activity to provide the essential technical and medical
experience for that more
 distant, but even more challenging, goal - a human exploratory
mission to Mars. We also note that among the recent NRC Solar System
Exploration "Decadal"
Survey recommendations is one that exhorts NASA "_to make significant
new
investments in advanced technology in order that future high priority
flight
missions can succeed."
 Particular stress was put on in-space power and propulsion systems
such as advanced RTG's, in-space fission reactor power sources,
nuclear electric
propulsion (NEP) and advanced ion engines. In the President's 2004
budget proposal, NEP figures strongly in connection with a future
mission to the icy satellites of Jupiter as part of the goal to
understand the origins and extent of life in the solar system.
"Mitigation," or even the gathering of the specific knowledge that
will be needed as a prerequisite for such an activity, was not dealt
with in the Survey, since it is a technical goal and not an
exploration or scientific goal. But it is now clear, as a result of
the mitigation workshop,
 that low thrust propulsion and the application of in-space power
systems to collision avoidance may now be the best way to proceed. It
is a small leap to imagine an experiment to deflect a small near-Earth
asteroid though the application of thrust from a NEP system (or an
advanced SEP) fueled by an advanced power source.
Moreover it is an objective that resonates with your agency's newly
stated objective of "...Protecting  the Home Planet... As only NASA
can!" In short, we see an important coupling between the requirements
for the long-term future of solar system scientific exploration, as
expressed by the Decadal survey, the needs of planetary protection,
and a worthwhile program that utilizes humans, the space station, and
robots in near-Earth interplanetary
space. 
 
 In public discussions of the President's in-space nuclear power and
propulsion system initiative, the issue of environmental safety can be
expected to arise even though extensive past experience has shown that
such systems are extremely safe. Nuclear safety is a matter of great
public concern that we share. However, we would also like to point out
that the likely application of these kinds of technologies to a future
NEO deflection system will also mitigate against the possibility of a
much greater environmental hazard:  that of a NEO impact itself. Thus,
from an environmental perspective, there may be much to be gained in
the application of these systems to the NEO collision problem.
 
 A cogent new goal is needed for human space flight and significant
investments and experimentation are required to develop in-flight
power and
propulsion systems for future solar system exploration. In addition, a
new program needs to be started at NASA to
 create an adequate scientific basis for a future mitigation system
and, simultaneously, to learn how to apply future collision mitigation
technologies.  There is a nexus between these goals and objectives
that we believe should become the basis of a new thrust for NASA as it
emerges from the analysis and public discussion surrounding the
Columbia tragedy. We advocate, and strongly believe, that by adopting
this goal the United States can go forward with human spaceflight
utilizing the space station with productive,
 well-supported and meaningful objectives. 
 
 We are, sincerely yours,   Michael J. S. Belton, Ph.D.
 Belton Space Exploration Initiatives, LLC, Tucson, AZ 
 
 Donald K. Yeomans, Ph.D.
 JPL/Cal Tech, Pasadena, CA 
 
 Steven Ostro, Ph.D.
 JPL/Cal Tech, Pasadena, CA 
 
 Piet Hut, Ph.D.
 Inst. Advanced Study, Princeton, NJ 
 
 Clark Chapman, Ph.D.
 Southwest Research Inst., Boulder, CO 
 
 Derek Sears, Ph.D.
 Univ. of Arkansas, AR 
 
 Michael F. A'Hearn, Ph.D.
 Univ. of Maryland, MD 
 
 Russell L. Schweickart
 Apollo 9 Astronaut,
 Chairman, B612 Foundation 
 
 Nalin Samarasinha, Ph.D.
 National Optical Astronomy Observatory, Tucson, AZ 
 
 Daniel Scheeres, Ph.D.
 Univ. of Michigan, MI 
 
 Michael Drake, Ph.D.
 Univ. of Arizona, AZ 
 
 Keith Holsapple, Ph.D.
 Univ. of Washington, WA 
 
 Erik Asphaug, Ph.D.
 Univ. of California at Santa Cruz, CA 
 
 Mark Sykes, Ph.D.
 University of Arizona, AZ 
 
 Alberto Cellino, Ph.D.
 Astronomical Observatory of Torino, Italy 
 
 Lucy McFadden, Ph.D.
 Univ. of Maryland, MD 
 
 Donald R. Davis, Ph.D.
 Planetary Science Institute, Tucson, AZ 
 
 Timothy D. Swindle, Ph.D.
 University of Arizona, AZ 
 
 Stephen M. Larson, Ph.D.
 University of Arizona, AZ 
 
 Larry A. Lebofsky, Ph.D.
 University of Arizona, AZ 
 
 Mark Trueblood
 Winer Observatory, AZ 
 
 Beatrice E.A. Mueller, Ph.D.
 National Optical Astronomy Observatory, Tucson, AZ 
 
 Joseph Spitale, Ph.D.
 Lunar and Planetary Lab., Tucson, AZ 
 
 Tod R. Lauer, Ph.D.
 National Optical Astronomy Observatory, Tucson, AZ 
 
 Robert Farquhar
 Johns Hopkins University
 Applied Physics Laboratory,
 Laurel, MD 
 
 Daniel Britt, Ph.D.
 Univ. of Central Florida, FL 
 
 Elisabetta Pierazzo
 Planetary Science Institute, Tucson, AZ 
 
 Kevin Housen
 The Boeing Co., Seattle, WA 
 
 Thomas D. Jones, Ph.D
 Planetary Scientist and Former Astronaut, Oakton, VA 
 
 Ronald Fevig
 Univ. of Arizona, AZ


________________________________________________________________________
________________________________________________________________________

Message: 6
   Date: Fri, 12 Sep 2003 08:25:18 -0700 (PDT)
   From: Ron Baalke <baalke@zagami.jpl.nasa.gov>
Subject: Optical Detection of Anomalous Nitrogen in Comets


http://www.eso.org/outreach/press-rel/pr-2003/pr-25-03.html

ESO Press Release 25/03
12 September 2003                                              
For immediate release

Optical Detection of Anomalous Nitrogen in Comets

VLT Opens New Window towards Our Origins

Summary

A team of European astronomers [1] has used the UVES spectrograph on the
8.2-m VLT KUEYEN telescope to perform a uniquely detailed study of Comet
LINEAR (C/2000 WM1). This is the first time that this powerful instrument
has been employed to obtain high-resolution spectra of a comet. At the
time of the observations in mid-March 2002, Comet LINEAR was about 180
million km from the Sun, moving outwards after its perihelion passage in
January.

As comets are believed to carry "pristine" material - left-overs from the
formation of the solar system, about 4,600 million years ago - studies of
these objects are important to obtain clues about the origins of the solar
system and the Earth in particular.

The high quality of the data obtained of this moving 9th-magnitude object
has permitted a determination of the cometary abundance of various
elements and their isotopes [2]. Of particular interest is the unambiguous
detection and measurement of the nitrogen-15 isotope. The only other comet
in which this isotope has been observed is famous Comet Hale-Bopp - this
was during the passage in 1997, when it was much brighter than Comet
LINEAR.

Most interestingly, Comet LINEAR and Comet Hale-Bopp display the same
isotopic abundance ratio, about 1 nitrogen-15 atom for each 140
nitrogen-14 atoms (14N/15N = 140 � 30). That is about half of the
terrestrial value (272). It is also very different from the result
obtained by means of radio measurements of Comet Hale-Bopp (14N/15N = 330
� 75). Optical and radio measurements concern different molecules (CN and
HCN, respectively), and this isotopic anomaly must be explained by some
differentiation mechanism.

The astronomers conclude that part of the cometary nitrogen is trapped in
macromolecules attached to dust particles.

The successful entry of UVES into cometary research now opens eagerly
awaited opportunities for similiar observations in other, comparatively
faint comets. These studies will provide crucial information about the
detailed composition of a much larger number of comets than hitherto
possible and hence, more information about the primordial matter from
which the solar system formed.

A better understanding of the origins of the cometary material (in
particular the HCN and CN molecules [3]) and the connection with heavier
organic molecules is highly desirable. This is especially so in view of
the probable r�le of comets in bringing to the young Earth materials
essential for the subsequent formation of life on our planet.

 PR Photo 28a/03: Comet LINEAR (C/2000 WM1) - direct image and UVES slit
 position.
 PR Photo 28b/03: Part of the UVES spectrum of Comet LINEAR (C/2000 WM1)
 with CN-band.
 PR Photo 28c/03: Identification of nitrogen-15 in the spectrum.
----------------------------------------------------------------------------

Cometary material

Knowledge of the abundance of the stable isotopes [2] of the light elements
in different solar system objects provides critical clues to the origin and
early evolution of these objects and of the system as a whole.

In order to gain the best possible insight into the origins and formation of
the niche in which we live, it is therefore important to determine such
isotopic abundance ratios in as many members of the solar family as
possible. This is particularly true for comets, believed to be carriers of
well-preserved specimens of the pristine material from which the solar
system was made, some 4,600 million years ago.

However, the detailed study of cometary material is a difficult task.
Measurements of isotopic ratios is an especially daunting undertaking,
mainly because of the extreme weakness of the spectral signatures
(emissions) of the less abundant species like carbon-13, nitrogen-15, etc..

Measurements of microwave emission from those atoms suffer from additional,
inherent uncertainties connected to the much stronger emission of the more
abundant species. Measurements in the optical spectral region thus take on
particular importance in this context. However, it is exceedingly difficult
to procure the high-quality, high-resolution spectra needed to show the very
faint emissions of the rare species.

So far, they were only possible when a very bright comet happened to pass
by, perhaps once a decade, thereby significantly limiting such studies. And
there has always been some doubt whether the brightest comets are also truly
representative of this class of objects.

Observations of fainter, more typical comets had to await the advent of
powerful instruments and telescopes.

First UVES spectrum of a comet

  [ESO PR Photo 28a/03]  ESO PR Photo   [ESO PR Photo 28b/03]  ESO PR Photo
                         28a/03                                28b/03

 [Preview - JPEG: 495 x 400 pix -      [Preview - JPEG: 502 x 400 pix -
 183k                                  115k
 [Normal - JPEG: 990 x 800 pix -       [Normal - JPEG: 1004 x 800 pix -
 450k]                                 290K]


 Captions: PR Photo 28a/03 displays an image of Comet LINEAR (C/2000 WM1)
 with the UVES slit viewer image. The colour composite in the large frame
 (sky field: 16 x 16 arcmin2) was obtained by Gordon Garradd (Loomberah,
 NSW, Australia). [Image Copyright (c) 2002 Gordon Garradd
 (loomberah@ozemail.com.au]. The UVES slit viewer photo (small frame; 40 x
 40 arcsec2) is a false-colour image taken in the (red) R-band with
 UVES+KUEYEN on March 22, 2002; it shows the position of the narrow
 spectrograph slit (0.45 arcsec wide and 8 arcsec long) crossing the inner
 coma and through which the comet's light was captured to produce the
 high-resolution spectra. The slit has been offset from the center of light
 to reduce contamination from solar light reflected off dust particles in
 the comet's coma - there is most dust near the nucleus. PR Photo 28b/03
 shows a small part of the UVES spectrum with an emission band (ultraviolet
 light at wavelength 390 nm) from CN molecules [3] in the comet's
 atmosphere. The emission lines are produced by absorption of the solar
 light by these molecules, followed by re-emission of lines of specific
 wavelengths. This physical process is known as "resonance-fluorescence" -
 it is the same process that causes glowing teeth and shirts in a Disco.
 The upper panel displays the "raw" spectrum; the lower is the "extracted"
 spectrum, now clearly displaying the individual emission lines.

Observations of Comet LINEAR (C/2000 WM1) were carried out with the
UV-Visual Echelle Spectrograph (UVES) mounted on the 8.2-m VLT KUEYEN
telescope at the ESO Paranal Observatory (Chile) on four occasions during
March 2002. At that time, the comet had moved past its perihelion and was by
far the faintest comet for which such a detailed spectral analysis had ever
been attempted.

A number of 25-min exposures were secured, resulting in a total observing
time of about 4 hours. The final spectrum covers the entire visual region
(330 - 670 nm) and is one of the most detailed and information-rich cometary
spectra ever obtained. PR Photo 28b/03 displays a small part of this
spectrum.

These observations are the first high resolution spectra of a comet taken
with the VLT.

Identification of nitrogen-15

  [ESO PR Photo 28c/03]  ESO PR Photo  Captions: PR Photo 28c/03 is an
                         28c/03        enlarged view of a small section of
                                       the high-resolution UVES spectrum of
                                       Comet LINEAR (PR Photo 28b/03) with
 [Preview - JPEG: 400 x 524 pix -      emission lines from CN-molecules
 109k                                  (blue line), compared to the
 [Normal - JPEG: 800 x 1047 pix -      "synthetic" spectrum based on
 285k]                                 theoretical calculations and
                                       laboratory measurements (black line
                                       ; some of the lines are labeled with
                                       quantum numbers). In the upper
                                       panel, the synthetic spectrum has
                                       been produced on the basis of the
                                       most abundant isotopic species
                                       (12C14N) . The lower panel shows
                                       that the observed spectrum is in
                                       nearly perfect agreement with a
                                       synthetic spectrum which includes
                                       contributions from two other
                                       isotopic species, 13C14N (emission
                                       lines at wavelengths indicated by
                                       red ticks) and 12C15N (blue ticks);
                                       they are added in proportions of
                                       1/115 and 1/140, respectively. The
                                       isotopic abundances of carbon-13 and
                                       nitrogen-15 are measured
                                       accordingly. Introducing instead the
                                       terrestrial ratio for nitrogen-15
                                       (1/272) significantly degrades the
                                       fit and thus that ratio can clearly
                                       be ruled out in Comet LINEAR.

At the time of the VLT observations, the comet was of 9th magnitude, i.e.
about 15 times fainter than what can be perceived with the unaided eye. The
distance from the Sun was about 180 million km; the distance from the Earth
was 186 million km. The observations included calibration spectra of
sunlight reflected from the lunar surface; they were used to "subtract" the
solar signatures in the comet's spectrum, caused by reflection of sunlight
from the dust particles around the comet.

As expected, in addition to emission from "normal" CN-molecules (12C14N),
the UVES data also show emission lines of the 13C14N-molecule that contains
the rare isotope carbon-13. The derived 12C/13C isotopic ratio is 115 � 20,
quite similar to the "standard" solar system value of 89.

However, there is also a series of weak features that are positioned exactly
at the theoretical wavelengths of emission lines from 12C15N-molecules, cf.
PR Photo 28c/03. The excellent fit that is evident in this diagram proves
beyond any doubt the presence of nitrogen-15 in Comet LINEAR and allows a
quite accurate determination of the isotopic ratio.

The "anomalous" nitrogen isotope ratio in comets

In 1997, the same group of astronomers obtained spectra of the (at that
time) much brighter Comet Hale-Bopp with the 2.6-m NOT telescope (Roque de
los Muchachos Observatory, La Palma, Canary Islands, Spain) in order to
investigate the isotopic ratio of carbon-12 to carbon-13. Claude Arpigny
remembers: "Interestingly, our spectra of Hale-Bopp showed a number of weak
and unidentified emission lines. We later realised that they were positioned
close to the theoretical wavelengths of some lines from the 12C15N-molecule.
This was a pleasant surprise, as lines from that molecular species were
previously believed to be so faint that they would not be observable."

He continues: "This identification is now fully confirmed with the UVES
observations of Comet LINEAR. Our detections in these two comets are the
first ever of those emission lines in comets".

The estimates of the 14N/15N isotopic ratios are very similar, 140 � 35 for
Hale-Bopp and 140 � 30 for LINEAR. These ratios are remarkably low and
different from the terrestrial value of 272. This means that these comets
have comparatively more nitrogen-15 than has the Earth. No measurement has
yet been made of the abundance of nitrogen-15 in the Sun.

So which of the values corresponds to the composition of the material from
which the solar system was made?

Different origins?

To date, only four cometary values of the 14N/15N isotopic ratio have been
reported: two in the radio wavelength range and the two now measured by
means of optical spectra.

The radio measurements concern the HCN-molecule (hydrocyanic acid) in Comet
Hale-Bopp, a "parent" molecule for the CN-molecules present in comets.
Contrary to the optical measurements, the radio values (about 330 � 75) are
compatible with the terrestrial value (272). But radio measurements of
carbon and nitrogen isotopic ratios are only possible on extraordinarily
bright comets like Hale-Bopp, and even then, the achievable accuracy is very
limited. This emphasizes the importance of performing this kind of research
by means of optical observations.

The origin of the isotopic discrepancy between different CN parents is
likely due to fractionation mechanisms in the forming presolar nebula, e.g.
when oxygen- and carbon-bearing molecules in high-density nebulae stick to
cold (10K) dust grains.

Macromolecules in space

The astronomers think that the new results indicate that the HCN-molecule
cannot be the only "parent" of the CN-molecule; the latter must also be
produced by some as yet unknown parent(s) in which the nitrogen-15 isotope
is even more abundant.

In this connection, it is very interesting that an "excess" of nitrogen-15
is also known to exist in interplanetary dust particles (IDPs), captured by
high-flying aircraft in the Earth's atmosphere. They represent the oldest
material in the solar system that can be subjected to detailed laboratory
analysis. Many of these particles are thought to originate from passing
comets - this possibility is obviously supported by the new measurements.

The nitrogen-15 carriers in IDPs have not been securely identified but are
possibly organic macromolecules or polycyclic aromatic hydrocarbons (PAHs).
It is thus possible that the additional parent(s) of cometary CN may belong
to this ensemble of organic substances.

Whatever the case, the longstanding question of nitrogen and its isotopic
ratio(s) in the solar system, whether present and primordial, is notoriously
enigmatic in several respects. However, the present results demonstrate that
a detailed study of comets may deliver very useful clues.

The team has now been granted more observing time with UVES and KUEYEN in
order to pursue this important study by observing more comets.

More information

The results described in this ESO press release are presented in a research
report published today in the "Science" journal ("Anomalous Nitrogen Isotope
Ratio in Comets", by Claude Arpigny and co-authors). The Li�ge University is
also issuing a press release (in French) on this occasion.

Notes

[1]: The team consists of Claude Arpigny, Jean Manfroid and Damien
Hutsem�kers (Institut d'Astrophysique et de G�ophysique de l'Universit� de
Li�ge (IAGL), Belgium), Emmanu�l Jehin (ESO-Chile), Rita Schulz (ESA/RSSD,
Noordwijk, The Netherlands), Joachim A. St�we (Leiden Observatory, The
Netherlands), Jean-Marc Zucconi (Observatoire de Besan�on, France) and Ilya
Ilyin (University of Oulu, Finland).

[2]: Different isotopes of the same elements have different numbers of
neutrons in their nuclei. For instance, carbon-12 nuclei contain six protons
and six neutrons (i.e., 12 particles in all) - this is the most abundant
carbon isotope; carbon-13 contains six protons and seven neutrons.
Nitrogen-14 - the most abundant isotope of this element - has seven protons
and seven neutrons; nitrogen-15 has seven protons and eight neutrons.

[3]: In chemical terms, CN is referred to as a "radical".

Contacts

Claude Arpigny
Institut d'Astrophysique et de G�ophysique
Universit� de Li�ge
Belgium
Phone : +32 (0)4 366 97 12
E-mail : arpigny@astro.ulg.ac.be

Emmanu�l Jehin
ESO
Santiago de Chile
Phone : +56 2 463 30 65
E-mail : ejehin@eso.org


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