NOTE:
 
This text is a summary of the COSIMAPAPER.ASC located in the DOCUMENT
subdirectory. The reader is suggested to use the more readable pdf
version of this document, COSIMAPAPER.PDF.
 
This document has an additional chapter 3, which simply lists the
properties of each substrate.
 
TABLE OF CONTENTS
- 1. Introduction
- 2. Functional Description
- 3.  Collection Substrates
- 4. In-Flight Operation
- 5. The Ground Laboratory Program
- 6. Anticipated Results
- 7. References
 
COSIMA  -  High   Resolution   Time-of-Flight   Secondary   Ion   Mass
Spectrometer for the  Analysis  of  Cometary  Dust  Particles  onboard
ROSETTA
 
 
1 Introduction
 
The ESA mission Rosetta, launched  on  March  2nd,  2004,  carries  an
instrument suite to the comet 67P/Churyumov-Gerasimenko. The  COmetary
Secondary Ion Mass Anaylzer - COSIMA - is one of three  cometary  dust
analyzing  instruments  onboard  Rosetta.  COSIMA  is  based  on   the
analytic  measurement  method  of  secondary  ion  mass   spectrometry
(SIMS). The experiment's goal is in-situ  analysis  of  the  elemental
composition (and isotopic composition of  key  elements)  of  cometary
grains. The chemical characterization will include  the  main  organic
components, present homologous and functional groups, as well  as  the
mineralogical  and  petrographical  classification  of  the  inorganic
phases. All this analysis is closely  related  to  the  chemistry  and
history of the early solar system. COSIMA covers a mass range  from  1
to 3500 amu with a mass resolution m/dm @ 50 % of  2000  at  mass  100
amu. Cometary dust is collected on special,  metal  covered   targets,
which are handled by a target manipulation unit. Once exposed  to  the
cometary dust environment, the collected dust grains  are  located  on
the target by a microscopic camera. A pulsed primary indium  ion  beam
(among other entities) releases secondary ions from the  dust  grains.
These ions, either positive or negative, are selected and  accelerated
by electrical fields and travel  a  well-defined  distance  through  a
drift tube and an ion reflector. A microsphere  plate  with  dedicated
amplifier is used to detect the ions. The arrival times  of  the  ions
are digitized,  and  the  mass  spectra  of  the  secondary  ions  are
calculated from these time-of-flight spectra. Through  the  instrument
commissioning, COSIMA took the very first SIMS spectra of the  targets
in space. COSIMA will  be  the  first  instrument  applying  the  SIMS
technique in-situ to cometary grain  analysis  as  Rosetta  approaches
the comet  67P/Churyumov-Gerasimenko,  after  a  long  journey  of  10
years, in 2014.
 
The in situ chemical analysis of solids in space is  among  the  tasks
that are technically most difficult. There are two  main  reasons  for
that: With a few exceptions, solids in space are  not  abundant,  and,
secondly, it is not easy to remove small samples from the  solid  into
the vacuum for the analysis in a mass spectrometer.
 
For COSIMA, the objects  of  interest  are  cometary  dust  particles,
which are abundant, indeed, in the neighborhood of the comet  nucleus.
It remains, however,  to  collect  and  bring  the  particles  to  the
entrance of the spectrometer.
 
Most mass spectrometers need the parts of the sample to  be  analyzed,
to carry an electric charge. The process of removing an ion  from  the
specimen is then the critical feature of the method to be chosen.
 
The only mass spectrometric data on cometary dust particles  available
to date come from the dust impact mass spectrometers  PIA,  PUMA,  and
CIDA on the GIOTTO,  VEGA,  and  Stardust  spacecrafts,  respectively.
(Far more and more detailed mass spectra of IDPs of supposed  cometary
origin are available from  laboratory  measurements,  and  soon  there
will be results  from  the  cometary  dust  particles  retrieved  from
Stardust.)  While   other,   remote,   or   indirect   methods   allow
measurements of collective properties of the cometary dust,  the  mass
spectrometers  allowed  the  analysis  of  individual  particles  (cf.
Kissel et al. 1986a, b). Since then, we know unambiguously  that  each
particle is an intimate mixture of a mineral component and  simple  as
well as complex organic  molecules.  Since  the  impact  velocity  was
large (>60 km/s), mostly atomic ions were formed and analyzed  in  the
Halley case. In a first attempt, however, Kissel  and  Krueger  (1987)
found evidence  for  the  chemical  nature  of  the  organic  cometary
material. It is clear  that  not  only  a  few  well  known  molecules
constitute  the  cometary  organics,  but  rather   several   chemical
classes, with each being represented by a large number  of  individual
substances. Indeed,  it  seems  possible  that  all  stable  molecules
compatible with the chemical environment are formed.
 
COSIMA therefore needed to be based on  a  method,  which  is  readily
available  in  laboratory,  and  which  allows  for  tracing  the  ion
directly to the molecular and structural form in which it was  present
in the solid. Since the size distribution of  the  dust  particles  is
known (cf. Mazets et al. 1987, McDonnell et al.  1989),  a  reasonable
ionizing beam focus should be achieved under the limitations of  space
instrumentation. Even though the  method  would  be  destructive,  its
sensitivity should  be  high  enough  to  allow  several  analyses  at
different depths for one individual ~20 um particle.
 
To satisfy all these requirements, we choose the method  of  Secondary
Ion Mass Spectrometry (SIMS). A fast primary ion, in this case  115In+
at 8 keV, impacts the sample and  releases  by  desorption  atoms  and
molecules of the sample, of which typically 0.1 to 10 %  are  ionized,
the so-called secondary ions. For sensitivity  reasons,  the  analysis
of a rather large mass range should be achieved simultaneously,  which
in turn leads to the type of a time-of-flight mass  spectrometer.  The
mass resolution must be high  enough  to  resolve  isobaric  ions,  at
least atomic from molecular ions.  The  mass  range  should  at  least
cover 3500 amu. In total, the  COSIMA  instrument  has  the  following
main functional hardware elements:
*     dust collector and target manipulator,
*     COSISCOPE, a microscope for target inspection
*     primary ion source, and
*     mass spectrometer including the ion extraction  optics  and  the
ion detector.
 
Of course, for autonomous operation, the entire  instrument  is  under
microprocessor based software control.
 
The overall parameters and resources describing COSIMA are:
* Atomic mass range 1 . . . 3500 amu
* Rel. atomic mass resolution m/dm (at m = 100  amu)  >  2000  at  50%
peak width
* Indium ion pulse duration about 3 ns
* Indium ion energy 8 keV
* Ion beam width about 50 um FWHM
* Telemetry rate about 500 bit/sec
* Mass 19.8 kg
* Power consumption from 28 V DC 20.4 W
 
 
 2 Functional Description
 
COSIMA is a time-of-flight secondary ion mass spectrometer.  Like  all
such instruments, primary ions generate secondary ions from a  target,
which they hit. Those secondary  ions  are  then  accelerated  to  the
same, constant kinetic energy,  and  their  flight  time  to  the  ion
detector is measured. This flight time follows the equation:
 
(1)   time-of-flight = a * (mass/abs(q))0.5  +  b;
 
with  a - is an instrumental constant depending on the length  of  the
flight path and the    electrical voltages applied, for COSIMA  it  is
about 3.1 us/(mass)0.5
      b - is a constant for the offset of the time measurement
      mass - is the ion mass in amu
      q - is the ion charge state, in most cases = -1 or +1
 
COSIMA  works  pretty  much  like  a  laboratory  instrument,  with  a
somewhat reduced performance  due  to  the  limitations  for  a  space
instrument, but remotely operated in a 'distant lab'. The  limitations
come first of  all  from  the  mass  and  power  available,  but  more
pronounced from the limited capacity of data transfer to and from  the
instrument, combined with a reaction time (round trip time  delay)  of
32 minutes during the main operation time.
 
Consequently the individual steps for the analysis of a dust  particle
are:
1) exposure of a collection substrate for a predetermined time
2) optical search of the substrate for dust particles  by  the  camera
system COSISCOPE
3a) moving a dust particle in front of the spectrometer
3b) either first clean the particle and surrounding by sputtering or
3c) start the particle characterization
6) perform onboard chemistry
7) do  another  detailed  analysis  in  both,  the  positive  and  the
negative, ion modes
8) move to the next particle
 
COSIMA  has  dedicated surfaces for the collection of  cometary   dust
particles. These may impact with their release speed of  the  order of
100  m/s.  Since  SIMS  is  a  very sensitive  method, the  collection
surfaces  need  to  be  a material,  which  does  not  interfere  with
the  type  of  materials expected in the dust. This excluded any  kind
of  organic  material. A study performed identified  metal  blacks  as
suitable materials from the structural, and  silver, palladium,  gold,
or platinum from the material properties point of view. The choice has
turned out to be very sensible, as these  blacks  are  also  efficient
pumps for contaminants unavoidable for a space instrument.  Since  the
cometary particles can have a wide range of speeds depending on  their
size and on the gas activity of the nucleus, each unit of targets  has
three 1*1 cm2 collection areas (substrates) and a separate  0.3*3  cm2
strip  as  an  unexposed  reference  area.  Always  an  entire  target
assembly is exposed at a time.
 
Manipulation  of  the  target  units  is  achieved  with  the   Target
Manipulator Unit (TMU), which was designed and added at a late  state.
It  is  a  semiautonomous  system,  which  provides  access   to   the
positions  'COLLECT', 'STORE', 'COSISCOPE',  'CLEAN',  'ANALYZE',  and
'CHEMISTRY' upon  simple (internal) commands.
 
The first inspection of the sample is  done  by  COSISCOPE,  a  COSIMA
internal camera. One of the 3 collection substrates is  checked  at  a
time. Light beams from two sets of LEDs left and right of  the  sample
illuminate it.  The  images  are  checked  for  features  like,  e.g.,
shadows and  interpreted  as  sites,  the  coordinates  of  which  are
transferred to the main instrument.
 
The next step is the decision if the target, or a part  of  it,  needs
cleaning by ion-sputtering. If so, it is moved in front of  a  DC  ion
beam at the 'CLEAN' position, else, it will be presented to  the  mass
spectrometer. The primary ion source (PIBS) has a  separate  beam  for
cleaning, providing 10-100 uA on a 100 um diameter spot equivalent  to
removing some 100 monolayers per second. The next step is  to  analyze
a site, i.e., to take a mass spectrum. The target is put in  front  of
the extraction lens  of  the  spectrometer,  with  the  selected  site
within 100 um of the lens' center. Operational values are  taken  from
the initial adjustment of  the  primary  ion  source.  Trains  of  ion
packages of 3 ns width at a rate of 1 kHz release secondary ions  into
the  spectrometer.  Its  second  order  focusing  design  provides  an
inherent mass resolution of m/dm @ 50 % peak height above 3000  (i.e.,
with 0-time spread  of  the  primary  beam).  A  typical  primary  ion
package has 500 ions and  releases  1  to  10  non-hydrogen  secondary
ions, depending on the material irradiated.
 
All secondary ions of the appropriate polarity are picked  up  by  the
electric field in front of the ion  extraction  lens.  This  field  of
about 1 kV/mm minimizes initial time-of-flight differences due to  the
acceleration process, which cannot  be  compensated  later.  The  lens
field also guides the ions into  the  time-of-flight  section  of  the
instrument reducing their drift energy to nominally 1 keV and  focuses
their arrival location on the detector into a 15 mm diameter area.  As
the  ions  travel  down  the  drift  tube,  they  pass  the  secondary
deflection plates, which are needed to reposition  the  secondary  ion
package, should the analysis site be off center. It is  also  used  to
compensate the small changes in ion trajectories between the  positive
and negative secondary ions modes. At the end of the  drift  tube  the
ions  enter  the  ion  reflector,  the  device,  which  improves   the
intrinsic mass resolution of the spectrometer  part  by  more  than  a
factor of 100. State-of-the-art would be a gridless reflector ( which
we  have  studied)  but  which  is  very  sensitive   to  the position
of  the  ion  entry  and  thereby  on  the  perfect  function  of  the
secondary  deflection plates.  The  actual  design  we   have   chosen
uses  several  grids  separating  the  drift  section,  the  retarding
section, and the reflecting section. As the ions enter under  a  small
angle of 1deg, they exit at a slightly different  location  but  again
into the same physical drift tube. At the end of this  tube  the  ions
hit the  ion  detector.  The  position  and  the  orientation  of  the
detector were carefully chosen, as both are part of the system,  which
determines the mass resolution of COSIMA. Since we expect some of  the
organic ions to have high masses (well above  350  amu)  the  detector
can be biased for a post-acceleration of the secondary ions by  almost
9 kV (with the appropriate polarity for the respective ion type).  The
active element is a microsphere plate, which for its thickness of  1.4
mm provides a gain value well above 107.  In  order  to  decouple  the
signal from its high electrical potential (up to 14 kV in the case  of
negative secondary ions), the microsphere output  is  directed  to  an
anode, which is one side of a  capacitor,  while  the  other  side  is
connected to the input of a pulse amplifier.  All  arrival  times  and
shot numbers are stored at 2 ns resolution.  The  differences  between
the modes for positive or negative secondary  ions  are  reflected  in
the  respective  operational  voltages.  Besides   the   reversal   of
polarity, minor adjustments need to be applied  to  the  voltages  for
the deflection plates of both, the primary beam and the secondary  ion
path. The safe switch-over from one ion type to the other will take  a
couple of minutes to allow the high  voltages  to  decay,  before  the
grounding of the power supplies is switched. The secondary  ion
arrival times are accumulated into the time-bins of a  time-of-flight
spectrum.
 
 
3. Collection Substrates
 
The 24 target holders are numbered with hexadecimal numbers  from  #C1
to #D8. The top substrate is marked with the number #100,  the  middle
with #200 and the low with #300. The combination of these numbers give
the substrate identification number used in the instrument  commanding
and data handling.
 
The list bellow gives the substrates ID, the surface layer  properties
and a possible comment
 
#1C1 'Palladium, black'
#2C1 'Platinum, deep black'
#3C1 'Platinum, deep black'
#1C2 'Silver, 73 micrometer thickness,
              blank with rectangular hole 3.5x3.5mm'
#2C2 'Silver, 69 micrometer thickness,
              blank with AgTe spot of about 3 mm size at center'
#3C2 'Gold, 17 micrometer thickness, olivine particles'
#1C3 'Gold, 8 micrometer thickness'
#2C3 'Gold, 15 micrometer thickness'
#3C3 'Gold, 20-30 micrometer thickness'
#1C4 'Palladium, black'
#2C4 'Silver, 14 micrometer thickness'
#3C4 'Gold, 12 micrometer thickness'
#1C5 'Platinum, light black,'
#2C5 'Platinum, deep black'
#3C5 'Gold, 13 micrometer thickness'
#1C6 'Platinum, deep black'
#2C6 'Platinum, deep black'
#3C6 'Gold, 8 micrometer thickness'
#1C7 'Silver, blank'
#2C7 'Silver, 21 micrometer thickness'
#3C7 'Gold, 15 micrometer thickness'
#1C8 'Platinum, deep black'
#2C8 'Platinum, deep black'
#3C8 'Gold, 20-30 micrometer thickness'
#1C9 'Gold, 5-8 micrometer thickness'
#2C9 'Gold, 5-8 micrometer thickness'
#3C9 'Gold, 11 micrometer thickness'
#1CA 'Gold, 5-8 micrometer thickness'
#2CA 'Gold, 16 micrometer thickness'
#3CA 'Silver, 10 micrometer thickness'
#1CB 'Gold, 17 micrometer thickness'
#2CB 'Gold, 14 micrometer thickness'
#3CB 'Gold, 20-30 micrometer thickness'
#1CC 'Silver, 21 micrometer thickness'
#2CC 'Silver, 21 micrometer thickness'
#3CC 'Silver, 24 micrometer thickness'
#1CD 'Gold, 5-8 micrometer thickness'
#2CD 'Gold, 14 micrometer thickness'
#3CD 'Gold, 20-30 micrometer thickness'
#1CE 'Gold, 5-8 micrometer thickness, Ag particles'
#2CE 'Gold, 11 micrometer thickness'
#3CE 'Gold, 20-30 micrometer thickness'
#1CF 'Gold, 8 micrometer thickness'
#2CF 'Gold, 12 micrometer thickness, Ag particles'
#3CF 'Gold, 20-30 micrometer thickness'
#1D0 'Gold, 20-30 micrometer thickness'
#2D0 'Gold, 20-30 micrometer thickness'
#3D0 'Gold, 20-30 micrometer thickness, Ag particles'
#1D1 'Silver, blank'
#2D1 'Gold, 13 micrometer thickness'
#3D1 'Gold, 13 micrometer thickness'
#1D2 'Gold, 8 micrometer thickness'
#2D2 'Gold, 8 micrometer thickness'
#3D2 'Silver, 30 micrometer thickness'
#1D3 'Silver, 10 micrometer thickness'
#2D3 'Silver, 10 micrometer thickness'
#3D3 'Silver, 32 micrometer thickness'
#1D4 'Platinum, sintered'
#2D4 'Platinum, deep black'
#3D4 'Platinum, deep black'
#1D5 'Platinum, deep black'
#2D5 'Silver, 22 micrometer thickness'
#3D5 'Silver, 21 micrometer thickness'
#1D6 'Platinum, deep black'
#2D6 'Palladium, black'
#3D6 'Platinum, deep black'
#1D7 'Silver, blank'
#2D7 'Platinum, sintered'
#3D7 'Platinum, sintered'
#1D8 'Silver, blank, square hole 3.5x3.5mm at center'
#2D8 'Silver, blank'
#3D8 'Gold, 8 micrometer thickness'
 
 
 4 In-Flight Operation
 
Rosetta commissioning was carried out in 2004, the  COSIMA  instrument
was operated in-flight after nearly a decade of development and  tests
on the ground. Positive and negative SIMS ion mass spectra were  taken
of one of the Ag metal targets, the resulting  spectra  are  shown  in
Fig. 18a and Fig. 18b, respectively. The inorganic  and  organic  ions
and molecules show up in separable and well resolved mass peaks,  such
as Si and C2H4 or Fe and C4H8.  Small  amounts  of  organic  molecules
being known to be present in cometary dust such as CN are adsorbed  on
the blank  metal  target  and  reveal  themselves  in  the  SIMS  mass
spectra. Since COSIMA carries also a heating station for  the  target,
the level of volatile contamination can be  further  decreased  before
exposure of the target to the  cometary  dust.  Comparison  with  mass
spectra taken of the same target in 2002 before launch  already  shows
a slight decrease of volatiles such as hydrocarbons  absorbed  on  the
target surface after residing only  about  6  months  in  space.  This
contamination by organic molecules was, in  part,  released  from  the
insulation material of the electrical harness and from boxes used  for
ground transportation. Note that the  Ag  peaks  are  caused  by  ions
released from the target and the In peak is due to primary  ions  from
the ion source. For high secondary ion rates, the  mass  spectra  show
saturation effects due to dead-times  inherent  in  the  ion  detector
counting electronics, best visible adjacent to each of the intense  Ag
isotope peaks.
 
 
  5 The Ground Laboratory Program
 
During the cruise phase to the comet as well as  while  the  probe  is
actually analyzing cometary dust, an active  laboratory  program  will
be  maintained.  While  the  SIMS  method  is  routinely  applied  for
relevant  geological  and   planetological   studies,   the   TOF-SIMS
technique will benefit from this terrestrial work with the  COSIMA  RM
reference    model.    Additionally,    growing    experimental    and
methodological expertise comes from the day-to-day work with  relevant
samples at the TOF-SIMS laboratory instrument currently in use at  the
University of Munster. The complex mixture of  organic  and  inorganic
material, expected to make  up  the  comet,  will  result  in  equally
complex  mass  spectra.  They  have  to  be  disentangled  to  provide
information on the chemical, isotopic, and  molecular  composition  of
the particles that reflect the origin, history, and present  state  of
cometary matter. The particle-to-particle variation  will  testify  to
its diversity, i.e., to the extent of the  pristine  nature  of  these
materials, and to its stellar sources. Interpreting the  mass  spectra
requires calibration. Calibration here  is  not  meant  to  mimic  the
experiment in a one-to-one scale in  the  laboratory,  but  rather  to
understand the processes, which control  ion  formation  with  complex
samples, as well as the instrumental  parameters  of  mass  separation
and ion detection. To that end, state-of-the-art  laboratory  TOF-SIMS
analyses with utmost lateral and mass resolution of various  materials
available on Earth will be  performed,  which  include,  but  are  not
limited to:
Interplanetary  dust  particles  (IDPs):  Some  of  these  small   and
difficult-to-analyze particles actually may stem from  comets.  It  is
an active research topic to sort these out and distinguish  them  from
asteroidal IDPs. IDPs of a certain class  are  mixtures  of  inorganic
and organic matter and as such represent the best analog material  for
the COSIMA case.
Carbonaceous chondrites: They are mechanical mixtures of  fine-grained
low-temperature matrix and carbon-rich  phases  (kerogen)  with  high-
temperature clasts, single minerals,  and  chondrules.  Their  overall
chemical composition is solar as far as the condensable  elements  are
concerned. They most closely represent and  witness  the  Early  Solar
System materials and processes. They are regarded  as  the  base  line
material in planetology.
 
Certain  IDPs  and  chondrites  contain  particles  with  non-standard
isotopic composition of a number of elements that point towards  their
nucleosynthetic  stellar  sources.  These   particles   (stardust   or
presolar particles) will serve to learn how  to  obtain  the  relevant
information from cometary matter.
 
The extraterrestrial materials mentioned above are not as pristine  as
we expect cometary dust to be. IDPs are altered to an  unknown  extent
during passage through  the  atmosphere,  deceleration  processes  and
residence in the stratosphere; carbonaceous  chondrites  were  subject
to  metamorphism  and  aqueous  alteration  on  their  parent  bodies.
Consequently,  for  the  analysis  of  organic  (and  icy)  components
anticipated in cometary particles artificial analogs are needed.  They
are  siliceous  vaporization  deposits   contaminated   with   organic
substances. Certainly not  all  possible  organic  substances  can  be
analyzed,  but  rather  we  will  perform  TOF-SIMS  measurements   of
relevant substance classes.
 
As mentioned above, these analyses  are  performed  with  the  highest
possible  mass  and  (where  appropriate)   lateral   resolution.   In
addition, the temporal evolution of the mass spectra is  evaluated  by
using the data from all primary ion pulses. This will give hints to  a
possible layering within the material and /  or  validate  influences,
which the TOF-SIMS  method  may  cause  in  the  material  (by,  e.g.,
'radiation damage').  New  statistical  and  chemometric  methods  and
procedures, now under test, will be further developed and applied.
 
The laboratory program will  benefit  from  and  be  adjusted  to  new
insights, which will come from the analysis of  the  samples  returned
by Stardust.
 
 
6 Anticipated Results
 
6.1 The Mineral Phase
 
 The anticipated results of the investigation of the mineral phase  of
 the cometary dust are manifold:
1.  First, we  shall  establish  the  mean  composition  of  the  main
   elements, and then check whether this varies from grain  to  grain,
   either within the statistical  variance  or  beyond  that.  In  the
   latter case we'll be able to identify various classes of minerals.
2.  Second, the distribution of molecular ions should be sensitive  to
   the order structure of the minerals, may they be in an amorphous or
   in one of several crystalline states. This would give an  important
   clue to the thermal and radiation history of the dust.
3.  Third, once an elemental and molecular distribution  of  the  main
   isotopic contribution is established, the contribution of the minor
   isotopes can be measured  from  grain  to  grain,  needed  for  the
   question whether various stellar sources have played a role to form
   the dust.
4.  Fourth (last but not least), a cross-correlation of the  types  of
   organics sitting upon the same grain will give insight into aspects
   of the real grain forming process as well as to possible  catalytic
   interferences between each phase. This is important for the 'Origin
   of Life' topic and its relation to nano-systems.
 
 
 6.2 The Organic Phase
 
 
 The refractory organic  phase  will  most  probably  be  an  intimate
 mixture of a lot of individual species. But  still,  the  history  of
 grain formation and the incorporation of them into cometary nuclei is
 reflected - at least partially - in the distribution of  the  organic
 species. Substance class analysis will provide clues to  whether  the
 organic phase is  mainly  produced  by  condensation  of  vapors  and
 subsequent   radiation   processing   with    polycondensation    and
 oligomerization, etc., or, if it is mainly produced  by  condensation
 of larger molecules and aggregation of small refractory particles.
 Another important question is, whether the organic material in comets
 is suitable to start the onset of life on earth. In  this  case,  the
 analysis will show that the precursors of such molecules  needed  for
 life's self-organization by exenthalpic reactions with  liquid  water
 are present.
 As water usually shows up in  different  ways  in  the  mass-spectra,
 clues to the source of water in the comet may be found,  too:  is  it
 just a condensation of water ice in the grains, or, is it the  result
 of long-term radiation induced processes, such as polycondensation or
 Born-Haber-type processes, or is perhaps a fraction of the water in a
 comet  produced  by  thermally  induced  reactions,  when  the  comet
 approaches the sun?
 COSIMA results thus address the main questions concerning the  origin
 of the hydrosphere, and further on, the biosphere on earth.
 
7 References
 
 Kissel, J. et al., COSIMA - High resolution
 time-of-flight secondary ion mass spectrometer for the analysis
 of cometary dust particles onboard Rosetta, Space Sci. Rev.,
 128(1-4), 823-867, doi:10.1007/s11214-006-9083-0, 2007.
 
 This document is available in the DOCUMENT directory.
 
-----------------------