LUCAS experiment: Spectroscopy of Earthshine in Antarctica for Detection of Life

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LUCAS experimentSpectroscopy of Earthshine in
Antarctica for Detection of Life

• Danielle BRIOT
• (Observatoire
• de Paris)

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• Main collaborators
• Eric Aristidi (LUAN, Nice)
• Luc Arnold (Obs. Haute-Provence)
• Jérome Berthier (Obs.Paris-Meudon)
• Danielle Briot (Obs.Paris-Meudon)
• Stéphane Jacquemoud (IPGP, Paris)
• Patrick Rocher (Obs.Paris-Meudon)
• Jean Schneider (Obs. Paris-Meudon)

and the winterover observers in Antarctica
Karim Agabi, Eric Aristidi, Erick Bondoux,
Zalpha Challita, Denis Petermann and Cyprien
Pouzenc
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Looking for life in Extrasolar Planets

• Today, 14 May 2009,
• 347 extrasolar planets are known.
• Possibly one super-Earth detected in the
  habitable zone (Gliese 581 d)
• Therefore, we have to prepare the analysis of the
  results to come from future space missions.

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Preparation of High contrast imaging projects

• Space projects
• - Coronagraphs or external occulters
• (visible-near infrared light) TPF-C, TPF- O
• - 1.5 m precursors See-Coast, EPIC, PECO etc.
•  Ground Projects
• - EPICS (E-ELT)

See-Coast
These instruments will (hopefully) provide us
with 1/ unresolved images of extra-solar planets
in the HZ 2/ spectra to give us first insights
into planet chemistry
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Shall we be able to detect life on an unresolved
Earth-like extrasolar planet ?

• Future space missions will provide us with the
  first images and low-resolution spectra of these
  planets.
• Let us consider an unresolved extrasolar
  Earth-like planet, the spectrum of the light
  reflected by the planet, when normalized to the
  parent star spectrum, gives the planet
  reflectance spectrum revealing its atmospheric
  and ground colour.

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What would the spectrum of an unresolved
Earth-like planet look like ?

• Life on an extrasolar planet would be probably
  very different from life on Earth, which is the
  only known planet sheltering life.
• So a way to answer this question is to consider
  how the spectrum of our Earth would look like
  when observed from a very long distance,
  typically several parsecs. This can be done from
  a space probe traveling into the Solar System and
  looking back at the Earth as Voyager 1 in 1990,
  or Mars Express in 2003.

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Earth viewed from 6.4 109 km Voyager-1, 14th
feb. 1990
Shall we be able to detect life on an
unresolved Earth-like extrasolar planet ?
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An alternative method to obtain the
Earth-averaged spectrum, according to an idea of
Jean Schneider (1998), consists in measuring the
reflectance spectrum of the Moon Earthshine, i.e.
the light back-scattered by the non-sunlit Moon.
A spectrum of the Moon Earthshine directly
gives the disk-averaged spectrum of the
Earth. Because of the lunar surface roughness,
any place of the Earthshine reflects the
totality of the enlighted part of the Earth
facing the Moon.
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Earthshine
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Pathway of the Light when observing the
Earthshine
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Some historic points.

• It seems that Leonardo Da Vinci was the first who
  clearly understood the origin of the phenomenon
  of Earthshine, but credit for the first
  publication should be given to Galileo !
• The potential of the Moons Earthshine for
  providing global data on the Earth was identified
  during the XIXe century (Flammarion, 1877), and
  maybe earlier.
• In 1912, Arcichovsky suggested looking for
  chlorophyll absorption in the Earthshine spectrum
  to calibrate chlorophyll in the spectrum of other
  planets. This approach was completely forgotten
  up to 1998

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What shall we look for in this spectrum ?

• Look for the signature of molecules in the
  atmosphere (biogenic products ?)
• O2, O3, CH4, H2O, CO2
• Look for biologic activity
• the planet colour vegetation, pigments
• Look for missing photons used in a photosynthesis
  
• Possible artifacts (i.e. false positive
  detection) minerals, rocks

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Detection of vegetable life

• Vegetation indeed has a very high reflectivity in
  the near infrared, higher than in the visible
  spectrum by a factor of approx. 9.
• This produces a sharp edge around approx. 700 nm,
  the so-called Vegetation Red Edge (VRE).

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Vegetation and water at 1.1?mVegetation appears
very bright and water very dark
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Reflectance spectra of green vegetation,
dry vegetation and soil
(Clark 1999)
Red edge
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• Since 2002, several observations have been made
  of the VRE.
• Even with a VRE of only a few percents,
  vegetation signature is detectable in an
  integrated (or disk-averaged) Earth spectrum.
• When an ocean is facing the Moon,
• the VRE is smaller than
• when a continental surface
• is facing the Moon.

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A blue Earth, O3, O2, H2O, vegetation signature
(Arnold et al 2002)
Clark 1999
morning
evening
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Hamdani et al. 2006 (AA) VRE 1 to
4 Observation from Chile (NTT_at_ESO with EMMI)
Dark Earth in near-UV (lt360nm) Ozone absorption
! Rayleigh visible down to 360nm
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VRE values from spectroscopy or models (L.
Arnold, 2008)
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Other features of the Earth spectrum revealed by
the Earthshine observations

• In addition to the Vegetation Red Edge,
• the red side (600 - 1000 nm) of the Earth
  reflectance spectrum shows the presence of O2 and
  H2O absorption bands,
• while the blue side (320 - 620 nm) clearly shows
  the Huggins and Chappuis ozone (O3) absorption
  bands (Hamdani et al. 2006)

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 Restrictions  of Earthshine observations

• As it is well known, at mean or low latitudes,
  Earthshine observations are possible during
  twilight just after the sunset or just before
  the sunrise. So observations can only be made
  during a short period of time.
• And roughly speaking, for one telescope, only two
  enlighted parts of Earth can be facing the Moon
  
• either the part located at the West of the
  observing telescope for evening observations
  (beginning of the lunar cycle),
• or the part of Earth located at the East of the
  observing telescope for morning observations
  (last days of the lunar cycle).

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Perspectives

• However, there are other possibilities.
• From an idea of Jean Schneider (2002), if
  observations are made from a site located at a
  high latitude, conditions of Earthshine
  observations are different. About 8 times in a
  year, around equinoxes, Earthshine can be
  observed during several hours, and even, in very
  high latitude places, during a 24 hour duration
  (total nycthemere).
• During these long observing windows, and due to
  the terrestrial rotation, different
   landscapes  alternately face the Moon.
• Actually, Antarctica offers a very good
  opportunity for this kind of observations.

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Possible observing timesin Antarctica

• Observations of Earthshine are possible during
  about 8 periods in a year, around the Equinoxes.
• Observations up to the June solstice correspond
  to the last days of the Lunar Cycle, from the
  Last Quarter to 2 or 3 days before the New Moon.
• Observations from the June solstice correspond to
  the first days of the Lunar cycle, from 2 or 3
  days after the New Moon to the Last Quarter.

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Preliminary observations at Concordia

• Checking the feasibility of Earthshine
  observations
• considering the darkness of the sky was the first
  point. Is
• the sky enough dark to allow observations of
  Earthshine ?
•  The first tests have been planned during the
  first
• Winterover campaign in 2005, by Karim Agabi.
• Unfortunately, bad weather conditions did not
  allow some
• conclusive observations.
•  In 2006, photographic tests made by Eric
  Aristidi clearly
• showed that Earthshine observations could be
  possible.

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Eathshine observed by Eric Aristidi at
Concordia, 26 February 2006
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• As soon as it appears that Earthshine
  observations are possible from Concordia, we plan
  to make observations to observe Vegetation Red
  Edge and biomarkers during the southern winter of
  2008.
• Funding has been obtained from the University
  of Paris 7, the PID-OPV of the CNRS and the PNTS.
  A collaboration has been established with
  specialists of the Vegetation remote-sensing.
• We designed and built a dedicated
  instrumentation for Earthshine spectroscopic
  observations in the extreme conditions
  corresponding to Concordia station.

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LUCAS design

• The telescope is a Celestron 8
• Diameter 203 mm, F/D 10
• The telescope has been  antarctized  by
   Optique et Vision 
• The spectrograph was designed by Luc Arnold and
  Pierre Riaud and built at the Haute-Provence
  Observatory.
• Grating 300t/mm
• CCD Camera Audine - KAF 402ME CCD
• ?? 461 ? 900 nm, resolution gt100

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3D assembly diagram of LUCAS
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LUCAS instrumentation during testing at the
Haute-Provence Observatory
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LUCAS technology

• Acquisition and storage of observational data
  will be provided by a computer located in a
   igloo  at about 20 meters from the telescope.
• Tests carried out at the Haute-Provence
  observatory validated the instrumentation.
•  Before their departure, winterover observers
  made a visit at the Haute-Provence observatory to
  see LUCAS.
• A very detailed handbook intented for winterover
  observers has been written.

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Position of the slit on the lunar surface The
observing slit is to be positionned  first on
both the lighted crescent and the sky,  and
then on both the Earthshine and the sky.
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The places to be observed on the Moon are
precisely defined to avoid different physical
characters corresponding to different places -
On East side, the slit is centered on Mare
Spumans, - and on West, on crater Hevelius,
both near the Equator.
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LUCAS at Concordia in 2008
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The feedback we got from the first observing
campaign in 2008 was very important to detect,
analyze and correct instrumental problems due to
extreme temperature and extreme physical
conditions. Some important instrumental
improvements were carried out for the 2009
winterover campaign.
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• Improvements for LUCAS 2009
• 1) Improvement of heat insulation
• A significant thermal leak was induced by an
  aluminium beam in the instrument. Therefore a new
  insulation has been carried out. 300W of heating
  resistances were installed.
• Moreover the instrument benefits from the ASTEP
  dome.
• Internal temperature is 20C.

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• 2) Problems with the shutter
• During the 2008 campaign, the shutter broke after
  one month of operation. The heat dissipated to
  warm it was probably not sufficient. We think
  that the friction in the shutter (the moving
  metal blades probably warped by the cold) becomes
  too high and killed the shutter motor.
• Actually, problems with shutters happened also in
  some other instruments. Moving parts are always
  weak points in an instrument in harsh environment
  and require special care during the instrument
  design!

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3) The flip-mirror was very unconvenient for the
observer and we replaced it by a static
beam-splitter. Here again, moving elements are to
be restricted as possible. 4) An eyepiece
initially installed to verify the pointing
reveals also highly unconvenient and almost
unsuable. It as been replaced by a videocamera
and the observer controls the accuracy of the
pointing from the "igloo".
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LUCAS in 2009
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LUCAS in 2009
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LUCAS in 2009
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Today, we have obtained several Moon spectra, but
adjustment of the pointing has to be improved to
avoid a bright ghost from direct Moon light that
currently still compromises the record of faint
Earthshine spectra. Tests are done right now to
adjust the pointing. The next observational run
is from the 17th of May to the 20th of May.
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Conclusion

• Actually, LUCAS is the first program with
  spectroscopic observations at Dome C.As such, it
  is also a test for the design and improvement of
  small instrumentation, data collecting and
  management of observations in Concordia extremely
  cold environnement.

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Thanks are due to Luc Arnold, Stéphane Jacquemoud
and Jean Schneider for their help during the
preparation of this talk. The End
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The dream of every exoplanetologist

• A planet with a very
• easily detectable
• vegetation, without
• clouds and without
• oceans
• The baobabs
• from  Le Petit Prince ,
• Antoine de Saint-Exupéry