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LUCAS experiment: Spectroscopy of Earthshine in Antarctica for Detection of Life. Danielle BRIOT (Observatoire de Paris). Main collaborators : Eric Aristidi (LUAN, Nice) Luc Arnold (Obs. Haute-Provence) Jérome Berthier (Obs.Paris-Meudon) Danielle Briot (Obs.Paris-Meudon)

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lucas experiment spectroscopy of earthshine in antarctica for detection of life
LUCAS experiment:Spectroscopy of Earthshine in Antarctica for Detection of Life

Danielle BRIOT


de Paris)

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

looking for life in extrasolar planets
Looking for life in Extrasolar Planets
  • Today, 14 May 2009,

347 extrasolar planetsare 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.


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)


Theseinstruments 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

shall we be able to detect life on an unresolved earth like extrasolar planet
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.
what would the spectrum of an unresolved earth like planet look like
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.

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 ?


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.

some historic points
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 Moon’s 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…
what shall we look for in this spectrum
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
detection of vegetable life
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).

Reflectance spectra of green vegetation, dry vegetation and soil

(Clark 1999)

Red edge


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.









A blue Earth, O3, O2, H2O, vegetation signature (Arnold et al 2002)

Clark 1999




Hamdani et al. 2006 (A&A)

VRE = 1 to 4%

Observation from Chile ([email protected] with EMMI)

Dark Earth in near-UV (<360nm) Ozone absorption !

Rayleigh visible down to 360nm

other features of the earth spectrum revealed by the earthshine observations
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)
restrictions of earthshine observations
« 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. Soobservations 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).

per spectives

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.

possible observing times in antarctica
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.
preliminary observations at concordia
Preliminary observations at Concordia

• Checking thefeasibility 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.

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.

lucas design
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 >100

lucas technology
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.


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.


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.


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.


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 +20°C.

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!

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".


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.

  • 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.

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

The End

the dream of every exoplanetologist
The dream of every exoplanetologist

A planet with a very

easily detectable

vegetation, without

clouds and without


The baobabs

from « Le Petit Prince »,

Antoine de Saint-Exupéry