Transcript The patchy surface of Europa

Evolution of the universe:
Exploring the Solar System - Missions and Techniques
From Astrophysics to Astrobiology
EGU 2008, Austria Center Vienna, Lecture Room 11; 15 April 2008: 9.15
Distinguishing
between signatures of
past life and nonlife
Julian Chela-Flores
The Abdus Salam ICTP, Trieste, Italia
and
Instituto de Estudios Avanzados, Caracas,
Republica Bolivariana de Venezuela
The Origins: how, when and where it all started,
Accademia Nazionale dei Lincei. Centro Linceo Interdisciplinare “Beniamino Segre”,
Roma, 22 May 2006
Authors
Julian Chela-Flores
The Abdus Salam ICTP, Trieste, Italia
and
Instituto de Estudios Avanzados, Caracas,
Republica Bolivariana de Venezuela
Narendra Kumar
Indian Institute of Science,
Bangalore, India
Joseph Seckbach
The Hebrew University of Jerusalem
Israel
Vinod Tewari
Wadia Institute of Himalayan Geology
Dehradun, India.
Future missions to Europa
 There is a possibility for returning to Europa
with both the LAPLACE mission,
and the Europa Geophysical Explorer.
Europa Geophysical
Explorer
The outline of LAPLACE has been
summarised by Blanc, M. and the LAPLACE
consortium (2008).
Habitability
 “Is Europa habitable?” plays a prominent role in ESA’s
Cosmic Vision Plan for 2015-2025 that has been adopted for
the LAPLACE mission. The other two Goals are related with
habitability:
 What have been the conditions for the formation of the
Jupiter system? How do they contribute to the possible
emergence of life?
 How does the Jupiter system work? How does the system
contribute to the conditions for habitability?
 For NASA's Science Mission Directorate habitability is also
the focus of its Solar System Exploration Roadmap.
Plan of the talk
 The patchy surface of Europa:
A major challenge in the exploration of Europa.
 Chemical elements on the surface of Antarctica and Europa.
 Biogeochemistry.
 A ‘fluctuation test’ for the exploration of Europa.
 Instrumentation.
 Discussion.
Part I
The patchy surface of Europa:
A major challenge in the exploration of Europa
International Journal of Astrobiology (2006), 5, pp. 17-22 (Cambridge University Press).
Ice-covered oceans over a silicate core:
The cases of Europa and Titan
 Galileo revealed evidence for an internal ocean,
but we argue that for determining the habitability of Europa,
waiting to enter the ocean by 2028 may be unnecessary.
Horvath et al, 1997
A hydrobot
Endurance, 2008
Possible sources of the stains
 External source:
Ions may be implanted from the Jovian plasma.
 Internal source:
Sulfur may be due to cryovolcanism.
 Could the source be biogenic?
We discuss the use of mass spectrometry
in the context of the available instrumentation.
Part II
Chemical elements on
the surface of
Antarctica and Europa
Antarctica’s
subglacial lakes
Antarctica’s
Dry Valleys:
Beacon
Taylor
Victoria
Wright
Lake Bonney (7)
Lake Hoare (9)
The Taylor (Dry) Valley
A cross-section of the icy surface of Lake Hoare
Algal mat pieces on the
surface of Lake Hoare
(Parker et al, Phycologia, 1982)
Annual escape of sulfur (kg)
by the loss of algal mats
The Europa icy and ‘patchy’ surface
(Spectrometer data from near IR)
albedo per pixel
4 km/pixel
High resolution
albedo image
Distribution of
non-ice component
McCord et al,
Science 280 (1998), 1242
Where
should
we
land?
Part III
Biogeochemistry
The delta 34S-parameter
The Canyon Diablo Meteorite (CDM) is a troilite (FeS), that was
found in Arizona:
 The meteorite coincides with the standard (st) terrestrial ratio of the
isotopes 32S and 34S. For a given sample (sa), we define with
respect to this meteorite:
Sulfate-reducing bacteria
Sulfate-reducing bacteria
 Unite H with S atoms from dissolved sulfate ( SO4-2 )
of seawater to form hydrogen sulfide H2S :
4H2 + H2SO4 –» H2S + 4H2O + 39 kilocalories
 The H2S then combines with Fe in sediments to form grains of
the biogenic mineral pyrite.
Iron sulfide, FeS2
The sulfur isotopes are divided between
biogenic minerals and sulfate minerals
 Dissolved sulfate on
evaporation
sulfate
depleted of
per mil.
forms
minerals
32S by 20
 The H2S given off by
the bacteria is enriched
in 32S by 20 per mil.
Sulfur ions on Earth, meteorites and the Moon
The delta34S-parameter
Terrestrial
From measurements in
basins off California:
insoluble sulfide,
mostly pyrite.
-40
Sulfate
coexisting with
seawater
Meteoritic
Lunar
Part IV
A ‘fluctuation test’ for the
exploration of Europa
The fluctuation test (Luria and Delbruck)
 Luria first assumed that mutations in a growing bacterial
culture could be acquired as a result of its exposure to
virus (phage).
 If this was the case, the number of resistant individuals
would vary very little from one experiment to the next.
 The observed number would then have very small
fluctuations (slight deviations from the mean).
Can bacterial fluctuations be large?
 Alternatively, Luria also assumed that a mutation can
occur before the bacterium was confronted with phage.
 The number of resistant bacteria would depend on the
time elapsed since the mutation. The number of resistant
individuals shows exponentially large fluctuations.
 The observed bacterial exponential growth suggests to
detect such deviations from Gaussianity with higher order
statistics.
Part V
Instrumentation
Difficulties with the the dust analyzers
 32S is isobaric (same m/z) with
16O
2.
There would not have
sufficient resolution with the current design to identify the
contributions from S and its interference with the O2 at m/z
32 and 34.
 The instrument required needs to count about 1x106
sulfur ions to get a precision of +/- 5 per mil on the delta34Sparameter. So the likely ion counts is a key issue.
The cloud generated around Europa
 We expect it to mirror the large S-isotope deviations on
the surface.
 Consequently, dust detectors in orbit should record
similar non-Gaussian distributions as conjectured for
the surface itself, with non-vanishing cumulants of
order greater than 2.
 On the other hand, the contributions from the O2
atmosphere should be described instead by a Gaussian
distribution with vanishing cumulants of order greater
than 2.
A possible instrument is a penetrator
 A UK Consortium has already argued in favour of
landing with penetrators on the icy surface of Europa.
 Penetrators are considered in the recent paper of
Blanc, M. and the LAPLACE consortium summarising
the mission.
 In this case, if the Europan surface is to be probed
with penetrators, MS would be a valuable alternative
for understanding the icy patches.
The mass constraints for MS on
penetrators are severe
 To illustrate that miniaturization
is not the main challenge, we point
out suitable instrumentation:
• The
current MS on Cassini
(Ion and neutral MS), and
•The work on miniaturised
MS by Peter Wurz and coworkers at the University of
Bern.
120 x 60 mm; 500 g
Discussion
 The work of miniaturization of the instrumentation does
not seem to be the greatest challenge in interpreting Sisotopes either in orbit or on the icy surface of Europa.
 The use of MS is suggested for a dust analyzer and, if
landers are possible, MS is also suggested for penetrators.
pdf files can be downloaded from:
http://www.ictp.it/~chelaf/ss16a.html