[meteorite-list] Science on a Surface of a Comet (Rosetta/Philae)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 31 Jul 2015 15:16:48 -0700 (PDT)
Message-ID: <201507312216.t6VMGmN7002666_at_zagami.jpl.nasa.gov>

http://sci.esa.int/rosetta/56250-science-on-the-surface-of-a-comet/

Science on the surface of a comet
European Space Agency
30 July 2015

Complex molecules that could be key building blocks of life, the
daily rise and fall of temperature, and an assessment of the
surface properties and internal structure of the comet are just
some of the highlights of the first scientific analysis of the
data returned by Rosetta's lander Philae last November.

Early results from Philae's first suite of scientific observations
of Comet 67P/Churyumov-Gerasimenko were published today in a
special edition of the journal Science.

Data were obtained during the lander's seven-hour descent to its
first touchdown at the Agilkia landing site, which then triggered
the start of a sequence of predefined experiments. But shortly
after touchdown, it became apparent that Philae had rebounded and
so a number of measurements were carried out as the lander took
flight for an additional two hours some 100 m above the comet,
before finally landing at Abydos.

Some 80% of the first science sequence was completed in the 64
hours following separation before Philae fell into hibernation,
with the unexpected bonus that data were ultimately collected at
more than one location, allowing comparisons between the touchdown
sites.

Inflight science

After the first touchdown at Agilkia, the gas-sniffing instruments
Ptolemy and COSAC analysed samples entering the lander and
determined the chemical composition of the comet's gas and dust,
important tracers of the raw materials present in the early Solar
System.

COSAC analysed samples entering tubes at the bottom of the lander
kicked up during the first touchdown, dominated by the volatile
ingredients of ice-poor dust grains. This first sniff revealed a
suite of 16 organic compounds comprising numerous carbon and
nitrogen-rich compounds, including four compounds - methyl
isocyanate, acetone, propionaldehyde and acetamide - that have
never before been detected in comets.

Meanwhile, Ptolemy sampled ambient gas entering tubes at the top
of the lander and detected the main components of coma gases -
water vapour, carbon monoxide and carbon dioxide, along with
smaller amounts of carbon-bearing organic compounds, including
formaldehyde.

Importantly, some of these compounds detected by Ptolemy and COSAC
play a key role in the prebiotic synthesis of amino acids, sugars
and nucleobases: the ingredients for life. For example,
formaldehyde is implicated in the formation of ribose, which
ultimately features in molecules like DNA.

The existence of such complex molecules in a comet, a relic of the
early Solar System, imply that chemical processes at work during
that time could have played a key role in fostering the formation
of prebiotic material.

Comparing touchdown sites

Thanks to the images taken by ROLIS on the descent to Agilkia, and
the CIVA images taken at Abydos, a visual comparison of the
topography at these two locations could be made.

ROLIS images taken shortly before the first touchdown revealed a
surface comprising metre-size blocks of diverse shapes, coarse
regolith with grain sizes of 10-50 cm, and granules less than 10
cm across.

The regolith at Agilkia is thought to extend to a depth of 2 m in
places, but seems to be free from fine-grained dust deposits at
the resolution of the images.

The largest boulder in the ROLIS field-of-view measures about 5 m
high, with a peculiar bumpy structure and fracture lines running
through it that suggest erosional forces are working to fragment
the comet's boulders into smaller pieces.

The boulder also has a tapered 'tail' of debris behind it, similar
to others seen in images taken by Rosetta from orbit, yielding
clues as to how particles lifted up from one part of the eroding
comet are deposited elsewhere.

Over a kilometre away at Abydos, not only did the images taken by
CIVA's seven microcameras reveal details in the surrounding
terrain down to the millimetre scale, but also helped decipher
Philae's orientation.

The lander is angled up against a cliff face that is roughly 1 m
from the open 'balcony' side of Philae, with stereo imagery
showing further topography up to 7 m away, and one camera with
open sky above.

The images reveal fractures in the comet's cliff walls that are
ubiquitous at all scales. Importantly, the material surrounding
Philae is dominated by dark agglomerates, perhaps comprising
organic-rich grains. Brighter spots likely represent differences
in mineral composition, and may even point to ice-rich materials.


>From the surface to the interior

The MUPUS suite of instruments provided insight into the physical
properties of Abydos. Its penetrating 'hammer' showed the surface
and subsurface material sampled to be substantially harder than
that at Agilkia, as inferred from the mechanical analysis of the
first landing.

The results point to a thin layer of dust less than 3 cm thick
overlying a much harder compacted mixture of dust and ice at
Abydos. At Agilkia, this harder layer may well exist at a greater
depth than that encountered by Philae.

The MUPUS thermal sensor, on Philae's balcony, revealed a
variation in the local temperature between about -180??C and -145??C
in sync with the comet's 12.4 hour day. The thermal inertia
implied by the measured rapid rise and fall in the temperature
also indicates a thin layer of dust atop a compacted dust-ice crust.

Moving below the surface, unique information concerning the global
interior structure of the comet was provided by CONSERT, which
passed radio waves through the nucleus between the lander and the
orbiter. The results show that the small lobe of the comet is
consistent with a very loosely compacted (porosity 75???85%) mixture
of dust and ice (dust-to-ice ratio 0.4???2.6 by volume) that is
fairly homogeneous on the scale of tens of metres.

In addition, CONSERT was used to help triangulate Philae's
location on the surface, with the best fit solution currently
pointing to a 21 ?? 34 m area.

"Taken together, these first pioneering measurements performed on
the surface of a comet are profoundly changing our view of these
worlds and continuing to shape our impression of the history of
the Solar System," says Jean-Pierre Bibring, a lead lander
scientist and principal investigator of the CIVA instrument at the
IAS in Orsay, France.

"The reactivation would also allow us to complete the
characterisation of the elemental, isotopic and molecular
composition of the cometary material, in particular of its
refractory phases, by APXS, CIVA-M, Ptolemy and COSAC."

"With Philae making contact again in mid-June, we still hope that
it can be reactivated to continue this exciting adventure, with
the chance for more scientific measurements and new images which
could show us surface changes or shifts in Philae's position since
landing over eight months ago," says DLR's Lander Manager Stephan
Ulamec.

"These ground-truth observations at a couple of locations anchor
the extensive remote measurements performed by Rosetta covering
the whole comet from above over the last year," says Nicolas
Altobelli, ESA's acting Rosetta project scientist.

"With perihelion fast approaching, we are busy monitoring the
comet's activity from a safe distance and looking for any changes
in the surface features, and we hope that Philae will be able to
send us complementary reports from its location on the surface."


Notes for editors

The 31 July 2015 /Science /special issue
<http://www.sciencemag.org/content/349/6247.toc#SpecialIssue>
includes the following papers:

"The nonmagnetic nucleus of comet 67P/Churyumov-Gerasimenko"
by H.-U. Auster et al.
http://dx.doi.org/10.1126/science.aaa5102

"67P/Churyumov-Gerasimenko surface properties as derived from
CIVA panoramic images" by J-P. Bibring et al.
http://dx.doi.org/10.1126/science.aab0671

"The landing(s) of Philae and inferences about comet surface
mechanical properties" by J. Biele et al.
http://dx.doi.org/10.1126/science.aaa9816

"Organic compounds on comet 67P/Churyumov-Gerasimenko revealed by
COSAC mass spectrometry" by F. Goesmann et al.
http://dx.doi.org/10.1126/science.aab0689

"Properties of the 67P/Churyumov-Gerasimenko interior revealed by
CONSERT radar" by W. Kofman et al.
http://dx.doi.org/10.1126/science.aab0639

"The structure of the regolith on 67P/Churyumov-Gerasimenko from
ROLIS descent imaging" by by S. Mottola et al.
http://dx.doi.org/10.1126/science.aab0232

"Thermal and mechanical properties of the near-surface layers of
comet 67P/Churyumov-Gerasimenko" by T. Spohn et al.
http://dx.doi.org/10.1126/science.aab0464

"CHO-bearing organic compounds at the surface of
67P/Churyumov-Gerasimenko revealed by Ptolemy" by I.P. Wright et al.
http://dx.doi.org/10.1126/science.aab0673

For a gallery of individual ROLIS images click here
<http://sci.esa.int/multimedia-gallery/30913-multimedia-archive/?t=1020>.
For a gallery of individual CIVA images click here
<http://sci.esa.int/multimedia-gallery/30913-multimedia-archive/?t=793>.


About Rosetta

Rosetta is an ESA mission with contributions from its Member
States and NASA. Rosetta's Philae lander is contributed by a
consortium led by DLR, MPS, CNES and ASI.


For further information, please contact

Nicolas Altobelli
Acting Rosetta Project Scientist
Email: Nicolas.Altobelli at sciops.esa.int

Jean-Pierre Bibring
Lead lander scientist and principal investigator of CIVA
Institut d'Astrophysique Spatiale (IAS), Orsay, France
Email: jean-pierre.bibring at ias.u-psud.fr

Stephan Ulamec
Philae lander manager
German Aerospace Center (DLR)
Email: Stephan.Ulamec at dlr.de
Received on Fri 31 Jul 2015 06:16:48 PM PDT