The Philae lander reveals low-strength primitive ice inside cometary boulders

Laurence O’Rourke (), Philip Heinisch, Jürgen Blum, Sonia Fornasier, Gianrico Filacchione, Hong Hoang, Mauro Ciarniello, Andrea Raponi, Bastian Gundlach, Rafael Andrés Blasco, Björn Grieger, Karl-Heinz Glassmeier, Michael Küppers, Alessandra Rotundi, Olivier Groussin, Dominique Bockelée-Morvan, Hans-Ulrich Auster, Nilda Oklay, Gerhard Paar, Maria del Pilar Caballo Perucha, Gabor Kovacs, Laurent Jorda, Jean-Baptiste Vincent, Fabrizio Capaccioni, Nicolas Biver, Joel Wm. Parker, Cecilia Tubiana and Holger Sierks
Additional contact information
Laurence O’Rourke: European Space Astronomy Centre (ESAC)
Philip Heinisch: Technische Universität Braunschweig
Jürgen Blum: Technische Universität Braunschweig
Sonia Fornasier: LESIA, Observatoire de Paris, Université PSL, CNRS, Université de Paris, Sorbonne Université
Gianrico Filacchione: Istituto di Astrofisica e Planetologia Spaziali
Hong Hoang: LESIA, Observatoire de Paris, Université PSL, CNRS, Université de Paris, Sorbonne Université
Mauro Ciarniello: Istituto di Astrofisica e Planetologia Spaziali
Andrea Raponi: Istituto di Astrofisica e Planetologia Spaziali
Bastian Gundlach: Technische Universität Braunschweig
Rafael Andrés Blasco: European Space Astronomy Centre (ESAC)
Björn Grieger: Aurora Technology BV for the European Space Agency (ESA), European Space Astronomy Centre (ESAC)
Karl-Heinz Glassmeier: Technische Universität Braunschweig
Michael Küppers: European Space Astronomy Centre (ESAC)
Alessandra Rotundi: Istituto di Astrofisica e Planetologia Spaziali
Olivier Groussin: Aix Marseille Université, CNRS, CNES, LAM
Dominique Bockelée-Morvan: LESIA, Observatoire de Paris, Université PSL, CNRS, Université de Paris, Sorbonne Université
Hans-Ulrich Auster: Technische Universität Braunschweig
Nilda Oklay: Independent researcher
Gerhard Paar: Joanneum Research Forschungsgesellschaft
Maria del Pilar Caballo Perucha: Joanneum Research Forschungsgesellschaft
Gabor Kovacs: Budapest University of Technology and Economics
Laurent Jorda: Aix Marseille Université, CNRS, CNES, LAM
Jean-Baptiste Vincent: DLR Institute of Planetary Research
Fabrizio Capaccioni: Istituto di Astrofisica e Planetologia Spaziali
Nicolas Biver: LESIA, Observatoire de Paris, Université PSL, CNRS, Université de Paris, Sorbonne Université
Joel Wm. Parker: Southwest Research Institute (SwRI)
Cecilia Tubiana: Istituto di Astrofisica e Planetologia Spaziali
Holger Sierks: Max-Planck-Institut für Sonnensystemforschung

Nature, 2020, vol. 586, issue 7831, 697-701

Abstract: Abstract On 12 November 2014, the Philae lander descended towards comet 67P/Churyumov–Gerasimenko, bounced twice off the surface, then arrived under an overhanging cliff in the Abydos region. The landing process provided insights into the properties of a cometary nucleus1–3. Here we report an investigation of the previously undiscovered site of the second touchdown, where Philae spent almost two minutes of its cross-comet journey, producing four distinct surface contacts on two adjoining cometary boulders. It exposed primitive water ice—that is, water ice from the time of the comet’s formation 4.5 billion years ago—in their interiors while travelling through a crevice between the boulders. Our multi-instrument observations made 19 months later found that this water ice, mixed with ubiquitous dark organic-rich material, has a local dust/ice mass ratio of $${2.3}_{-0.16}^{+0.2}:1$$ 2.3 − 0.16 + 0.2 : 1 , matching values previously observed in freshly exposed water ice from outbursts4 and water ice in shadow5,6. At the end of the crevice, Philae made a 0.25-metre-deep impression in the boulder ice, providing in situ measurements confirming that primitive ice has a very low compressive strength (less than 12 pascals, softer than freshly fallen light snow) and allowing a key estimation to be made of the porosity (75 ± 7 per cent) of the boulders’ icy interiors. Our results provide constraints for cometary landers seeking access to a volatile-rich ice sample.

Date: 2020
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DOI: 10.1038/s41586-020-2834-3

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