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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. This article is mirrored from the main ESA Web Portal.
Images taken by Philae’s ROsetta Lander Imaging System, ROLIS, trace the lander’s descent to the first landing site, Agilkia, on Comet 67P/Churyumov–Gerasimenko on 12 November 2015. Credits: ESA/Rosetta/Philae/ROLIS/DLR
Images taken by Philae’s ROsetta Lander Imaging System, ROLIS, trace the lander’s descent to the first landing site, Agilkia, on Comet 67P/Churyumov–Gerasimenko on 12 November 2014.
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.
A timeline of the science operations that Rosetta’s lander Philae performed between 12 and 15 November 2015, following touchdown on the surface of Comet 67P/Churyumov–Gerasimenko. Following Philae’s unexpected flight across the surface of the comet, the planned first science sequence had to be adapted according to the new situation. The graphic shows the approximate times (to the nearest 15 minutes) that each of Philae’s 10 instruments was activated; however, it does not indicate the success of data acquired.
A timeline of the science operations that Rosetta’s lander Philae performed between 12 and 15 November 2014, following touchdown on the surface of Comet 67P/Churyumov–Gerasimenko. Following Philae’s unexpected flight across the surface of the comet, the planned first science sequence had to be adapted according to the new situation. The graphic shows the approximate times (to the nearest 15 minutes) that each of Philae’s 10 instruments was activated; however, it does not indicate the success of data acquired.
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.
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 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.
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. ...
The MUPUS thermal sensor, on Philae’s balcony, revealed a variation in the local temperature between about –180ºC and –145ºC 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 x 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 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.”
“Energetic signature from within comet”: