NASA’s Rosetta mission began with what some would call a streak of bad luck.
After the successful separation procedure, Philae’s anchoring harpoons failed to fire and the 220-lb. (100 kilograms) lander bounced off 67P’s surface, clipped a crater rim and then bounced a second time before finally coming to rest nearly two hours after first making contact with the comet’s surface.
The plan was for it to recharge its power supply using photo-voltaic panels, but the place it eventually landed on was quite shady. The stranded probe transmited preliminary data until its primary battery was depleted (about 60 hours), and then went into hibernation.
The initial observations, published on July 30 in the journal Science, show that the comet is a porous body with a fairly homogeneous interior. It also has a diverse surface that harbors many different carbon-containing organic molecules, the scientists said.
“What really blows my mind is to have this combination of complementary results, allowing us at the same time to ‘feel’ the surface of the comet, very locally, as if we were there, while also getting the bigger picture through the sounding of the cometary interior structure,” Nicolas Altobelli, acting Rosetta project scientist, told Space.com via email.
“The implications of these measurements, and in particular the fairly homogeneous, very porous structure of the interior, will help constrain the formation models of planetesimals in the solar nebula, by a better understanding of the accretion processes,” Altobelli added, referring to the process by which planetary bodies, stars, comets and so on are formed from spacedust.
Not elegant but effective
While the landing definitely had scientists on the edge, in the end it seems to have been a boon in disguise, as it allowed observations of different locations on 67P’s body, in its initial and final landing spots (which have been dubbed Agilkia and Abydos, respectively).
And those two sites are quite different, it turns out. Agilkia’s surface is relatively soft, covered with a layer of granular material about 0.82 feet (0.25 meters) deep, while Abydos is much harder.
“Before the landing of Philae, we believed cometary surfaces might be very soft (loose regolith under low gravity). Some colleagues even feared the lander may sink deeply into the surface at touchdown,” Philae project manager Stephan Ulamec, of the German Aerospace Center (DLR), told Space.com via email. “Although we were aware of our limited knowledge, the fact that some of the material is so hard, and that the surface is so heterogen[eous], was indeed a bit surprising.”
Images captured by Philae’s Comet Infrared and Visible Analyser camera, or CIVA, highlight the diversity and complexity of 67P’s surface, showing fractured, boulder-studded terrain with a variety of grain sizes and reflectivity.
The soft layer of “dirt” goes up to 6.5 feet (2 meters) deep in some places on the surface of the comet, and nonexistent in others, suggest images taken from the ROLIS (Rosetta Lander Imaging System) during the probe’s descent.
The images also show a boulder about 16.5 feet (5 m) wide, which is partly surrounded by a depression resembling a “wind tail,” an erosional feature also seen on our planet, and Mars. Another 17 such structures have since been identified by mission scientists, with lengths ranging from 16.5 feet to 100 feet (5 to 30 m). They are caused by particles abrading the surface of the comet during its travels, like an interstellar sandblasting.
Temperatures also vary on the surface from very uncomfortable to extremely uncomfortable, without the thermal balance offered by a thick atmosphere – daytime temperatures on the comet’s surface in November 2014 ranged from minus 226 degrees Fahrenheit to minus 298 degrees Fahrenheit (minus 143 to minus 183 degrees Celsius). However, as the comet is closer to the sun, those temperatures have probably risen by now but the difference between the dark and lighted side is presumed to be higher.
An organic cocktail
Two different Philae instruments, known as Ptolemy and COSAC (Cometary Sampling and Composition), hunted for organic compounds— the building blocks of life as we know it — on and around Comet 67P.
While the initial data burst received from the lander did hint at the existence of organics on its surface, the data was limited and its meaning not very clear.
The new data is much more interesting. Both instruments detected lots of molecules. COSAC, for example, found 16 different organics, including four (methyl isocyanate, acetone, propionaldehyde, and acetamide) that had never been spotted on or around a comet before.
“If such cometary material falls onto a planet in the right environment, emerging life could make use of it,” COSAC principal investigator Fred Goesmann, of the Max Planck Institute for Solar System Research in Germany, told Space.com via email.
Ptolemy’s observations also revealed a rich mix of organics, along with lots of water and carbon dioxide.
“I think an understanding of the organic compounds that are present in this particular comet will have tremendous ramifications for origin-of-life studies,” Ptolemy principal investigator Ian Wright, of the Open University in the United Kingdom, told Space.com.
The newly reported Ptolemy data were gathered during a calibration run, Wright said, adding that more results from the instrument will be published soon.
Internal structure also charted.
Using its CONSERT (Comet Nucleus Sounding Experiment by Radiowave Transmission) instrument, the Rosetta lander also studied the interior structure of the comet. This instrument picks up long-wavelength signals beamed through 67P by the orbiting Rosetta mothership.
Data suggest that the “head” of the comet is homogeneous -on the scale of a few tens of meters- and really porous, with open space making up 75 to 85 percent of its volume, researchers said.
Observations done with this instrument have also narrowed down the area where the lander might be found -we lost it a little– to a ribbon about 69 feet wide by 112 feet long (21 by 34 m).
“Philae provided us unique information on a comet’s surface properties (and interior) that could not be obtained from orbiter measurements alone,” Ulamec said. “We learned so much about comets that now future missions can be adapted in a much better way to this challenging environment.”
And Philae’s not out yet!
The newly released studies are not necessarily the last word from Philae, as the lander woke from hibernation in mid-June.
Communication between Philae and its handlers here on Earth remains extremely spotty — the last contact occurred on July 9 — but the mission team holds out hope that it can get the lander up and running again soon.
“We keep listening and sending commands to Philae, every time we have an opportunity for communication,” Altobelli said.