A new study spearheadedby researchers from the Rheinische Institut für Umweltforschung an derUniversität zu Köln, Germany, has used data collected by ESA'sRosetta spacecraft to establish that the comet67P/Churyumov-Gerasimenko (67P) is devoid of any large interior caverns. Ithad previously been theorized that the relatively low mass of thecomet in regard to its volume may have resulted from cavernoushollows within the celestial wanderer.
Mankind has sent robotic pioneers to a grand total of eight comets since the adventof space exploration. Whilst these explorers have been successful in solving numerous mysteries regarding the nature of these celestial bodies, the riddle remains as to why comets possesssuch a low density.
The new study looked toshed light on the question, making use of Rosetta's Radio ScienceExperiment (RSI) to probe the interior of 67P for large hollows bymeasuring the gravitational effect exerted by the comet on the probe'sradio signal to Earth.
In order to accuratelymeasure the comet's effect on the signal, the Rosetta team had toremove any extra gravitational influences and the influences of other forces in oursolar system that could be distorting the signal. This involvedsubtracting the gravitational pull of our Sun andevery other celestial body in our solar system, and even the pressures exerted by solar radiation and theoutgassing emanating from 67P itself.
Thankfully, complicated processes such as this have become routine in space explorationmissions, and with some work, the scientists were able to subtractthe myriad of conflicting influences leaving only that of 67P.
Upon analysis of theradio signal, it was clear that 67P was devoid of any major caverns,which would have been evidenced by drops in acceleration of thesignal. It was however discovered that the comet boasts a massslightly below 10 billion tonnes, which, factoring in the lack oflarge caverns and an overall volume of roughly 18.7 km3 (4.5 cubic miles) places thedensity of the comet at 533 kg/m3.
With large hollowsruled out as a factor, it is now most likely that the low density ofthe comet is due to the properties of the dust particles thatcomprise the interior of the comet.
A previous study based on data collected byRosetta's COSIMA and GIADA instrument revealed that the particlesthat mix with ice to make up the interior of the comet are far fromcompact, instead taking on a "fluffy" aspect. This resultsin a high volume, low density porous interior.
Source: ESA