Gravimetry, performed by the Rosetta orbital station, showed that the body of comet 67 R / Churyumov-Gerasimenko consists of 75 percent dust and 25 percent ice, as a study published on Wednesday shows.
The European spacecraft went into orbit around comet 67P August 6, 2014, and three months later sent Phil descent to the surface of the comet. After being fixed to the comet, Phil completed 80 percent of the programmed three-day series of scientific experiments and sent the results back to Earth on the radio before his batteries ran out. Attempts to return the device to a working condition were unsuccessful.
Meanwhile, Rosette’s mother apparatus accompanied the comet during its closest approach to the Sun, about halfway between the orbits of Earth and Mars, in August 2015. Rosetta remains in orbit around 67P, which is currently outside Mars.
By measuring small shifts in the wavelengths transmitted by the Rosette, scientists were able to determine how the comet's gravity affected the spacecraft. They found that 67P is a very porous body, in which there is about four times more dust than ice by weight and two times more dust than ice by volume. The density is constant throughout the core, indicating the absence of large voids. The discovery is consistent with previous findings from two other Rosette research teams.
"High porosity seems to be an inherent property of the core material," concludes a team of German, American and French scientists in a study published in the journal Nature this week.
Comets are believed to be among the oldest and most primitive bodies in the solar system, containing materials preserved from the original cloud of gas and dust, from which the Sun and the planets formed about 4, 5 billion years ago.
Rosetta is expected to remain in working condition until September 2016, when she joins Phil, dropping to 67P.