Image taken by Rosetta during Philae's landing on November 13, 2014 -


Before landing definitively on comet "Tchouri" six years ago, the robot Philae bounced twice on its ground, discovering a mixture of ice and dust "softer than a cappuccino foam", revealed a study Wednesday.

For its lead author, Laurence O'Rourke of the European Space Agency (ESA), the location of this event was the "last mystery to be solved" about Philae.

The robot was released by the Rosetta probe on comet Tchourioumov-Guérassimenko, or “Tchouri”, more than 500 million km from Earth, in November 2014. We knew that after a first contact with the small celestial body, a fault in the robot's ground spear system had sent him back, in a two-hour leap, to another site, before stopping definitively 30 meters later at a third place.

The latter was not identified precisely until almost two years later, when a camera fixed on Rosetta, still in orbit, spotted Philae, hidden in the shadow of a ridge.

A shadow which, by depriving him of the solar radiation essential for his activity, quickly led him into an eternal sleep.

"Extraordinarily soft"

Finding out the exact location of the second bounce was important, O'Rourke said in an ESA statement, because the Philae robot's sensors "indicated that it had penetrated the surface, thus likely exposing the hidden primitive ice. below it ”.

A treasure dating back to the formation of Tchouri, 4.5 billion years ago, according to the study published in the journal Nature.

It provides striking images, playing on the contrast, of dazzling white spots.

Scientists have established that Philae spent about two minutes there, in a series of four contacts that "plowed" the surface, one of which sank into the ground about 25cm.

The mixture on display was found to be "extraordinarily soft", according to O'Rourke, "softer than the foam of a cappuccino, a bubble bath or even the foam of the waves on a beach".

The study also confirmed the observations of previous work on the high porosity of the rock of the comet, which is of the order of 75%, the proportion of empty space between the grains of ice and dust that constitute it.

The importance of comets

These findings enrich the knowledge of the small celestial object, which is the age of our solar system.

Comets are of interest to scientists because it is assumed that, being rich in carbon, they could, by rushing into it, "seed" with complex organic molecules primitive environments like that of our Earth.

The data collected make it possible to "better understand the hardness of a comet for future missions involving a lander", according to a scientist from the Rosetta mission, Matt Taylor, quoted by ESA.

And prevent a successor of Philae from experiencing the same fate.

“The fact that the comet has such a soft interior is very important information both for the design of landing mechanisms and for the mechanical processes that may be needed to collect samples,” said Matt Taylor.


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