Rosetta: selection of the landing site of Philae

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This Monday, Sept. 15, ESA has officially announced the selection of the site where Philae will land on Comet 67P / Churyumov-Gerasimenko. The chosen site is the “J” site which was screened on August 24 from a pool of five potential sites, as the probe was still 100 kilometers away from the comet. The “J” site offers a great scientific potential while ensuring the best conditions of landing for Philae and the ability to make the most of its energy resources.

Site “J” is located on the “head” of the comet, an irregularly shaped object measuring just over 4 km at its widest point. Site “J” was unanimously chosen as the main site. The backup site, “C”, is on the comet’s “body”.

Landing site of Philae © ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

The lander is expected to reach the comet’s surface on November 11 and will perform extensive measurements to characterize the nucleus in situ, a first of its kind.
Over the weekend, teams from CNES and DLR, its German counterpart, the team responsible for Rosetta at ESA, as well as French researchers particularly involved in a large number of the mission’s instruments1, met at CNES in Toulouse to study the available data and choose the main and back-up sites.
A number of critical points were analysed, including the need to find a safe trajectory for deploying Philae on the comet’s surface, in an area where the number of identified hazards was expected to be minimal. After landing, other factors had to be taken into account, such as the day/night balance and the frequency of communication links with the orbiter.
Since the descent to the comet is passive, the only predictable element is the landing point, which will be in an ellipse measuring a few hundred metres.

View of the 5 pre-selected sites on August 24th © ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

An area of one square kilometre was assessed for each pre-selected site. At site “J”, most of the slopes are less than 30° from the local vertical, which limits the risk of the lander tipping over when it hits the surface. The site is also not very rocky and receives enough light on a daily basis for Philae to recharge its batteries and continue its scientific mission at the surface after the initial phase of being powered by a battery.
A preliminary estimate of the trajectory to site “J” showed that Philae’s descent time would be about seven hours, a time that would not compromise the in situ observations by consuming too much battery power.
It is not possible to predict the activity of the comet between now and landing, or even on the day of landing. A sudden increase in activity could change Rosetta’s position in its orbit at the time of deployment and thus the exact location where Philae will land. In addition, site “J”, like other sites, is not smooth and flat, and in the Philae landing ellipse, there are steep slopes. The risks are therefore real, but the “J” site nevertheless brings together great operational and scientific advantages, in particular it should satisfy all of the mission’s scientific experiments and instruments.

All these elements combined give us an idea of the challenge that all the players in this formidable mission set themselves 20 years ago.

Note(s): 

  • Les expériences auxquelles les laboratoires du CNRS contribuent :
    • Orbiteur (9 instruments sur les 11) : ALICE, CONSERT, COSIMA, MIDAS, MIRO, OSIRIS, ROSINA, RPC, VIRTIS.
    • Atterrisseur (5 instruments sur les 10) : APXS, CIVA, CONSERT, COSAC et SESAME.
  • Les laboratoires CNRS impliqués dans Rosetta-Philae :
    • LESIA (Observatoire de Paris/CNRS/Université Paris Diderot/UPMC)
    • IPAG (CNRS/Université Joseph Fourier)
    • IAS (CNRS/Université Paris Sud)
    • LATMOS (CNRS/UPMC/UVSQ)
    • LPC2E (CNRS/Université d’Orléans)
    • IRAP (CNRS/Université Paul Sabatier – Toulouse III)
    • LPP (École Polytechnique/CNRS/Université Paris Sud/UPMC)
    • LAM (CNRS/Aix-Marseille Université)
    • LERMA (Observatoire de Paris/CNRS/ENS/Université Cergy Pontoise/UPMC)
    • LISA (CNRS/Université Paris Diderot/UPEC)

Further Resources :

IRAP Contact :

  • Christian Mazelle : christian.mazelle@irap.omp.eu

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