Philae, a landing module weighing about 100 kg that is part of Rosetta (robotic space probe), will probably touch down Nov 11 on the surface of Comet Churyumov-Gerasimenko, which the unmanned spacecraft has been orbiting and observing from a distance of less than 100 km since Aug 6.
The ESA announced Aug 25 the five possible landing sites, photos of which scientists were examining in detail for three weeks to work out the operating and orbital strategies needed to get the probe to each one.
To do that, Rosetta approached to about 50 km from the comet, which allowed scientists to "gather more detailed information about each site", in particular high-definition photos of the comet's rocky, dusty and uneven surface, temperature readings and pressure measurements of the density of the gas surrounding the nucleus.
The ESA Monday will announce the prime landing site and a backup site, and discuss what the specific challenges are with each one, and also other scientific results acquired so far.
Authorities have warned that the landing manoeuveur will be "complicated" and could last several hours because of the relatively small mass -- and corresponding very light gravity -- of the comet, which looks something like a potato the size of a mountain.
Once the probe has landed and attached itself to the surface, it is expected that Philae will be able to deliver valuable information to scientists for a period of about four months.
The orbiting module will continue observing the evolution of the comet's activity through the end of 2015.
Rosetta was launched in 2004, and, over the past 10 years, has traveled almost 6.4 billion km on its odyssey to try and obtain data relating to the solar system's origin.