'J' marks the spot for historic comet landing

The European Space Agency on Monday unveiled the spot on a comet in deep space where it will attempt a high-stakes landing in November, a first for humankind.
The landing target is one of five that ESA shortlisted after its Rosetta spacecraft met up with Comet 67P/Churyumov-Gerasimenko in August, following a marathon chase across the cosmos.
Codenamed "J", the site offers the best chance for meeting scientific goals and for making a safe landing on an exceptionally difficult target, ESA said.
"The comet is a beautiful but dramatic world -- it is scientifically exciting, but its shape makes it operationally challenging," said Stephan Ulamec, in charge of the landing.
On November 11, Rosetta is scheduled to let down a robot lab called Philae to carry out experiments that scientists hope will shed light on these strange, icy bodies, which were born along with the Solar System.
Gently descending from a height of 10 kilometres (six miles), the 100-kilo (220-pound) lab will use harpoons to anchor itself and then drive screws into the surface for better grip.
Its experiments will include drilling up to 30 centimetres (18 inches) into the comet to extract pristine material for onboard chemical analysis.
Mission scientists had scrutinised five potential sites, named A, B, C, I and J, vetting each for the scientific return they offered, as well as landing risks and the amount of light available from the Sun for Philae's solar cells.
Comet "67P" comprises two lobes joined by a narrow neck, making it resemble a rubber duck -- though one that is pitch black, darker even than charcoal.
Three of the candidate sites were on the smaller lobe, or head of the "duck", and two on the larger lobe, or body. The oval-shaped landing site called "J" is roughly where the duck's forehead would be; a backup site, "C", is on the larger lobe.
Comets have in the past been considered iconic portents of good or evil.
Doomed to orbit the Sun, their outer layers are stripped by solar heat as they draw nearer, leaving a trail of dust and ice crystals that is reflected in sunlight and looks like a tail viewed from Earth.
Astrophysicists say they are balls of ancient ice and dust left from the building of the Solar System some 4.6 billion years ago.
This cosmic rubble is essentially a time capsule -- the oldest, least-touched material in our stellar neighbourhood  -- and understanding them may advance knowledge of how Earth came to bear life.
Water and molecules providing the building blocks for life came from comets that whacked into the fledgling planet at a time when the Solar System was a shooting gallery, according to one theory.
- No spud in space -
Jean-Pierre Bibring, lead Philae scientist, said mission managers were initially dismayed when the weird shape -- two blobs joined by a neck -- hoved into view as Rosetta raced towards the target in July.
Conceived two decades ago, the mission had broadly expected a rounded, "potato-shaped" object which would have made a landing far easier, Bibring said at a press conference.
"We were very scared at the beginning," Bibring said.
Weeks of further work showed "reachable areas" where a landing could be made amid a jagged topography of cliffs, slopes, boulders and indentations.
Confirmation of the November 11 landing date is expected on September 26. ESA said it would also stage a competition for naming the site.
Rosetta, now looping around the comet at an altitude of 30 km, is equipped with 11 cameras and sensors that have already provided astonishing material.
But some of the biggest discoveries could be made by the 10 instruments aboard Philae, experts hope.
The four-km comet is on a 6.5-year Sun orbit.
Rosetta caught up with it after a six-billion-km trek that required four flybys of Earth and Mars, using the planets' gravity as a slingshot to build up speed.
At their closest approach on August 13, 2015, the comet and Rosetta will be 185 million km from the Sun.
Source: AFP