SKY REPORTER: Comet Bull’s-eye

Image taken by the Rosetta mission on August 19, 2014 from a distance of about 48 miles from comet 67P/Churyumov-Gerasimenko.
Credit: ESA/Rosetta/NAVCAM

If you enjoy classic tales of Robin Hood and William Tell hitting challenging targets, this month’s Rosetta landing on Comet 67P/Churyumov–Gerasimenko should evoke similar excitement. One day, this current encounter may itself become the stuff of legends. It promises to be a superb technical and scientific achievement that could help safeguard humanity’s future.

In 1980 Nobel Laureate Luis Alvaraz, his geologist son Walter, and their colleagues reported a possible extraterrestrial cause for the great Cretaceous-Paleogene dinosaur extinctions 65 million years ago. Subsequent investigations of the Chicxulub impact event at the northern edge of the Yucatan Peninsula, coupled with images of huge ragged blemishes on Jupiter after Comet Shoemaker-Levy 9 collided with that planet in July 1994, inspired renewed interest in the notion that spectacular apparitions of comets may not always be beautiful and benign occasions.

Wednesday, November 12, the European Space Agency’s Rosetta spacecraft is scheduled to release a lander named Philae to begin a seven hour descent to a level site on the larger of Comet 67P/Churyumov–Gerasimenko’s two main lobes. The landing site, originally known as site "J" has now been dubbed Agilkia, named after an island in the Nile from where the Temple of Isis was removed, then rebuilt on the island of Philae; preserving it from rising waters resulting from Aswan dam construction.

Rosetta was launched ten years ago aboard an Ariane 5 G+ rocket from Kourou in French Guiana on a mission to land upon, survey from orbit, and, via Philae, attach itself to and probe surface and substructure features of a frosty relic from the Solar System’s birth 4.5 billion years ago. The mission will ride with the comet in its orbit around the Sun. One goal of the mission is to glean information useful if the time ever comes when a comet must some way be dealt with before it whacks Earth. As Neil deGrasse Tyson famously noted, “Dinosaurs didn’t have a space program.” For that they paid a terrible price.

Reaching its destination in early August, the mission did a month long topographical survey to identify a landing site on the roughly 2 by 3 mile wide “dirty glacier”. While the Rosetta mother ship orbits the comet and begins its examination of the comet’s global environment, the Philae lander will gently set down on the fast rotating irregular surface and drive barbed arrows into the ice for firm anchorage. A drill and nine instruments aboard Philae will then begin studies of the comet’s surface and sub-surface during variations in comet activity, such as tail development, as it orbits the Sun.

In mid-November the Rosetta mission and its comet are about 320 million miles from Earth amid the main asteroid belt between the orbits of Mars and Jupiter. In the background extends a star strewn region of the Milky Way east of Sagittarius’ Teapot asterism and several degrees of arc from the current direction of Mars. This month that area is low in the southwestern sky for a few hours after sunset. Although we may watch Mars while also contemplating the Rosetta mission, Comet 67P/Churyumov–Gerasimenko is invisible without a substantial telescope; from Earth the comet is about 10 million times fainter than the Red Planet.

Leonid Meteor Shower

The night of Monday into Tuesday November 17-18th is the peak of the Leonid meteor shower. However, only a dozen or so meteors per hour are expected, as remnants from comet 55P/Tempel-Tuttle enter Earth’s atmosphere from the direction of the constellation Leo.

The Moon

Planets

Mercury is now in the predawn sky and, as usual, its quite close to the horizon during twilight. This month Venus is very low in the western sky for a short time during evening twilight and is quite difficult to see. Mars remains a feature of the evening sky, low in the southwest for several hours after sunset. The waxing crescent Moon passes the Red Planet’s direction on the 25th and 26th. Jupiter rises just before midnight at the start of November and its vivid presence arrives in our eastern sky a half hour earlier each week. During the night of Friday the 14th this largest solar system planet may be seen six degrees of arc to the upper left of the last quarter Moon. Saturn is too near the Sun’s direction to be currently seen, as the great ringed planet transitions from evening to early morning sky after its conjunction with the Sun on the 18th.