by Kim Malville
The month starts out with Mars low on the western horizon in the constellation of Capricorn. It moves eastward into Aquarius on January 8. Jupiter is in Leo, rising about 8pm. By the end of the month, Jupiter is easily visible in the early evening above the eastern mountains.
January 3/4: The Quandrantid meteors are often as spectacular as the famous showers of the Perseids in August and the Geminids in December. This year its meteors will be overwhelmed by the nearly full moon. The meteors are named after a defunct constellation, Quadrans Muralis, created by a French astronomer in 1795, that appears on a few star charts, but which never caught on. Located near the tip of the tail of the Great Bear, it was named after the quadrant, a mechanical device for measuring the altitude of stars.
January 4: Full Moon
January 21: Low on the western horizon soon after sunset look for Venus close to the two-day-old moon. Venus moves from Capricorn to Aquarius on January 25.
January 22: The moon has now moved close to Mars.
Landing on a comet is a difficult task
The past few months of the astronomy column in the Eagle have been filled with stories and pictures about the rendezvous of the Rosetta spacecraft with Comet 67P and the landing of Philae upon its surface. The editors of Science magazine just have identified the landing of Philae as the Scientific Breakthrough of 2014.
As you may remember Philae, equipped with harpoons, screws, and reverse thrusters that didn’t work, failed to gain purchase in the surprisingly hard crust of the comet, and bounced not once but twice, coming to rest on its side, far from its intended landing spot, in the shadows of a cliff.
Comets are lumps of dust, ice, and organic molecules and do not contain rocks. Nevertheless, Philae was caught between a hard place and something that looked very much like a rock. With too little sunlight to recharge its batteries, the lander had 57 hours to gather and transmit data before it expired. This wasn’t your grandmother’s space vehicle. Philae has its own Twitter account and sent out this final message: “I’m feeling a bit tired, did you get all my data? I might take a nap.”
As it plunges sunward, its subsurface ice has already started to sublimate, producing jets of gas and dust, which can be seen in the photograph. Peak activity should come in August 2015 when it is closest to the sun (perihelion), passing halfway between the orbits of Earth and Mars. Much of Rosetta’s scientific power comes from its ability to continue to orbit the comet at close range for months on end. Previous missions to comets were over in a few hours. The next very important flyby of an icy body—NASA’s New Horizons mission to Pluto—will whiz past the dwarf planet on 14 July 2015. At its closest, New Horizons will pass Pluto at a distance of 10,000 kilometers, close enough to make out features with a camera resolution of 12 kilometers per pixel). By contrast, Rosetta’s camera can resolve objects that are only centimeters across.
One of the important mission results so far, published online on 10 December in Science, reported a high ratio of heavy hydrogen (deuterium, D) to regular hydrogen. Because this D-to-H ratio is so much higher than that found in Earth water, it suggests that comets like 67P coming from the Kuiper belt, a region beyond Neptune, could not have played a major role in delivering water to Earth. Other comets, with lower D-to-H ratios, similar to that of the Earth’s oceans, formed closer to the sun, and these are the ones that may have produced our oceans and those of Venus, which have evaporated. Those comets were jostled about furiously in the young solar system and were pushed far out into the giant swarm of comets known as the Oort cloud. The Oort cloud contains trillions of comets extending to nearly two light years away from the sun.
Rosetta orbiter is not only seeing interesting things; it also sniffs. The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) has been aiming its spectrometers at the gas molecules in 67P’s thin halo of an atmosphere, called the coma. In addition to detecting water, methane, and hydrogen, it has started to find more complex molecules such as formaldehyde and hydrogen cyanide.
Methane and life on Mars
The Rover on Mars known as Curiosity is also sniffing methane, but in the case of Mars, methane may be a hint of life on the Red Planet. Within Gale Crater, where Curiosity is slowly climbing the hill of sedimentary rock called Mount Sharp, methane exists at a background concentration of slightly less than one part per billion by volume in the atmosphere (ppb). However four times during the past two months the rover measured bursts of much higher methane abundances, at about ten times the background level. Most of the methane on Earth is produced by biology, and the current excitement among planetary astronomers is that methane on Mars could mean some form of primitive life on Mars.
The one-part-per-billion methane that is present permanently in its atmosphere amounts to about 200 metric tons of the gas flowing through the Martian atmosphere. By comparison the earth’s atmosphere contains about half a billion metric tons of methane. Most of our methane comes from anaerobic bacteria living in low-oxygen environments, such as stagnant water and the flatulence of cows and other animals. Methane also leaks out in the process of drilling for natural gas and in combustion of coal, although drilling leaks are much small sources than coal. On Earth, the presence of methane is a significant element in climate change, because methane is a more powerful greenhouse gas than carbon dioxide. Mars’s minuscule methane background is probably produced by ultraviolet light striking the carbon-rich debris of meteorites, comets, and interplanetary dust that fall on to its surface. But, this process cannot explain the methane spikes that Curiosity observed, because there have been no recent meteoritic impacts or airbursts in the vicinity of Gale Crater. So the exciting possibility remains that Martian microbes may now be belching methane from subsurface refuges, protected from lethal solar ultraviolet light by thin layers of soil and ice. What a fun challenge for future human explorers on Mars, not so different from the adventures faced by early explorers in the Antarctic, though enormously more expensive.