by Kim Malville
This month in the sky
December 5: Aldebaran will be very close to the almost full moon.
December 13/14: Geminid meteors best viewed just before midnight, before the last quarter moon rises.
December 21: Shortest day of the year: December solstice at 4:03pm. MST.
December 22: Look for a thin crescent moon just to the right of Venus low in the west-southwest just after sunset.
December 23: The moon will have moved well above Venus.
December 24: Ruddy Mars will be to the left of the moon.
The continuing saga of Rosetta & Philae
It had been a journey of 10 years and a 6 billion miles on a long curved and looped path through the solar system. Rosetta had increased it speed by four gravity assists, one around Mars and three around Earth. On the second loop around Earth it was initially misidentified by asteroid hunters as a dangerous object coming within 3500 miles of the earth. Once it reached its destination and started orbiting Comet 67P/Churyumov-Gerasimenko, its 12 instruments, including a spectrograph called ALICE built in Boulder, began making unprecedented measurements, which will continue for another 13 months. The final adventure of the spacecraft was planned to occur on November 14 when the lander Philae would drop on to the comet’s surface. Because jets of gas were beginning to develop on the comet, the drop was moved up to November 12. Although Rosetta was only 14 miles above the comet it took seven hours to drift to the surface. When Philae signaled it had arrived, the command center of the European Space Agency (ESA) exploded with exuberant cheers and hugs of scientists and engineers.
Then, Philae bounced. It was a long bounce, reaching one kilometer above the comet, which was dangerously high, considering the comet is only four kilometers long. The bounce lasted nearly two hours. And then, after second shorter bounce, Philae landed at the bottom of a cliff, partly in shadow. Actually, a problem of this sort had been feared. The day before landing, engineers discovered that reverse thrusters on top of the lander, designed to pin Philae to the surface after touchdown, were unlikely to work. Mission managers considered postponing the landing. But, the delay would solve nothing, and they went ahead. Further problems occurred at touchdown. Not only did the reverse thrusters not thrust, but also ice screws on the legs did not screw into the surface and two harpoons meant to fasten the probe to the ice failed to fire.
The height of the bounce was indeed a surprise. The comet’s black crust of dust and ice behaved more like a trampoline than expected. After the dust settled, scientists made the most of their new home and collected data from its instruments for 57 hours, before the lander’s batteries were exhausted.
The Rosetta orbiter will continue to orbit 67P as it moves closer to the sun and its subsurface ice outgases, driving jets of gas and dust. Even now, there are still plenty of data to be thankful for. Instruments on Philae were able to sniff the gases present near the surface. The sniff after the second bounce was unexpectedly rich, perhaps as a result of dust was stirred up by the landing and sucked into his machine. The sniff indicated the presence of carbon-containing pre-biotic molecules, about which we’ll learn more in the next few weeks. Although those incredible close-up pictures of its surface seem to reveal rocky cliffs, boulders, and landslides, the comet is mostly ice, dark (very dark, in fact, as dark as coal) sculptured, shattered ice, but still ice.
Now Philae is sleeping in blissful hibernation. We are hopeful that as the comet approaches the sun in the coming months, Philae’s solar panels will gradually recharge its batteries, and that it will awake from hibernation and reveal to us more about the presence of pre-biotic molecules on this strange dark object from outer space.
Volcanoes and life on Mars
If life on Earth has been built upon organic molecules from comet impacts billion of years ago, so too Mars may have been seeded by the ingredients of life. The rovers that have been crawling across the surface of Mars for a number of years have provided solid evidence that water once flowed freely across its currently frozen surface. Flowing water is still a puzzle on a planet that has been so cold for so long. When and how did ancient Mars ever get warm enough to host liquid water? Were those periods of a wet Mars long enough for simple organic molecules dropped by comets to reorganize themselves into primitive living beings?
New research suggests Martian volcanoes may have helped warm the planet for brief periods of time, for as much as few hundred years at a time, just long enough to allow water to exist in a liquid state and move downhill in flash floods. Unlike on Earth, where major volcanic activity has a cooling effect, an influx of volcanic gases allowed Mars’ atmosphere to better trap heat, not reflect it. Volcanic minerals like sulfur dioxide and sulfuric acid would have adhered to dust particles, increasing the absorption of solar radiation. About a third of the surface of Mars was resurfaced by lava flows. Such a huge amount of lava could have had a huge affect on the planet’s atmosphere.
Elsewhere in the solar system, on the frozen continent of Antarctica there are dry valleys, where the average yearly temperature is far below freezing. However, peak summer daytime temperatures can briefly exceed the melting point of water, forming transient streams. Endolithic photosynthetic bacteria have been found living in the Dry Valleys, sheltered from the dry air in the relatively moist interior of rocks. An endolith is a bacterium, fungus, lichen, algae or amoeba, that lives inside rock, coral, animal shells, or in the pores between mineral grains of a rock. These dry valleys are perhaps the closest of any terrestrial environment to the planet Mars. Endoliths survive by feeding on traces of iron, potassium, or sulfur, which they can access by excreting an acid to dissolve the minerals. But they do it very slowly. There are reports of endoliths in the ocean floor which have a generation time of 10,000 years. Most of their energy is spent repairing cell damage caused by cosmic rays and very little is left over for sex. Be grateful we live on Earth.