by Kim Malville
What’s in the sky this month?
The great mystery of December will be comet ISON. Is it alive or dead? The comet is just appearing as a faint object near Spica in the morning skies as I write this column in mid-November. It will pass through a baptism by fire in the sun’s corona on Nov 28, at which time its 3-mile-wide nucleus may evaporate due to the radiation of the sun or break apart by the sun’s gravity. What happens is anyone’s guess. It may appear as a bright object in the morning skies, in which case the finding chart will be useful.
This comet is a total stranger to us in the inner solar system. For the last four billion years it has been in the cloud of icy debris left over after our solar system was formed. A passing star may have nudged it out of its deep sleep, causing it to plunge downward toward the sun. Its ancient ices are sublimating heat of the sun, producing its beautiful filamentary tail, blown away from the sun by its radiation. Like Halley’s Comet, it appears to be largely covered by a coating of a tar-like substance. Gas escaping through holes in that coating producing multiple jets of gas, resulting in the filaments of the tail visible in the photographic negative in the figure.
December 1-17: Look for Comet Ison in the morning skies
December 13-14. The Geminid meteor shower will be best seen in the hour between moonset and the first light of dawn. The peak of the shower should be around 11pm MST on the thirteenth. These meteors are relatively slow and are often yellowish. They plunge deeper into the atmosphere than most meteors because they are chunks of rock instead the fluffy dust of most meteors coming from comets. The Orionids come from a small asteroid or the remains of a dead comet, which is gradually cracking as it heats and cools in its orbit around the sun. Every 1.4 years when it is closest to the sun its surface heats up to 1300°F.
December 17: Full moon
December 18: The almost-full moon comes close to Jupiter in the constellation of Gemini
December 21: Winter solstice occurs at 10:11 pm local time: the shortest day of the year.
MAVEN is on its way to Mars
There were celebrations in Boulder on the morning of November when the rocket carrying MAVEN blasted off flawlessly. Five hundred school kids crowded into the Glen Miller Ballroom of the University Memorial Center, joined in a boisterous count down, and then broke into earsplitting cheers. Astronomers at CU’s Laboratory for Atmospheric and Space Physics were elated, to put it mildly, that the space experiment into which they had devoted 10 years of planning made it off the ground. A maven is a trusted expert in a particular field, a knowledgeable enthusiast, who seeks to pass knowledge on to others. The word comes from the Hebrew and means one who understands, based on an accumulation of knowledge. The LASP astronomers had to work hard to create this acronym, but it works very nicely.
MAVEN will be studying the thin Martian atmosphere and, perhaps, will be watching in real-time as it gets peeled away, molecule by molecule, by the solar wind.
Upon arrival at Mars September 22, 2014, MAVEN will fire its braking rocket to put itself into a highly elliptical orbit around Mars, dipping as close as 65 miles from the ground to gather air samples and then retreat to its greatest distance of 3728 miles. The purpose is to determine how much of the atmosphere is being lost to space today and try extrapolating back to the time when Mars had a dense atmosphere.
In the 49 years since NASA’s Mariner 4 spacecraft flew by Mars we have learned that Mars was once much more like the earth, with braided river channels and the shores of ancient lakes inside impact craters. There are minerals on its surface that could have formed only in the presence of liquid water. Indeed, once it may have been similar to the Mars of Ray Bradbury’s Martian Chronicles. But that would have been long, long ago. There are two explanations for its loss of water and air: they disappeared either down into the ground or upward into interplanetary space. MAVEN is designed to explore the upward possibility. Escape of its atmosphere may have started about 4 billion years ago when the planet’s protective magnetic field turned off and ceased protecting the atmosphere from the solar wind.
MAVEN should reach Mars two days before India’s Mars Orbiter Mission, which was launched on November 5. India’s probe initially didn’t reach its target altitude and Indian scientists and engineers have been using a series of carefully designed rocket burns to raise it in its orbit around Earth. The space craft, named after the Hindu counterpart to the Roman god Mars, Mangal, should be in position on December 1 to begin its own journey to Mars.
Some have questioned the $72 million price tag for a country of 1.2 billion people still dealing with widespread hunger and poverty. But the government has defended the Mars mission by noting its importance in providing high-tech jobs for scientists and engineers. One of Mangalyaan’s experiment is to search for methane in Mars’ atmosphere, which could be the result of a primitive from of life currently living on the planet. One thing is certain: if methane is found, it will not be evidence of water buffalos or sacred cows on Mars.
Planets, planets everywhere
One out of every five sun-like stars in the Milky Way galaxy has a planet about the size of Earth that is properly located for liquid water to exist on its surface. The analysis, performed by Eric Petigura, a graduate student at the University of California, was based on three years of data collected by NASA’s Kepler space telescope. That adds up to 40 billion Earth-size potentially habitable planets. The closest habitable planet may be a mere 12 light years away. That distance is still an enormous distance away for an interstellar jaunt. Phone conversations would have a 24-year delay built into them. But such a planet could be easily studied by telescopes to learn if it has oceans of water and an atmosphere in which some creature could take breaths. We could even listen in on 12-year-old broadcasts. Once, we thought we might be alone in the universe. Now it seems livable planets, maybe even blue-green jewels like ours, may be the rule rather than the exception in our galaxy.