by Kim Malville
July 5: The earth reaches its greatest distance from the sun (aphelion). It’s a nice paradox. You’d thing the earth should be colder with sun farther away. However, because of the tilt of the earth’s northern axis toward the sun at June solstice, June is warmer in the northern hemisphere.
July 8: New Moon
July 15: Spica is close to the nearly first quarter moon. In certain parts of Central and South America the moon will cover Spica.
July 16: First quarter moon. The moon moves between Saturn and Spica.
July 22: Full moon.
July 29: Last quarter moon
On June 14 astronomers at NASA announced the Kepler space craft has produced evidence for 503 more exoplanets, bringing the total number of candidates for planets beyond the solar system to a whopping 3216. Kepler has operated since May 2009, lasting nearly two years longer longer than its planned one year life time and far exceeding original expectations for planet discoveries. It spots exoplanets by detecting tiny brightness dips caused when a planed passes in front of its star. The spacecraft accomplishes this precision work by locking onto some 150,000 target stars using three gyroscope-like wheels to stabilize the observatory with extraordinary accuracy. Kepler was launched with four functioning wheels—three for immediate use and one spare. But one wheel failed in July 2012, and a second failed last month, robbing the spacecraft of its precision pointing ability. If at least one of the failed wheels cannot be recovered, Kepler’s planet-hunting days are almost certainly over and a new mission will have to be drawn up for the spacecraft, requiring less precision. Engineers have identified a number of tests that could help determine the chances of bringing the balky wheels bask to life. They’re currently developing these commands on the Kepler test bed at Ball Aerospace in Boulder, Colo., where the spacecraft was built.
The Childhood of Mars: warm wet and rusty
Mars’ atmosphere could have been rich in oxygen four billion years ago, well before Earth’s air became oxidizing. A paper just published in the journal “Nature” suggests that the planet was once warm, wet and quite habitable. The much later rise of atmospheric oxygen on Earth 2.5 billion years ago was due to the appearance of carbon dioxide eating and oxygen expelling plants.
This surprising conclusion comes from a comparison of Martian meteorites found on Earth and data from Nasa’s Spirit rover, which examined surface rocks at Gusev Crater on Mars. Both meteorites and surface volcanic rocks originated in the deep interior of Mars, but the surface rocks come from a more oxygen-rich environment. This result is surprising because while the meteorites are geologically young, around 180 million to 1.4 billion years old, the Spirit rover was analyzing a very old part of Mars, more than 3.7 billion years old.
How did Mars get so much oxygen so early in its lifetime? Water vapor molecules can be split by sunlight into oxygen and hydrogen. Most of that hydrogen and oxygen would have recombined back to water. However, because of the weak gravity of Mars (about one-third that of Earth) a small fraction of the hydrogen would have escaped, leaving a small oxygen excess on Mars. A similar loss of hydrogen did not occur on Earth because of our stronger gravity. Thus, early Mars had more oxygen than early Earth. Oxidation is what gives Mars its distinctive color. It’s rust that has given Mars its identity as the god of war. So our neighbor was warm, wet and rusty billions of years before Earth’s atmosphere became oxygen-rich. Life more ancient than anything on Earth may have established a brief foothold on that planet.
Plate tectonics and life on other planets
Neither Mars nor Venus has plate tectonics or magnetic fields. Neither one has life. Can there be a connection? When new planets form their interiors contain radioactive elements such as uranium, thorium and potassium. The heat from the decay of these elements produces a molten core, which is a crucial element in this story. If the planet is rotating, the core will generate a magnetic field. The magnetic field shields the planet from the hot winds of charged particles coming from their sun, which can strip away a planet’s atmosphere. The magnetic field also shields life on the planet from lethal doses of these particles. In the case of the earth, flow of heat from the core results in large plates of rock which slide horizontally, jostle each other, and sink below one another. The collision of these plates creates mountain ranges such as the Himalayas, the volcanic rings of fire of the Pacific, and deep oceanic trenches.
At the boundaries of colliding plates one plate dives below another, and this process, subduction, depletes carbon dioxide in the atmosphere by carrying carbon dioxide bearing rocks deep underground where they are locked into the earth’s mantle. Without this moderating process, carbon dioxide would build up to produce a run-away greenhouse similar to that of Venus.
Water is the key that unlocks life upon a planet. Water converts the minerals into weaker compounds, turning basaltic rock into soft mushy stuff like talc, which enables the plates to slide smoothly. And of course, biological life as we know it cannot exist without water. As astronomers sift through the data on the 3000 or so exoplanets detected by Kepler, they are looking not only for planets in the so-called Goldilocks zone around their star (neither too hot nor too cold) but also for planets with oceans of water, magnetic fields, continents, and evidence of plate tectonics. Although it is necessary for life, water is not sufficient for the evolution of sentient life. Worlds covered with water cannot carry evolution very far. For one thing, they can be boring places, lacking the environmental changes that spur evolution. For another, without dry continents, evolving intelligences would not have fire. Without fire metals could not be worked to create electronics for computers, to build automobiles, or search for planets among the stars.