by Kim Malville
What’s in the sky this month?
May 5-7: In the early morning hours there is one of year’s best meteor showers for folks in the southern hemisphere, the Eta Aquariids. A few of these meteors may reach to northern skies as earthgrazers, skimming across the upper atmosphere, like skipping rocks in a pond. They will be coming out of the east-southeast, from the direction of Aquarius, the Water Jar and are debris from Halley’s Comet. There should be better meteors on May 24.
May 10: Bright, reddish Mars is just to the left of the moon.
May 10/11: Saturn is in opposition to the sun and closest to the earth for the year.
May 13-14: The full moon is close to Saturn
May 23/24: A new meteor shower may stun us. A small periodic comet, 209/LINEAR, will pass within 280,000 miles of the earth’s orbit, close enough to drop debris onto our orbit to produce a spectacular meteor shower. It may rival the Perseids of August. The predicted rates are 100 or more per hour in the morning hours of May 24. Or, there could be none! But, be there!
May 26-28: Best views of Venus this year. It will be just above the west-northwest horizon as the sky darkens.
The Earth has a distant cousin!
The Kepler Spacecraft has detected over 3000 planets. Only one so far is the right size and lies at the right distance from its star in the habitable zone (otherwise known as the Goldilocks zone, neither too hot nor too cold). That planet known as Kepler-186f, orbits a red dwarf star 500 light years from Earth in the constellation of Cygnus. Only 10% larger than Earth, it may have oceans and an atmosphere lit by auroras. There is no way to tell whether any life forms on this cousin of ours are looking toward us at this moment. Nor do we know what constellation of their skies we might lie in. They could have pointed radio transmitters in our direction 500 years ago, and said hello. But that message has not yet arrived. For us to send them a message and get a reply will require waiting 1000 years.
The designation “f” means that there are four other planets closer to its sun. The four companion planets, Kepler-186b, Kepler-186c, Kepler-186d, and Kepler-186e, whiz around their sun every 4, 7, 13, and 22 days, respectively. Too close to their sun, they would be too hot for life as we know it. They would shine in the skies of Kepler-186f around dawn or dusk, just as Venus and Mercury do on Earth.
Kepler-186f orbits its red dwarf star once every 130-days and receives one-third the energy from its star that Earth gets from the sun. On the surface of Kepler-186f, the brightness of its star at high noon is only as bright as our sun appears to us about an hour before sunset. Red dwarf stars are highly active, producing frequent flares and strong winds of charged particles. Kepler-186f is slightly larger than Earth, and, if it has a similar internal structure, it might produce a stronger magnetic field, depending on how fast it is rotating. In that magnetic field there could be local versions of Van Allen Belts which could create frequent auroras.
Being in the habitable zone does not mean this planet is habitable. The temperature on the planet is dependent on whether or not there is carbon dioxide in its atmosphere producing a benign greenhouse like the Earth’s. It’s another Goldilocks situation. Too little carbon dioxide would leave the planet too cold for life. Too much and the planet would become too hot for life (like our sister Venus). As more telescopes are pointed its way, we shall be learning more about this long lost cousin very soon.
Geysers, falling snow, & life on Enceladus
Enceladus is the sixth-largest moon of Saturn. It was discovered in 1789 by William Herschel, but little was known about Enceladus until the two Voyager spacecraft passed near it in the early 1980s. The Voyager showed that the diameter of Enceladus is only 310 miles, and that it is one of the most highly reflective objects in the solar system. Its high reflectivity is due to freshly fallen snow on its surface.
In 2005, the Cassini spacecraft started multiple close flybys of Enceladus, revealing its surface and environment in greater detail. In particular, Cassini discovered water-rich plumes venting from Enceladus’s south polar region. Long cracks in its ice crust near the south pole shoot geyser-like jets of water vapor, ice particles, and organic compounds into space, totaling approximately 440 lb. per second. That’s a lot: the equivalent of a 2000-ton iceberg each hour. Some of this material falls back as snow. Features on Enceladus are named after characters and places from Burton’s translation of The Book of One Thousand and One Nights. These particular cracks, each known as a sulcus, have been named after Cairo, Alexandria, Baghdad, and Damascus (see the figure).
On April 3 of this year planetary astronomers announced that Enceladus probably has a liquid water ocean beneath its frozen surface. Their results came from astonishingly careful measurements of tiny changes in the speed of Cassini as it passed through Enceladus’ gravitational field and detecting a slight change in speed due to a change in gravity. The most likely explanation is the presence of an ocean of water beneath a 20 mile thick ice crust. It’s a huge ocean, some 6 miles deep. It rivals our Mariana Trench which has a depth of 6.8 miles, where, it should be noted, there is evidence of flourishing microbial life. Cracks in the ice sheet above the ocean release the geysers, which in addition to ordinary water contain hydrocarbons such as methane, propane, acetylene and formaldehyde, enormously increasing the likelihood that some form of primitive life grows in its ocean.
What a bizarre conjunction of astronomy and war! The cracks of Baghdad and Damascus reveal possible life, while, at the same time, the guns of Baghdad and Damascus are destroying life.