Bakersfield Night Sky – January 17, 2015
By Nick Strobel
Earlier this month the Kepler team announced the 1000th verified exoplanet found using NASA's planet-hunting space telescope called Kepler. That milestone was reached in the release of eight more verified exoplanets and 554 more candidates. Kepler finds planets by looking for the telltale periodic dimming of a star as a planet passes in front of the star. Because it is possible that a periodic dimming of a distant star could be caused by something else besides an exoplanet, each candidate exoplanet system has to be investigated by a ground-based telescope to see if the candidate exoplanet makes the star wobble due to the exoplanet's gravity tugging on the star as it orbits the star or rule out other possibilities such as eclipsing binary stars. The process of analyzing the periodic dimming of the stars that leads to putting an object in the "exoplanet candidate" category is quite sophisticated and accurate with about 90% of the candidates being verified as real bonafide exoplanets.
Three of the verified exoplanets are in their stars' habitable zone, so the temperatures on the planet surfaces could be nice enough for liquid water to exist. Two of these, Kepler-438b and Kepler-442b, are less than 1.5 times the diameter of the Earth. The closest one, Kepler-438b, is 475 light years away, so no plans to visit it any time soon. Both exoplanets orbit stars smaller and cooler than our star, the Sun. Here's what struck me about this news story. These worlds could be even more habitable than the Earth!
How can a planet be "more habitable" than the Earth where everywhere you look you find some form of life, from over a mile below the surface in rock to thousands of feet above the surface? Well, it turns out that the Earth is past its prime in the big picture view of geologic timescales. In their followup to their best-selling book "Rare Earth", authors Peter Ward and Don Brownlee detail in their 2002 book, "The Life and Death of Planet Earth", the life cycle of our home planet. Thirteen years later, Rene Heller in an article about "superhabitable worlds" in the January 2015 issue of Scientific American discusses many of the same things but now with the sure knowledge of hundreds of exoplanets slightly larger than the Earth orbiting stars smaller and cooler than the Sun and the possibility of billions more in our galaxy.
Over hundreds of millions of years, the Sun has slowly brightened and it will continue doing so into the future. Humans still have plenty of time. We are talking about geologic timescales here. About 500 million to 700 million years from now, Earth will become too warm for complex, multi-cellular life to exist. Microbes existed on the Earth for about 3 billion years before complex life arose and will still be able exist for about that long after complex life disappears from the Earth in the future. About 350 million to 300 million years ago during what geologists call the "Carboniferous period", the Earth was warmer and wetter and the atmosphere was more oxygen-rich than it is today. The biosphere was more productive than today. This time period was lavishly illustrated in the tenth Cosmos episode broadcast last spring called "The Lost Worlds of Planet Earth" with host Neil deGrasse Tyson dodging centipedes and scorpions the size of large dogs and ducking as eagle-sized dragonflies swooped overhead.
Although the far future promises to be warmer, it won't be as biologically productive as today. Earth is near the inner edge of the Sun's habitable zone. As the Sun brightens over the next few billion years, the habitable zone will move outward, leaving the Earth scorched. Smaller and cooler stars brighten as well over their lifetimes but at a much slower rate. That could give complex life arising on habitable exoplanets many hundreds of millions to billions of years more to live and develop advanced, intelligent civilizations, hopefully with enough sense to learn from their mistakes and take care of their environments. Exoplanets slightly larger than the Earth would also be able to sustain volcanism and plate tectonics for longer than what the Earth will be able to do. Volcanism and plate tectonics are what is responsible for cycling carbon, particularly carbon dioxide, into and out of the atmosphere, regulating the climate over geologic timescales.
The Kepler team continues to look for Earth's twin: an Earth-sized planet taking one year to orbit a star just like our Sun. In the recent slate of 554 candidates, one with a catalog name of 5737.01 is the most similar so far, a planet just 30% larger in diameter than the Earth and taking 376 days to orbit a star that is 98% the mass of the Sun and just 140 deg C hotter than the Sun. This desire to find a twin of the Earth-Sun system very much reflects our Earth bias. My guess is that our gut instinct won't make us satisfied until we find that Earth twin even though our rational, scientific investigations show that finding superhabitable worlds is probably a better goal. The Kepler team has amassed enough statistics for us to reasonably conclude that our galaxy has had an easier task of making superhabitable planets than planets identical to Earth. Granted, these superhabitable worlds are easier to find but it does make me even more confident to say that finding life existing beyond our solar system is a matter of "when" and not "if".
On a more philosophical note, the Kepler news story and the superhabitable worlds article also struck me as another example of the Copernican revolution that removed Homo Sapiens from the center of the universe, a revolution we are still trying to come to terms with at an emotional level. We are not at the center of the solar system, the Sun is. We are not at the center of the galaxy, we're in the suburbs of the Milky Way. The Milky Way is not the center of the universe, it is at one end of a small group of galaxies that itself is one small part of a galaxy supercluster made of many hundreds of galaxy clusters. In fact, no galaxy is at the center of the four-dimensional universe. (Perhaps, even the universe is part of a multiverse.) Now with the idea of superhabitable worlds, the Earth is not even the best place for life to exist. However, though the Earth might not be the best place for life to exist, it is still the only place we know that life does in fact exist. It is our home and that makes it a very special place.
In other space exploration news, the Soil Moisture Active Passive (SMAP) spacecraft will hopefully launch at the end of the month on a three-year mission to measure soil moisture and the freeze-thaw state of all regions of land on the globe.
Now for the night sky. Venus and Mercury are still both visible shortly after sunset tonight. Look low in the southwest to see them with Venus the brighter of the two. Mercury is now moving downward toward the Sun after its close conjunction with Venus last Saturday. By next weekend Mercury will be too close to the Sun to spot. Mercury will be between us and the Sun (inferior conjunction) on January 30th. Later this week on the 21st, see if you can spot a hair-thin Waxing Crescent Moon just to the right of Venus. You might have to use binoculars to spot it. The next evening on the 22nd, a slightly fatter crescent Moon will be to the right of orange-red Mars. The Moon will be at First Quarter on January 26nd. See the second star chart below for the view of the early evening sky. The Planetarium's website will also have the spring schedule of evening public shows, the first of which will be on February 19th.
Shortly after Venus sets, you'll be able to see the second-brightest planet, Jupiter, rising in the east. It is between the stars of Leo and Cancer. A Full Moon will pass below Jupiter on February 3rd. Those of you under dark skies might be able to spot Comet Lovejoy, C/2014 Q2, without any optical help passing almost a fist width at arm's length to the upper-right (west-southwest) of the Pleiades for the next several days. The rest of us will need to use binoculars.The comet was closest to the Earth on January 7th at 44 million miles. It will reach perihelion (closest point to the Sun) on January 30th. As it nears the Sun, its intrinsic brightness will increase but it will be getting farther from us, so its apparent brightness in our sky will be about the same for the next week or so. The first star chart below shows its position for the next few days. It will move higher in the sky past Aries and by month's end it will be between Triangulum and Andromeda but it will probably have faded beyond easy viewing by then.
Want to see more of the stars at night and save energy? Shield your lights so that the light only goes down toward the ground. See www.darksky.org for how.
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com