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  Night Sky

Enjoy the starry night skies
Be a considerate neighbor. Reduce nighttime glare.
Shield your outside lights downward.
Let the stars light up the night.

May 2016 night sky

—Charlie Christmann


Since January 22, 1992, when the first exoplanet was discovered, astronomers have been looking for another Earth. Have they finally found it? Recent reports think so, and it is only twenty light-years away. But first, let me digress.

From the first realization in 1609 by Galileo Galilei that Mercury, Venus, Mars, Saturn, and Jupiter were actually planets orbiting the sun, that Earth was just another planet, and Jupiter had its own moons, to the recognition in 1923 that large groups of stars, known as Nebulae, were actually distant individual galaxies, man has wondered if there was another place like our own world. There was wide belief in the plurality of worlds from the 1600s to the 1800s where distant planets likely held intelligent lifeforms.

Radio astronomers have been looking for alien signals for many decades. A big surprise came on August 15, 1977 when the now-defunct Big Ear radio telescope at Ohio Wesleyan University received an unexpectedly strong radio signal from the eastern portion of the Sagittarius constellation. They dubbed it “the Wow Signal.” It has never repeated. Some astronomers recently found two new comets, and think the Wow Signal originated from those comets. Projections show them to be in the right place in 1977. Comet tails interacting with the solar magnetic field are known to emit radio waves at the right frequencies.

Nobody had actually found a planet orbiting a distant star; not until Aleksander Wolszczan was looking at minute variations in the timing of a pulsar named SR B1257+12P in the constellation Virgo.

No one fathomed the idea that a planet could survive the cataclysmic creation of a pulsar. When a medium-weight star explodes in a super nova to make a fast spinning neutron star, called a pulsar for its very regular emission of radio waves, it should destroy or expel any planets it had. Yet here is a planet four-and-a-half times the mass of Earth, bathed in all kinds of nasty radiation from the pulsar. Nothing we know could possibly live on this planet, now officially named Poltergeist, in a close 66.5 day orbit. It was later discovered that Poltergeist had two siblings named Draugr, orbiting even closer to the pulsar, and Phobetor, orbiting a bit farther away from the pulsar.

Then, on October 6, 1995, Michel Mayor and Didier Queloz saw the star 51 Pegasi slightly wobble back and forth. A planet was gently pulling on the star as it orbited. That planet, now named Dimidium, orbits its star at a close seven million miles. This was the first exoplanet discovered around a sun-like star. Yet, with a tight orbit, taking just over four days to complete, it would cook anything on its surface.

Since that time, more and more exoplanets have been found. Between the Kepler spacecraft and earth-bound telescopes, 1,963 planets are known, and another 3,699 are suspected. Those planets are spread among 1,228 solar systems and include 93 terrestrial planets. Terrestrial planets have rocky surfaces.

Among Kepler’s discoveries is planet Kepler-452b. It is only one-and-a-half times larger than Earth, and orbits its star in a pleasing 385-day orbit around its sun-like star. That places the planet in the middle of the “Goldilocks zone” where liquid water could exist. Too bad, at 1,400 light-years away, with today’s fastest rockets, it would take us 28 million years to get there.

But do not despair wondering if Kepler-452b holds life, a new Earth 2.0 candidate was found closer to home. Gliese 832, only 16 light-years away, is known to host two planets (Gliese 832B and Gliese 832C) in its solar system. We could get there in a mere 320,000 years.

Circling a Red dwarf type star, Gliese 832B is about half the size of Jupiter orbiting 348 million miles from its star, comparable to Jupiter’s orbit. Gliese 832C is a Super-Earth about five times as massive as Earth. Its orbit is closer to its star than Mercury is to the sun, but in the liquid water zone. Though much cooler than our sun, red dwarfs are very active, spewing out large solar flares that would likely fry the surface of Gliese 832C with deadly radiation.

With the discovery of planets around Gliese 581, hope for an Earth-like planet has been renewed. At a distance of twenty light-years, it has three known planets and two additional suspected planets. Gliese 581 is also an active red dwarf star. Planet Gliese 581 e, 1.7 times more massive than Earth, is closest to the star blisters in the heat and radiation. Gliese 581 b is 15 times heavier than Earth, similar to Neptune, but also inhospitable due to flares. Gliese 581 c, over five times more massive than Earth, is a candidate for life. It potentially has regions with just the right temperature, and may be far enough from the red dwarf to avoid the solar flare bath. Being tidally locked, with one face always pointing toward the star, life’s best chance would be in the perpetual twilight zone between the sunlit front side and the always dark back side.

Newly suspected planet Gliese 581 g is in the middle of the habitable zone. With an orbit of 32 days around its parent star, it is believed to 1.3 times the radius of Earth with a rocky surface. It too is tidally locked to the star. Habitability would depend upon the temperature extremes between the light and dark sides, and any atmosphere’s ability to moderate the climate. If it has an Earth-like atmosphere, surface temperatures could range from a balmy ten degrees Fahrenheit to a cold -35 degrees. A thicker atmosphere would likely create a warmer planet.

Who knows—as we find more Earth-sized planets in habitable zones, and our telescopes get better at discovering their atmospheres and compositions, we may one day know for sure there is an Earth twin with living things.

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