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Night Sky

January 2011 Night Sky

—Charlie Christmann

The Zoo of Worlds

Since humans first recognized that stars were more than mere points of light in the sky and were actually “suns” like our own, they have wondered if they, too, had planets and life. As of 1992, we no longer had to wonder—the first extrasolar planet, or exoplanet, was found orbiting a pulsar 980 light-years from Earth in Virgo. Astronomers were amazed to find a planet there; pulsars are the deadly, highly radioactive remains of an exploded star. No one thought a planet could survive a supernova, but this planet and another sibling managed to beat the odds.

Since that time, the floodgates of discovery were opened. As of December 20th, 2010, 515 exoplanets have been cataloged. Hundreds more are suspected. Of these, many are giant gas balls orbiting close to their parent star. These are the easiest, and quickest, to find using the “wobble” method. This technique looks for the pull of the planet on the parent star causing it to move back and forth. Others are being found using a newer transit method. This method looks for the light from a star to be slightly dimmed as a planet passes between the star and Earth. When scientists say “slightly,” they are talking about a small fraction of a percent change in brightness.

The Kepler spacecraft, operating from an Earth-trailing orbit around the Sun, has located eight confirmed and more than 750 candidate planets using the transit technique. Kepler may have found many new and strange worlds, but those we already know to exist are very diverse.

The largest exoplanet in size found so far is TrES-4. This planet is about 1.7 times the size of Jupiter and belongs to a small group of puffy planets that have extremely low densities. The planet is so light, so large, and so close to its parent star that it theoretically should not exist. One year on TrES-4 is three-and-a-half Earth days.

The closest exoplanet to us is Epsilon Eridani b. It orbits an orange, Sun-like star 10.5 light-years away from Earth. It is so close telescopes might soon be able to take a photograph of it.

The triple-star system known as HD 188753, 150 light-years from Earth, is home to a hot gas giant planet that enjoys multiple sunsets.

Eight hundred and fifty light-years distant is WASP-12b, the hottest planet ever discovered. Orbiting its star at a distance of about 2 million miles every Earth day, its surface temperatures are estimated to be about 4,000 degrees Fahrenheit. While WASP-12b wins the hot category, SWEEPS-10 wins the speediest orbit title. This planet orbits its parent star from a distance of only 740,000 miles, so close that the planet starts a new year every 10 Earth hours.

The most distant exoplanet known is also the coldest. OGLE-2005-BLG-390L b is only five-and-a-half times larger than Earth and orbits a red dwarf star 28,000 light-years away. Its surface temperature is thought to be -364 degrees Fahrenheit.

Planet GJ 1214b is the only known super-Earth exoplanet with a confirmed atmosphere. It orbits a red dwarf star about 40 light-years away. The planet is about three times the size of Earth and about 6.5 times as massive. Researchers think it is likely a water world with a solid center.

Most planets orbit in a plane that corresponds to their parent star’s equator. But XO-3b orbits at an angle of 37 degrees from its star’s equator. The only other known example of such an oddly angled orbit is Pluto (at least until it was demoted from planet status). There is, however, a planet known to orbit backwards around its parent star.

HAT-P-1, a planet about half the mass of Jupiter, but about 1.76 times larger, gets the prize as the least dense. It would float in water, if there was a bathtub large enough to hold it. On the other end of the scale is COROT-exo-3b. It is about the size of Jupiter, but 20 times more massive, making it about twice as dense as lead.

The most promising worlds for life orbit Gliese 581. Of the five confirmed planets, the d and e planets are located inside the so called “Goldilocks Zone.” A possible sixth planet in the system, Gliese 581g, orbits between the d and e planets. One scientist has proclaimed the probability of life on Gliese 581g is almost a certainty.

With all of the planets already discovered, one must wonder: How long will it be before we find another Earth-sized planet in an Earth-like orbit around a Sun-like star? Then we can wonder if it is inhabited and if they, too, are wondering if they are alone in the universe.

The Planets and Moon

  • Mercury is for morning observers. The best chance to see Mercury will be on the 9th, one hour before sunrise in the east, as this planet reaches it greatest elongation (farthest from the Sun as seen from Earth) at 23 degrees west of the Sun. On the 2nd, look five degrees to the upper left of the Moon for Mercury. The bright star to the right is Antares.
  • Venus is also a morning “star.” It reaches its greatest elongation, 47 degrees west of the Sun, on the 8th. Look east three to four hours before sunrise this month. On the 30th, look for the Moon and Venus in the east an hour before sunrise.
  • Mars is a no show this month.
  • Jupiter is in the west south-west after sunset. On the 9th, look four hours after sunset to find the Moon eight degrees to the lower left of Jupiter.
  • Saturn is rising in the east around midnight. On the 25th, an hour before sunrise, Saturn will be 10 degrees to the upper right of the waning gibbous Moon.
  • Get out your binoculars and telescopes to find Uranus. On the 4th, Uranus is just above and to the right of Jupiter. For a simple way to locate Uranus, look on the 9th between the Moon and Jupiter; Uranus is an easy find.
  • The Moon is new at 2:03 a.m. MST on the 4th and will produce a partial solar eclipse for those lucky enough to live in western Europe. The new Moon occurs at 2:21 p.m. on the 19th. An hour before sunrise on the 29th, look south south-east. The Moon will be seven degrees to the lower right of Antares, with bright Venus to the left of the waxing crescent Moon.
  • Check out the Quadrantid meteor shower that peaks at 6 p.m. on the 3rd.
     

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