Published: December 11, 2008 10:55 pm      

Solar system grows, now has 13 planets

New dwarf planets with Pacific names

The number of dwarf planets orbiting our sun recently increased from three to five. This gives us a total of 13 planets orbiting our sun (eight regular planets and five dwarf planets). Dwarf planets have other bodies with significant mass along their orbit, while regular planets have no significant bodies moving along their orbits.

The eight regular planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The Earth is the largest of the inner four planets (often called terrestrial planets), that are mostly rock and metal. The four giant planets consist mostly of light elements, have no solid surface (their atmospheres liquefy into deep oceans), have encircling rings and numerous moons.

The category of dwarf planets was created by the International Astronomers Union in August 2006. A few years earlier, a distant object named Eris had been discovered, and it had been found to be bigger than Pluto. So if Pluto was considered a planet, then Eris would have to be a planet as well. Astronomers realized that there are likely many more large objects beyond Pluto, so the number of planets would grow, perhaps to dozens in the next few decades.

So it was decided to specify criteria for an object to qualify as a full fledged planet. First, a planet must have its own orbit around the sun. (Moons go around planets so they fail this first requirement.) Second, a planet must have a rounded appearance due to the force of gravity that will compact the planet into a round shape. (So no cubical or pyramid shaped planets are possible.) Third, a planet must have an orbit that is free of significant debris or other bodies with significant mass.

There are hundreds of Plutinos, hefty bodies in orbit about the sun that are close to or cross Pluto’s orbit. So Pluto was demoted to a dwarf planet, satisfying the first and second condition but not the third. Eris was also classified as a dwarf planet, being considerably farther from sun than Pluto. Ceres, the biggest asteroid is nearly spherical but lies in the asteroid belt with many nearby asteroids in its vicinity and along its orbit. So the initial list of dwarf planets in order from the sun included Ceres, Pluto and Eris.

Just after Easter 2005, another large object was discovered beyond the orbit of Neptune. Its provisional name was 2005 FY9. This object has an orbit that takes it close to Neptune’s orbit when closest to sun and about 70 percent farther when at its greatest solar distance. The discoverers choose to name this dwarf planet after the god Make-Make, from Easter Island. (Easter Island was first visited by the Dutch on Easter Sunday in 1722.)

Make-Make was the creator of humanity, also the god of fertility and its image often carved on Easter Island’s great stones. The International Astronomical Union (IAU) declared Make-Make to be a dwarf planet in July 14, 2008.

In mid-September 2008, the IAU announced that the object 2003 E61 was also a dwarf planet; the name Haumea (the goddess of childbirth and fertility in Hawaiian mythology) was given. This object was discovered about Christmas in 2003 and had been known unofficially as “Santa.”

About two months ago, the discoverers of Haumea found two moons. The larger moon is Hi’iaka (the matron goddess of the island of Hawaii); the smaller moon is Namaka, a water spirit who was born from Haumea’s body. Further observations have revealed that Haumea has a shape of a fat cigar. Hamuea’s longest dimension is about a thousand miles. Haumea has a very rapid rotation period of 3.9 Earth hours, making it the fastest spinning of the dwarf planets and significant asteroids.

There are a number of small icy bodies near Haumea, which likely resulted from two planets colliding and tossing their icy mantles into space, forming the smaller bodies.

Bright planets and meeting

The evening moon was full last Friday evening and is now waning (shrinking in lighted width), rising later each night. So the brilliant planets Venus (higher, on left) and Jupiter (lower, to right) dominate the early evening western dusk. Later in the evening, the star group Orion is prominent in the southeast with his belt of three stars in a row.

To the left of the belt is the pinkish star Betelgeuse (Orion’s second brightest star); to the right of the belt is white-blue Rigel, Orion’s brightest star.

The Cumberland Astronomy Club will meet this Friday at 7:30 p.m. at the LaVale Public Library, just off U.S. Route 40. All interested sky gazers are welcome.

Continuing at the Frostburg State Planetarium is “Ancient Skies of the Holy Lands” with free public programs on today and next Sunday at 4 p.m. and 7 p.m. that last about an hour.

The Planetarium is just off the front lobby of Tawes Hall, across the street from the large Compton Science Center. Please come a few minutes early as late comers can’t be admitted once the program starts. Call (301) 687-4270 for road directions or visit the FSU website ( http://www.frostburg.edu ) to see a campus map.

Readers are invited to contact Bob Doyle with any comments or questions; his voice mail is (301) 687-7799 and his email is rdoyle@frostburg.edu .