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A Comparison of the relative sizes of the Fomalhaut system and the solar system (image created by NASA and ESA)

Fomalhaut is a star with twice the mass of the sun located approximately 25 light-years from Earth in the constellation Piscis Austrinus.  It is a bright young star 100 to 300 million years old (out of a projected lifespan of 1 billion years). Coinicientally  the name Fomalhaut is Arabic and means “mouth of the Southern fish.”  Fomalhaut has at least one planet—Fomalhaut b, which is believed to be approximately the same size as Jupiter (but could be anywhere from the size of Neptune to 3 times as large as Jupiter).  Just as Saturn is surrounded by a ring of debris, the entire star system of Fomalhaut is surrounded by a giant toroidal circumstellar disk.   This torus is vastly greater in diameter than our entire solar system (including the Oort Belt) and is made up of somewhere between 260 billion and 83 trillion comets which are constantly colliding and annihilating each other!  The Herschel Space Observatory recently captured an infrared image of this immense comet storm.

An infrared image of the Fomalhaut system--and its huge cloud of disintegrating comets) captured by the Herschel Space Observatory (credit: ESA)

Artist's Interpretation of Sedna (Credit: Gemini artwork by Jon Lomberg)

After the discovery of Pluto in 1930, there was a long hiatus in discovering objects of comparable size. Then in 2003, a team of astronomers led by Mike Brown of Caltech discovered a distant icy sphere which was quickly heralded as “the tenth planet.”  Mike Brown announced the discovery on his website along with his team’s rationale for naming the object.  He wrote “Our newly discovered object is the coldest most distant place known in the Solar System, so we feel it is appropriate to name it in honor of Sedna, the Inuit goddess of the sea, who is thought to live at the bottom of the frigid Arctic Ocean.

It turns out that Sedna is only one of many similar snowball-like planetoids beyond Neptune.  In fact, Ferrebeekeeper has already described the dwarf planet Eris (named after the Greek goddess of Strife) which is the largest currently known Kuiper belt object.  Sedna was the first to be discovered since Pluto and it sparked a debate about such objects which ultimately resulted in Pluto’s downgrade to dwarf planet.  Sedna also has some unique features which make it remarkable in its own right.

The orbit of Sedna (red) set against the orbits of Jupiter (orange), Saturn (yellow), Uranus (green), Neptune (blue), and Pluto (purple)

Sedna takes 11,400 years to complete its orbit around the sun and its bizarre highly elliptical orbit has given rise to much conjecture among astronomers.  Although some astronomers believe it was scattered into a skewed orbit by the gravitational influence of Neptune, other astronomers believe it originated in the inner Oort cloud and was never close enough to Neptune to be affected by the giant’s gravity.  Some scientists speculate that its lengthy orbit may have been caused by a passing star (perhaps from the sun’s birth cluster).  A few theorists have gone one step further and conjectured that Sedna is from a different solar system and was captured by our Sun billions of years ago.  A final school contends that Sedna is evidence of an unknown giant planet somewhere in the depths of space (!).

A photo of Sedna taken from a powerful telescope on Earth

We don’t know much about Sedna except that is probably 1,200–1,600 km in diameter and that its surface is extremely red.  After Mars, Sedna is one of the reddest astronomical objects in our solar system.  This color comes from the profusion of tholins covering the methane and nitrogen ice of which the little world is formed.  Tholins are large, complex organic molecules created by the interaction of ultraviolet light on methane and other simple hydrocarbons.  It is believed that early Earth (prior to obtaining an oxidizing atmosphere) was rich in Tholins and they are one of the precursors to the rise of life.

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