Journey to the center of Jupiter

The new research results now show a Jovian planetary core that is composed of extremely dense layers of metals and rocks surrounded by methane, ammonia and water ices. Above these outer core layers is an atmosphere of mostly hydrogen and helium. At the planet's very heart, a metallic ball of iron and nickel makes up the deep, inner core.

With last month's finding, it now looks like Jupiter's interior more closely resembles what recent data has revealed about the interiors of Neptune and Uranus; these smaller "gas giants" have rocky cores, too, surrounded by icy hydrogen and helium. However, Neptune and Uranus lack the ultra-dense and forbidding atmospheres of Jupiter and Saturn.

As Jupiter accreted from the solar nebula 4.5 billion years ago, its heavy rocky core captured-and held on to-hydrogen, helium, and other gases.

What's in the Sky: On Dec. 7, look for the Dog Star or Sirius (the name that inspired the popular satellite-radio company). This bright star, of special meaning to the ancient Egyptians, rises in the southeast during mid evening. Since Sirius is the brightest star in the night sky, it's very easy to locate. Sirius is close to our Sun-it's a mere 2.6 parsecs (8.6 light-years) away. The Little Dog Star or Procyon, is Sirius' nearest neighbor (to its left from Earth). The Little Dog Star is located 3.5 parsecs (11.41 light years) away. Why the term "dog star"? Perhaps the stars were observed during the dog days of summer? We really don't know. Both dog stars are visible until morning.

Lou Varricchio, M.Sc., is a former NASA senior science writer. He is involved with the NASA/JPL Solar System Ambassador program in Vermont and is a senior member of the U.S. Civil Air Patrol.

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