Halema'uma'u crater on the Big Island continues to erupt, sending lava 50 feet into the air. Hawaii and the Pacific Plate are sliding atop a volcanic plume that has remained hundreds of millions of years. The long life of this hot spot suggests that it comes from deep within Earth. Our Hawaiian soil is red from high iron content. Since Earth's crust and mantle are relativiely low in iron, the plume probably originates near the core-mantle boundary, thousands of miles down.
The MESSENGER probe flew by Mercury January 14, and will make another pass October 6. In the July 4 issue of SCIENCE, mission scientists present some preliminary results. The prediction of vulcanism on Mercury is confirmed, the planet has shield volcanoes, just like Hawaii! One volcano is 95 kilometres in diameter, nearly large as the Big Island. Mercury therefore has an internal heat source. MESSENGER also found that the magnetic field is dipolar, like that of Earth.
Puzzling to the scientists, MESSENGER found no evidence of iron. Though the planet's volcanic surface is full of materiel erupted from within, none of the volcanic plains show traces of iron. Mariner 10 found that Mercury is dense with a strong magnetic field. This led scientists to infer an iron-rich core, like Earth. Iron in Mercury is solely an inferrence, with no direct evidence. A hot iron core could not account for the magnetic field, since iron loses its magnetism when heated.
Someday humans may figure out that planets like Mercury and Earth formed around tiny Black Holes left over from the Big Bang. In the case of Mercury, the Black Hole would account for both internal heat and magnetic field. No iron would be necessary in this scenario: Radiation from the singularity would turn Mercury's centre into a whirlpool of charged particles. These ions would spin around the singularity, generating a dipolar magnetic field as on Earth.
In April 2011 MESSENGER will settle into orbit around Mercury. This is the first mission to the planet since Mariner 10 in the 1970's. The closest planet to the Sun could yield many surprises, even a tiny Black Hole. Since we can't reach the centres of planets, the Hole in the Earth may take a long time to get noticed.