Mystery of The Blast from the Past

BBC.co.uk; Oct. 30, 2000; Sci/Tech: "Mystery space blast 'solved'"

Fallen tries of Tunguska -- decades after the blast.

The space object was traveling at 11-km-per-second -- Earth escape velocity. It wasn't escaping Earth but stalking it. It bore down on our unsuspecting planet near the day-night terminator above the Northern hemisphere. Over land, and moving to the northwest, it exploded in the morning sky. The force of a large hydrogen bomb -- 10-15 megatons -- easily flattened everything below and ignited raging flash fires. A shock wave propagated through the Earth's atmosphere and circled the planet twice. So much dust was thrown into the atmosphere that it scattered the Sun's light into the night side of the planet to form a perpetual twilight.

No dinosaurs died, nor was this scenario taken from a Hollywood disaster film. But it did happen. The morning of June 30, 1908 is known worldwide for what transpired in the forested Siberian region known as Tunguska. The few human witnesses described the unbelievable blinding flash and explosion.  It would take the above-ground nuclear testing of the '50s and 60s for the rest of the world to grasp the destructiveness of the event. Survey expeditions in later decades would find thousands of square kilometers of burned and toppled trees. This is still true almost a hundred years later.

Luckily the object exploded in one of the remotest and unpopulated places on the Earth. If this had happened over a major city, the death tool would have been of nuclear war proportions. But the remoteness of the site, political climate in Russia, and the Second World War delayed serious study of just what happened for many decades to come. And serious study was needed, since no survey of the site has revealed an impact crater or yielded fragments of the space object.

Now, over nine decades later, a team of Italian researchers has pulled together enough clues to fill in the blanks of the Tunguska puzzle. Several Italian universities have made repeated trips to Tunguska in recent years. 60,000 fallen tries were surveyed to characterize the location of the blast wave, data from seismic stations was analyzed, eyewitness accounts were translated and all available scientific literature was evaluated.

The researchers gathered enough evidence to calculate possible orbits of the space object. The overwhelming majority of the orbits indicated that an asteroid was the object. But why did the object break-up completely without a crater or large fragments on the ground? The answer could not have been possible until recent developments in space exploration. Spaceprobe Near Shoemaker imaged asteroid Mathilde in 1997 and found it to be a low-density pile or rubble floating through space. The Tunguska asteroid had to be of this nature for it to completely fragment and allow only a gigantic shockwave to reach the ground.

Energy Hole?

Science@NASA; Oct. 23, 2001; Headline: "Energy from a Black Hole"

We all know you can't squeeze water from a stone nor energy from a black hole, or can we? A new insight into the energy dynamics of blacks holes has been made by the European Space Agency's X-ray Multi-Mirror Mission Newton (XMM-Newton) satellite. Scientists were able to observe the X-ray spectrum of iron gas as it circled a supermasive black hole at the heart of galaxy MCG-6-30-15. 100-million light years from Earth, the black hole is the size of our Solar System and 100-million times more massive then the Sun.

Observers studying the energy of the iron spectrum found it was too bright be solely powered by the gravitational interaction of iron gas with the black hole. They found that the additional energy in the spectrum could be explained by the Blandford-Znajek theory, proposed 25-years ago to explain particle jets in quasars. In the theory, as applied to MCG-6-30-15, the black hole must be spinning and dragging the fabric of space-time around it. Magnetic field lines around the black hole are also twisted and tend to slow the hole's spin, extracting rotational energy from it. This energy pours out of the hole's magnetic field in the form of "cable-like" field lines, that extend into the disk of matter falling around the hole. They add energy to the already hot disk and thus lead to the increased spectral luminosity observed by the XMM-Newton satellite.

Christopher Reynolds, a University of Maryland member of the international team says: "Never before have we seen energy extracted from a black hole. We always see energy going in, not out."

Dance of the Lights

NASA/Goddard; Oct. 25, 2001; Press Release: "Earth's Auroras Make Rare Joint Appearance in a Feature Film"

Dueling aurora -- NASA

The aurora borealis, a multicolored complex of shimmering lights in the sky, predominately visible in the Northern regions of our planet on special nights, has a counterpart in the aurora australis that circles the Southern pole of our world. Each aurora forms 4,000-km wide ovals over their respective poles.

The Aurora phenomenon is triggered when the Sun sends bursts of charged particles hurtling through space toward the Earth. These particles encounter and follow the magnetic field lines that emanate from the magnetic poles of our world. They slam into atoms of nitrogen and oxygen, from 60 to 1000-km above the Earth, and force them to emit photons -- the whole process is a lot like a neon light works.

It has longed been suspected that the aurora borealis and australis are mirror images of each other. The earliest reports of simultaneous sightings of northern and southern aurora dates to September 1770, when Captain Cook in the Pacific Ocean sighted the southern aurora and a Chinese scribe made note of the same phenomena in the northern sky that night. Aurora of both poles had been imaged by satellite and Space Shuttle, but not simultaneously.

Now, NASA's Polar spacecraft has imaged auroral storms that occurred simultaneously over both poles on October 22 of this year. The resulting movie reveals northern and southern auroras brightening and expanding in conjugate with each other. "For the first time, the northern and southern auroral ovals were observed simultaneously with enough resolution to confirm that the northern and southern aurora are mirror images of each other on a global scale," says University of Iowa physicist Dr. John Sigwarth.

While the gross aspects of the auroras mirror each other, it is expected that fine details will differ.