by Kim Malville
What’s happening in the sky this month?
November 3: A partial solar eclipse will be visible from the eastern shores of the US, southern Europe, and most of Africa.
November 6: Look to the southwest for a slender crescent moon paired with Venus
November 17: Full moon
November 17/18: In the evening the full moon will be close to Aldebaran and the Pleiades.
Before dawn the Comet ISON may be visible to the unaided eye as it passes close to Spica in the eastern morning sky. The comet comes less than a solar diameter from the sun on November 28. On that day, the nucleus of the comet should be heated to 4900°F, hot enough to melt iron. The gravity of the sun will overpower the weak self-gravity of the nucleus, and the comet may be dismembered. We don’t know what the comet will be like when it returns to our skies in the first half of December. A break-up of the comet could be good news for us. The more gas and dust released by the nucleus means a better show for us on Earth next month.
A meteorite over Russia
Perhaps you remember the event. On Feb. 15, 2013, soon after sunrise, an asteroid streaked across the skies of the town of Chelyabinsk in the Urals of Russia, producing a brilliant flash that some described as bright as the sun. Incredibly, residents had to wait 2 minutes 23 seconds for the sound to arrive. Unfortunately those standing by windows were blasted by glass fragments as the town was shaken by a stupendous shock wave. The shock wave produced all of the destruction in the area, which included injuries to 1400 people and damage to 7200 buildings. One of the heroes is a fourth-grade teacher in Chelyabinsk, Yulia Karbysheva, who saved 44 children from the imploding window glass cuts. Most of those who were injured rushed to the windows to see what had happened, but Ms. Karbysheva thought it prudent to order her students to stay away from the windows and to hide under their desks. Ms. Karbysheva, who remained standing, was seriously lacerated when the air blast arrived and window glass severed a tendon in one of her arms. Not one of her students suffered a cut. The meteorite exploded at a height of some three miles and produced an explosion equal to 460 kilotons of TNT.
The object plunged into Lake Chebarkul, leaving a 6 meter-wide hole in the ice. Live TV footage shows a team of divers pull out the five-foot-long rock from the lake. Once ashore, the meteorite was placed on top of an industrial scale, which promptly broke at the 1,255lb mark. What are the odds of death by asteroid? They are lower than a plane crash, but higher than death by lightning.
A wet asteroid falls into a white dwarf
A white dwarf star at a distance of some 170 light years contains evidence of the death of a giant asteroid that may have once been flooded with water. A white dwarf is the cooling cinder of a dying star, left over after the star has used up its fuel for nuclear fusion. That star started out roughly the size of our sun and collapsed into a dense object roughly the size of the earth: a teaspoon of its stuff weighs as much as a locomotive.
The star appears to be surrounded by rubble, the remains of a large asteroid that came too close to the star such that it was ripped shreds. Some of the asteroid’s remains are now scattered over the surface of the star, where they show up as chemical signatures in the Hubble Space Telescope’s Cosmic Origins Spectrograph, which was designed by astronomers at the University of Colorado and built by Ball Aerospace in Boulder. The researchers also found a huge excess of oxygen, an amount that indicates the asteroid was originally composed of 26% water. That is a wet asteroid or huge comet. The earth, by contrast, is only 0.02% water. This is pretty interesting because Earth, having formed too close to the sun for water to survive, got its oceans from just such large, wet asteroids that impacted Earth long ago. To add to the fascination of this story, it is likely that several planets orbit the white dwarf, and one of them pushed the asteroid to its doom. This planetary graveyard is a peek at the future of our sun, when our star will run out of fuel and become a white dwarf in some five billion years.
A comet over Egypt
Some 28 million years ago a comet exploded over the sands of Egypt, heating up the sand to over 3,600° Fahrenheit. The result is a 2,316-square-mile area of yellow silica glass known as Libyan Desert Glass. A piece of that glass is in the center in Tutankhamun’s brooch, discovered by Howard Carter in 1922 when he uncovered King Tut’s tomb in the Valley of the Kings in Egypt.
The silica glass was one the clues that led Professor Jan Kramers of the University of Johannesburg, South Africa and colleagues to their proposal about the ancient comet over Egypt. In addition to the silica glass scarab, a strange black pebble was found years ago by an Egyptian geologist in the area of the silica glass. Described as angular, black, shiny, extremely hard and intensely fractured, the pebble has been a major puzzle for geologists. After conducting chemical analyses on this pebble, Kramers concluded that it represented the very first known specimen of a comet nucleus, rather than an unusual type of meteorite.
The impact of the explosion produced microscopic diamonds found within the pebble. Diamonds are produced from carbon-bearing material formed deep in the earth, where the pressure is high. But diamonds can also be produced by the shock wave of an explosion. Kramers named the diamond-bearing pebble “Hypatia” in honour of the first well known female mathematician, astronomer and philosopher of Alexandria. There is some sad and perhaps unwitting irony in naming a part of this dismembered comet after Hypatia. In AD 370 Hypatia was murdered and dismembered by a mob in Alexandria.