Organization: Travelers in The Night
Description: Today’s 2 topics:
Bio: Dr. Al Grauer is currently an observing member of the Catalina Sky Survey Team at the University of Arizona. This group has discovered nearly half of the Earth approaching objects known to exist. He received a PhD in Physics in 1971 and has been an observational Astronomer for 43 years. He retired as a University Professor after 39 years of interacting with students. He has conducted research projects using telescopes in Arizona, Chile, Australia, Hawaii, Louisiana, and Georgia with funding from NSF and NASA.
He is noted as Co-discoverer of comet P/2010 TO20 Linear-Grauer, Discoverer of comet C/2009 U5 Grauer and has asteroid 18871 Grauer named for him.
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4E – A Bad Day for Dinosaurs
Scientific evidence suggests that it was a bad day for non-avian dinosaurs when a large asteroid or a comet crashed into the Earth about 66 million years ago.
The Chicxulub [cheek-she-loob] impact, is coincident with the geological K-T event. ¾ of the plant and animal species on Earth vanished at this time.
The Chicxulub crater is approximately 110 miles in diameter just off of the coast of the Yucatan Peninsula in Mexico. The original object is estimated to have been 6 or 7 miles in diameter. It was traveling at a speed of 12 miles/second when it entered the Earth’s atmosphere. Its impact created a mega-tsunami as well as clouds of superheated gas and dust. The impact of this asteroid delivered 2 million times the energy of the most powerful hydrogen bomb ever exploded. Global shock waves radiated from the impact site triggering earthquakes and volcanic eruptions. Material ejected from the impact site probably ignited wildfires when it re-entered the Earth’s atmosphere. An iridium rich clay layer found around the entire globe is the likely result of this impact event.
It is possible that the K-T extinction could have been produced by a combination of an asteroid impact and widespread volcanic eruptions. These two forces would have worked together to produce a months of darkness and cooler temperatures around the globe.
Some species, including mammals, flourished under the changed conditions after the Chicxulub event. It is interesting to speculate that the rise of the human race may have been enabled by an asteroid impact.
5E – The Tunguska Event
The Tunguska [ Tun·gu·ska] event occurred on June 30, 1908. It appears to have been caused by a small asteroid or comet which exploded 3-6 miles above the Earth’s surface. It is the largest impact event in recorded history.
Over the years there have been a number of scientific theories put forth to explain what happened.
NASA estimates that the original object was a space rock perhaps 40m [120 feet] in diameter which was traveling at 33,500 miles/hour when it entered the Earth’s atmosphere. At about 28,000 feet it heated the air around it to 44,500F producing a fireball. It released an energy roughly equivalent to a hydrogen bomb. It did not leave a crater because it was vaporized as it exploded. Its blast wave knocked down 80 million trees over an 830 square mile area. The trees were laid out in a radial pattern pointing away from the apparent blast center.
An eyewitness 40 miles away was knocked to the ground by the blast and reported that the heat made him feel as though his shirt was on fire.
Sensitive barometers thousands of miles away in England registered atmospheric shock waves from this event.
Objects of this size enter the Earth’s atmosphere every few hundred years.
The Tunguska event demonstrates that even relatively small objects which hit the Earth can have significant effects.
A Tunguska type explosion event could devastate a large modern city.
Fortunately we have not discovered any such objects on a collision course with planet Earth.
For Travelers in the Night this is Dr. Al Grauer.
End of podcast:
365 Days of Astronomy
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