Tunguska | BEYONDbones

On Feb. 15, 2013, with no warning, an asteroid 20 meters in diameter and weighing more than the Eiffel Tower plunged into the Earth’s atmosphere over the Russian city of Chelyabinsk at speeds in excess of 19 kilometers per second. At such a high speed, the 14,000-ton object exploded at altitude, creating a flash 30 times brighter than the sun and panicking Siberian residents.

The Chelyabinsk meteor injured 1,500 people and damaged 7,200 buildings in 2013.

The air burst damaged 7,200 buildings and injured 1,500 people, mostly due to cuts from broken glass, but many reported ultraviolet burns similar to sun damage and blindness from the flash. It was not the impact that caused the most damage, but the explosion as it suddenly fell apart in the atmosphere, about 25 times more energy than the atomic bomb detonated over Hiroshima.

The impact crater caused by the Chelyabinsk meteor.

The largest meteor impact since the Tunguska event on June 30, 1908 that flattened 80 million trees, Chelyabinsk served as a grim reminder that asteroids still pose a credible threat to the planet the same way they did for the dinosaurs. A massive asteroid collided with the Earth 65 million years ago, bringing about the demise of megafauna like Tyrannosaurus rex and Triceratops, along with more than half of the plants and animals living in the late Cretaceous. Scientists agree the asteroid responsible for this mass extinction hit the Yucatan, causing the Chicxulub crater. And the threat remains, this time for us.

Dr. David Kring, the man who discovered and named the Chicxulub crater.

Dr. David Kring of the Lunar and Planetary Institute, the scientists who discovered and named the Chicxulub for a Mayan village near the center of the crater, will pay a visit to the Houston Museum of Natural Science on Asteroid Day, June 30, at 6:30 p.m. His lecture will examine methods to mitigate the threat of meteor impacts to humanity, and guests will have a chance to engage in a Q&A session during the lecture. The Burke Baker Planetarium will offer special screenings of Impact at 6 and 8 p.m., complimentary with a ticket to Kring’s lecture.

Join us to learn more about asteroid impacts and other phenomena on Asteroid Day. Survival favors the informed. Tickets $18, Members $12.

Thomas D. Jones, PhD is a veteran NASA astronaut, scientist, speaker, author, and consultant. He holds a doctorate in planetary sciences, and in more than eleven years with NASA, flew on four space shuttle missions to Earth orbit. In 2001, Dr. Jones led three spacewalks to install the centerpiece of the International Space Station, the American Destiny Laboratory. He has been privileged to spend fifty-three days working and living in space.

Many of you may remember when Dr. Jones spoke here in May 2008 on spacewalking. He’ll be back on Tuesday, Nov. 17 with an all new lecture on near-Earth objects, potential impacts, the search for alien life, and the formation of planets.

500-m-wide NEO Itokawa, imaged by the
Japanese Hayabusa probe in 2005 (JAXA)

On November 6, we had a close encounter with a near-Earth object, 2009 VA (a NEO is a near-Earth object, including both asteroids and dormant comets). The space boulder, a 7-meter-diameter asteroid, streaked by at a distance of only 14,000 km, well inside the orbits of our geosynchronous satellites. NASA’s Jet Propulsion Lab estimates that we have two such encounters each year, on average, with objects of this size. About every five years, Earth is struck by such a body, but objects this small burn up in the atmosphere, resulting in a fireball and the release of several kilotons of energy (TNT equivalent).

The close pass of 2009 VA surprised some news outlets, which speculated on why the small asteroid had not been detected sooner by astronomers (The University of Arizona’s Catalina Sky Survey picked up 2009 VA about 15 hours before the closest approach). The answer is that these small cosmic rocks are so numerous, and so difficult to observe, that we only discover them at random. NASA runs a search program, Spaceguard, to detect larger objects, 1 km and up, that may pose a civilization-ending threat to Earth. So far about 85% of those objects have been found; none pose an immediate threat to Earth, but may in future decades.

Jet Propulsion Lab depiction
of recent close pass by 2009 VA

Impacts of small objects like 2009 VA create only sky-high fireworks, no harm to us here on the ground. But the Tunguska impact in Siberia a century ago devastated 2,000 square km of Siberian forest. That airburst of about 5 megatons (Mt) of TNT equivalent was caused by an object 30-40 m in diameter; large enough to level a city center. Such an object strikes us every few hundred years. The last one was a century ago; the next one to come along may hit us tomorrow. With current telescopes, we have only a small chance of seeing such an object before it strikes Earth.

Congress has asked NASA to look into what it would cost to search systematically for NEOs down to 140 m in diameter; if we found most of those objects, we would have greater confidence that no “city-buster” NEO is headed for an imminent collision with a populated area on Earth. A report to NASA on the prospects of detecting and even deflecting such potentially hazardous NEOs is due out by year’s end from the National Research Council.

Impact, or cosmic bombardment, is a process that has been altering the faces of the planets since the dawn of the solar system 4.6 billion years ago. Impacts by giant comets and asteroids have changed the course of life on Earth, possibly ending the reign of dinosaurs 65 million years ago, and possibly causing other mass extinctions through Earth’s long history. We now have the technology to both detect damaging NEOs heading for Earth, and with proper warning, to nudge them out of the way. What we lack is the international will to take action should a hazardous NEO be found on a collision course with Earth. The Association of Space Explorers is working with the United Nations to draft such a NEO decision-making agreement.

At the Houston Museum of Natural Science on Tuesday, Nov. 17, I will be speaking about impact and the other processes that shape the worlds of the solar system, in a talk called Planetology. My talk will discuss these processes — tectonics, volcanism, erosion, for example — and our search for life and “other Earths” across the galaxy. Please join me for the lecture that evening at 6:30 p.m., or turn the pages of Planetology, written by me and noted planetary geologist Ellen Stofan. After the talk, I’ll be answering questions and signing copies of the book.

See reviews and more info on Planetology at:
www.AstronautTomJones.com