114 years ago Thursday a meteor two football fields wide streaked across the skies above Siberia, near the Podkamennaya Tunguska River at 65,000 miles per your. It broke apart about 5 miles above the ground releasing a ~20 megaton explosion which leveled about 830 square miles of forest. For comparison, that is well over double the area inside the Raleigh beltline. That’s equivalent to the size of the blast that removed the top of Mount Saint Helens.
International Asteroid Day is now observed on the anniversary the Tunguska event, the asteroid event all other asteroid events are compared to. Established in 2014 by the United Nations, Asteroid Day aims to raise awareness about asteroids and other near Earth objects (NEOs), the missions to learn more about them, and planetary defense efforts underway by NASA, the European Space Agency and others.
The key to doing something about NEOs is know the risk. While discovery rates have increased as technology has improved and dedicated missions and sky surveys have launched, scientists have been challenged to increase the rate new discoveries of asteroids to 100,000 per year over the next 10 years.
Once discovered, observations continue around the globe to build up the data needed to calculate the orbits of these space rocks. This data helps create predictions of when and where an asteroids path might intersect Earth’s path around the Sun.
NASA’s Center for Near Earth Object Studies (CNEOS) is leading the way with more than 1.2 million planets, moons, asteroids and comets in their database. Of those, fewer than 30,000 or about 2.4% ever enter our neighborhood earning the NEO label. Less than 0.2% are considered potentially hazardous asteroids (PHA), coming within about 4.6 million miles of Earth.
NASA and other agencies are thinking through what to do should an impact be imminent. Scientists share ideas during an annual Planetary Defense Conference which include interagency table top exercises which put leaders through the paces of handling a possible impact from the object’s discovery on.
Back in the real world, it is important to note that NEOs pass harmlessly every day. Two will pass by just tomorrow July 1, at a well over double the distance to the Moon respectively. S
cientists are keeping their eye on 2012 HG2, an Apollo asteroid about double the size of the one which shattered windows causing injuries over Chelyabinsk, Russia. There’s no measurable risk until 2052 when the odds are one in a million of the object entering the atmosphere. Those odds increase to 1 in 23,000 chance two years later.
But orbits change as these objects are tugged on by the gravitational pull of the Sun and giant planets like Jupiter and Saturn, and new objects are discovered each day. CNEOS and its international partners are on the job.