Evan Hazard: Space rocks: Large and larger
Page 24 in June’s “Sky & Telescope” has a color illustration of the Pittsburgh Steelers’ Heinz Field. Artist Michael Carroll has painted two stationary blackish rocks in the air above the game, casting ominous shadows below. Both roughly potato-shaped, the larger casts a 55-yard shadow, the smaller a 15-yard shadow. These show the comparative size, respectively, of two unrelated space rocks that made headlines last February: the larger asteroid 2012 DA14 and the smaller meteor that exploded in the air 37 miles above Chelyabinsk in Russia the morning of Feb. 15.
We do not have clear photos of either object, but various observations by scientists plus many dashboard cam images from Chelyabinsk vehicles made calculation of their orbits and estimates of their masses and volumes possible, as well as determination of their chemical compositions.Actually, the orbit of 2012 DA14 was already known from earlier observations starting with its discovery in 2012. As predicted, it did pass us some 17,000 miles above Earth’s surface, on the far side of Earth from Sol. Passing that close, our gravitational pull altered its orbit, reducing it to lie mostly inside our orbit, and reducing its “year” from 366.2 to 317.2 days. Earth gained the angular momentum 2012 DA14 lost, but the effect on this 8,000 mile rock of gaining that angular momentum from a 55-yard rock is hardly measurable. We shortened its year 49 days and I’m guessing it lengthened ours by a second or two. Someone else do the math.However, its orbit does not lie entirely within ours. All planet and satellite orbits are ellipses and that of 2012 DA14 will still cross ours. It could still hit Earth someday, and we do not want a rock roughly 30 times the mass of the Chelyabinsk meteor to explode in the air above either land or water, or worse, to hit the surface intact.Even if, like the Chelyabinsk meteor or the large rock that exploded over Tunguska in Siberia in 1908 (www,skypub.com/tunguska), it exploded high above the surface, large enough chunks to hit the ground or ocean would cause serious damage, probably loss of life and serious weather or tidal effects.Why didn’t we see the Russian meteor coming? We didn’t know it existed until that morning. Chelyabinsk is at 55 degrees north latitude, farther north than Edmonton, Alta., where February mornings are much later than here.It arrived from the ESE, where Sol was rising. Determination of its orbit from webcam images showed two things. One, its orbit around Sol was a much more elongated ellipse than ours or that of 2012 DA14.Its far point was in the asteroid belt between Mars and Jupiter, its near point just outside the orbit of Venus. Two, it was on its way back from that near point when it ran into our upper atmosphere.It was coming at us from the direction of the rising sun. And none of our current near-Earth satellites is likely to detect anything that small.We are lucky it arrived in time to graze the atmosphere rather than, say, at high noon, when it would have smashed more or less vertically into Earth’s land or ocean before it could heat up enough to explode in the air.We clearly need to put more research and effort into detecting all space rocks the size of the Russian meteor or larger. This includes refining our detection of relatively small objects, and constant monitoring of a large region of space around us.This is no time to quibble about public vs. private funding. One proposal, funded by Bell Aerospace and the B612 Foundation, is to construct and put in orbit a wide-field infrared telescope. Its orbit would be near that of Venus, and it would survey a 180 degree field of view of Earth’s orbit. Being closer to Sol than Earth is, it would move as rapidly as Venus does, surveying our entire orbit more than once each Earth year.Most of the info in this column is in Daniel Durda’s article, “The Chelyabinsk super-meteor,” p. 24-31, Sky & Telescope. You may have to be a subscriber to read the full article online. Try the Bemidji or BSU library. Two useful websites are http://en.wikipedia.org/wiki/2012_DA14 and http://www.youtube.com/watch?v-qZ6oiaSm00 .Dedication: to the Rev. Marva Jean Hutchens, who will retire at the end of June. She served the Bemidji UMC from 1984 to 1991, and currently serves the Grand Rapids UMC.EVAN HAZARD, a retired BSU biology professor, also writes “Northland Stargazing” the fourth Friday of each month