The Celestial Shooting Gallery

by Michael Mackowski

APTOPIX Russia Meteorite

Outer space may literally be mostly empty space, but our solar system is full of large and small chunks of rocks. A few days ago, a couple of these rocks made a close pass to our home planet. One object, called asteroid DA14, was large enough to be detected about a year ago. It came within 17,200 miles of the Earth’s surface, within the ring of geostationary communications satellites we all rely on. There was enough information on this object to know in advance that it would come close, but miss us. Still, this asteroid was the closest large object to pass by the Earth that we saw ahead of time.

Meanwhile a smaller object, perhaps the size of a school bus, whizzed over Russia, and when it exploded several miles above the ground, the shock wave was strong enough to smash windows over a large area, injuring over a thousand people from flying glass. This object was too small to be detected in advance, at least with the technology we are using today.

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Nevada – California Fireball Photographed

Fireball
Image Near Reno of the Minivan Sized Bolide that Exploded over California
Image Credit: Lisa Warren

Estimated to have released the energy equivalent to a 5 kiloton nuclear bomb when it exploded over the Central Valley of California, a minivan sized meteor was photographed (above) as it passed East to West over the Sierra Nevada mountains near Reno Nevada, around 8:00 AM Phoenix time last Sunday (1500 UTC).

The bolide, or extremely bright meteor, weighed around 70 tons, according to Bill Cooke of the Meteoroid Environments Office at NASA’s Marshall Space Flight Center in Huntsville, Alabama.

Lyrid Meteor Shower in April

Lyrid
Sky Map Locating the Lyrid Meteor Shower
Image Credit: Starry Night Software

With the Moon out of sight, the early morning of 22 April, will provide good seeing for the Lyrid meteor shower. These meteors are the result of the dusty tail of Comet Thatcher (C/1861 G1). Thatcher has an elliptical orbit, with a period of about 415 years. It will return in 2276. Space Weather has a good article about the Lyrids.

This year, the peak is expected on the evening of 21 April and the early morning of 22 April after midnight. The shower can last from 16 – 25 April. Typically, there are 10 to 20 meteors per hour. However, there is a large variation in the density of the shower. NASA has a long article (from the North American Meteor Network) concerning the shower and other events, and quotes an 1803 description from a newspaper in Richmond, Virginia on April 23rd, 1803:

Shooting stars. This electrical phenomenon was observed on Wednesday morning last at Richmond and its vicinity, in a manner that alarmed many, and astonished every person that beheld it. From one until three in the morning, those starry meteors seemed to fall from every point in the heavens, in such numbers as to resemble a shower of sky rockets…

For the techies on the audience, the radiant at maximum is at 271 degrees, i.e. RA 18h 04m, Dec +34, which is about halfway between theta and nu Hercules, and not actually in the constellation of Lyra at all.

Crater Drains Into A Cavern on Mars

Crater
Crater on the flank of Pavonis Mons on Mars
Image Credit: NASA / JPL / University of Arizona

Earlier this year, NASA’s Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) captured an image of a crater with a block dot in the center on the slopes of the Pavonis Mons volcano. Mission managers decided to have another look, this time with the High Resolution Imaging Science Experiment (HiRISE).

The black dot turned out to be a skylight 35 meters across leading into a cavern below. The cavern is likely a lava tube located beneath the surface of the volcano. Based on the shadow, the floor is about 20 meters below the skylight.

Speculation centers on the formation of the crater. It could be a sink hole formed from the loose dust on the volcano flowing into the cavern when the roof collapsed. In this closeup, one can see how the walls of the crater have slumped and material has flowed into the cavern below.

The hole might also be from a small meteorite that punched a hole through the lava tube. There does not seem to be much (if any) rim from a meteorite strike and the crater it would have created. Then, there is speculation that the underground cavern is a former ice deposit that has been exposed and sublimated into the Martian atmosphere.

Later this year, the HiRISE mission plans another image of the crater, creating a stereo picture that may help resolve the mystery.