A group of scientists spotted a Tunguska splashdown crater, striking at the heart of a great 20th-century mystery. The team began with this classic science fiction or horror starting point:
"We searched its bottom looking for extraterrestrial particles trapped in the mud. We mapped the basin and took samples. As we examined the data, we couldn't believe what they were suggesting.
(cue ominous music) A gouged-out hole appeared in nearby Lake Cheko's bottom, plowed out by something huge.
Gasperini's team says that the basin's unusual shape is the result of a fragment thrown from the Tunguska explosion that plowed into the ground, leaving a long, trenchlike depression.
"We suggest that a 10-meter-wide [33-foot-wide] fragment of the object escaped the explosion and kept going in the same direction. It was relatively slow, about 1 kilometer a second [0.6 mile a second]," Gasperini said.
William Hartmann, senior scientist of the Planetary Science Institute in Tucson, Arizona...: "If one large fragment hit the ground, we would normally expect thousands of smaller fragments also to hit the ground along the path, and many searches have failed to find such meteorite fragments. So, why no smaller pieces?"
Because the alien ship destroyed itself, of course. Or buried itself far too deeply under the soil. Or the black hole plummeted into the Earth's core. And it/they wait, plotting their eventual and irresistible return to the surface...
(pic from Astronomy Pic of the Day, which also has nice background info)