A nearly half-minute time-lapse video stitched together from images taken by NASA’s Hubble Space Telescope shows Comet 252P/LINEAR spinning like a lawn sprinkler after it zoomed by Earth on March 21 in one of the closest encounters between a comet and our planet.
The comet traveled within 3.3 million miles of Earth, reports NASA, or about 14 times the distance between our planet and the moon. Hubble took the images on April 4, about two weeks after the icy and gaseous space rock, estimated to be less than one mile across, made its closest approach to Earth. At that point, it was 8.7 million miles from here. It is now more than 25 million miles away from our planet in an elliptical orbit that will bring it back to the inner solar system in 2021.
Each frame of the movie depicts about 30 to 50 minutes. It shows the jet of dust and gas being ejected by the comet’s icy nucleus as it is warmed by the sun. This tail of gasses in the Hubble images is illuminated by sunlight, and appears to change directions, which suggests that the comet is spinning.
The comet, a remnant from the formation of our solar system 4.5 billion years ago, was first discovered by MIT's Lincoln Near Earth Asteroid Research (LINEAR) survey in 2000, according to Space.com. The day after it passed Earth in March researchers saw another, smaller comet pass even closer. That one could have been a piece that had broken off of 252P.
Sometimes, comets do reach Earth, as do their more solid cousins, asteroids, and other space debris, such as chunks of manmade satellites. In fact, space debris strikes Earth every year, almost always without causing damage or injuries. The chances of a catastrophic event are very low. Only a handful of meteorites – rocks that don’t fully burn up in the atmosphere and make it all the way to Earth – have even damaged property, and until recently, there were no records of a meteorite impact ever killing a human.
Nonetheless, Tulane University environmental sciences professor Stephen A. Nelson has calculated the odds of getting killed by a meteorite at about 1 in 250,000; much lower than dying in a tornado (1 in 60,000), but much higher than winning the PowerBall (1 in more than 195 million).
NASA, fortunately, keeps tabs on near-Earth flying objects. The agency’s Planetary Defense Coordination Office monitors space debris that could potentially come close enough to cause damage.
The space agency’s goal is to keep track of the space junk near our planet using ground-based and space telescopes, and to alert government disaster agencies if an object looks likely to strike. In the long term, says the agency, its goal is to defend the planet from extraterrestrial intrusion with technology that can knock asteroids or comets off their course toward Earth.