When the asteroid named 3200 Phaethon passed by our planet earlier in December, people were watching. The asteroid is not a huge space rock, but it zipped close enough to Earth that NASA classified Phaethon as a “potentially hazardous asteroid.”
This does not mean that Phaethon posed any immediate danger. Potential space hazards are matters of cosmic perspective: On Dec. 16, the nearest Phaethon has been since the 1970s, it was 6 million miles from us. The moon, in comparison, is 240,000 miles away.
In Puerto Rico, the Arecibo Observatory watched Phaethon's passage. The world's second-largest radio telescope has not had an easy year. Hurricane Maria roughed up the observatory Sept. 20, destroying a 40-foot dish and damaging other instruments. All told, the hurricane caused between $4 million and $8 million in damage, National Science Foundation acting assistant director James Ulvestad told The Washington Post.
But the telescope escaped total devastation. All staff evacuated safely, an NSF representative told The Post in September, and the massive main dish remained intact. The Universities Space Research Association, which helps operate the observatory, distributed generators to some Arecibo employees. By December, the observatory had resumed normal operations. (Meanwhile, a recent estimate by Puerto Rican engineers showed that 50 percent of the island's 3.3 million people still lacked power, the AP reported on Monday.)
The hurricane was not the only threat to Arecibo's future. The observatory's funding has been shrinking, and under some proposals, it would have been demolished or turned into an educational facility. The NSF, which owns the observatory, announced in mid-November that it was committed to keeping Arecibo operational.
The observatory, once back online, captured the best-resolution images of Phaethon, which NASA released in late December. The asteroid has a curious dark splotch near one of its poles. “The dark feature could be a crater or some other topographic depression that did not reflect the radar beam back to Earth,” said Patrick Taylor, a scientist at Arecibo Observatory and the Universities Space Research Association, in a news release. The new, detailed inspection of Phaethon showed that it is shaped like ball, although it has a depression along its middle.
Radar revealed that the asteroid was 0.6 miles wider than thought, at 3.6 miles in diameter. If an asteroid of Phaethon's size hit Earth, planetary scientist Dan Durda recently told NBC News, the impact would be so devastating that it would destroy the ozone layer “several times over,” plunging the planet into a period of global chill.
Phaethon remains too far away to be a threat, but its influence may, on occasion, take a dramatic turn. The asteroid spews out dust in a trail behind it. When the granules of space rock collide with Earth, fireballs appear in the atmosphere. These are the Geminids, a meteor shower that peaked earlier this month.
This is not the last such encounter we will have with Phaethon. It will dash by the Earth even closer in 2093.