I hope you had pleasant dreams overnight. In one of mine, I couldn’t get my shoe tied right. Glad I woke up from that one. While many of us slept, a tiny near-Earth asteroid named 2017 GM passed exceptionally close to Earth, just 9,942 (15,000 km) miles overhead at 5:31 a.m. CDT (10:31 UT). That tiny distance put it in the Top 10 closest recorded approaches.
It was discovered only yesterday by the Mt. Lemmon Survey in Arizona. Based on its distance and brightness, astronomers estimated its size at around 13 feet (4 meters) across. Even if it had made a direct hit, this boulder from the asteroid belt would probably have broken to pieces when it rammed the atmosphere at tens of thousands of miles an hour.
It’s still in the neighborhood as I write this at noon CDT at 251,000 miles away or a little beyond the moon’s distance. The asteroid passed harmlessly by and will continue to distance itself from Earth as the minutes tick by. Millions of small asteroids like this one remain to be discovered. Robotic surveys, where telescopes automatically take pictures of one piece of the sky after another with the images fed into a computer to scan for moving objects, pick up a couple dozen or more every month.
Astronomers are watching the skies and trying to track every object they’re able with the aim of identifying any that might come back to smack us. To date, no asteroid impact is foreseen for at least the next century. But we shouldn’t be surprised that some objects get away or aren’t discovered until the last moment. This is true in the case of asteroids that might approach us from the direction of the sun. Lost in the daylight sky, we can’t know they’re en route until they’re practically on our doorstep.
In other small body news, comet C/2017 E4 Lovejoy is healthy and still brightening. Observers are calling it magnitude +6.5 and though small, the comet is still visible in binoculars just before the start of dawn. I’ve included a chart showing its location in the eastern sky the next couple mornings — for a longer view, please use the map included in this earlier blog.
The comet has a remarkably narrow tail, skinnier than a 1960’s businessman’s tie. Called an ion tail, it’s made of carbon monoxide gas vaporizing from the comet. Ultraviolet light from the sun knocks electrons off the gas (a process called ionization) which allows the magnetic field embedded in the solar wind to carry the ionized gas directly behind the comet’s head opposite the sun. The UV light energizes the gas to fluoresce pale blue.
Moonless skies will rule before dawn through about April 8, so try to see this interesting comet if you can before the moon spoils the fun.