Becky Ferreira explains how lucky we are to only have to deal with a massive blizzard today:

[Yesterday] morning, an enormous space rock missed Earth by a narrow margin of 745,000 miles, or about three times the distance from the Earth to the Moon. With a diameter of 550 meters and a velocity of about 35,000 miles per hour, the asteroid, known as 2004 BL86, will be so bright in the evening sky that it will be visible through binoculars. Scientists don’t expect another object of this size to pass so closely to Earth until August 7, 2027.

What you’re seeing above:

NASA has released radar observations of the 325 meter-wide asteroid that flew safely past Earth [yesterday] at 8:19 a.m. PST (11:19 a.m. EST), but in those grainy observations, asteroid 2004 BL86 appears to have company — a small moon.


Bob King has more on that exciting find:

Among near-Earth asteroids, about 16% that are about 655 feet (200 meters) or larger are either binary or triple systems. While that’s not what you’d call common, it’s not unusual either. To date, we know of 240 asteroids with a single moon, 10 triple systems and the sextuple system of Pluto (I realize that’s stretching a bit, since Pluto’s a dwarf planet) – 268 companions total. 52 of those are near-Earth asteroids.

With a resolution of 13 feet (4-meters) per pixel we can at least see the roughness of the the main body’s surface and perhaps imagine craters there. No details are visible on the moon though it does appear elongated. I’m surprised how round the main body is given its small size. An object that tiny doesn’t normally have the gravity required to crush itself into a sphere. Yet another fascinating detail needing our attention.

Circling back to Ferreira, she imagines how bad today could have been:

What if [2004 BL86] hurtled towards us just a little earlier, and instead of flying freely through the wake of Earth’s orbit, it collided with us head on? How bad would the damage be?

Fortunately, there is an online tool for calculating the apocalyptic potential of various impact scenarios. Run by Purdue University, Impact Earth allows users to input details about asteroids, comets, and other cosmic death traps, then crunches the numbers on the fallout. I gave the calculator the known details about asteroid 2004 BL86, including its diameter and velocity. I entered a hypothetical mid-range angle of 45 degrees, and specified that the asteroid hit sedimentary land, not water. Then, I asked it to tell me what the damage would be like one kilometer away from the impact site. After a dramatic animation of an asteroid hitting New England, Impact Earth gave me a rundown of the designer catastrophe.

Naturally, it wasn’t pretty. “The projectile begins to breakup at an altitude of 49,800 meters (16,3000 ft),” Impact Earth predicted. It would be fractured by the time it hit the ground, striking the surface at a velocity of about 7.95 miles per second. The energy released would be about 5,120 megatons, which is 100 times more powerful than the strongest nuclear bomb ever detonated. It would leave behind a crater with a diameter of 3.64 miles and a depth of 1.26 miles—similar dimensions to Alabama’s Wetumpka crater. But as the calculator noted under the “Global Damage” category, the impact would not be enough to disrupt the Earth on a global level by altering its orbit or its axial tilt.