Asteroid flyby ... 2020 LD passed within the moon’s distance

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Biggest asteroid to pass close (and undetected) this year
Eddie Irizarry in SPACE | June 11, 2020

Asteroid 2020 LD passed within the moon’s distance on June 5, but wasn’t discovered until June 7. It’s the 45th known and the largest asteroid to sweep within a lunar-distance of Earth so far in 2020.

We hear a lot about asteroids or comets passing close to Earth, but what does “close” mean? For a comet, it might mean millions of miles. For an asteroid, it might mean enormous distances as well, beyond the moon’s orbital distance of about a quarter-million miles. On the other hand, space rocks coming closer than our moon catch people’s attention, especially if the asteroids are good-sized! That was the case with asteroid 2020 LD, which swept closest to Earth on June 5, flying by at only about 80% of the moon’s distance (190,559 miles or 306,675 km). At around 400 feet (122 meters) in diameter, 2020 LD is the largest asteroid to have come within 1 lunar-distance this year … or last year … in fact, since 2011. And it also ranks as one of the biggest asteroids ever to fly this close to Earth, without being previously detected. That’s right. 2020 LD passed undetected on June 5. No one noticed it until 2 days later, on June 7.

That’s when astronomers using the 0.5-meter ATLAS telescope at Mauna Loa, Hawaii, astronomers first noticed this Apollo type asteroid traveling at 60,826 miles per hour (97,890 km/h) relative to Earth.

It was only after analyzing the space rock’s orbit that scientists realized its closest approach to Earth had happened two days before, on June 5.

Asteroids fly between the moon’s orbit and Earth pretty frequently. You might be surprised at how frequently. The chart below – via The Watchers – shows the asteroids that have come that close from January 1 to June 9, 2020.

Image via The Watchers.

But 2020 LD isn’t your typical close-passing asteroid. Again, it’s the biggest asteroid to have passed within the moon’s orbit since 2011.

Is a 400-foot asteroid a big one, in an absolute sense? Not particularly. On the scale of asteroids in general – those orbiting mostly in the asteroid belt between Mars and Jupiter – we might say that 2020 LD falls somewhere between medium and small. The biggest asteroids are hundreds of miles in diameter. That said, asteroid 2020 LD is big enough to cause consider damage if it were to hit us. Consider, for example, the space rock that caused the 0.75-mile diameter (1.2-km diameter) Meteor Crater near Flagstaff, Arizona. That asteroid, which struck some 50,000 years ago, was estimated to be about 150 feet (about 46 meters) in diameter.

Or consider the asteroid that entered Earth’s atmosphere as an amazing meteor over Chelyabinsk, Russia on February 15, 2013. The shock wave from that meteor broke windows in six Russian cities. The original asteroid was an estimated 66 feet (20 meters) in diameter.

Did you know you can calculate the effects of any asteroid impact via this cool impact calculator created by Jay Melosh, an atmospheric scientist at Purdue Uniersity? You could take the numbers of the various asteroids mentioned in this article – and plug them into that calculator – and scare yourself handily! Visit the impact calculator.

In the meantime, space rock 2020 LD is nothing to worry about. At this writing, 50 years is the length for which its orbit has been well calculated. It won’t come so close to Earth again as it did this month for at least that many years … and likely much, much longer.