
Amateur astronomer Rolando Ligustri took this photo of an incoming comet dubbed "Hartley 2" near the Pacman cluster.
Do you remember what you were doing on September 8, 2010? It was the Wednesday right after Labor Day long weekend. Do you remember what you had for lunch? Or who you talked to on the phone? Did you send a funny text to a friend who lol’d you back? You were probably distracted by the widely publicized upcoming 9/11 protests that were all over the evening news, fuelled by talks of building a mosque near Ground Zero in New York and coming to a head when that wacky American pastor Terry Jones decided to tell everyone that he was planning to burn Qurans at mass on September 11. There were also a lot of TV show premieres that week as most networks’ fall schedules came into effect. Oh, and not to mention it was back-to-school week for most students and their parents, meeting new friends, changing schools and the parents’ last minute scramble to buy school supplies, new clothes and lunchbox-friendly snacks items.

On September 8, 2010, 2 asteroids whizzed by the Earth within the orbit of the Moon.
So I really don’t blame you if you didn’t know that the Earth was almost struck by not one, but two asteroids on September 8, 2010. These two asteroids were spotted at the last minute (astronomically speaking) just three days before they blasted past Earth, both passing within the orbit of the Moon (known as the Lunar Distance or LD, equal to 384,000 kilometers).

Showing the altered trajectory of asteroid 2010 RF12 due to its nearness to Earth's gravity.
The first rock, dubbed 2010 RX30, shot past the Earth at about 3:51 am MDT, when most of us were probably still sleeping—it was 10–20 meters in size (about the size of a semi-trailer) and passed within 0.6 LD (248,000 kilometers) of Earth. The second asteroid, dubbed 2010 RF12, rattled our cages at 2:21 pm MDT from a ridiculously close distance of 0.2 LD (79,000 kilometers), close enough to be affected by Earth’s gravity. To put that distance into perspective, all of our orbiting geosynchronous satellites (for weather, communication, broadcasting, etc) have to be stationed at an altitude of 36,000 kilometers in order to stay fixated on a specific geographic location, meaning 2010 RF12 was only twice as far away from hitting Earth as an orbiting FoxNews satellite. Luckily, this second asteroid was only 6–14 meters in size (about the size of a stretch limo), a likely candidate for atmospheric dispersal.
In fact, to allay your blooming panic and fear, most of the asteroids that blaze past Earth are usually not big enough to penetrate our atmosphere (which also protects us from dangerous solar winds and produces aurora borealis). Unless the asteroid were at least 100 meters in size, it wouldn’t last long enough to get anywhere near the Earth’s surface—you might get to see a wicked fireball, but there won’t be a smoking hot meteorite to pick up afterwards. At least once a year, a car-sized asteroid flashes through Earth’s atmosphere and leaves a wicked contrail; not to mention all the smaller, basketball-sized meteors (so-called ”shooting stars”) that constantly blaze through the sky. That isn’t to say that there isn’t a slight risk that an incoming asteroid might strike the atmosphere at exactly the right angle to avoid being burnt to a total crisp, but in any case, the rock would have to be pretty huge to cause catastrophic, wide-spread damage—about 2 kilometers in size is a typical large-impact asteroid.

One of the telescopes at Catalina Sky Surveys in Tucson, Arizona.
Unfortunately, we have a veritable treasure trove of Near Earth Objects (NEOs)—comprising Near Earth Asteroids (NEAs) and Near Earth Comets (NECs)—to worry about, all within 116 LDs (44,590,000 kilometers) of Earth. For example, just recently, on October 1, 2010, NEO 1998 UO1, an asteroid with a diameter of 1.3–2.9 kilometers, passed within 32.1 LDs of Earth (12,326,400 kilometers). Then, coming up on October 14, we can expect to not even notice as NEO 1999 VO6, another massive hunk of rock with a diameter of 1.1–2.5 kilometers, breezes past Earth, narrowly missing us by about 34.3 LDs (13,171,200 kilometers). And, more notably for backyard astronomers, comet 103P/Hartley 2—a highly visible, blue-green tailed comet about 1.6 kilometers across—is expected to come within 47 LDs of Earth (18,048,000 kilometers), putting on a spectacular show in the constellation Cassiopeia for the next couple weeks.
To make matters even worse, as of October 3, NASA has counted no less than 1147 potentially hazardous asteroids (PHAs) within 20 LDs (7,500,000 kilometers) of Earth, all of which are over 150 meters in size and, due to the tug and pull of other planetary objects, might potentially pass fairly close to Earth at one point in their oblong orbits. For an exhaustive list of other NEOs and their approximate close approach dates, please click here.
To me, what’s even more impressive than Earth’s constant dodging of such an Armageddon-like disaster is that we can know so much about it. In 1998—which, ironically (or sadly, maybe not), is the same year that the movie Armageddon was released—NASA instigated a program known as “Spaceguard,” which had the vested purpose of “discovering and charting over 90 percent of the near Earth objects larger than one kilometer in size by the end of 2008.” In aiming so high, however, the program drastically underestimated just how many NEOs there actually are out there. To date, they’ve discovered over 6400 NEAs and 84 NECs, but which is admittedly only about 60 percent of the total number of NEOs thought to be spinning around Earth’s immediate vicinity. Spaceguard eventually expanded their search to include the “far more numerous, perhaps hundreds of thousands” NEOs that are less than one kilometer in size, creating a massive catalogue of years and arbitrary numbers that look like this: 2010 RT30, 2004 RQ252, 1998 MQ, 2002 EZ16, etc.

A graph depicting the rapid increase of newly discovered NEOs since 1995.
Today, Spaceguard is known as the Near Earth Object Program and brings together observatories from all across the world, such as the Lincoln Near-Earth Asteroid Research (LINEAR) in Socorro, New Mexico, the Catalina Sky Survey (CSS) in Tuscon, Arizona, the Siding Spring Survey (SSS) near Coonabarabran, Australia, and—by far the most creatively named—Japanese Spaceguard Association (JSGA) in Bisei Town, Japan. As you can see in the graph above, the amount of newly discovered NEOs found as a result of all the extra observation jumped from a paltry 40 discoveries per year in 1995 to over 800 per year in 2009, and those numbers just continue to grow.
Most of these NEOs are chunks of rock culled from the asteroid belt, that giant hula hoop of planetary debris orbiting out past Mars. In my experience, I’ve found that astronomy books and orthodox opinion paints a rather benign picture of our solar system’s asteroid belt, like it’s just a couple dozen hunks making up a harmless interstellar pearl necklace—when in fact, the asteroid belt is a terrifying conglomeration of atmosphere-piercing space missiles, some of which occupy orbits that keep them coming close to Earth on a regular basis just to say “hi.”
These asteroids are caught up in the same unyielding solar gravity field as we are and, because of their smaller size, aren’t locked into the same steady orbit as Earth—they often collide and fracture, spin-off and change direction, impacting one another and moving into different, more elliptical orbits. Asteroids can also be knocked off course by passing high-speed comets (like Hartley 2 on October 20) that are on a bee-line towards the Sun, thereby inadvertently pushing more PHAs into Earth’s airspace. The moon, just like the Earth, is visibly pockmarked with evidence of hundreds of thousands of years of asteroid impacts, though most terrestrial evidence has been masked by erosion, geology, vegetation and ocean water.
According to conservative estimates, there are no less than 450,000 asteroids comprising the asteroid belt, most of which are completely unknown to us other than the fact that they exist. To put it into perspective, here’s is a startling graphic depicting the absolutely crowded nature of our inner solar system.
(The green fringe shows the sheer density of the asteroid belt, while the red dots demarcate the potentially dangerous NEAs, spinning and cavorting right through Earth’s orbit.)

The inner sanctum of the asteroid belt. NEAs are marked in red.
Of particular concern to scientists and astronomers is a future close pass by the asteroid Apophis, scheduled for Friday, April 13, 2029. Apophis is an asteroid 270 meters in size that was discovered in 2004, and it is expected to pass by only about 29,470 kilometers above sea level, over 6000 kilometers closer than Earth’s geosynchronous satellites, which—needless to say—is pretty damn close. At first, astronomers figured that Apophis had a 2.9 percent chance of striking Earth, but after some intense calculations, they finally determined that we should probably be safe, but just barely. Now, the concern lies in how much Earth’s gravity will alter Apophis’ trajectory for its next pass, expected in 2036, although there are so many factors in play that such a determination is nearly impossible to lock down. As it stands, we’ll just have to wait and see how Apophis responds.
Now, I’m not trying to scare you with any of this, nor do I think you should lose any sleep over it. Asteroids have been circling overhead for millions of years and have been exploding in Earth’s atmosphere for longer than any of us have been alive, so it’s not a sudden development that we should be increasingly wary of. Just rest easy knowing that if a giant destructive space rock was about to tear its way through the Earth’s atmosphere and destroy civilization as we know it, you will probably have enough warning to get your affairs in order.