Advertisement
  1. News

Largest fireball since Chelyabinsk falls over the Atlantic — and almost no one notices

This is the fireball that exploded over the city of Chelyabinsk, about 930 miles east of Moscow, Russia, in February 2013. A much smaller fireball exploded off Brazil on Feb. 6 of this year. [Chelyabinsk.ru | Yekaterina Pustynnikova via AP]
Published Feb. 23, 2016

On Feb. 6, 2016, around 14:00 UTC (or 9 a.m. EST), a tiny chunk of interplanetary material plunged into Earth's atmosphere and burned up — likely exploding — about 30 kilometers above the Atlantic Ocean. The energy released was equivalent to the detonation of 13,000 tons of TNT, making this the largest such event since the (much larger) Chelyabinsk blast in February 2013.

Okay, so first, off: Don't panic! As impacts go, this was pretty small*. After all, you didn't even hear about until weeks after it occurred. Events this size aren't too big a concern. Had it happened over a populated area it would've rattled some windows and probably terrified a lot of people, but I don't think it would've done any real damage.

ALL EYES: Wildflowers burst forth in Death Valley super bloom

For comparison, the Chelyabinsk explosion, which was strong enough to shatter windows and injure over 1,000 people (due to flying glass), had an equivalent yield of 500,000 tons of TNT, 40 times the energy of this more recent impact.

The event was reported on the NASA/JPL Near-Earth Object Fireball page, which lists some of the brightest such things.

NASA / JPL

The statistics for the impact reported on the NASA / JPL fireball page.

NASA / JPL

The statistics for the impact reported on the NASA / JPL fireball page.

A little background: The Earth is bombarded by debris from space to the tune of about 100 tons every day. Most of this stuff is quite small, like the size of a grain of sand or smaller, and burns up 100 kilometers or so off the ground. We call the solid bit of debris a meteoroid, the bright phenomenon a meteor, and, if it hits the ground, a meteorite.

If the piece is bigger, it can get deeper into our atmosphere before burning up. Moving at orbital speeds, they can enter our atmosphere from roughly 10 to 100 kilometers per second. For comparison, a typical rifle bullet moves at 1 kps. As they plow into the air, they compress the gas in front of them violently, heating it up. This in turns heats up the meteoroid, which starts to glow. Material can vaporize and blow off (this is called "ablation"), and usually within seconds the meteoroid is either slowed so much it no longer glows, or it vaporizes entirely.

If it's much bigger, centimeters or more across, it can start to disintegrate as the air in front of it imparts enormous pressure on it. It flattens (called "pancaking"), and breaks up. Now we have several smaller pieces, and each starts to burn up; the increase in surface area means more heating and glowing, then those pieces break up and get smaller, and you get a runaway cascade. This happens very rapidly on a human timescale; the Chelyabinsk asteroid broke up is it came in and this was seen as a series of very bright pulses of light. It can happen so rapidly that it may as well be called an explosion; a huge amount of energy released all at once. In the end, the huge energy of motion (the "kinetic energy") is converted into light and heat (and also to break up the meteoroid).

Given the explosive energy of the Feb. 6 meteoroid, if it were made of rock like the Chelyabinsk asteroid then it was very roughly 5-7 meters across; the size of a large living room, say. I calculated that by a straight comparison to Chelyabinsk: We know that was from a rock about 19 meters across; the energy released scales as the mass, and the mass increases with radius cubed for a sphere. So this is all approximate with a few guesses thrown in, but it's probably close.

It would've been a dramatic sight to say the least. But, it happened about 1000 km off the coast of Brazil, ESE of Rio de Janeiro. That's far enough out over the ocean that it's unlikely anyone saw it. So how do we know about it?

Good question. The report came to the JPL folks via the US government; as you might imagine, various arms of the military are curious indeed about atmospheric explosions. However, not much information is revealed by the source; just the time, direction, explosive yield, and things like that. I can think of three ways to detect a big fireball in this case: Satellite observations, which would image them directly; seismic monitors, which can detect the explosion as the sound wave from the blast moves through the ground; and atmospheric microphones, which can detect the long-wavelength infrasound from an event. This may have been detected by any combination of these (though since it was over the open ocean, seismic monitors seen unlikely).

Impacts like this happen several times per year on average, with most going unseen. The Earth is mostly water, and even where there's land it's sparsely populated overall. Chelyabinsk was both relatively energetic and happened over a populated area (the city of Chelyabinsk has over a million people). Still, I would assume the military sees most if not all events this size, but chooses not to report them for their own reasons. I understand the desire for them to keep their technology and capabilities secret. It would be nice scientifically to have this data available, but then again they don't have to release any of it at all, so even having this much is better than nothing. And it's useful.

And as usual, all of this underscores the need to be on the lookout. A rock this small is almost impossible to see more than a few hours before impact, but the flip side is that it's also really unlikely to do any damage. But once they get into the 20 – 50 meter range that changes; explosions from impacts like that rival nuclear bombs. Happily, they're very rare — here we're talking fewer than once per century, statistically speaking — but it would be nice if we knew they were coming. It's hard to say just what we would do if we saw one, but right now we don't even have that option.

Tip o' the Whipple Shield to Ron Baalke.

* Astronomers call anything that hits our planet an impact, even if it burns up high in the atmosphere.

ALSO IN THIS SECTION

  1. Reynaldo Figueroa-Sanabria, accused of stabbing and killing John Travlos and Germana Morin aboard their houseboat in 2013, testified on his own behalf at his murder trial in Pinellas County this week. MARTHA ASENCIO-RHINE  |  Times
    It took the jury about four hours to find Reynaldo Figueroa-Sanabria guilty. Next they must decide whether to send him to Florida’s death row.
  2. Harold Fritz, 75, was awarded the nation's highest and rarest honor, the Medal of Honor, for his actions in 1969. The Army lieutenant saved his platoon during an ambush in the Vietnam war. He spoke to students at Farnell Middle School in Tampa. MARLENE SOKOL  |  Times
    Harold Fritz wanted to talk about teachers’ salaries and education. The kids wanted selfies with one of the 71 living recipients of the nation’s highest honor.
  3. PDQ's new Trinity location features a self-serve sauce bar with seven signature sauces perfect for dipping chicken tenders. Courtesy of PDQ
    Both chains are expanding locally and held grand opening celebrations this month with giveaways and free food.
  4. Casey Cane has resigned as chair of Pinellas County’s Housing Finance Authority in the wake of a Tampa Bay Times story about his failure to disclose an arrest for a financial felony when he was 19. He also serves as a Palm Harbor fire commissioner. Casey Cane
    Casey Cane failed to disclose his arrest for a financial felony in 2006. He said he didn’t think he had to reveal that information.
  5. Tampa Mayor Jane Castor speaks to about 75 people Tuesday at a city conference on innovation and collaboration. (City of Tampa photo by Janelle McGregor) Janelle McGregor
    City Hall brought together startups and the nonprofits that nurture them for a discussion of possible ideas to improve city operations and service.
  6. Scott Purcell, a senior geophysicist with GeoView, left, and Mike Wightman, president of GeoView, use ground-penetrating radar to scan a portion of King High School campus in search for Ridgewood Cemetery. OCTAVIO JONES  |  Times
    Preliminary answers from the ground-penetrating radar could come as soon as next week.
  7. A federal judge gas stayed the Nov. 7 execution of death row inmate James Dailey, 73, for the 1985 murder of 14-year-old Shelly Boggio. Left: Dailey at his 1987 trial, where he was convicted and sentenced to death. Middle: Dailey in 1993, when he was again sentenced to die. Right: The most current photo of Dailey on Florida's Death Row. Tampa Bay Times
    Dailey was set to be put to death Nov. 7. A judge ordered his execution to be postponed to give his attorneys time to present their claims. But the state can appeal.
  8. Markeith Loyd, suspected of fatally shooting a Florida police officer, attends his initial court appearance Thursday, Jan. 19, 2017, at the Orange County Jail, in Orlando, Fla. Loyd spoke out of turn and was defiant during the appearance on charges of killing his pregnant ex-girlfriend. He was injured during his arrest Tuesday night following a weeklong manhunt.
    The same jury found Loyd guilty last week of first-degree murder in the fatal shooting 24-year-old Sade Dixon outside her home in 2016.
  9. The new owner of a dilapidated mobile home park on Gandy Boulevard has sued the city of Tampa over a record-setting fine levied against the property for a massive tree removal in August. [CHARLIE FRAGO | Times]
    A Gandy Boulevard mobile home park owner is suing the city of Tampa over a record $420,000 fine .
  10. Dashboard camera video shows a Tampa police cruiser pursuing Dusharn Weems through a parking lot. A second later, Weems is fatally injured when the car strikes him. Courtesy Haydee Oropesa
    The family of Dusharn Weems, 23, claims an officer intentionally struck him after he was spotted driving a stolen car.
Advertisement
Advertisement
Advertisement