How Many Tiny Chelyabinsk-Class Asteroids Buzz Earth?

astroengine writes "The meteor that exploded over the Urals region of Russia in February was a violent reminder that our planet exists in a cosmic shooting gallery. Now, astronomers are focusing on these mysterious small and possibly dangerous objects in the hope of understanding what they are made of and what kind of threat they pose in the future. However, a recent paper accepted for publication in the Astrophysical Journal has identified a possible 'Achilles Heel' of visible light surveys. Using data from NEOWISE (the near-Earth object-hunting component of NASA's Wide-field Infrared Survey Explorer mission), there appears to be a bias in visible light asteroid surveys against finding small (100 meters) dark space rocks. 'With our previous NEOWISE studies, we found that about a third of NEOs larger than 100 meters are dark. It's possible that a population of smaller dark asteroids exists, but we don't have the right sample to test that theory with what we've done so far (in this research),' NASA JPL scientist and NEOWISE principal investigator Amy Mainzer told Discovery News. 'In my opinion it is probable that a similar fraction of small NEOs are dark, but the visible surveys are biased against finding them. They do find some but not many.' On considering the impact of the small Chelyabinsk object earlier this year, it is perhaps sobering to realize that while around 90 percent of NEOs with diameters larger than 1 kilometer are thought to have been discovered, less than one percent of asteroids the size of the Chelyabinsk meteor (17-20 meters in diameter) have been detected."

Comments

Asteroid class

[Curunir_wolf]

Chelyabinsk-class? So would that be the size of a large elephant, an olympic-sized pool, or a football field?

Re:Asteroid class

[P-niiice]

2.3 vwbeetles

Re:Asteroid class

[Razgorov Prikazka]

About 0.9999999999999 Chuck Norris that is...
That said, nothing is >1 CN except for CN himself of course

Re:Asteroid class

[MozeeToby]

I understand your complaint, I really do. But if they had said "15-20 meter" asteroid, no one would have any idea the destructive potential the asteroid poses. Since the primary topic of the article is that they want to gauge the danger that similarly sized asteroids pose, it makes sense to talk about asteroids using a known sample as a reference point. What they should have said was "looking for asteroids in the same size range as what caused the Chelyabinsk meteor" but that is several times longer and more awkward.

Re:Asteroid class

[ComputerGeek01]

If you think of "Class" in the same context as it is used when describing Naval ships then it seems to be an appropriate way to describe a meteor.

Re:Asteroid class

[TWiTfan]

It's half a football field smaller than a Plavnik class submarine, or 8 car-lengths.

Re:Asteroid class

[icebike]

But what they did say was:

"less than one percent of asteroids the size of the Chelyabinsk meteor (17-20 meters in diameter) have been detected."

Which wasn't that long and not all that awkward.

It is however, something of an un-provable statement.

Re:Asteroid class

[steelfood]

Chuck Norris > 1 CN only when he wants to be.

Re:Asteroid class

[khallow]

Meteor populations are based on a Poisson distribution. Here, that the log of the population of meteors vary inversely with the cross-sectional area of the meteors. It's a decent fit at the end we can observe.

Re:Asteroid class

[cusco]

I wonder how accurate our current asteroid population estimates are. When Shoemaker-Levy hit Jupiter astronomers were saying that it was a "once in a century, or maybe even once in a millennium" event. Since then we've seen the impact marks of at least three and maybe four more comparable strikes that we didn't see coming. When the first asteroid striking the moon was caught on film it was also thought to be a rare event, now we find that it's fairly common. It's possible that our current low rate of meteor strikes is a statistical fluke.

In related news

[symbolset]

Reports just in of a Torino 1 level asteroid to possibly hit in 2032. Just your garden variety 400m wide space pebble.

Re:In related news

[swb]

The news article said it would be 2.5 megatons of TNT, which I would equate to a 2.5 megaton nuclear bomb (which AFAIK, uses the same explosive yields).

While that would be, well, a disaster if it hit near something occupied, it seems too small to wipe out the earth.

Re:In related news

[Anonymous Coward]

that was a typo; they were off by an order of magnitude.. try 2500 megatons of TNT; much bigger than any bomb ever conceived.

Re:In related news

[bobstreo]

Yep, about 43 Tsar Bomba's

https://en.wikipedia.org/wiki/Tsar_Bomba

too many?

[green is the enemy]

Is it really practical to find and track these objects? There may be just too many of them. These small objects also probably have relatively unstable orbits, so would require constant observation not to lose them again.

Re:too many?

[RenderSeven]

Is it really practical to find and track these objects?

If you're applying for a research grant with a modest staff and tidy stipend? Then yes, absolutely!

Re:too many?

[VortexCortex]

Is it really practical to find and track these objects? There may be just too many of them.

Perhaps try looking at things from a different perspective: Is it really practical to keep living on one celestial object? There may be just too many threats to justify putting all your eggs in one basket. Uncoincidentally, more space faring capabilities will expand your threat tracking and deterrance options immensely. There is too many of them, only while there is only one of us...

Re:too many?

[mac.mcrae2623]

all it will take is one the size of the rock involved in the Tunguska event leveling a major city for countries to start pouring trillions into tracking and lasing these things. If we just put a portion of our military budget into tracking these smaller rocks - we would be much safer.

Does it matter?

[BenSchuarmer]

The Chelyabinsk asteroid scared a lot of people and injured a few people, but it wasn't nearly as destructive as your average day of Russian traffic.

Re:Does it matter?

[FireFury03]

The Chelyabinsk asteroid scared a lot of people and injured a few people, but it wasn't nearly as destructive as your average day of Russian traffic.

But if it had exploded (or impacted) over the centre of Moscow, London, Washington...

Re:Does it matter?

[cusco]

If it had come in over a major military base on either side the assumption would have been a nuclear attack, which worries me a lot more.

Invoking Betteridge's Law

[OglinTatas]

No

Seven

[geekoid]

is it seven? I'm going to guess seven.

Use Satellite orbiting other planet

[failedlogic]

One of the problems seems to be that the asteroid struck in day-time so was obscured by the Sun. The Sun seems to be an obstacle to proper tracking of these 'smaller' asteroids on Earth or using satellites orbiting earth.

I'm not suggesting this will be practical or affordable. Has there been any discussion of using a satellite to orbit the moon? Perhaps a potential use of deep-space probes like Voyager 1 will be to track these asteroids in the future (if V1 hasn't been doing this already).

Re:Use Satellite orbiting other planet

[cusco]

No, Voyager doesn't have the resolution. From beyond the orbit of Neptune it took a look back towards the Sun and took a panoramic shot of the Solar System. At that point Earth was barely 1/10 of a pixel in size, a "pale blue dot" as Carl Sagan referred to it. From its current location it couldn't even see a major comet at maximum brightness.

Bam!

[wonkey_monkey]

Right in the Urals.

Large Synoptic Survey Telescope

[Required Snark]

The LSST, which is scheduled to start operation in 2020 will do a complete (Synoptic) sky survey twice each week. It will be used for looking at transient events including supernovas and asteroids. It has features specifically intended for Near Earth Object Detection

The 100 meter limiting size for significant near-Earth asteroids corresponds to a limiting magnitude of 26. In addition, short exposures are needed since the asteroids trail very quickly at more than 20 second exposures. So large aperture is important. This instrument would be unique. Its utility is diminished if it cannot cover the entire visible sky several times per month as there would be no competing telescopes to cover its holes or even follow its discoveries. At the present time, systematic surveys like Spacewatch have difficulty finding all 21st magnitude near-Earth Asteroids.

With its capability to detect objects as faint as 25th magnitude in 15 seconds, only the LSST will be able to find virtually all significant PHAs 100 meters in size and over 50% of all NEOs 100 meters in size. During its survey of the sky LSST can find 90% of the PHAs over 140 meters in diameter.

A PHA is a Potentially Hazardous Asteroid.

The Chelyabinsk meteor had an 85 meter size, so it would most likely not be found by LSST. There are some other studies to use satellites in the IR band to look for smaller size objects.