Chelyabinsk meteorite fragment

Some of our readers will recall the work we did on the Chelyabinsk meteor event that occurred on 15th February 2013. Now it has been reported in the Russian media that a large meteorite fragment has been collected from an impact point in the lake. The piece weighed over half a tonne and measured between 1 and 2 metres in size. During the recovery and assessment operation, the piece fractured. Representatives from the Chelyabinsk State University have confirmed that the piece is a fraction of the Chelyabinsk event and is, to date, the largest meteorite fragment related to that event. In fact, it is also one of the largest meteorite pieces found.

Meeting at Kirkkonummi

A joint workshop was held between Sodankylä Geophysical Observatory (SGO) and the Finnish Geodetic Institute (FGI) at Kirkkonummi. The purpose was to consider together how EISCAT, KAIRA and EISCAT_3D will make better orbit determinations for Space Rocks, meteoroids, temporarily captured objects, space debris and small asteroids. The pizza boxes of course allow working during lunch break, too!

Joint FGI/SGO working meeting. (Photo: E. Turunen)

Rocks in our Solar System

There will be a special session at the European Week of Astronomy and Space Science (EWASS 2013) to discuss "Rocks in our Solar System - bridging the gap between meteor, meteorite and asteroid studies".

EWASS 2013 is being held on 8 - 13 July 2013, Logomo Centre, Turku, Finland, and this special session will be held on Friday, 12 July. The session will bring together scientists working on all aspects of Solar System rocky material properties. The topic includes laboratory analysis of meteorites and cosmic dust as well as observations and modeling of both meteoroids and asteroids. The contributions bridging the gap between properties of meteors, meteorites and asteroids are highly welcome.

The session will also focus on recent Chelyabinsk fireball / meteorite fall event in order to put together knowledge acquired from studies of fireball trajectory, orbital analysis, and recovered meteorites.

Abstract submission, registration, and conference programme is available on the EWASS 2013 main page.

Session details: http://www.physics.helsinki.fi/conf/EWASS2013

Closing the loop... a fragment from Chelyabinsk

Today at the EISCAT_3D User Meeting, held in Uppsala, we've had a plethora of fascinating presentations and discussions. There has been plenty of interesting information, and we've learned a lot. However, for me at least, the best talk has been given by Maria Gritsevich. Her presentation was entitled "Physical properties of meteoroids based on observations" and discussed a number of meteoroid events as well as some theoretical considerations of such events and where radar observations fit in with the ongoing research effort.

However, what made this presentation special was the reference to the Chelyabinsk meteor event. As our regular readers will remember, we were caught up in the initial investigation of that event, as it was coincidentally on the same day as our observations 2012 DA14. That lead to our team doing that initial work on disassociating the meteor event and the asteroid and the initial trajectory and size calculations.

Since then, many other researchers have become involved in the event and the subsequent detailed analysis. And today's presentation was a good chance to reflect the progress that has been made.

Maria Gritsevich giving the presentation of meteoroid research.

And, to top it off... the speaker had brought in a fragment from the Chelyabinsk event to pass around.

A fragment of the Chelyabinsk event.

It was indeed a strange experience to hold this tiny fragment from such a dramatic event that caused such upheaval on that cold February morning, not so long ago.

Meteoroid strikes Saturn's rings

Recently, scientists have been investigating something strange with the rings of Saturn. These are strange lines that appear... quite brightly too. It is now believed that these are debris clouds, formed when meteoroids impact with the material in the rings themselves. An news item has just be posted up on the U. Oulu website about this exciting finding and announces the article that has been published on 26th April, with contributions from J. Schmidt from the University of Oulu. Quoting from it...

Meteoroids, for instance visible as bright meteors in earths atmosphere, exist all over the Solar System and it has long been anticipated that they constantly erode Saturn's rings. The rings are made of water ice particles that are partly pulverized when struck by an impact of several tens of km/s. The erosion rate of the rings, and also their pollution with external material provided by the meteoroids, is of ultimate importance for the ongoing controversial scientific debate on the age of Saturn's ring system and how it has been created.These debris clouds, providing direct evidence for the meteoritic ring erosion, were observed now for the first time. This was possible in images taken at a very special geometry, when in 2009 the sun was illuminating the Saturn system edge on, which happens only every 15 years. In this geometry the rings remain relatively dark, while the debris still stands out in full sunshine above the ring plane, making the detection possible.

 Full details:

http://www.oulu.fi/english/news/2013/04/meteoroid-impacts-shatter-saturns-rings

Dash-cam astronomy

One of many YouTube-posted videos. A GPS- or GLONASS-set
clock would have provided accurate time information though and
location and direction would have also helped us enormously.

The recent Chelyabinsk event demonstrated the power of distributed sensors for reconstructing incidents after the event. With cheaper and cheaper consumer electronics, miniaturisation, lower power requirements and the increasing distribution of these systems across the world, it is clear that we are entering a new era of Earth (and sky!) observation.

So, what is needed?

Firstly, there is the image itself. This is now widely available with resolutions and linear-responses far exceeding anything that astronomers could only dream of a few decades back. Generally speaking, there is no need to "flat-field" images or remove artefacts. The dynamic range continues to improve as well, making them increasingly sensitive to relatively faint events.

Then there is time. Most of these systems now have built in clocks which can stamp the image with the date and time. Although may have this information on the associated image files, it is embedding the information visually within the image that then allows others to derive useful scientific information. Some require manual date and time setting, which is subject to error and inaccuracy. Better still is a system which synchronises to satellites (GPS, ГЛОНАСС/GLONASS, etc.).

Which brings us on to position. Knowing the view point of the observation is also an extremely useful piece of information. It was the association of  Chelyabinsk videos with known land marks that made it possible for us (with no local knowledge whatsoever) to find references and therefore establish positional information. Again, by embedding this information visibly in the image it removes the need for the camera user to post this meta-data separately (thus saving time, making it easier and also reducing risk of errors).

Direction is also a useful piece of information and can supplement information, especially if other records of the event are scarce. For our own assessment of the Russian meteor, it certainly would have helped in the early stages (when were we trying to dis-associate the meteor with 2012 DA14), although later data helped clear this up. In some cases, this can be done by hand. If lucky, it may even be able to be solved automatically (such as with the astrometry.net project).

Image scale is the final thing that lets us work out the reference frame. This is especially important in wide-field images, which often have large amounts of pin-cushion distortion.

Whether dash-cams, all-sky cameras, CCTV, or from the hand-held devices of quick-reflexed users it is inevitable that there will be a rise in the quantity and distribution of sky data. No doubt, the ubiquity of computing, the influence of social internet media and a growing awareness of the public will contribute to a very new and fascinating era of incident astronomy.

Understanding the terms

Asteroids? Or Small Solar System Bodies?
(Image: Wikipedia)

Over the past few days, there has been a bit of confusion over the difference between the Chelyabinsk event (a meteor) and the 2012 DA14 flyby (a small asteroid)

How we classify the objects in our Solar System is defined by the International Astronomical Union (IAU). In 2006, they voted on a modification to the system previously used. This resulted in the nomenclature that scientists now use today.

Starting with the largest, the objects are:

Planets must orbit the sun, must have achieved "hydrostatic equilibrium" (that is, they are more or less round) and have "cleared the neighbourhood of its orbit". In other words it must be the dominant gravitational force in that orbit area. There are currently 8 recognised planets around our Sun (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune).

Dwarf Planets are the next category. These orbit the sun and have achieved hydrostatic equilibrium, but they have not cleared the neighbourhood of the orbit. At the moment the IAU recognises five dawrf planets (Ceres, Pluto, Haumea, Makemake, Eris), although more are likely to be added to the list as we discover them or as other unclassified objects are evaluated.

There there are the Small Solar System Bodies. Essentially, this is everything that orbits the sun, that is not in the first two categories. So this includes comets and asteroids.

Comets are typically made of ice and dust. Their distinguishing feature is that they  have a coma or tail. This is caused by solar radiation vapourising volatile material.

And then the others are asteroids; chunks of inert rock.

There are a few terms around which have been used in the past, but are no longer recommended by the IAU. Examples include "minor planet", "meteoroid" or "planetoid".


2012 DA14 and the Chelyabinsk meteor were both asteroids and, thus, small solar system bodies. The difference is that 2012 DA14 missed the Earth during the recent flyby, whereas Chelyabinsk did not. This brings us to meteors and meteorites.

When an object enters the Earth's atmosphere, the friction of the entry can sometimes be sufficient to heat it to cause it to give off light. This visible "streak across the sky" is a meteor. Particularly bright ones are often referred to as fireballs.

This heating usually causes the object to burn up completely. Thus, it never reaches the ground.

However, if the object survives the burning in the atmosphere, and survives the impact as well, then it is called a meteorite.

The Chelyabisk event is definitely a meteor. At present there are searches being carried out to try to find debris on the ground, with some candidates having been collected. This is an on-going effort and no doubt more news will come from this during the next few weeks.

However, the bulk of the original object was destroyed on entry and, as yet, no substantial fragments have been found on the ground. Thus it continues to be referred to as the "2013 Russian Meteor" for the time being. However, that may change!

References

• http://www.iau.org/
• http://solarsystem.nasa.gov/
• http://en.wikipedia.org/wiki/2012_DA14
• http://en.wikipedia.org/wiki/2013_Russian_meteor_event

Request for data — other meteor events?

We are now investigating reports of other events that might be related to the Chelyabinsk Meteor. Although we have discounted the possibility of any relationship between the Chelyabinsk event and 2012 DA14, there are several other reports that we are looking into.

Another bolide? And is it related to the Chelyabisk event? (Image: proufu,ru, LINK)

The above image is from a single dash-cam report from the Bulgakovo Ufimsky District (Russian: Булгаково Уфимского района). The time for this was approx. 19:43 of 11-Feb-2013, placing it well before the Chelyabinsk event. Irregularities in the video, and discrepancies with the event suggest that it may be a hoax.

However, if you know of additional supporting (or discrediting) evidence for this or other events, you can let us know either by posting a comment below, via Twitter @KairaProject or by contacting the project directly. Many thanks!

Size estimates for the Chelyabinsk event

There are several sets of video footage with audio. Just a few examples include:

• http://www.youtube.com/watch?v=N8Z3giHwcYg
• http://www.youtube.com/watch?v=LS3yFNjiVT8
• http://www.youtube.com/watch?v=xPe9uOGOhkg

The have audio blasts at various intervals. What is unknown, however, is their location with respect to the incident vector of the meteor. There is one super-loud explosion which is followed by various minor secondary noises. This is somewhat confused by echoes, local noise (e.g. falling debris), microphone noise, etc. These follow for many seconds after the main event.

The blast is not the meteor hitting objects, but rather the shock wave from the air burst. The meteor explodes during re-entry due to thermal stress. Essentially the surface of the meteor is super-heated due to friction against the atmosphere during re-entry. The interior, however, will still be extremely cold.

Relying only on reports, and in the absence of any confirmed finds of fragments, we can only estimate the composition. However, it is more likely to be a stony meteor based on the explosion and statistical likelihood, given the populations of this size of small object in the solar system.

There are no reliable reports of craters. The smoke trail burns out at high altitude, and while fragments may certainly have reached the ground, these will be at terminal velocity free fall (and also relatively cooler). The smoke trails indicate that the air-burst was occurring several kilometres up in the atmosphere.

The initial impact angle (on the atmosphere) will be around 50 degrees. This is based on the radiant location and the distance from zenith (earth travel direction). There is still a good degree of uncertainty in this, though, due to lack of precise information about the incoming orbit. There is a large error associated with this though and it remains a weak point in our findings. Impact velocity is probably 25 km/s. This is based on fact that the earth is moving at about 20 km/s and the impact is coming from the sun-side.

Based on these assessments, particularly audio shock information, and correlating damage reports, we can revise our estimate to make it larger than our first estimate.

Again, we must stress that the associate errors with these estimates remain large, but we are probably looking and initial object size of 10 to 20 metres across.

We will continue to provide updates and we continue to process the information that we have.

Difficulty estimating size

In addition to the question of the meteor trajectory, we have been trying to estimate the size of the object. This is extremely difficult as there are a large number of parameters that can affect the result of any impact.

Of course, for the Chelyabinsk event, we are trying to work backwards, based on reports, video footage, and any other data we can obtain. In the excitement of the moment, we need to bear in mind that some reports can be exaggerated in the excitement, so it is necessary to be cautious.

The result of the impact can be affected by the size and density of the object. How it is formed (and how it fractures) can be significant. Video footage from some angles suggests that the object split into two roughly equal parts (based on smoke patterns). There have been suggestions of fragments (and even a crater!), but we don't have any details. When confirmed, this will be critical in not just size estimates, but also in improving our estimate of the trajectory.

The velocity of the object is also of importance. Faster moving objects will do more damage. Therefore, for an equivalent explosion, a slow-moving fragment would be comparatively bigger than one that was fast moving. The movement of the Earth through the Solar System means that "near dawn" events may be compounded by the "head-on-collision" effect. Again, as our knowledge of the trajectory improves, so too will our impact parameter set.

As more data comes to hand, we will continue to revise our information and will post something when we can.

However, the Chelyabinsk event is certainly much smaller than the 2012 DA14 asteroid.

Are 2012 DA14 and the Chelyabinsk meteor related?

This morning, there was a spectacular meteor event over the city of Chelyabinsk, unfortunately resulting in damage and injuries. Of course, with the increasing attention around the asteroid 2012 DA14, this event has immediately sparked the question if the two are related.

They are not.

The reason that we can discount the possibility of the two being associated in any way can be reduced to the following reasons.

Firstly, we need to look at the trajectories. The asteroid 2012 DA14 is approaching from the south. It will slingshot past the Earth and continue rising to the North.

However, the Chelyabinsk event is coming from a different direction. The city is at 55°09′N 61°23′E and the event radiant (the position of origin of the meteor) is above and to the left of the rising sun.

Early appearance of the meteor.

General trajectory.

This puts the meteor origin/radiant at approx. RA 22h and Dec +10.

UPDATE at 10:25 GMT: Revised estimate is now approx, RA 22h Dec +20°

UPDATE: Improved radiant estimate.

Piecing this together is difficult, as video footage does not always come with an associated position. Angle and direction needs to be calibrated from nearby objects (buildings, people, etc.) and using these are ways of estimating scale. Also, we do not always know the location of the observer, which introduces additional uncertainty. Fortunately, as more footage is being posted, we are getting a better estimate of the origin of this meteor.

However, even with the uncertainty, this is still in a COMPLETELY different direction.

Also, we can consider the timing of the events. The closest approach of 2012 DA14 will occur at approximately 19:24 UTC. The Chelyabinsk event occurred at about 9:20 am local time... which is 03:20 UTC. (UTC is Coordinated Universal Time, and provides a common time-zone to allow the comparison.)

If we consider the difference, it is approximately 18 hours. The asteroid is travelling at approximately 8 km/s and, if the Chelyabinsk object was related, it would have required a deep space velocity of about the same. Even if the two were related, this would put the two objects some half a million km apart.


In any case, the two events are not related.

This is just a VERY unusual coincidence.

API

This week me and Antti Kero are up in Tromsø doing artificial periodic irregularity (API) experiments with the EISCAT heater, which has recently been upgraded to include a radar receiver.

The idea with the experiments is to first produce a standing wave in the ionosphere, which heats up the plasma, and creates small enhancements of electron density at lambda/2 intervals. These irregularities are then probed with short radar pulses, which are used to probe the decay time of the irregularities. From this, it is possible to determine several ionospheric parameters: ionospheric chemistry, electron density, winds, and neutral density.

5.423 MHz X-mode API echo. There is also a meteor head echo accompanied with a decaying trail echo in this measurement.

We managed to actually get an API echo on our first try! Here is a picture from our second day of measurements. This is an API echo with 5.423 MHz at X-mode heating and probing polarization. We were also lucky to observe a meteor head echo and associated trail echo.

Do meteors smoke?

Meteor smoke originates to the meteor ablation which takes place typically between 70 and 120 km. Estimates for the total meteoric input to the atmosphere vary from few tens to hundreds of tons per day.

After metal species are evaporated into atoms they start to interact with the atmospheric species forming metal oxides, hydroxides and carbonates which tend to coagulate by Brownian collisions into nm-scale particles called meteor smoke. Formation of the smoke takes place in timescales of a week, while the meteor smoke is redistributed by the global air circulation to maximize its concentration in the polar wintertime. In fact, due to sedimentation of the large meteor smoke particles, some fraction of the smoke will eventually enter to the ground level, especially in the polar regions and found from the ice-core drilling samples.


In general, the meteor smoke particles are of versatile scientific interest in the upper atmospheric research. As said, meteor smoke plays a key role in the chemistry of metallic species. Meteoric dust is thought to play a role in formation of noctilucent clouds and closely related anomalous polar mesospheric summer (and possibly winter) radar echoes (PMSE and PMWE). Charged meteor smoke particles, positive or negative, obviously contribute to the electron density budget of the D-region ionosphere which must be taken into account in the modelling. Despite of the scientific interest, relatively little is known about the meteor smoke properties. Even the fundamentals, like the actual chemical composition, size distribution, charging and finally what is the daily meteoric input to the atmosphere - all these are more or less open questions at the moment.

Charged meteor smoke can be detected in the incoherent backscattering as a narrow peak in the ion line. Novel radar techniques applied in the KAIRA will potentially provide a new insight to the meteors smoke and its role in the polar atmosphere.

Related links: http://www.sgo.fi/~j/kaira_ks.png