A very unusual fireball over NW Europe on 22 September 2020 (that went in and out of the atmosphere again)

 

The fireball of 22 sept 2020, ~3:53:40 UT. Image (c) Cees Bassa (stack of 2 images)

In the early morning of 22 September 2020, around 3:53:40 UT (5:53:40 local time), a very unusual long duration fireball appeared in the skies of NW Europe. It had a duration of over 20 seconds, and for several Dutch all-sky meteor camera's that captured it, it was a horizon-to-horizon event.

In this blog post, I provide a preliminary analysis of (mostly) Dutch camera records of this fireball. As it turns out, the meteoroid survived its brief passage through the upper atmosphere and came out unscathed at the other end!

The image above (which is a stack of two images, each showing a part of the trail) was captured by the all-sky camera of Cees Bassa in Dwingeloo, the Netherlands. The image below is one of several images captured by the cameras of Klaas Jobse in Oostkapelle. Other Dutch photographic meteor stations that caught it were that of the Bussloo VST (Jaap van 't Leven), Twisk (Marco Verstraaten) and Utrecht (Felix Bettonvil). Oostkapelle delivered both the sectored all-sky image below, and additional widefield images. A wide-angle image taken from Over in the UK by Paul Haworth was also kindly made available for analysis.

 

Click to enlarge

This was a fireball that entered the Earth's atmosphere under a very shallow, grazing angle: a so-called 'earthgrazer'. Because of the horizon-to-horizon aspect, I immediately suspected that this could be a very rare subcategory of 'earthgrazer': for a few of these have been known to enter the atmosphere, reach a lowest point above earth surface, and then leave the atmosphere at the other side again! 

 In other words, the situation of the schematic below:

 

The most famous case of this kind is the 1972 Grand Tetons daylight fireball (the first with instrumental records), but there have been a handful more since.

Analysis shows that the fireball from 22 September 2020 indeed belongs to this rare class of objects. The meteoroid approached the earth surface to a minimum distance of 91.7 km and then left the atmosphere again, on an altered orbit.

The Dutch photographic images plus Paul Haworths' image from the UK document some 745 km of ground-projected trajectory. The fireball moved from East-Northeast to West-Southwest, over Germany, the Netherlands, the southern North Sea basin and Britain. 

AOS from the photographic images was at 101 km altitude over Germany, around 53^o.26 N 10^o.22 E near Lüneburg just south of Hamburg. LOS was at 105 km altitude around 51^o.98 N 0^o.60 W, between Luton and Milton Keynes in the UK. 

The point of closest approach (indicated by a cross in the map below) was near 52^o.80 N 5^o.23 E at 91.7 km altitude above the geoid, over Lake IJssel in the Netherlands, not too far from the Twisk camera station which had it nearly overhead.

Click to enlarge

As this was a horizon-to-horizon event, it is likely that the actual trajectory started a bit more eastwards, and ended a bit more  westwards (although Paul Haworth's image shows that by the time it left view of his camera in the UK, the object was rapidly fading).

The plot below shows the atmospheric altitude of the fireball along its ground track. It reached a lowest point at 91.7 km (where it was moving parallel with the earth surface), and then moved away again, surviving the close encounter:

 

Click diagram to enlarge

Note that the trajectory was, of course, not as 'curved' as the diagram might suggest: the fireball was moving along a nearly straight path and the 'curve' in the diagram is in reality due to the curved earth surface below it (incidently proving again that Flat Earthers are wrong)!

The Twisk, Oostkapelle and Utrecht camera's had an electronic periodic "shutter" in front of the sensor, providing speed data for this fireball. The fireball entered the atmosphere with an initial speed of 33.6 km/s. It barely slowed down during it's grazing encounter with our atmosphere, leaving it again at a speed of ~30 km/s. It hence was too fast to be captured by the Earth: it moved on in a heliocentric orbit after the encounter.

The object was likely not particularly big. Some first quick calculations suggest something in the 20-40 cm range for the initial pre-atmospheric size (but this will need more study). The object was not very bright (Klaas Jobse, who saw it visually, estimated a brightness of magnitude -5) and it did not penetrate deep into the atmosphere. There will obviously have been some mass ablation, but probably limited: a sizable part of the original mass should have survived and moved along into space again.

The observed radiant of the fireball was near RA 163^o.7, DEC +6^o.4. It's geocentric radiant was near RA 165^o.8, DEC +3^o.5. The fireball hence came out of the direction of the sun (the sun was at RA 179^o.4, DEC +0^o.2 at that moment). 

click map to enlarge

 

The orbit calculated from the 33.6 km/s initial speed and the geocentric radiant of the fireball using METORB 10, is a short-period cometary orbit of the Jupiter family type (Tisserand 2.8) close to the 13:4 orbital resonance with Jupiter. The descending node of the orbit is close to Mercury, so it could have had close encounters to this planet in the past. Perihelion was at 0.30 AU, aphelion at 4.45 AU with an orbital inclination of 3^o.4 and orbital eccentricity of 0.87. The object passed perihelion on August 12.

 

click to enlarge

 

These results are preliminary, although probably close to the eventual values. The standard way of reconstructing meteor trajectories (the intersecting planes method) which I used here works fine for regular meteors, but for meteors with these extremely long, very shallow trajectories, the trajectory can get a  non-negligible curvature due to gravity. This effect is small, but I nevertheless want to re-analyze the trajectory the coming month, splitting it up in parts, so that I can account for this curvature. It will be interesting to see what the effect is on the position of perigee (the point of closest approach to earth), and on the radiant position.

Added note:  

Jelle Assink of the Royal Dutch Meteorological Institute (KNMI) reported on Twitter that infrasound from this fireball has been detected.

(a few small edits and additions have been made after this blogpost was originally posted)

Acknowledgement: 

I thank Paul Haworth, Cees Bassa, Klaas Jobse, Marco Verstraaten, Jaap van 't Leven and Felix Bettonvil for making their imagery available for analysis.

California 30 January 12:30 UT: the "space debris" reentry that wasn't

On 30 January 2020 near 12:30 UT (10:30 pm PST), a bright, slow, spectacularly fragmenting fireball swooped over southern California. It was seen and reported by many in the San Diego-Los Angeles area. The video above was obtained by a dedicated fireball all-sky camera operated by Bob Lunsford. The fireball duration approached 20 seconds.

In the hours after the fireball, the American Meteor Society (AMS) initially suggested that this was a Space Debris reentry, i.e. the reentry of something artificial from earth orbit.

But it wasn't.

Immediately upon seeing the video, I had my doubts. Upon a further look at the video, those doubt grew. To me, the evidence pointed to a meteoritic fireball, a slow fragmenting fireball caused by a small chunk of asteroid entering our atmosphere.

A discussion ensued on Twitter, until NASA's Bill Cooke settled the issue with multistation camera triangulation data, which showed that this was an object from an Apollo/Jupiter Family comet type heliocentric orbit with a speed of 15.5 km/s. In other words: my doubts were legitimite. This was not a space debris reentry but indeed a chunk of asteroid or comet.

I've already set out my argumentation about my doubts on Twitter yesterday, but will reitterate them again below for the benefit of the readers of this blog.

My doubts started because while watching the video I felt that the fireball, while slow and of exceptionally long duration, was still a tad too fast in angular velocity in the sky, and too short in duration, for this to be space debris. In the video, it can be seen to move over a considerable part of the sky in just seconds time.

The image below shows two stills from the video 6 seconds apart in time. The fireball passes two stars, alpha Ceti and beta Orionis, that are 35 degrees apart in the sky, and it takes the fireball a time span of about 6 seconds to do this, yielding an apparent angular velocity in the sky of about 5-6 degrees per second. That is an angular velocity that is a factor two too fast for reentering space debris at this sky elevation, as I will show below.

stills from the fireball video, 6 seconds apart, with two stars indicated

Orbital speed of a satellite is determined by orbital altitude. Reentering space debris, at less than 100 km altitude, has a very well defined entry speed of 7.9 km/s. This gives a maximum angular speed in the sky of about 5 degrees/second would it pass right above you in the zenith (and only then): but gives a (much) slower speed (2-3 degrees/second) when the reentry is visible lower in the sky, such as in the fireball video.

To gain some insight in the angular velocity a reentering piece of space debris would have at the elevation of the California fireball, I created an artificial 70 x 110 km reentry orbit over southern California that would pass the same two stars as seen from San Diego.

The map below shows that simulated track, with the object (marked by the green rectangular box) at 70 km altitude and positioned 6 seconds after passing alpha Ceti (marked by the green circle):

Simulated reentry track. click to enlarge

The angular velocity in the sky for a reentering object at this sky elevation suggested by this simulation is barely half that of the fireball. During the 6 seconds it took the fireball to move over 35 degrees of sky passing alpha Ceti and beta Orionis, the simulated reentering object would have moved over only 15 degrees, i.e with an angular velocity of 2.5 degrees/second rather than the 5-6 degrees/second of the fireball.

So this suggested that the fireball was moving at a speed a factor two too high for space debris. This therefore pointed to a meteoritic fireball, not a space debris reentry.

There were other reasons to doubt a reentry too. There were no matching TIP messages on Space-Track, the web-portal of CSpOC, the US military satellite tracking network. A reentering object as bright as the fireball in the video would have to be a large piece of space debris: this bright is clearly not the "nuts and bolts" category but suggests a large object like a satellite or rocket stage. It is unlikely that CSpOC would have missed a reentry of this size.

To be certain I ran a decay prediction on the full CSpOC catalogue with SatEvo myself: no object popped up that was expected to reenter near this date either, based on fresh orbital elements.

The fragmentation in itself, one of the arguments in the AMS' initial but mistaken conclusion of a "space debris reentry", is not unique to space debris reentries. It is also a common occurence with slow, meteorite dropping asteroidal fireballs, especially when they enter on a grazing trajectory. Take the Peekskill meteorite fall from October 1992 for example:




Likewise, while a 20-second meteor is not everyday, it is not a duration that is impossible for a meteor. Such durations (and even longer ones) have been observed before. Such long durations are especially the case with meteors that enter in a grazing way, under a shallow angle.

At the same time, a 20 seconds duration would be unusually short for a satellite or rocket stage reentry. Such reentries are usually visible for minutes, not a few seconds or a few tens of seconds.

So, to summarize:

1) the angular velocity in the sky appeared to be too large for space debris;
2) the fireball duration would be unusually brief for space debris;
3) and there were no obvious reentry candidates.

On the other hand:

a) the angular velocity would match those of slow ~15 km/s meteors;
b) the 20 second duration, while long, is certainly not impossible for a meteor;
c) the fragmentation observed occurs with slow asteroidal origin meteors as well.

Combining all these arguments,  my conclusion was that this was not a space debris reentry, but an asteroidal origin, slow meteoritic fireball. This was vindicated shortly later by the multistation camera results of Bill Cooke and his group, which yielded an unambiguous speed of 15.5 km/s and as a result a heliocentric orbit, showing that this was not space debris but a slow chunk of asteroid or Jupiter Family comet.

In defense of the American Meteor Society (who do great work on fireballs): it is not easy to characterize objects this slow, certainly not from single camera images and visual eyewitness reports. Given the slow character and profuse fragmentation, it is not that strange that the AMS initially (but incorrectly) thought it concerned a space debris reentry. It does go to show that you have to be extremely careful in drawing conclusions about slow moving fireballs: not every very long duration fragmenting fireball is space debris.

OT: the bright fireball of 29 June 2018, 21:30:14 UT

image (c) Felix Bettonvil, Utrecht. Click to enlarge

Barely two weeks after an earlier brilliant twilight fireball discussed in a previous post appeared over the Netherlands, another bright fireball was observed, again in bright evening twilight. This fireball of about magnitude -6 occurred on 29 June 2018 at  21:30:14 UT (23:30:14 local time). It had a duration of over 3.6 seconds.

The fireball was photographically well covered this time, as it was captured by six all-sky meteor cameras (Borne, Bussloo, Dwingeloo, Ermelo, Utrecht and Wilderen) plus by an amateur astronomer from Kerkrade who was making a time lapse of the night sky. The image above (courtesy of Felix Bettonvil)  shows the fireball as it appeared over the camera station in Utrecht. Almost literally right over it: the lateral distance between the camera position and the nominal ground projected meteor trajectory is only 185 meters!

As several stations were equipped with an electronic or rotating shutter in front of the lens (see the interuptions in the trail in the image above, at 10 breaks/second), there is speed information for this fireball as well. In fact, it delivered a very fine deceleration curve (data from stations Borne, Utrecht and Dwingeloo), showing how the meteoroid rapidly slowed down upon entry into the atmosphere due to friction with the atmosphere:

click diagram to enlarge

click to enlarge

The fireball entered from the south-southeast with a  speed of 21.5 km/s and under a low 27 degree entry angle. It first became visible at 80 km altitude over the Betuwe area near 5.416 E, 51.822 N. It ended at 43 km altitude over the western suburbs of Amsterdam, near 4.837 E, 52.360 N, with an end speed of 9 km/s. End altitude and end speed point out that nothing was left at that point: there are no meteorites on the ground.

click to enlarge

The radiant of the fireball is located in Scutum: the geocentric radiant is at RA 276.4, DEC -11.4, with a  geocentric velocity of 18.2 km/s. The resulting orbit is an Apollo orbit with an orbital inclination of 7 degrees, an orbital period of 2.15 years and aphelion at 2.7 AU. The object was hence of asteroidal origin: a very small piece of asteroid.

click to enlarge

Acknowledgement: I thank Mark-Jaap ten Hove, Johan Pieper, Koen Miskotte, Jean-Marie Biets, Felix Bettonvil and Peter van Leuteren for making their imagery available for analysis.

OT: The brilliant fireball over the Netherlands of 21 September 2017, 19:00 UT, a piece of comet Encke

The fireball as photographed from Ermelo, the Netherlands. Image (c) Koen Miskotte

In the evening of 21 September 2017 at 21:00:10 CEST (19:00:10 UT), a brilliant fireball, as bright as the first quarter moon, appeared over the Netherlands. It was widely seen and reported and garnered quite some social media and press attention (e.g. here). The next day I was live in a Dutch TV program to talk about it.

The fireball was captured by six all-sky camera stations of the Dutch-Belgian all-sky meteor camera network operated by amateurs of the Dutch Meteor Society and KNVWS Meteor Section: stations Ermelo, Oostkapelle, Borne, Utrecht, Twisk and Wilderen, operated by respectively Koen Miskotte, Klaas Jobse, Peter van Leuteren, Felix Bettonvil, Marco Verstraaten and Jean-Marie Biets.

The image in the top of this post shows the photograph taken by the all-sky camera in Ermelo (courtesy Koen Miskotte), where the fireball appeared almost right overhead. The image below was taken by the all-sky camera in Utrecht (courtesy Felix Bettonvil), showing it slightly lower in the sky (click the images to enlarge).

The fireball as photographed from Utrecht, the Netherlands. Image (c) Felix Bettonvil

In the photographs above, the "dashed" appearance of the fireball trail is caused by an LCD shutter between the lens and the camera CCD, which briefly interupts the image at a set interval. For Ermelo this was 14 interuptions per second, for Utrecht 10 interuptions per second.

Knowing the shutter frequency you get the duration of the fireball by counting the number of shutter breaks in the trail: in the case of this fireball, it lasted over 5.3 seconds. Together with triangulation information on the path of the trail in the atmosphere, it gives you the speed of the fireball in km/s, which is necessary to calculate the orbit in the solar system. It also provides you with information about the deceleration of the meteoroid in the atmosphere. In this case, it entered the atmosphere with a speed of 31 km/s and by the time it had completely burned up at 53 km altitude, the speed had decelerated to 23 km/s.

The fireball fragmented into pieces quite early during its atmospheric entry. Some of these fragmentation events can be seen as brief brightenings (flares) in the images.

Triangulation of the six all-sky images yields the following atmospheric trajectory:

Atmospheric trajectory of the fireball, calculated by the author. Camera stations in yellow.

The  fireball moved almost due east-west. It started over Deventer, crossed over southern Amsterdam and Schiphol airport, and ended over sea. The end altitude at 53 km and end speed of 23 km/s indicate that nothing was left of the original meteoroid by the time the fireball extinguished: no meteorites reached earth surface, it completely ablated away.

The apparent radiant of the fireball was located low in the sky, at 16 degrees elevation and almost due east. The grazing entry into the atmosphere resulted in a long trajectory length of over 150 km.

The geocentric radiant of the fireball is located on the Pegasus-Pisces border, just north of the ecliptic. The radiant and speed, and the resulting orbit in the solar system, show that this was an early member of the northern branch of the Taurid stream complex, a meteor stream complex associated with comet P/Encke. It is active from September to December with a  peak in activity in November. The stream is broken up in several substreams, and the early Northern Taurids from September are sometimes called Northern delta Piscids, one of these substreams in the Taurid complex.

The radiant position and heliocentric orbit for this fireball are shown below.

apparent (observed) and geocentric radiant of the fireball

calculated heliocentric orbit of the meteoroid

Acknowledgement: I thank the photographers (Koen Miskotte, Klaas Jobse, Peter van Leuteren, Felix Bettonvil, Marco Verstraaten and Jean-Marie Biets) for providing their imagery for this analysis.

OT: the slow, 13.8 second duration earthgrazing fireball over the Netherlands of 28 Nov 2016, 04:40 UT

the long duration (13.8 s) fireball of 28 Nov 2016, 4:40 UT 
image (c) Jos Nijland, Benningbroek, NL - click to enlarge

In the early morning of 28 November 2016, near 04:40 UT (05:40 am local time), a bright, slow fireball with an extremely long duration occurred over the Netherlands.

The image above was captured by the all sky meteor camera of Jos Nijland in Benningbroek and shows how the fireball trajectory spanned much of the sky. This camera was  equipped with a rotating shutter, and the number of breaks visible in the trail amount to at least 13.8 seconds visibility. That is very long for a fireball.

With such slow, long duration fireballs, one of the first questions asked usually is: is it a meteor, or is it the re-entry of artificial space debris? In this case, the analytical results clearly show it was not an artificial object, but a meteoric fireball of asteroidal origin - i.e. a small chunk of asteroid entering the atmosphere.

A total of 7 all sky photographic cameras captured the fireball: apart from Benningbroek (Jos Nijland) shown above,  it was also captured by stations Ermelo (Koen Miskotte), Oostkapelle (Klaas Jobse), Utrecht (Felix Bettonvil), Bussloo (Jaap van 't Leven), Borne (Peter van Leuteren) and Twisk (Marco Verstraaten). Benningbroek also captured the last few seconds of the fireball on video with a CAMS camera. Koen Miskotte in Ermelo in the center of the Netherlands also observed the fireball visually, estimating it magnitude -5. He reported fragmentation.

Click to enlarge

The photographs allow to reconstruct the atmospheric trajectory, speed, radiant point and heliocentric orbit of this fireball, and whether something survived at the end or not.

The fireball appeared between 04:40:26 and 04:40:40 UT. It entered the atmosphere on a grazing shallow angle of only 11.2 degrees. The trajectory was over 180 km long - the average trajectory for all stations combined is 183 km long, but some stations captured an even longer part, with Benningbroek topping all with 212 km trajectory length! The fireball started over the North Sea at an altitude of 77 km near 53.0 N, 3.1 E (average of all stations), and moved on an almost due West-East trajectory, over the tip of North Holland province and Lake IJssel, ending at 42 km altitude over the northern part of the Noordoost Polder near 52.8 N, 5.7 E.

Four of the 7 stations were equipped with a rotating shutter in front of the lens, allowing speed reconstructions. Combined with the radiant point determination, this yields the orbit in the solar system.

The fireball entered the atmosphere with an initial atmospheric speed of 15.45 km/s. At the end of the trajectory, at 42.3 km altitude, it had slowed down to a terminal speed of 9.3 km/s. At that point, nothing was left of the original meteoroid: no meteorites reached the ground, it had completely ablated away. The deceleration curve obtained is actually quite nice:

Click diagram to enlarge

The apparent radiant of the fireball was low in the western sky, at RA 53.2 degrees, DEC +13.0 degrees in Taurus. The geocentric radiant (the radiant point corrected for amongst others gravitational influence) was at RA 43.8 degrees, DEC +0.4 degrees. The geocentric speed was 11.1 km/s.

Click star map to enlarge

The resulting heliocentric orbit is that of an Apollo asteroid, with perihelion at 0.874 AU, aphelion squarely in the asteroid belt at 2.76 AU, an orbital eccentricity of 0.518 and an orbital inclination of  4.9 degrees.

Click to enlarge

 

Reentry of Soyuz rocket upper stage from Progress MS-03 launch seen from New Zealand, 19 Jul 2016

On July 19, 2016, near ~6:30 UT (~18:30 local time), a bright very slow and long-lasting fireball was reported by many people from New Zealand's South Island. Several images are available, e.g. here and here and here. The fine video below is from YouTube user Ralph Pfister:



Perhaps the most accurate time given for the event is 6:26 UT as given by amateur astronomer Paul Stewart from Timaru on New Zealand's South Island. Stewart captured  the fireball on several all-sky images. A fine animation of his images is on his weblog.

From the video's it is immediately clear that this is not a meteoric fireball, but the re-entry of an artificial object (i.e. artificial Space Junk).

Time, direction of movement  and geographical position moreover match well with an obvious decay candidate: the Russian Soyuz upper stage (2016-045B, NORAD #41671) from the July 16 launch of Progress MS-03 to the International Space Station. In other words: this was a Space Junk re-entry.

At the moment of writing, the elements that are available for the Soyuz rocket stage are almost a day old and not unproblematic. For unknown reasons the B* drag value of the elsets is zero and the NDOT/2 value unrealistic.

This hampers analysis slightly, but using the almost a day old elements face-value, the upper stage would have passed over New Zealand's Southern Island near ~6:33 UT (~18:33 local time). This is within minutes of the time of the New Zealand event. The direction of movement of the rocket stage also matches that in Paul Stewart's imagery.

The maps below show the predicted position and track of the Soyuz upper stage for 19 July 2016, 16:30 UT (18:30 local time in New Zealand). They are based on the almost a day old element set  16200.42841345.

click map to enlarge

click map to enlarge

The few minutes discrepancy between predictions and actual sighting from New Zealand is not unusual for a re-entering object. The last available elements (at the moment of writing) for the Soyuz stage are actually from many hours before the reentry, and during the last moments of its life the orbital altitude drops quickly (i.e. the orbit alters).

Old elements hence will place it in a too high orbit compared to the reality of that moment. As it drops lower in orbital altitude, the rocket stage will get a shorter orbital period and hence appear somewhat earlier,  "in front" of predictions made using the old element set. Discrepancies of a few minutes are therefore normal in cases like these.

When it is "early" on the ephemerids, the orbital plane will be slightly more to the east as seen from a locality. In this case, the nominal pass predicted for Paul Stewart's locality would have been a zenith pass: but the a few minutes earlier pass time compared to the predicted time and the lower actual orbital altitude at the time of the re-entry would result in a sky track that is shifted eastwards and lower in the sky. This matches Paul Stewart's all-sky imagery.

Fireball seen over Eastern Australia, 13 June 2013 6:05 pm AEST, was NOT the decay of Molniya 3-53

On June 13, 2013, near 6:05 pm local time (AEST - corresponding to 10:05 UTC), many people in Eastern Australia observed a bright fast light falling down in the sky. It was even recorded by one of those new-fangled dashboard-cams (one of these days, I must get me one for my bike).

The Australian news website "The Chronicle" claims it was a satellite decay - more exactly, that of the Russian Molniya platform Molniya 3-53 (2003-029A).

It was however most definitely not a satellite decay.

All descriptions talk about a fast object. The dashcam video shows a pretty fast fireball indeed.

It is much too fast to be a decaying satellite. The latter move at relatively slow speeds - 8.5 km/s. At that speed, it takes them several minutes to traverse your sky, not just a few seconds. As low over the horizon as the dashcam video shows it, it would have been very, very slow, taking several tens of seconds to traverse the distance it does in the video.

In addition to it being too fast to be a satellite decay, the proposed connection to Molniya 3-53 can be rejected right away.

First: Molniya 3-53 did not decay on June 13. Orbital data by Strategic Space Command ("NORAD") show it was still in orbit in the early hours of June 15 - two days after the Australian fireball. At the moment of writing (12 UTC, June 15), the last available orbit is for epoch 13166.42726929 ( = 15 June 2013, 10:15 UTC). The moment of decay is currently predicted as 15 June 14:04 UTC, with an uncertainty of 2 hours. [Update 22/6: SSC's final TIP-message issued 15 June 15:30 UTC gives 15 June, 14:10 UTC +/- 26 minutes for the moment of decay)

Now, given that the apogee of the satellite was at a very low altitude already, could it have been the case that it briefly started to burn but survived after it passed perigee?

The answer is "no" in this case and brings us to a second point against the identification with this satellite: Molniya 3-53 was not over Australia at June 13, 10:05 UTC. It was at very high altitude over Northern Europe at that time (see map below). It would not pass over (central) Australia untill 10:55 UTC (6:55 pm AEST), i.e. a full hour later than the fireball sighting.

So what was it then? Given the speed, it is very clear this was a meteoric fireball, a small piece of cosmic rock or ice (debris from a comet or an asteroid) entering the atmosphere.

[updated] HUGE fireball over Russia this morning! Not 2012 DA14 related.

A HUGE fireball has appeared over Chelyabinsk, Russia, this morning. And with HUGE I mean: HUGE. Apparent brightness rivalling the sun, and very strong sonic booms leading to glass damage and people being wounded by flying glass. This must have been a seizable object entering the atmosphere.

Phil Plait, the "Bad Astronomer" has very good coverage including some amazing videos here, so I will refer to him for imagery and the general story (apart from two I include below: one showing the meteor, the other one the arrival of the shock wave).





Below, I will briefly explain why this fireball cannot have been a fragment of 2012 DA14, the ~50 meter wide asteroid that will pass very close to earth coming evening (Feb 15, 2013).

First of all (and Phil Plait points this out as well), the fireball in Russia came from the wrong direction. Several of the videos show it appearing in the east near the rising sun, coming from a N-NE direction. That is the wrong direction: fragments of 2012 DA14 are on a south-north trajectory.

What is even more important: fragments of 2012 DA14 could never enter the atmosphere as far north as latitude 55 N (Chelyabinsk). Fragments in orbits similar to that of the asteroid, have a theoretical geocentric radiant at declination -81 degrees, i.e. almost at the southern celestial pole. They hence approach earth from due south. This means that the northern hemisphere is out of reach of these fragments: the northern hemisphere represents (as seen from these approaching fragments) the "far side" of the earth.

[video added 18/02/2013]


[added 18/02/2013] In the above video I explain this more visually, with the help of an orange. In reality, it is slightly more complicated than I present it in the video, as objects grazing the earth's limb are actually slightly attracted by earths gravity and can end up a little bit over the line between "front" and "far" side of the earth. Ending up at latitude 55 N is nevertheless out of the question.

The funny thing is that the latitude of Chelyabinsk and the approach direction of 2012 DA14 (and fragments in a swarm around it) are well established facts, even if the trajectory of the Russian fireball is less so at the moment. So it is quite nice that from the encounter geometry with the 2012 DA14 orbit and the latitude of the Russian meteor alone, we can actualy already exclude a connection between the two with a quite strong certainty.

Fragments in 2012 DA14-like orbits and the Russian fireball itself are also too fast to be temporarily captured in earth-orbit, so that is no explanation either.

This fireball was not man-made space junk either. Besides coming from an unlikely direction, it is too fast and much too bright for that.

These are amazing times: the reentry of a Russian rocket stage seen from NW Europe on the evening of the 13th, then this hughe meteoric fireball over Russia this morning, and a close pass of asteroid 2012 DA14 tonight. Wow!

Fireball over NW Europe of the evening of 13 February 2013: Re-entry of a Soyuz r/b

Reports are pouring in of a very long duration, bright fireball near 22:15 CET (21:15 GMT) seen from Belgium, the Netherlands and Germany. Reports indicate 30-40 seconds visibility, and an "explosion" halfway, and some reports indicate sonic booms.

This fireball was with a high degree of certainty the re-entry of a Russian Soyuz 3rd stage, #39083 (2013-007B), the 3rd stage from the Soyuz that launched the Progress cargoship Progress-M 18M towards the ISS on February 11th.

USSTRATCOM issued a TIP message indicating decay at 21:15 +/- 1 m UTC near 49N, 13 E.

Below is a quick map (made using Orbitron) of the trajectory and approximate position of the re-entry.

click map to enlarge

Time, general description and reentry data all fit quite well.

[UPDATED] The 21 September fireball: a small Aten asteroid?

-- edited/corrected 25/9 15:25 UT. I initially made a small error in the used trajectory azimuth (not properly taking into account effects of a spherical earth). That is corrected, but the conclusions do not alter. --

In my previous post I presented clear evidence that the splendid fireball seen over NW Europe on September 21st, 2012, was a meteoric fireball. I also presented a first, very preliminary idea of its trajectory.

Based on that trajectory, I can now present some very first, very cautious conclusions about the heliocentric orbit of this meteoroid.The solutions strongly favour an identification as an Aten asteroid.

The entry azimuth of the fireball from the reconstructed preliminary trajectory is around 80 95 degrees. Based on observations by Ramon van der Hilst who observed the fireball from Bussloo, the estimated entry angle for the fireball is about 5 degrees only: a very shallow, earthgrazing angle which explains the long trajectory. (I asked Ramon to estimate the angle of the fireball with respect to the horizontal at the moment Ramon was looking roughly perpendicular to the preliminary trajectory. That angle, about 5 degrees as Ramon reports, should be close to the entry angle)

I used these values and an 18-20 km speed estimate to compute a nominal heliocentric orbit: and then played around by widely varying the values for speed, entry angle, entry azimuth around these nominal values.

The interesting point is, that for all of these, I get an Aten orbit as a result. Aten asteroids are asteroids whose perihelion lies within the orbit of the earth and who's aphelion lies only just outside the orbit of the earth. They have a semi-major axis < 1.0 AU and aphelion (just) over 1 AU.

The aphelion values I get for the approximate fireball orbit, are in the range 1.0 - 1.15 1.05 AU, the semi-major axis values are in the range 0.9 to 0.6 AU. Solutions based on higher speeds (I varied between 12 km/s and 30 km/s in my calculations) favour the slightly larger aphelion values and shorter semi-major axis.

A wide variation in entry azimuth (I tried between 60 and 110 120 degrees) and entry angle (I tried for values between 5 and 45 degrees, the latter clearly a too large value by the way) does not alter this picture much: they all result in Aten orbits.

I need to alter the trajectory direction to values significantly larger than entry from a direction of  120 degrees (well past due east) to get aphelion values that start to get well beyond 1.15 AU and semi-major axis values > 1.0 AU.

For the current very preliminary nominal trajectory solution (entry azimuth ~82 ~95 degrees, entry angle ~5 degrees) I get these values when varying the assumed entry speed of the fireball:

[editted table 15:25 UT to reflect new calculations/correction of error]

Vini    q    Q     a     e     i

12.0   0.82  1.00  0.91  0.10  6.5
15.0   0.46  1.02  0.74  0.39  15.0
18.0   0.31  1.04  0.67  0.55  20.7
20.0   0.24  1.05  0.65  0.62  24.8
25.0   0.16  1.09  0.62  0.76  37.4
27.0   0.13  1.11  0.62  0.79  43.7
30.0   0.11  1.14  0.62  0.83  54.5

Vini is the initial speed (in km/s), q the perihelion distance (in AU), Q the aphelion distance (in AU), a the semi-major axis (in AU), e the eccentricity, i the inclination.

These values should be taken with caution and only as rough indications. There are (still) large uncertainties in the trajectory and entry angle, as well as the speed of the fireball. They do show however (as well as variations on the trajectory not listed here) that an Aten-orbit is the implied solution.

The Earth encountered the meteoroid close to the meteoroid's aphelion, when it was moving almost in parallel with the Earth.

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NOTE / UPDATE 26/09/2012, 19:25 UT: There is some confusion on the web regarding my analysis and the "retrograde"/ "prograde" character of this object.
The "retrograde"character is only true for an earth-centered orbit (i.e., an object orbiting the earth, such as an artificial satellite). An east-west movement in that case means it is "retrograde" (against the motion of the earth's rotation).
This is not necessarily the case for a sun-centered orbit however. An east-west moving object then can be (and is, in this case!) in a normal, "prograde" orbit (=moving in the same direction around the sun as the planets). The difference is the frame of reference: earth-centric versus sun-centric.
So beware: the "retrograde" orbit refers to what the orbit would be for an earth-orbiting satellite (which this object was not). The Aten heliocentric orbit presented here, is however prograde.

More on the 21 September 2012 fireball: why it definitely was a meteor

I should have done this analysis earlier but did not have the time available until now. What follows now is a quick and back-of-the-envelope kind of calculation, but in my (not so) humble opinion it is adequate to the question at hand.

It concerns, of course, the splendid slow fireball seen widely over NW Europe near 21:55 UT on 21 September 2012. I posted on it before, focussing on saying "no" to the suggestion that this could have concerned a satellite reentry. In the post that now follows, I further strengthen the conclusion that it was not a satellite reentry, but a genuine meteoric fireball.

The map above gives a quick (and not particularly accurate) back-of-the-envelope reconstruction of the fireball trajectory. It is based on trajectory descriptions from Bussloo in the Netherlands and Dublin in Ireland: by taking reported altitudes (with respect to stars) and general directions of reported start and endpoints, and an assumed altitude of 50 km, the trajectory above is what approximately results. (update 19:10 UT, 24 Sep: an updated version of the map is at the bottom of this post).

The resulting trajectory is some 1000-1200 km long. In what now follows, I have taken 1100 km as the distance travelled by this fireball.

Observers near the western and eastern ends of the trajectory would probably not see the complete trajectory. Observers approximately mid-way, in mid-Britain, would potentially see most if not all of the trajectory (from experience I know you can see bright fireballs from distances of 500 km).

Observers report durations between 20-60 seconds: most video's on the web suggest a 40+ seconds duration.

It would take a reentering satellite travelling at 8 km/s (the orbital speed at decay altitudes) about 138 seconds or roughly 2.25 minutes to travel this distance. While the reported fireball durations are long, none of the reports nor videos comes even remotely close to that value.

A meteoric fireball travelling at the lowest speed possible for such an object, 11.8 km/s, would take 93 seconds to travel that distance. This is still longer than almost all of the reports suggest, but clearly getting closer.

If we take an estimated duration of 60 seconds, the 1100 km trajectory length results in a speed of  approximately 18 km/s.

18 km/s is a very reasonable speed for a slow, asteroidal origin fireball.

(it is, let me repeat, also way too fast for a satellite reentry).

Meteorite dropping fireballs typically have speeds between 11.8 and 27 km/s. A speed near 18 km/s sits squarely in the middle of that speed interval.

(update: diagram added 14:45 UT, 24 Sep)

(click diagram to enlarge)

The 60 seconds probably represents the upper boundary value for the duration of the fireball. If we take a shorter duration of 40 seconds, the speed already increases to 27.5 km/s.

This quick back-of-the-envelope reconstruction therefore shows that this must have been a meteoric fireball, quite likely of asteroidal origin, and we definitely can exclude a satellite reentry.

The fragmentation described and filmed is not unusual for meteorite dropping fireballs (see the video's of the Peekskill meteorite fall in my previous post). The object probably entered the atmosphere under a very shallow angle, which together with the slow speed explains the unusually long duration of the event.

Meteors of this kind are rare, but they have been seen before. Think of the Peekskill meteorite fall, but also the famous 1972 daylight fireball over the Grand Tetons (that had a duration of over 100 seconds) and the Cyrilid Meteor Procession from 1913 (that lasted minutes).

Note: a previous post gives a number of other lines of evidence which likewise suggest this fireball was not man-made space debris.

UPDATE: a further update is given in a new post: a very cautious orbital solution suggests an Aten orbit.

Note 2: on how I made this quick and (emphasis) rough trajectory reconstruction. I took observations that contain clear sky locations: e.g. a sighting from Dublin stating it went "through the pan of the Big Dipper"; the description from Bussloo observatory in the Netherlands; and later adding a.o. a photo from Halifax, UK, showing it just above the tail of Ursa Major. These descriptions can be turned into directions and elevations. Next, I drew lines from these sighting points towards the indicated directions, marking distances roughly corresponding to 30, 50 and 80 km altitude as indicated by the observed elevation [ distance = altitude / tan(elevation) ]. Near the start of the trajectory I marked 50 and 80 km, for Britain and Ireland I marked 30 and 50 km. These points then provide you with a rough trajectory.
From Dublin the object passed through North towards west. From Bussloo the object started NE (azimuth 60 degrees): these are important points of information too as it shows that the object started at least as far east as the Dutch-German border (and more likely over Sleswig-Holstein in N-Germany) and had its endpoint at least as far west as the northern part of Ireland.

Above: Updated map version, 24 Sep 19:10 GMT , also showing the principle of how it was reconstructed for three sighting locations. With thanks to Ramon van der Hilst for providing more detailed information on sky trajectory as seen from Bussloo (NL) on request.

Fireball over N-Europe on 21 September 2012, 21:45 GMT was likely NOT a reentry

UPDATE (24/9/2012): more and definite arguments that this was not a reentering satellite, can be read here in my follow-up post from Sep 24th. This includes a first rough trajectory reconstruction for this fireball.

Reports are pouring in from The Netherlands, Britain, Ireland and other N-European countries about a very bright, extremely slow fragmenting fireball appearing around 21:45 - 21:55 GMT (23:45 -23:55 CEST) on the evening of 21 September 2012.

Various video's have been posted on Youtube, notably by observers from Britain (large parts of the Netherlands were clouded out, including the all-sky stations):





Because of the unusually long duration and slow movement, some people have suggested the possibility of a satellite reentry. For various reasons, this is however very unlikely.

Multiple reports make clear the object was moving from east to west. A report of observers from Bussloo Observatory, the Netherlands, for examples states that the fireball appeared in the north, moving from Perseus  to Bootes, almost horizontally from east to west. Similar reports (e.g. here and here) come from Ireland.

Almost all non-polar satellites move prograde,  from west to east (or north-south and v.v. for a polar orbit). An east to west movement would necessitate the object to have a retrograde orbit (meaning that it moves counter to the earth's direction of rotation). Such objects are extremely rare: they literally amount to only a handful of objects (including the US FIA Radar satellites, and the Israeli Ofeq/Shavit satellites/rb). For this reason, it is extremely unlikely that this fireball was a reentering satellite.

Update 24 Sep: in the comments to this blog post, the issue was raised of the potential reentry of a classified object. However, the larger classified pieces are tracked by us amateurs. We have no likely decay candidates among the retrograde objects that we track. We can account for and hence exclude the FIA's for example (the rocket bodies of that launch were deliberately de-orbitted right after launch so are no candidates either). The Israeli Ofeq/Shavit are no candidates as their orbital inclinations never take them over the Netherlands and the British Isles. And there are simply no other suitable retrograde objects -- end of update.

There are moreover no unclassified reentry candidates for this date listed by USSTRATCOM on their space-track portal. Given the brightness of the fireball, this should have been a seizable chunk of space debris, that really would have been tracked (and predicted). Again, this makes it very unlikely that this fireball was a satellite reentry.

While the duration of the fireball is unusual, it is not unprecedented. In many ways, the descriptions and video are reminiscent of the Peekskill fireball that dropped meteorites near Peekskill in 1992:

(below: two video's of Peekskill fireball, 1992)

It is therefore my opinion that the 21 September fireball was most likely of meteoric origin: a chunk of asteroid. Alas, any surviving remains appear to have splashed down in sea (update: or possibly Scotland - N. Ireland).

The duration of the event, though not unprecedented, is certainly unusual and for this reason, I am saying "most likely not" rather than "certainly not".

UPDATE (12:45 GMT, 22 Sep):  another bright fireball was widely seen from the US and Canada that same night near 20:30 GMT. There was at least one hour inbetween the two events, so they do not appear to be related (i.e. they do not concern the same fireball).

UPDATE 2 (13:30 GMT, 22 Sep): Suggestions that the fireball might be related to Chinese CZ-4 space debris, catalogue #26213, are plainly incorrect. That object (and any fragments of it) are in a 98 degree polar orbit. This is completely incompatible with the reported movement of the fireball. As seen from Bussloo in the Netherlands and Dublin in Ireland, the fireball moved perpendicular, not parallel, to the orbital plane of this Chinese space debris (and that of any related fragments).

 IMPORTANT UPDATE 3 (24/9/2012): more and definite arguments that this was not a reentering satellite, can be read here.

OT: a multistation filmed meteor from 27 March - some results on the trajectory

In the early morning of March 27, while waiting for a pass of ATV-3, I accidentally filmed a nice meteor from Leiden. As it turned out, the same meteor was also filmed by the meteor surveillance video of Martin Breukers in Hengelo. Hence, we have this approximately mag. -1.3 meteor multistation, allowing triangulation to determine the 3-dimensional atmospheric trajectory and orbit in the solar system. Martin used UFOanalyzer software to process the images and arrive at an atmospheric trajectory. I used my orbital spreadsheet Metorb85 to compute a heliocentric orbit for the meteor.



The movie above shows the meteor footage as obtained from Leiden and Hengelo, plus a 360-degree fly-by around the reconstructed atmospheric trajectory.

The meteor started at 51.745 N, 6.267 E, at 100.4 km altitude. It ended at 51.961 N, 6.707 E and 75.2 km altitude. It had an initial velocity of 27.8 km/s.

Above are two integrated frames images of the meteor, a still image showing the 3D trajectory, and images showing the orbit in the solar system. As the convergence angle between the trails as seen from both video stations was not particularly large, the resulting orbit has some inaccuracy. Nominal orbital element values are:

a = 1.87 AU,
q = 0.450 AU,
e = 0.759,
i = 10.47 deg,
omega = 285.84 deg,
node = 6.696 deg.

The geocentric radiant was near RA 198.20 deg, dec. +4.01 deg, Vgeo 25.67 km/s. The radiant position has some leeway due to the low convergence angle. Hengelo saw the meteor appear in Corona Borealis: Leiden in the Aquila-Sagitta-Delphinus border area.