Once again, we – on Earth – will be passed by a Near-Earth Asteroid. This time on April 12th. Don’t worry! Its nearest approach will be about 38 thousand kilometers (23,800 miles). For reference, the diameter of the Earth is about 8000 miles. The size of this is a rock that you could hide a Ford Expedition behind.
Near Earth Asteroid…Date……….Miss Distance…..Velocity (km/s)…..Diameter (meters)……
Figure 1: Parameters of Near-Earth encounter with 2021GW4
Figure 2: Orbits of Earth, the Moon and 2021GW4. These are calculated without the Earth’s gravity effect on the asteroid’s orbit. The red line suggests what might happen in reality.
The question on everyone’s lips is always what will happen IF this asteroid were to collide with the Earth. It will not do that, OK?
People just love to imagine catastrophe and asteroids are their greatest opportunity. So, I have developed a macro to calculate such a disaster given the mass of the asteroid and the relative velocity of that asteroid with the Earth. Now, there are many variables (also referred to as “parameters”) that effect such calculations and I have made many assumptions – based on “average” values of density – and so forth. So, if you calculate a different number, please let me know – and show your work!
With all those disclaimers, I will say that the asteroid’s impact – if its course were to coincide with the position of the Earth (which WILL NOT HAPPEN, by the way!) – would generate an explosion equivalent to 1.3 kilotons of TNT. This is calculated by the Kinetic Energy using the estimated mass of the NEA and the velocity from the table in figure 1.
For reference, the bombing of Hiroshima yielded an explosion estimated at 12 to 18 kilotons. For an extreme example the “Tsar Bomba” detonated by the Soviet Union in 1961 yielded about 50 Megatons (50,000 Kilotons). So, we have already done far more damage on our own than this particular object could heap upon us.
As a lifelong Astronomy Nerd (perhaps not at birth, but not long after) I cannot help but notice how Planetary Science has advanced over the last half century. To say that much has been discovered is a ridiculous understatement. This theme of Solar System Astronomy can also be noticed in my other Categories (Comets, Planets, Asteroids, Urban Astronomy, Science and occasionally even in Going Walkabout, Energy, One Climate Fact and Humor*.
As related below the body now officially named 486958 Arrokoth was indeed described and analyzed at the 50th Lunar and Planetary Science Conference in 2019.
Prolog – March 2019
As expected, the LPSC has revealed much greater detail about the Kuiper Belt Object 2014 MU69 (A.K.A. Ultima Thule)
The flyby of this Kuiper Belt Object was declared a 100% success by the Principal Investigator Alan Stern. The closest approach was at about one fourth the distance as the previous KBO encounter with Pluto. This is not surprising when the new target is comparable to a small mountain on Pluto. That, and the fact that the velocity of the probe is about seven miles per second (yes, per second) complicates the task. Other compounding circumstances were the light level comparable to a moonlit night on Earth, a spacecraft design that does not allow continuous contact and a download rate that is agonizingly slow. As discussed earlier these were design trade-offs that made a long, difficult exploration effort possible – and quite successful – on a limited budget.
At the time of the Special Session at the LPSC, it had been 80 days since the encounter and considerable data had been received. However, more than a year separates us from the completion of that transmission. The state of knowledge at this time was summed up by the PI in the first presentation and those items are presented below along with details filled in by the presenters that followed.
An earlier comparison to a “snowman” shape were based only on a 2D view. Both the bodies that makeup this contact binary are thinner in the third dimension. The larger one (now popularly called “Ultima”) is actually shaped more like a thick hamburger patty. The smaller body (Thule) is more nearly spherical, but still visibly “flattened”. This is not unprecedented. There is a moon orbiting Saturn called Hyperion that has a similar shape to Ultima’s.
As promised, the resolution now available is greatly improved. The panel below is a stereo “cross-eyed” view. It takes a bit of practice, but it is possible to focus the left eye on the right image and vice-versa to get a clear and vivid 3-D view that appears between the two. Sit up straight and view with no tilt on the image. Hold your head very still and adjust by tilting slightly right or left. It should resolve into a clear and quite impressive 3-D image. I find it works best, with minimal eye-strain at about 2 feet (about 60 cm) away.
Figure 1: Raw images of the contact binary MU69. These are from the LORRI instrument and therefore lack the red coloring or the previous, low resolution image. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.
The crater on the smaller body (Thule) is seen to be quite deep. It may be an impact feature, but no one has dared to unambiguously claim so. Other craters may have been caused by faulting, perhaps during the merger. None of the few craters seen can definitely said to be caused by impact.
A comparison was made to Phobos, the greater moon of Mars, and its biggest crater named Stickney. The two bodies are roughly the same size. Phobos is one of the darkest objects in the inner solar system and in that sense, also very similar to Thule. See Figure 2 for a side-by-side images.
Figure 2: Left: MU69-B (Thule) and Crater “Missouri” Right: Martian Moon Phobos and Stickney Crater
Phobos and the lesser moon of Mars, Deimos were discovered by American astronomer Asaph Hall in 1877. Hall was about to abandon his search for Martian moons, but was convinced to struggle on by his wife, Professor Chloe Angeline Stickney Hall.
Somewhere in the vast body of writings by Issac Azimov (and almost certainly somewhere in the shelves and piles of ancient paperbacks I still possess – and have forbidden my wife from recycling) is told the anecdote about a presentation wherein the speaker related this story and hoped – that when Phobos was ultimately imaged – a major feature might be named for the mathematician, suffragist and abolitionist who would not let Hall give up the search in which he ultimately succeeded. When the presenter (who may well have been Azimov, himself) admitted his ignorance of her name, an attendee stood up and shouted, “Angeline Stickney” (for she did not use her first name). And, in the fullness of time, it came to pass that the crater that dominates the surface of Phobos is so named.
More Points about 2014MU69 / Ultima Thule
Bright spots tend to be in low zones. Troughs and mounds are clearly discernable.
The merger of these two bodies into one was determined to be a “gentle one”. In the distant realm of the Kuiper Belt, and especially among the “Cold Classical”, objects that find themselves near each other tend to be moving with the same velocities. Willian McKinnon described this method of simulating the velocity of merger: “Walk into a wall”.
No satellites were detected. Nor was there any detectable atmosphere.
This may be because any satellites there might have been would have been ejected from orbit during the “merger” process.
It is my (your humble narrator) own interpretation (2021) that this system once consisted of five or six main bodies – all orbiting in the same plane – that were slowly accumulated onto the larger of the two. And then the accumulated “hamburger patty” (whose shape indicates the co-planar rotation IMHO) and the smaller body finally merged. Tidal stresses in orbiting bodies tend to slow down the mutual rotation – thus bringing them all together.
The period of rotation has been pinned down to 15.9 hours.
The New Horizons spacecraft probably has enough fuel to re-direct to another Kuiper Belt Object. There is not yet a target body known to be in reach and Ultima Thule was found at the limits of the Space Telescope capability. It is expected that the probe’s own long-range imager (LORRI) will be the instrument to find the next destination. It is estimated that one more target will be the last possible. There is no hurry, however, since the probe will be in the Kuiper Belt until 2027 or so.
It happened yesterday and you missed it completely! An asteroid passed way inside the moon’s orbit – about 5 Earth diameters away. Called 2021 AH, it was discovered only this (new) year! These things can sneak up on us all unbeknownst, sometimes.
It is bigger than the building you park your car in, and probably made of solid rock. It is traveling at a speed that would make its impact the equivalent of an atomic bomb.
Don’t worry, though. It missed by 41,641 miles – a bit more than five Earth diameters.
And if I tell you that this happens like every six months or so, I am sure you will be comforted and re-assured. 😉
Another Near Earth Object encounter. This time with a unique announcement:
Notice that 2020 JJ has an anomalous distance of encounter of zero AU. It is rounded off, of course. The managers of this source will be contacted to encourage more decimal places! By other sources, I find the “miss” distance to be about 16,200 miles which is indeed less than 0.1 Lunar Distances.
This, again is worthy of a more detailed diagram with a better picture of the Earth (Thanks, NASA!).
The approaching asteroid did not pass across the celestial equator – where all the geosynchronous communication satellites are – but further to the South.
The JPL Small Body Database Browser, which is also the source for the “circle and arrows” diagrams you have seen on these pages, has undoubtedly given us a more accurate figure. However, it does have some limitations, which are clearly explained in the website:
“This orbit viewer was implemented using two-body methods, and hence should not be used for determining accurate long-term trajectories (over several years or decades) or planetary encounter circumstances.”
The alert readers (most of you) will point out that “planetary encounter circumstances” is exactly what I am talking about. That statement means that when asteroids get close to a planet, their mutual gravity has a significant effect that is not calculated in this utility. So, that 16,200 miss distance is not keenly accurate and almost certainly too large. Not only that, but it also means that the orbit after the near encounter will have been altered. It will need to be recalculated and replaced in the database.
JPL has a utility for that, called the “Horizons system” and NASA has an organization to keep track of these things (and studies methods to avoid collisions) called the Planetary Defense Coordination Office. That said, rocks this small (about 13 feet across) are not easily detected far in advance. They are also less destructive should they fall to Earth. This one was small compared to the Chelyabinskmeteor.
In 1979, Skylab – America’s first space station – was falling out of orbit and my sister called me – her space nerd brother – to worry about this thing that she feared would fall on her new baby. I tried to explain that the Earth is so big and the Skylab so small (relatively speaking) that the chances were nil that any person on Earth would be anywhere near where it fell.
I went on to point out that there are natural meteorites that fall to Earth constantly and they could amount to the equivalent of thousands of Skylabs every year. She never worried about those!
After that, she was not just worried – more like terrified!
I have since learned to advise people that they are more likely to be hit by a train, bitten by a shark and struck by lightning – all at the same time – than to be struck by anything falling from the sky. There is exactly one case of a person being hit by a meteorite. The lady was badly bruised, but not fatally.
I told you that to blunt the effect of telling you the following:
Another Near Earth Object passed by the Earth on April 28th, 2020. I have checked a couple of reliable sources and I can tell you that the nearest it came was about 29 thousand miles. And that sounds like a lot, since the earth itself is only about 8000 miles in diameter,
However, the NEO does come into our “territory” since we have satellites orbiting the Earth. You might think that satellites are only hundreds of miles above the Earth and that is where you are mistaken. I decided that those little diagrams with circles and arrows are insufficient for this one. Please see the diagram in Figure 1 for details.
As you see, the NEO this week is close enough to be of definite interest. However, it passed to the South of Earth – nowhere near the “belt” of geosynchronous satellites over the equator and over twice as far as the “cloud” of GPS satellites. And, of course nowhere near the Space Station.
The asteroid is about 60 feet across. Satellites are flimsy aluminum gadgets and would crumble before the NEO. But Space is big and satellites are small.
Another Near Earth Asteroid has zoomed by while no one was looking on April 22nd. It may surprise the readers to learn that these things are so common that I only consider the ones that pass as close as the Moon to be of interest. This one was at 0.4 Lunar Distances or about 95,542 miles.
The culprit is 2020 HF5 – a small rock, as asteroids go – that is only 52 feet across. These encounters are listed at https://spaceweather.com/ – just scroll down a bit to find a table.
The rock in question is very much is roughly the same size as an asteroid that exploded over Челябинске in Russia on my 58th birthday. (Feb 15, 2013) . The heat of re-entry, combined with the tremendous air pressure of its hyper-sonic trajectory caused it to explode at 12 to 15 miles above the surface.
There was a Russian teacher – Yulia Karbysheva – about my age who, like me, had been trained in Civil Defense exercises in elementary school. They taught us what to do in a nuclear attack. When the meteor lit up the sky, she had her students hide under the desks – as she (and I) had been trained to do. When the asteroid exploded and the shock wave arrived, it shattered all the windows and sent shards of glass over the desks – with the students safely beneath same. After almost a half century, that training finally paid off – for the students. Unfortunately, she was so concerned with the fourth-graders that she remained standing and was seriously injured. In all, about 112 people were hospitalized, mostly cuts from flying glass. There were some cases of flash blindness and ultraviolet burns. Don’t look at the flash! I learned that instinctively as a welder.
Our more recent visitor was similar in size, but with only about 1/2 the relative velocity as that meteor and would have about the one fourth the explosive potential. About 117 kilotons – 9 Hiroshima bombs equivalent.
What’s that? Oh…it’s the town’s name – “Chelyabinsk”.
There is a class of asteroids called NEO’s (Near Earth Objects). As the name implies they hang around where the Earth does. None have been found to threaten the Earth with collision, but some come close – if a quarter million miles may be considered “close”.
On April 15th 2020 an NEO designated 2020 NH 4 will pass closer to the Earth than the Moon. Since its closest approach is still over two hundred thousand miles – about 25 Earth diameters – it is nothing to worry about. The diagram in figure 1. Shows its trajectory through the Earth-Moon system.
There is a subclass of NEOs called “Potentially Hazardous Objects” (PHOs), but that requires a diameter of 140 meters and this one is only 18 meters (59 feet) across.
Figure 1: The Earth, the moon and 2020GH 4
To answer the inevitable question, yes this asteroid, had it hit the Earth, would have made a very big explosion.
Use the “Reply” window below for questions, please. If the reply window is not visible, just click on the title at the top of the page. That will bring up the individual post instead of the categorical collection – and with it, a reply window.
March 12, 2019 (I was rummaging around on some thumb drives and found this from 2001. The Alert Reader will point out that USB drives were not around then. True. This was in a folder called “Floppy_Recovery”. I actually bought a 3 ½ inch floppy disk drive and copied a pile of floppies into this particular USB some years back. I added some “file photos” that would never have fit on a floppy, anyway). Homepage
The Leonids are neither a sixties group, nor a box of stronger breath mints, nor followers of a religion devoted to a deity named Leon , as you may have thought by the name but rather an event that takes place once a year around November 18th, when meteors rain down from the general direction of a point in the sky near the constellation Leo. Well, perhaps “rain” is a misleading choice of words since the normal Leonid meteor “shower” consists of one meteor every few minutes and I personally have sat out in the November damp chill and not seen a meteor for fifteen or twenty minutes at a time. Only the most demented Astronomy Nerds (A.N.’s) would put up with the amount of inconvenience involved to see what, for the non-Astronomy Nerd is less interesting than counting the number of cars with one headlight at four in the morning on a dark stretch of country road.
It is especially taxing for the urban A.N. because it involves a trip out of town of at least an hour to an isolated dark spot. You might think that there are plenty of dark spots out there, but I dare you to find one! About anywhere you can drive to in an hour around here (here is Houston) is lit either by passing cars or billboard lights or gleaming florescent signs. In Texas, more than a few of the people who like to hang out in the country also like to mount a half dozen searchlights on their vehicles. The one hope is to find a State Park and even then the non-Astronomy Nerds will wander around all night with flashlights that could illuminate the Grand Canyon. They mean no harm, you understand, but these folks have never heard of the concept of night vision and routinely put their beam of light directly on your face as a sort of a greeting. and say “Hi! Whacha’ doin’?”
There is one exception, a state park that actually has made an effort to keep illumination off the sky and provided areas down twisting footpaths away from the roads where one can find uninterrupted darkness. It’s Brazos Bend State Park and there is a nice dark place get a wide angle view of the sky or to set up telescopes. If you go there, please keep the flashlight use to a minimum and never illuminate anyone’s face. I didn’t manage to reserve a campsite early enough because all the other Astronomy Nerds thought four months ahead as opposed to my three. I did find a spot in Stephen F. Austin State Historical Park. It’s located near San Felipe which was the capital of newly declared independent Texas before it was burned to prevent it from falling to the advancing Mexican Army, who wanted Texas to be dependent again. There are some reconstructed buildings (one’s a museum), statues and historical markers near the park entrance. (Trivia question: What does the F. in Stephen F. Austin stand for?)
Those unfamiliar with astronomical events always assume that you will be looking at a meteor shower with a telescope. As an exercise to prove how silly that is, extend your arm at the sky with your thumb up. That tiny piece of sky covered by your thumb is many times the field of view of an average telescope. You could see more of the sky by looking through a two-foot-long pipe than through a telescope! Meteors happen all over the sky, during a shower or otherwise. Why on earth would you limit your view to a tiny patch of sky?
It is obvious that hardly anyone bothers to look at the sky anymore. I’ve had people swear to me that they’ve seen the space station hovering overhead (turned out to be Jupiter). Others expect to see Venus always near the moon. A few are not even aware that the moon can be seen in the daytime. But, shoot, is there any real reason for your average person to look at the sky these days? Especially urban dwellers for whom the night sky is a brown haze, illuminated from below, at the best of times?
I go out to see these things because I find it fascinating but I am aware that some do not share my enthusiasm. Nevertheless, I dragged my wife and children along on this last expedition. When I make the journey with other A.N.’s we throw lawn chairs in the trunk and leave at midnight. Provisions such as beef jerky and Shiner Bock beer (with appropriate designated driver, of course) are to be found in fueling depots along the way. Stay up most of the night, doze off in the chairs and drive back with stiff necks in the morning. This will not do for a family outing, however. Especially with small children…who will only stay awake at night when you desperately want them to sleep.
It becomes a regular camping trip, then, complete with tent, sleeping bags, flashlights, blankets, pillow, portable propane stove and an ice chest with the entire contents of the kitchen refrigerator (as opposed to the garage refrigerator). Might as well take along the telescope (for looking at planets and stars, not meteors, you understand) and the bicycles because we’ll have some daylight hours to kill. Appropriate stuffed animals and annoying hand held electronic games to keep the offspring occupied. The target for leaving had been ten o’clock. It was eleven thirty when we left.
The first thing we found out at the campsite is that we have forgotten what to do on camp-outs. We rode bicycles, walked around for a while and played twenty questions. It was still only four o’clock in the afternoon and we were sitting around looking at each other. So we did what any bored campers would do, we went into town. Not really into town, but that peninsula of fast-food and big-box retail that grew up around the interstate. There we bought charcoal, which we’d forgotten. I’m not sure how we were planning to cook the hotdogs for dinner unless we boiled them on the propane stove…in a pot, which we also forgot. And while it might be possible to roast marshmallows over a propane flame, I doubt it would be much fun. Of course, any cooking would require matches, which we had also forgotten.
“So,” you are perhaps thinking, “Just when is he going to get to the part about the meteor shower?”
Meteor showers are best after midnight ’cause that’s when the Earth (the part of Earth where it’s after midnight, that is) is plowing “head-on” into this cloud of dust that makes meteors. The cloud itself has been spewed out along the orbit of a comet that crosses the Earth’s orbit. Now, I know what you’re thinking. It’s the same question reporters ask astronomers (in an urgent voice) every time the subject of comets and or near Earth asteroids comes up.
You’re thinking “Crosses the Earth’s orbit! But what if it hit the Earth?”
Relax, you are far more likely to be struck by lightning, hit by a bus and bitten by a shark, all simultaneously. The orbits don’t actually cross but just come close enough to where the Earth will run into that scattered dust cloud. And, even if they did cross exactly, then a collision would require that they both arrive at the same point in their orbits at the same time, which almost never happens neither.
So, there are times when there is a particularly thick cloud of dust that we happen upon. Not really thick, but just relatively thick, it’s still a dead ringer for absolute emptiness. That’s what’s called a meteor storm. Or the shower is said “to storm”.
Like this: “I understand that some predictions say the Leonids are going to storm this year”
This is a particularly cool thing to say around Astronomy Nerds because somebody is always predicting a “storm” and so you would sound like you actually know what you’re talking about. Of course you would be saying this to impress a bunch of people who hang out in the dark all night, staring up at the sky, so I’m not sure how useful this advice is.
The Leonids were supposed to storm last year, too – and the year before. I made the trip back then with the largest of my two sons and we saw a few good meteors. I always thought it would be cool if I could call them “My Three Sons” like the early sixties sitcom but I only have the two. I suppose I could say “three” if I count the cat who is indeed a male albeit a “repaired” one. (Fixed? Heck, I didn’t even know he was broken!) .
Yes, I know, you’d like to hear about the meteor shower. Well, I arose after a fitful few hours of sleep to look at the sky and was extremely disappointed to see a complete cloud cover. I wasn’t surprised because this sort of thing happens all the time with meteor showers ’round here. I sat down in my lawn chair to be miserable about it for a while.
While we are sitting here being miserable, let us discuss the difference between meteors, meteorites and meteoroids. Way out in space is the particle of dust or bit of rock or chunk of stone that is cruising along, unaware that it is about to run into a planet. That is a meteoroid. Anything that ends with “oid” is out in space and usually relatively small. I say relatively because a “planetoid” or “asteroid” can be the size of, say, North Dakota and still be small when compared to a planet or an asteroid like Ceres, which is bigger than Texas. When this unsuspecting meteoroid actually passes through the atmosphere it makes a streak of light that can be seen by all the Astronomy Nerds and anyone else foolish enough to be out in the cold, damp night, assuming its not completely clouded over like now. That is a meteor. Most of these streak-makers – the vast majority – burn up completely, but a meteorite is a chunk of rock that you can pick up off the ground that once was a meteoroid and made a meteoric flash of light before its arrival.
I used to say wait till it cools off before you pick it up, but a meteorite, (I find out) by the time it hits the ground, has slowed to mere “falling rock” speed and has cooled off considerably. I suppose it might still be warm, but it won’t be red hot. Small comfort to anyone who happens to be in its path. Relax! As far as I know, there is only one documented case of a meteorite hitting a person. Those who minds retain such useless information (yo!) remember seeing a black and white picture of a huge ugly bruise on the unfortunate lady’s abdomen. She recovered. These days meteors bring in big bucks from collectors so it might be worth the pain if it did happen. But it’s actually far more likely that you’ll win the state lottery so hope for that instead.
I sat there for a while thinking what a bummer it was that I had planned this for months and here I was going to miss the whole thing. I could have driven out to West Texas, maybe, where the climate tends to be drier. I noticed a small hole in the clouds with a few stars visible and decided that maybe a few meteors would pass across it. This is what is metaphorically called “grasping at straws”.
Over the next hour, to my great astonishment, the sky cleared off completely. I saw a meteor, then another, then more. It was about two A.M. with a peak expected around four. I’d seen enough to wake up the family. You have to be careful about waking up your family at two A.M. It is absolutely essential that you have something impressive to show them or the next time you try this silliness you’ll be out there alone. Nobody was disappointed. This was a major meteor storm to be sure. At first I’d counted for a minute and found about six firm meteors. That is to say, I’m sure they weren’t fireflies. That’s an hourly count of 360 – impressive enough. I don’t want you to think that I did this in any scientific way. In fact, I didn’t have my watch on. I counted, one-thousand-one, one-thousand-two. And since I can’t walk and chew gum, I kept a tally of meteors on my fingers. I belong to that group that prefers the one-thousand-one method to the more popular one-mississippi method.
Around three or three thirty or so (I didn’t have my watch, remember?) I counted 12 in a minute. Then, sometime after four there were 22 in a minute. I had my shoes off, you see, to count toes and used eyelids and was lucky that there weren’t more than 22, or I’d never have seen ’em.
(Since then, I have learned a new method of finger-counting, which I described in “On Zeno’s Swim Team”. It’s good up to 99. )
I didn’t have a clear view of the whole sky by any means and there was a bit of haze, but it was still an experience of a lifetime. A published “official” count in the newspaper the next day was 1250 for the peak. These are from people who count for an entire hour with stopwatches and click-counters. My 22 in a minute calculates out to 1320 per hour. Not bad for fingers and toes and “one-thousand-one”!
I kind of hated to call my friend who is a fellow Astronomy Nerd who was unable to make the trip and tell him what he missed. I already have a cousin who’s mad at me since I described the experience. She knew about the shower but didn’t go see it because I didn’t call up and tell her how good it would be. Truth is, I didn’t know how good it would be either.