2008 CT1
Published on Feb 7, 2008 at 1:20 pm.
9 Comments.
Filed under asteroids.
Very early in the morning, on February 3, 2008, just a few days ago, observations made by the Lincoln Near Earth Asteroid Research (LINEAR) project discovered a new asteroid. This tiny asteroid, estimated to be about 10 meters across, is one of probably millions of similar bodies orbiting the Sun. What makes this one unusual, though, was its location. It was discovered very near Earth, and it was approaching us. It made its closest approach to Earth only 47 hours later. As it passed by, it was moving at a bit less than 18 kilometers per second (that’s a little less than 11 miles per second). None of that is particularly noteworthy. What is noteworthy, though, is that it passed very close to Earth. It missed us by about 126,000 kilometers ( just over 75,000 miles!). That is less than 1/3 of the distance to the Moon!
Asteroid 2008 CT1 has a rather elliptical orbit that is not very inclined with respect to the ecliptic, meaning that it crosses Earth’s orbit regularly. It ranges from as near the Sun as 0.48 AU (nearly as close to the Sun as Mercury) out to about 1.30 AU (not quite as far as Mars). Note: 1 AU (Astronomical Unit) is Earth’s average distance from the Sun. 2008 CT1 passed us heading inward, so it is now closer to the Sun that Earth. In early March it will be crossing Venus’ orbit. It won’t be anywhere near Venus at the time, though, since Venus will be clear across its orbit on the other side of the Sun at the time. In mid April, the asteroid will be a perihelion (nearest the Sun), just outside of Mercury’s orbit. It won’t be near Mercury, either, since that planet, too, will be on nearly the other side of the Sun in its orbit as the asteroid passes. In mid May, 2008 CT1 will again cross Venus’ orbit, this time heading outward from the Sun. At that time, it will be closer to Venus than in March, but still not very close. By mid June, the asteroid will again be crossing Earth’s orbit. At that time, though, Earth will be on the other side of the Sun from the asteroid. The asteroid and planets keep this dance up for a long time. For quite some time, 2008 CT1 will not be passing particularly near Earth. But, since the orbits cross, eventually they’ll be at near the same point in space at the same time, again.
Looking into the future, we find several very close approaches to Earth. NASA’s Near Earth Object Program has an impact risk assessment page for 2008 CT1. We find that February 4, 2041, the asteroid’s orbit is computed to come a staggering 2.76 Earth radii from our planet, with an uncertainty in position of about 1 Earth radius. Even more sobering, though, is that on February 5, 2060, the asteroid’s computed orbit comes less than 0.7 Earth radii from Earth’s center. Anything less than a miss of 1 Earth radius is an impact. The known uncertainty in position at that point is about a quarter of an Earth radius. Oops. That sounds like a near certain impact. However, remember, that these calculations are based on on a handful of observations. They are FAR from certain. So, there is likely far more error in the observations that we know. That may well mean that the body will miss us.
However, if it did hit, what would be expect? The estimates for the impact energy are only a few times larger than the energy released by the atomic bomb dropped on Hiroshima. Now, that might seem scary, but Earth gets hit by something this size every decade or so. Most of the time, the impact is over water. Most of the rest of the time, it is over a very poorly inhabited part of the planet. Even if it were over a rather well inhabited part of the planet, there may still be little effect felt. These small bodies have a variety of compositions, and many of them are not very sturdy. The shock of hitting the atmosphere would cause them to break apart, and they’d detonate in the upper atmosphere, with the blast wave mostly dissipating by the time it reached the ground. Of course, there are the few that are pretty solid … .
So, does this mean time to panic? NO! There are still a lot of uncertainties in these calculations. Remember, there are only a few observations, so the actual uncertainties may be quite large. Also, if the asteroid passes be a bit early or late, then Earth won’t be in the right spot, even if the asteroid is exactly on target. Orbital perturbations of the asteroid’s path by the planets can change things, and the smaller asteroids are easier to perturb. And, there is also the Yarkovsky Effect, which can alter the path of the asteroid between now and then. It is still far too early to worry. Besides these factors, the current handful of observations of the asteroid are not all that precise to really compute an orbital path of such precision. All told, the estimates are that 2008 CT1 has only about a one in ten thousand chance of hitting Earth in the foreseeable future. But, that is high enough that it does mean that this asteroid is something to keep track of. And, this is something that is good to catch the attention of my students.
Oh, and I don’t want to come off as a scare monger here. Really, this is something to keep an eye on, but nothing to really worry about. It is no worse than the weather forecast being for a line of severe storms in your area with a chance of hail or tornadoes. You don’t panic, you just take some precautions. In almost every case, there turns out to be nothing to worry about. Sometimes things turn out bad, but most of the time, you’ll be OK. This is like that. I wanted to point out all the scary figures and possibilities first, though, and say that there is nothing to unduly worried about, because I am sure that someone is going to see these numbers and start predicting the end of the world again. There is cause to be concerned enough to keep an eye on this thing, but at this point that is all. Once there is more data, then we’ll know if we need to worry.
-Astroprof
Orbit Diagram courtesy NASA, JPL, Solar System Dynamics
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DavidG on February 10, 2008 at 1:54 pm: 2
Please help me understand this a bit better. The NEA risk page and FAQ only give limited insight.
So this year it came withing 19 Earth Radii. All of the encounters listed on the Neo risk page are closer than this. And all of these are from 2041 on. There are
CT1 takes about 307 days per orbit, so there are about 38 orbits before the 2041.
In some cases in the table there are several values for the same day. There are two for February 5, 2060.
2060-02-05.60 at 0.69
2060-02-05.58 at 0.12
I’m guessing that the system posts all solutions where multiple solutions are possible.
And in the 118 or so orbits in the next 100 years, the risk page has 15 years where the pass is projected at
DavidG on February 10, 2008 at 3:37 pm: 3
(continued) less than 1.0 Earth Radii.
These stick out visualy and are more obvious than Sigma Impact.
Now I would expect that some of the other close passes will change the orbit of this thing. Something that I expect the risk page doesn’t try and predict.
And, although I may be reading too much into this, it seems like this spends a long time away from the Earth and then a bunch of close passes. Would it be reasonable to think that this has been close before? I suspect that trying to look back is frought with potential error.
(Sorry for the split article, I used the symbol for less than and got caught by an input filter).
Astroprof on February 10, 2008 at 5:44 pm: 4
I haven’t spoken to any of the folks doing this, but my take on the table is that the asteroid passes by now and then, but that they only record passes that are closer than some value. So, the orbit likely gets closer and farther with time, so that is why it looks like no approaches for several decades. And, yes, I’d imagine that it has been nearby before … lots of times. Fortunately, space is big. But, give it enough near misses, and …
DavidG on February 10, 2008 at 6:31 pm: 5
Thanks that helps a bit. I last took an introductory astrophysics course around 1980 and my math beyond 1st year drips with rust. But I can’t help thinking there is a way to make these pages clearer.
I get that the result is a simulation of many virtual asteroids that fit the observations.
I also get that the criteria is more along the lines of some measure of error along the LOV. The some value seems to be a function of distance and uncertainty. That’s why some of the entries look like hits with small errors and other look like comfortable misses but have big errors.
I’m assuming if there is an entry in the table it’s significant. Some of the better observed rocks have only a few table entries. CT1 has many.
So, just guessing and not having followed many of these in detail, it looks like there is a lot of error in CT1 as expected. But to the casual observer the number that jumps out is the distance.
Actually when I saw the tables, I had the (completely unsupported thought) … I wonder where this beast was in 1972?
Space is certainly large and the chances of something hitting a sphere of a certain size should vary with the cube of the radius. Should do for a first cut. But I can’t even recall how to take into account how gravitational attraction will change that.
I have a blog for Cub Scouts that has a large astronomy content so far. I started down the path of explaining near misses. But so far I’ve really just hinted at it and just stuck to the fact that we are watching so that we can do something about the ones that count even if we need long lead times.
Astroprof on February 10, 2008 at 6:38 pm: 6
I agree, these tables could be made much more transparent. They are written for someone who knows what these values mean. They can easily be misunderstood, and I am pretty sure that someone will misunderstand them and set themselves up as some prophet of doom.
DavidG on February 11, 2008 at 10:41 pm: 7
Ok. I thought I had a partial handle on this and then I looked at the February 11th data for 2008 AF4.
http://neo.jpl.nasa.gov/risk/2008af4.html
It’s rated a 0 on the Torino scale, but the Earth Radii and Sigma Impact don’t look at all comforting.
What have I missed?
heather on February 16, 2008 at 4:42 pm: 8
Correct me if I am wrong (I hope I am understanding this), but there are several other even more close approaches on the list now for 2008 cti
2107-02-06.28 = .25
2080-02-06.09 = .19
2079-02-05.09 = .06
2072-02-05.62 = .38
2060-02-05.58 = .12
and there are more.
If anything under 1 earth radius miss is an impact, why do they not at least raise it to a 1 on torino?
I understand that it is probably impossible to predict anything this far out as all the parts of the math equation are probably not available, but could you describe some of the things they have to do going forward to nail its path down better? Also, just how early, before projected impact date, can they project an accurate path of orbit?
heather on February 16, 2008 at 4:48 pm: 9
i actually found this animation that explains a lot
http://neo.jpl.nasa.gov/gif/mea-orbit-big.gif