Last fall I wrote about the history of an asteroid family in which I showed that detailed analyses of pieces of a broken up asteroid reveal that the asteroid family is very old. This argument for long ages was based on very simple laws of physics and was completely independent of radiometric dating. A couple of weeks ago I ran across a description (see references) of rotating vs tumbling asteroids that really struck me as an even more straightforward argument for the age of these objects and wanted to share.
So how can the rotation of asteroids tell us the age of the solar system?
There are millions of asteroids orbiting the solar system most of which are found in the asteroid belt between Mars and Jupiter. Studies of these asteroids, as part of an effort to assess the threats to earth, have allowed us to track and paths, sizes and rotational frequencies of over 1000 asteroids. All asteroids rotate but they don’t all rotate like planets. Some rotate around their principle axis (like the earth and moon) which is the lowest energy state for rotation and thus the end-state rotation for an object. Other asteroids don’t rotate around their principle axis but rather are tumbling chaotically and have irregular rotational frequency.
The important physics principle here is that tumbling objects are at higher energy states overall and inertia, internal friction and tiny gravitational forces from planets and the sun will cause a tumbling object to dissipate energy resulting, given enough time, in the object to eventually rotate around its principle axis unless energy is continually added to them which in this case would mean being hit by another object resulting in a reversion to tumbling again.
So if there are asteroids that do and don’t rotate around their principle axis can we predict which ones will be and which won’t be? There are and yes, a predication can be made because there is a simple formula based on rotational speed and diameter of the object that allows one to predict how long it would take a tumbler to become stable. For example if a large object were to strike the earth and cause it to change its rotational axis and tumble it would take only 17 years for its rotation to stabilize around its principal axis. The smaller and object and slower the rotational period the longer it will take. Based on other estimates that the solar system is 4.6 billion years old it is predicted that asteroids present at the time of its formation there will have had 4.6 billion years of time to find their principal axis of rotation. It is predicted then that asteroids with small diameters and long rotational periods should be still tumbling even after 4.6 billion years. On the other hand there should be many asteroids that are rotating about their principal axis and the sizes and rotational periods can be predicted and then measurements of asteroids can test those predictions.
Do actual measurements of asteroids from the solar system support the predictions of physics and other estimates of the age of the solar system? Yes, there is a remarkable agreement with actual measurements and what is expected. There are thousands of asteroids that rotate round their principal axis and all of them are below the size and diameter limits required to acquire that rotation in less than 4.6 billion years. On the other hand ALL of the asteroids that are small enough or have very long rotation periods such that it would take more than 4.6 billion years to stabilize are tumblers! Here are just a couple of numbers demonstrating predicted time for particular objects to obtain rotation about their principal axis:
Earth – ca. 17 yrs.
433 Eros (34 km diameter with a rotation period of 5 hr 16 minutes) – ca. 100,000 yrs.
4-Vesta – (572 km diameter with a rotation period of only 5 hours) – <10,000 years
25143 Itokawa: (530 miles in diameter with a rotation period of 12 days) – 929 million yrs.
4179 Toutatis (4.5 km diameter with a rotation of 5 to 6 days) – ca. 60 billion yrs.
The first four are rotating around their principal axis, the last one , Toutatis, is a tumbler. These data represent strong independent confirmation of the age of the solar system.
Asteroid rotation and young earth creationism:
We can see that chaotic and regular rotating asteroids represent positive outcomes of tests of predictions based on an old solar system. What are the predictions of those that say that the solar system is very young regarding these asteroids? This is a bit tricky since there are several possible scenarios so let’s go through each possible alternative hypothesis and apply the observations of tumbling vs non-tumbling asteroids.
In the YEC worldview there are three possible initial states of asteroids in creation: 1) all tumblers, 2) all with regular rotation and 3) a mixture of some tumblers and some with regular rotation. Remember that many YEC’s like to put questions like this into the ‘origins science” category, which I discussed in a previous post (Origin Science and Misconceptions of Historical Science), so that they can claim that these phenomena can’t be studied but is there nothing that can be said about these asteroids? Lets look at predictions from each of these. If all asteroids were created (originated) in the 6 days or somehow came into existence later (see below about Brown’s hypothesis) and they were all tumblers, creation science would predict that only a very very few asteroids would be found to be rotating about their principal axis today. But the majority of those tested are so this directly refutes that prediction. What if all asteroids were created with regular rotation? Maybe some asteroids could be expected to bump into each other causing them to become chaotic but then one would predict that the size and rotation periods of asteroids should be randomly associated with tumbling vs not tumbling but they are most definitely not random. More below on this but the last hypothesis that asteroids were created with some as tumblers and some not as tumblers is harder to test. Not knowing the initial condition of each asteroid it may be difficult to predict what we should see today, but there is still a pattern that suggests the solar system is more than 4 billion years old. This pattern would then point to God having created tumblers and non-tumblers in ratio that tells us he created the solar system with the intention of their appearing to be the result of a particular age (4+ billion years old).
Two examples of creationist speculations about asteroids:
#1 We have already written about the wildly speculative theories of Dr. Walter Brown (Walter Brown and the Origin of Asteroids and Impact Craters on other Planets). Quickly, Brown believes that the asteroid belt originated as the result of water and material blown off the earth when the water beneath the earth erupted in the initial stages of the Flood. That water froze in space to become the asteroids many of which fell back to earth causing bombardment later in the Flood year but the rest became the asteroids between Mars and Jupiter. Aside from being completely implausible already Brown should know enough astrophysics to realize that all these pieces blown off earth would have entered into space as tumblers with a random assortment of rotational speeds and diameters. So in this case the “origin” of asteroids is only some 4000 years ago. What should all these asteroids be doing today? Aside from possibly Vesta, one of the very largest asteroids (possibly a dwarf planet even), all other asteroids would be predicted to be tumblers the majority of the 1000s of them that have been examined are not. Brown makes no mention of this problem in his book.
#2 In a recent article on creation.com (Creation Ministries International) entitled “4 Vesta, achondritic meteorites and Flood bombardment” Froede is making the argument that asteroid bombardment which many YECs believe helped start the Flood was the result of asteroids from the asteroid belt thrown toward earth. Toward the end he makes the following statement:
While asteroids could have been ejected from the asteroid belt shortly after its creation, this is unlikely since everything that was created was proclaimed “very good”—implying perfection.
I never cease to be amazed when I see this argument that something could have been a certain way because the creation was “very good” and therefore perfect. Why is it that these authors always seem to know just what perfection is? So what is perfection here. Well, if the asteroids were created by God in the asteroid belt as part of the original creation then they had to be perfect which means they were somehow perfectly in place. What does this mean? I guess they has perfectly circular orbits about the sun (just like the Earth did allowing for no seasons!), would never have bumped into each other and I would imagine could not possibly have been tumblers because this is chaotic motion and God took chaos and made it perfect. So that perfect world of perfect asteroids was somehow corrupted by sin and the asteroid started to bump into each other sending them into chaotic orbits which led them to intersect with the Earth causing a global Flood.
Even if this were at all plausible what would be the predictions with respect to asteroid tumbling? If two asteroids collide, and they do have marks of collisions all over them, they will be sent into a tumbling rotation. Given that all asteroids looks like they have been involved in thousands of collisions if these all happened in the past 10,000 years every asteroid should be tumbling. But most are not tumbling, almost all large asteroids are covered in craters but are rotating around their principal axis. This can only be if they were created with all the craters (apparent collisions) and already in rotation around their principle axis. In an 4.6 billion year old solar system, the collision may have happened hundreds of millions or even billion years ago but there has been time for the tumbling to be converted to rotation around the principal axis that we see today.
I think we have a case here were very simple physics provides a powerful case for asteroids as very old objects in the solar system. Only an old universe provides the context to easily interpret this data. Creationists ultimately have to propose an ad hoc explanation that includes God miraculously making some asteroids tumble and others not in a pattern that just happens to match the pattern predicted by an old universe (ie. created with the appearance of age).
Rotational properties of asteroids, comets and TNOs – an article that summarizes data collected on rotations of asteroids. Includes several figures which are helpful.
http://crimesagainstdivinity.wordpress.com/2012/05/05/so-does-common-sense/ – This is where I first came across a description of this problem and I got some of the data from this page. The videos embedded are helpful but I hesitate to recommend since they are rather sarcastic in nature. While I disagree with creationists on their interpretations and am troubled by their influence on other Christians I don’t wish to be rude to fellow believers and these videos are not meant to be helpful only ridicule. However, with respect to the logic and conclusions they are probably very much right.
It’s an interesting thought that if Earth was not at all tilted, but it still had the same mildly (and varyingly) elliptical orbit there would be some slight seasonality temperature wise though not daylight wise (similar seasonality in both hemispheres at the same time) – as the planet drew closer to or further from the Sun during the year.
Hello, I looked up 25143 Itokawa, and wikipedia is telling me that actually it’s more like 520 meters in diameter, not miles. Could you double-check that? Does it change the calculation for time to rotate about principle axis? Thanks !