Asteroids are Missing in Asteroid Belt - Gaps in Asteroid Belt
Have you ever seen these abnormality in the Asteroid Belt in the regions as shown in this picture below? Why are there these gaps in the belt as if the asteroids are missing somewhere?
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| Red arrows pointing towards the gaps in the region facing Jupiter, and yellow arrows pointing towards gaps in the region facing the Sun. |
Scientists from all over the globe sat down together to solve this mystery of missing asteroids and to suggest and possibly find out a subtle reason as to why these regions are devoid of asteroids.
At University of Arizona or UA in short, scientists revealed that there ought to be more number of asteroids than they had observed. Well, this can suggest only one thing: There had been a massive planetary migration in the earliest formative years of this Solar System which dates back to 4 billion years. This massive planetary migration might be the most probable candidate responsible for this curious and strange deformity in the Asteroid Belt.
Massive Planetary Migration
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| Earliest years of Solar System. Credits: huffingtonpost.com |
But what is this massive planetary migration in the first place? We actually need to learn a little of this as well to understand the root of this irregularity in the Belt. As the words suggest; four billion years ago, Solar System's biggest or giant planets migrated from their position to the position as we see them today through telescopes. This indicates that our Solar System was not exceptionally stable and due to this instability, massive planetary migration occurred.
This migration of huge planets like Jupiter and Saturn with their massive gravity suggests evidently that these planets were responsible for fierce chapter of asteroids pounding the inner planets especially including our own gem, Earth.
Gaps in Sun facing region of Asteroid Belt
The doughnut shaped Asteroid Belt as we see today is devoid of a number of asteroids greater than what scientists calculated and predicted. As there are two regions to consider, the inward region facing the Sun, and central region facing the gas giant.
There are asteroids missing on both the inward region facing the Sun, and central region facing the Jupiter. The exposition of the missing asteroid in the inward region goes in this way: The asteroids facing the Sun are fried off or disintegrated when they get too close to the yellow heating ball of dust, the Sun.
Researchers then went on to not to consider the asteroids anymore rather form a hunt for Near Earth Objects or NEOs in short. NEO is what it seems to be - a small sized asteroids or a comet. As NASA describes the NEO:
Near-Earth Objects (NEOs) are comets and asteroids that have been nudged by the gravitational attraction of nearby planets into orbits that allow them to enter the Earth's neighborhood.
This suggests that NEOs are closer to Earth or for an asteroid, it should be atleast at a distance 1.3 times the distance between Earth and the Sun. Scientists and researchers began their hunt for NEOs and observed 9000 objects in about a time span of 8 years. However, there was a discrepancy in their calculations when they did not find their expected asteroid in the inward region. Robert Jedicke of the University of Hawaii Institute for Astronomy comments on this discrepancy:
If we weren't scientists, we might have said it's close enough, but something didn't feel right.
Yes, it didn't. There must be some reason for it to what it is. A scientist from University of Helsinki by the name of Mikael Granvik proposed that the asteroids are missing due to the reasonable fact that Sun is causing a tear down in the thermal forces of the asteroids which is responsible for the destruction of asteroids. Studies were carried on and this proposal became the most probable reason for this case of absent asteroids. And Robert Jedicke praises this explanation on missing asteroid by:
That's exactly what you would expect to see (in the asteroid belt).
So this case of missing asteroids in the inward region is closed, solved, and done. But what about the region facing the Jupiter.
Major Gaps in the region of Asteroid Belt facing Jupiter
The gaps in the central region which are now called Kirkwood gaps are present in the belt where the gravity of two of the biggest planets, Jupiter and Saturn, influences each other and tends to change its normal state. This ejected the asteroids which later cause the evident asteroid bombardment on inner planets including Earth. This later proved precious event for life on Earth. Since that period evolution began on Earth and it changed to what it is today, a habitable blue gem.
The region where this phenomenon exists is deprived of asteroids in the belt. David Minton, a graduate of planetary sciences from his alma mater, UA, says:
What we wanted to know was, how much of the structure of the asteroid belts could be explained simply by the gravitational effects of the giant planets, as are the Kirkwood gaps.
Renu Malhotra, a professor of planetary sciences from UA, and David Minton observed the asteroids with a diameter larger than 50 kilometer or approximately 30 miles. This gave the researchers in UA a thoroughgoing set of data. Minton, after the collection of data, says:
We ran massive sets of simulations with computer planets where we filled up the Asteroid Belt region with a uniform distribution of computer asteroids.
When the simulated Asteroid Belt was compared with the real one, it matched pretty well with the side facing the Sun, but there was a pattern in the differences as compared with the side facing the Jupiter. We know now where few of the asteroids from a region facing the Sun go, but what about this region facing the Jupiter. And also, this difference was huge!
Minton and crew then ran the simulation again but now with a difference. He reports:
Then we simulated the migration of the giant planets. The perturbing effects of the migrating planets sculpted our simulated Asteroid Belt. After the migration was over, our simulated Asteroid Belt looked much more like the observed Asteroid Belt.
In addition to this, Malhotra also concluded:
Our interpretation is that as Jupiter and Saturn migrated, their orbital resonances swept through the Asteroid Belt, ejecting many more asteroids than is possible with the planets in their current orbits. And the peculiar patter of missing asteroids is characteristics of the pattern of Jupiter's and Saturn's migration.
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| Animation of Jupiter and Kirkwood Gaps |
But still it could not explain as to why this had happened. To know this, we need to discuss a little about those Kirkwood Gaps. As described by Space.com: Resonant effects can be clearly seen in the radial distribution of the asteroids. Some orbital resonances are destabilizing, creating minima in the distribution, called Kirkwood Gaps; after Daniel Kirkwood who first recognized them.
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| Kirkwood Gaps resonance effects. Credits: cefns.nau.edu |
As seen from above graph, the 3:2 to 1:1 resonances are stable, Moreover, these resonances represents the Hilda family asteroids and Jupiter Trojans.
Minton explains this in the following words:
The patterns of depletion are like the footprints of wandering giant planets preserved in the asteroid belt.
Now as for the migration of planets, this study verifies with other results that due to the strong arrangement of all the gas giants except Jupiter pushed Jupiter slightly nearer to the Sun while all the other gas giants moved away from Sun and away from each other as well. And therefore, the Jupiter getting closer to Sun caused all the chaos as discussed all above. Minton comments on asteroid bombardment on inner planets during this massive planetary migration:
Our result doesn't directly answer the question of whether the timing of this can be tied to the inner solar system heavy bombardment. But what it does say is that there was an event that destabilized asteroids over a relatively short period of time.
We still have no appropriate answer or explanation to this curious question of an open case of asteroid gone missing, but all the above calculations and theories are based on evidently real events. We have surely more to uncover.
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