Near-Earth asteroids aren't all that rare, but today two researchers at Armagh Observatory in Northern Ireland say they've found an extremely rare near-Earth object in an orbit very similar to Earth's. Asteroid 2010 SO16 is not exotic because of it's closeness to the home planet, but because it is stuck in a rare horseshoe orbit.
Horseshoe orbits only happen under a specific set of circumstances, so it is believed they are pretty rare. The name "horseshoe" is derived from the shape of the object's orbit as seen from Earth--that is, it doesn't stop mid-orbit, turn around, and travel in the other direction. It has everything to do with shifts in the object's orbital path and our perspective of the object as it gets closer, shifts orbit, and then gets further away without ever passing Earth.
To better understand this, one only needs to keep in mind that objects closer to the sun orbit faster and objects further away orbit more slowly. So here's what happens: the asteroid is in a slightly smaller orbit than Earth's, and thus moves faster. But as it approaches Earth on the inside track, the Earth's gravity begins to pull on it. As Earth pulls the asteroid toward it, the asteroid's orbit grows larger and it begins to orbit more slowly.
Eventually Earth pulls the object to an orbit slightly outside that of Earth's--now it is moving more slowly than the planet and Earth begins to pull away (or, from our perspective, the asteroid approaches on the inside, moves to the outside, and begins to recede away from us).
Many, many years later, Earth catches up to the asteroid on the other side, at which point the process works in reverse: Earth slowly approaches the slower asteroid from behind, its gravity pulls the asteroid back toward the inside orbit, and the asteroid speeds up. From our perspective, we're getting nearer the asteroid, then it begins to move away again. At no point does the asteroid pass the earth, nor does the Earth pass the asteroid.
So the asteroid orbits the sun in the same direction at varying speeds depending on its orbit, but from our perspective it never appears to close its orbital loop (see the diagram above). Hence: horseshoe orbit.
Right now, SO16 is near one of its closest points of approach, chasing the Earth on its inside orbit. As such it will be a fixture in the sky for the next few decades, the researchers say, until it is pulled all the way over into the outside orbit and it slowly recedes from view.
The full paper is here (PDF).
Hmm this asteroid must have heard our plans to blow them up with nukes/lasers.
YA! You better run!
Here is what I heard: blah, blah, blah, science, science, science, science... horseshoe. I like horsehoes. =)
@lavahothand, funny... real funny.. :)
Seriously though, even though the Earth is obviously much more massive than this asteroid it must affect our orbit as well and I wonder if this accounts for changes in the length of our year?
Ah, so the Earth hasn't yet "cleared it's neighborhood" therefore it isn't a planet anymore .....
+1 to Earth as the new Dwarf Planet
@basildave: What exactly are you referring to? The every 4 years we add a day to make up for unaccounted time? That's because our day's are actually just slightly longer than 24, and it adds up to be a discrepancy of roughly 6 hours a year.
If that's not what you're talking about, then I urge you to consider the moon. Much closer, much more massive, and is actually drifting away from the Earth, roughly 3.8cm per year. The changing gravity fields between the Earth and moon can lead to minute changes in the Earth's orbit, which accumulate over time.
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Fallacy i agree with you i heard that before and that what strikes fear in me if we are slowly moving away from the moon earth will not last till 3000 i think this is really bad i think we go the good oll american way plant a large unblievable amount of nuclear explosives and blow the moon back into a more stable orbit that is what i think we should do
I think you mean a year is slightly longer than 365 days. If a day was longer than 24 hours after a few months at 6pm the sun would be rising instead of setting.
Both you and Fallacy are correct. The actual length of a year is 365.2422 days. Technically you could break this down and say that each day is actually 24.0159 hours long. Thus it is really just a matter of semantics saying that our year is longer or that each day is longer...
Glade I wasn't the only one that noticed that.
After 1000 years (in the year 3000), the Moon would have moved 38 meters further from the Earth... if it drifts away at 3.8cm per year.
Why exactly would this cause the earth "not to last" till the year 3000 CE?
actually convictus is right and wrong, the reason the sun doed not eventually get out of wack with our clocks (sun setting instead of rising) is because we add the one day after 4 years instead of adding .0159 hours each day, this keeps the sun and clocks insync with each other
Fascinating article. I would not have believed such an orbit was possible. It must be very rare indeed if it is essentially perpetual.
LOL ... our day and our year are not related! A day is 24 hours. It would be very lucky indeed if our planet returned to the same spot in it's orbit each year at the same time that a day was ending. However, we are currently not that lucky so there is about a quarter of a day deviation each cycle of our orbit. We need to add a day to our calendar every four years to prevent our seasons from drifting in relation to that calendar.
In other words, changing our orbit would shorten or lengthen our year but would have no affect on the length of our days! During the history of the Earth, there would have been some brief periods where the year had a whole number of days.
Alright I have been doing some research on this and I found something interesting. I found this orbit to be so odd and after watching it I noticed a pattern of 175 years when it comes close to the earth. Now you are not going to believe this so google them yourself. The 10 years before and after the comet comes its closest is when our largest volcano have erupted on this planet. At least for the last 2000 years. I didn't go back any farther. Frankly I dont think there is any reliable information before that. Im talking about huge earth quakes and eruptions and I didn't catch it until I seen one of the headings it said "from 1630 til 1830"
there were not any eruptions I think Etna or Krakatoa.
So then I read more and it fits the pattern. I asked myself how could a 60 meter rock have any effect on our planet at all. Why does this rock seem to come very close and then turn around and go the other way. First there are elements in the universe that a spoonful would weight tons. Second it could be repelling the rock because of an opposite pole like a magnet. Third guess what year its at the closest this time. Could this have been mistaken for evil planet long ago
and this is why the Myan calendar ends? I'm not a conspiracy theorist but I think we need to study this rock a lot closer. If it does cause us grief every 200 years blast it...
@ Far Out Man
Ack!!! should have seen that. i got caught in the maths web, i didn't even think about in relation to the actual concept of a day and a year. ::facepalm::
B. B. Bop