Posted on 10/21/2002 2:37:19 PM PDT by blam
Monday, 21 October, 2002, 16:27 GMT 17:27 UK
Earth's little brother found
The asteroid was found almost by accident
By Dr David Whitehouse BBC News Online science editor
Astronomers have discovered the first object ever that is in a companion orbit to the Earth.
Asteroid 2002 AA29 is only about 100 metres wide and never comes closer than 3.6 million miles to our planet.
But it shares the Earth's orbit around the Sun, at first on one side of the Earth and then escaping to travel along our planet's path around the Sun until it encounters the Earth from the other side. Then it goes back again.
Researchers are speculating that 2002 AA29 could be visited by astronauts or used to understand the threat to our planet posed by such rocks from space.
Co-orbital object
2002 AA29 was discovered by the linear automated sky survey project on 9 January 2002.
Martin Connors of Athabaseca University in Canada writes in the journal Meteoritics and Planetary Science that it, "moves in a very Earth-like orbit," and is the "first true co-orbital object of Earth."
2002 AA29 has a bizarre horseshoe orbit around the sun
General Simon Worden of the United States Space Command described it as a "near Earth object that is close to being trapped by the Earth as a second natural satellite".
According to Helena Morais of the University of Lisbon and Allesandro Morbidelli of the University of Nice, writing in a paper to be published in the journal, Icarus: "2002 AA29 seems to be in a temporary horseshoe-like orbit with the Earth."
This puts 2002 AA29 is in the same class as 3753 Cruithne, a similar rocky body in a horseshoe orbit around the Earth.
But astronomers classify 2002 AA29 as the first real co-orbital body found associated with the Earth because it more completely shares the Earth's path around the Sun.
Co-orbiting asteroids have been found around other planets.
near Earth object that is close to being trapped by the Earth as a second natural satellite
General Simon Worden US Space Command
Over 1,200 so called "Trojans" have been found moving either ahead or behind Jupiter.
Eight such objects have been found associated with Mars.
But despite detailed searches no one has yet found any Trojan objects near the Earth.
It is clear that 2002 AA29 was discovered by accident at a time when it was at one end of its horseshoe orbit and, being at its closest to the Earth, was bright enough to be detected in an automated sky survey.
Detailed observations of its trajectory through space show that 2002 AA29 will reach its minimum close approach to the Earth - 12 times the distance between Earth and the Moon - at 1900 GMT on 8 January 2003.
Cat-and-mouse game
Thereafter it will travel ahead of the Earth moving faster than our planet does, until after 95 years it will catch up with the other side of the Earth and then reverse its motion.
Analysis of 2002 AA29's motions have revealed a remarkable event that happens to it every few thousand years.
In 550AD, and again in 2600AD and 3880AD, for a while it will become a true satellite of our planet, in effect Earth's second moon, although technically it will remain under the gravitational control of the Sun.
It remains a second moon to Earth for about 50 years until it escapes.
Although only about 100 metres across 2002 AA29 may play a role in the manned exploration of space out of all proportion to its size.
Already researchers are speculating that it could be visited by an unmanned spaceprobe or even become the first object after the Moon to be stepped on by astronauts.
The object could tell us a lot about the composition of asteroids.
Some have speculated that it could be nudged into a permanent Earth orbit where it could be studied at greater length.
Or it could be nudged into an Earth intercept if NASA is in charge of the project. Let's just go to the asteroid, let's don't bring it here, eh?
For luck, you know...
The new one needs a name, something unpronounceable like Cruithne or the forgettable name of the new planet in the Kuiper Belt.
Note to Blam: The orbit appears horseshoe shaped, sort of, as seen from earth.
I wonder when the previous temporary capture was? The period is a little irregular, but looks like about every 2100 to 2300 years.
What is that, Thera? Sodom and Gomorrah?
That was my thought too. Let's not start nudging asteroids unless the are already in an Earth intercept.
On an orbit very closly matching earth, as it catches up with earth from "behind", it would speed up approaching earth, making its orbit larger, and thus its year would be less than earth, and then move away.
When earth next catches up to it, it would be slowed down, making its orbit lower, and revolve faster around the sun.
This ping-pong action is, what did the article say, 85 years? The part I really wonder about is how they know enough about its orbit to know that Earth would catch it as a new moon at three different points. Maybe it would enter from a Lagrange point, the way the Saturn third stage from Apollo 12 recently did.
Yes, start loading the silver bird.
Anyone got a Tongva-English, English-Tongva dictionary handy?
Now, now. Any Gaelic-speaker (a bheil Ga\idhlig no Gaeilge agaibh?), even a learner, could tell you:
From Near-Earth asteroid 3753 Cruithne: The Dalriada Celtic Heritage Trust inform us the Cruithne were "the first Celtic racio-tribal group to come to the British Isles, appearing between about 800 and 500 B.C., and coming from the European continent. They were also known as the Picts. The correct pronunciation for 'Cruithne' is 'croo-een-ya'. The emphasis should be on the -een-".
Now, now, go easy on the Gaelic orthography (it's really pretty simple):
From Near-Earth asteroid 3753 Cruithne: The Dalriada Celtic Heritage Trust inform us the Cruithne were "the first Celtic racio-tribal group to come to the British Isles, appearing between about 800 and 500 B.C., and coming from the European continent. They were also known as the Picts. The correct pronunciation for 'Cruithne' is 'croo-een-ya'. The emphasis should be on the -een-".
LOL! Pete Worden keeps showing up like a bad penny in articles of this sort. He's been angling for years to position himself for the Terrestrial Defense command, if such a thing ever comes to pass.
I'm pretty sure the Brits are forming one. ...and I think we will also eventually.
Nope -- just plain ol' orbital mechanics. The operative principle is: "speed up to slow down, slow down to speed up."
When its orbit is closer to the sun than ours it goes faster, and catches up to us from behind. This speeds it up, and raises its orbit. Then we are behind it. When we catch up to it from behind, we pull back on it, slow it down, and its orbit drops below ours, and the cycle starts again. Pretty nifty business.
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