Earth always has a second temporary moon, researchers claim

Dec 21, 2011 By Amy Shira Teitel, Universe Today
Saturn's moons Rhea and Dione as seen by the Cassini spacecraft. Could this be a future view from Earth? Image credit: NASA/JPL/Space Science Institute

In the fall of 2006, observers at the Catalina Sky Survey in Arizona found an object orbiting the Earth. At first, it looked like a spent rocket stage -- it had a spectrum similar to the titanium white paint NASA uses on rocket stages that end up in heliocentric orbits. But closer inspection revealed that the object was a natural body. Called 2006 RH120, it was a tiny asteroid measuring just a few metres across but it still qualified as a natural satellite just like out Moon. By June 2007, it was gone. Less than a year after it arrived, it left Earth’s orbit in search of a new cosmic companion.

Now, astrophysicists at Cornell are suggesting that 2006 RH120 wasn’t an anomaly; a second temporary moon is actually the norm for our planet.

Temporary satellites are a result of the gravitational pull of and the . Both bodies pull on one another and also pull on anything else in nearby space. The most common objects that get pulled in by the Earth-Moon system’s gravity are near Earth objects (NEOs) — comets and asteroids are nudged by the outer planets and end up in orbits that bring them into Earth’s neighbourhood.

The team from Cornell, astrophysicists Mikael Granvik, Jeremie Vaubaillon, Robert Jedicke, has modeled the way our Earth-Moon system captures these NEOs to understand how often we have additional moons and how long they stick around.

They found that the Earth-Moon system captures NEOs quite frequently. “At any given time, there should be at least one natural Earth satellite of 1-meter diameter orbiting the Earth,” the team said. These NEOs the Earth for about ten months, enough time to make about three orbits, before leaving.

Luckily, and very interestingly, this discovery has implication well beyond academic applications.

Knowing that these small satellites come and go but that one is always present around the Earth, astronomers can work on detecting them. With more complete information on these bodies, specifically their position around the Earth at a given time, could send a crew out to investigate. A crew wouldn’t be able to land on something a few metres across, but they could certainly study it up close and gather samples.

Proposals for a manned mission to an asteroid have been floating around NASA for years. Now, astronauts won’t have to go all the way out to an asteroid to learn about the Solar System’s early history. NASA can wait for an asteroid to come to us.

If the Cornell team is right and there is no shortage of second satellites around the Earth, the gains from such missions increases. The possible information about the solar system’s formation that we could obtain would be amazing, and amazingly cost-efficient.

Explore further: NASA team lays plans to observe new worlds

More information: The population of natural Earth satellites, arXiv:1112.3781v1 [astro-ph.EP] arxiv.org/abs/1112.3781

Abstract
We have for the first time calculated the population characteristics of the Earth's irregular natural satellites (NES) that are temporarily captured from the near-Earth-object (NEO) population. The steady-state NES size-frequency and residence-time distributions were determined under the dynamical influence of all the massive bodies in the solar system (but mainly the Sun, Earth, and Moon) for NEOs of negligible mass. To this end, we compute the NES capture probability from the NEO population as a function of the latter's heliocentric orbital elements and combine those results with the current best estimates for the NEO size-frequency and orbital distribution. At any given time there should be at least one NES of 1-meter diameter orbiting the Earth. The average temporarily-captured orbiter (TCO; an object that makes at least one revolution around the Earth in a co-rotating coordinate system) completes $(2.88pm0.82)rev$ around the Earth during a capture event that lasts $(286pm18)days$. We find a small preference for capture events starting in either January or July. Our results are consistent with the single known natural TCO, 2006 RH$_{120}$, a few-meter diameter object that was captured for about a year starting in June 2006. We estimate that about 0.1% of all meteors impacting the Earth were TCOs.

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User comments : 11

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Isaacsname
3 / 5 (2) Dec 21, 2011
Almost makes me wonder if NEO's have grazed other atmospheres in our solar system and inadvertently brought things here when they got too close,... like Nitrile from Pluto ?
eigenbasis
not rated yet Dec 21, 2011
That's cool, maybe they will 'sweep' away all the crud orbiting the earth due to high altitude nuclear tests and space junk! ^_^
scidog
not rated yet Dec 22, 2011
some sort of dock and return would be quite the event.why get a spoon full when a meter size rock could be locked in a cargo bay of some sort and be landed like the Russia crew capsule.
SleepTech
3 / 5 (2) Dec 22, 2011
In this article, NEO = Moons. Ugh! I thought Physorg was beyond fabricating hype in their article titles.
HydraulicsNath
not rated yet Dec 22, 2011
The moon believed that they should see other people...
Isaacsname
not rated yet Dec 22, 2011
The moon believed that they should see other people...


" The course of true love never did run smooth.. "

~ W. Shakespeare
alq131
not rated yet Dec 22, 2011
so, objects a couple meters across should be pretty easy to capture. What about a robotic probe that would gather these and put them in a holding lagrange point? or bring them slowly down to LEO and the space station for analysis? What if one was full of platinum or other rare elements, it would be a pretty "easy" mining method. Pop a heatshield cone on one and drop it into the desert....we could be analyzing these things!!!!
Nanobanano
1 / 5 (1) Dec 22, 2011
8,000kg moving about 11km/s...

Woo hoo.

Match velocity with a robotic probe, and then slow it down and put it back on course for the earth, with a big parachute.

Doing that would be about as compliated as a round trip mission to the moon, maybe even more complicated.

In fact, it would probably be easier to go catch an asteroid from the main belt and bring it back, since matching velocity and orbits would be more manageable.

the lunar missions worked primarily by abusing gravitational acceleration and conservation of momentum.

The NEOs are on some chaotic orbits not on the same planes, etc, so you'd have to go out there and intercept, "brake", match velocity, attach a rocket, and then accelerate back to Earth.

Cost probably 2 or 3 times as much fuel, if not a great deal more than that...
nkalanaga
5 / 5 (1) Dec 22, 2011
Solar sails would be ideal for this project, although the return would be slow. Once the sail was in orbit no fuel would be needed.
Xbw
2 / 5 (4) Dec 22, 2011
so, objects a couple meters across should be pretty easy to capture. What about a robotic probe that would gather these and put them in a holding lagrange point? or bring them slowly down to LEO and the space station for analysis? What if one was full of platinum or other rare elements, it would be a pretty "easy" mining method. Pop a heatshield cone on one and drop it into the desert....we could be analyzing these things!!!!

I'm sure it's a bit more complicated than that but yes, that is a neat idea. It would save fuel costs compared to sending probes much further into the solar system :)
WhiteJim
3.7 / 5 (3) Dec 22, 2011
just put instruments on it and see where you go. use it as a shuttle to get closer to other objects and then launch from near there to land on something else in motio. We can have all kinds of instruments autonimously moving about between the planets jumping from rock to rock to rock