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July 29, 2011 7:11 AM   Subscribe

Jupiter has lots. Mars has some, too, as does Neptune. Turns out Earth's got a trojan asteroid of its own. Meet 2010 TK7, the blue planet's new baby brother.
posted by Sys Rq (51 comments total) 11 users marked this as a favorite

 
So in terms of exploration - how does this compare in difficulty to visiting the moon or Mars?
posted by odinsdream at 7:15 AM on July 29, 2011


Well I must say I was a skeptic until I checked that "circled in green" enlarged image. Removed all doubt for me!
posted by Mike D at 7:16 AM on July 29, 2011


The proof is the thing that's circled in green moving across multiple images.
posted by empath at 7:18 AM on July 29, 2011


Wait, so this asteroid is basically waiting for us to bring it inside our gates so a bunch of Ancient Greek Aliens can suddenly leap out and sack our planet? I say that blowing it up is the only way to be safe.
posted by GenjiandProust at 7:19 AM on July 29, 2011


I imagine it's fairly tricky but no more difficult than going to the moon. You'd need more delta-v at the end than you would to orbit the moon because there's not something big enough to get into orbit of there (how's that for an awkward sentence). There have been a couple probes sent out to Lagrange points, and that's where the James Webb Space Telescope will go if it ever flies.
posted by zomg at 7:20 AM on July 29, 2011


I've never had a brother before! ^-^
posted by Tarumba at 7:20 AM on July 29, 2011 [1 favorite]


So... um...
posted by Mike D at 7:22 AM on July 29, 2011


Not to worry; it won't collide with Earth for at least a hundred years.

(That's how far ahead the space nerds have traced the asteroid's orbit.)
posted by Sys Rq at 7:25 AM on July 29, 2011


I always thought it would have been neat if earth had a sister planet sharing the same orbit, yet always directly on the other side of the sun and undetected. (although I remember reading that this was ruled out when Voyager turned around to take a family photo). A little brother instead is a good consolation. To think the earth was once a ring of dust around the sun billions of years ago...this asteroid might be made of the same primordial stuff.
posted by samsara at 7:26 AM on July 29, 2011


Well, NASA's current goal is to visit an asteroid by 2025. Not sure a 1,000 foot rock is worth it though.
posted by Brandon Blatcher at 7:38 AM on July 29, 2011


This thing's orbit is inclined more than 20 degrees from the ecliptic, yet it's described as "sharing Earth's orbit." So what exactly does "sharing an orbit" mean?
posted by gubo at 7:39 AM on July 29, 2011 [2 favorites]


Wait, so this asteroid is basically waiting for us to bring it inside our gates...

No, it's keeping us save from venereal diseases.

someone please get that whole joke
posted by DU at 7:39 AM on July 29, 2011 [5 favorites]


earth had a sister planet sharing the same orbit, yet always directly on the other side of the sun and undetected.

You'll say that's cool until the day the insect overlords sponsor raiding parties to capture earth's women, who will only discover true womanhood in slavery, and it's twenty-nine novels before they knock that shit off.
posted by Phalene at 7:48 AM on July 29, 2011 [3 favorites]


someone please get that whole joke

i.e. when Galactus turns up he's going to stick this asteroid on his giant space-cock before he fucks our planet into smithereens.
posted by the quidnunc kid at 7:48 AM on July 29, 2011 [6 favorites]


@gubo as shown in this NASA animation "sharing an orbit" seems to mean that it orbits in such a way that it crosses the plane of the ecliptic every couple of years. In 2015, it might well be 20 degrees below it...
posted by Mad_Carew at 7:51 AM on July 29, 2011 [1 favorite]


According to TFA, the asteroid's orbit is stable for at least 10,000 years, and it would be very hard to visit because of the distance it sweeps above and below the plane of the ecliptic.
posted by localroger at 8:02 AM on July 29, 2011


samsara, any "counter-Earth" is also ruled out by the gravitational pull of Venus and Jupiter.
posted by Guy Smiley at 8:05 AM on July 29, 2011


This is a good opportunity to again link to my (now totally inaccurate) minor planets venn diagram.
posted by Plutor at 8:08 AM on July 29, 2011 [3 favorites]


...this NASA animation...

What is it orbiting around?
posted by Brandon Blatcher at 8:08 AM on July 29, 2011


With a name as cute as 2010 TK7, why isn't this Earth's little sister?
posted by TDavis at 8:10 AM on July 29, 2011


What is it orbiting around?

The Sun. But the animation is in a weird frame of reference where the Earth-Sun position is fixed, so as the astroid moves up and down out of the Earth's orbital plane, and as it moves closer and further from the sun due to the ellipticity of its orbit, the animation makes it look like it's moving in a circle. It's kind of cool when you decode the motion, but it looks very weird initially.
posted by kiltedtaco at 8:29 AM on July 29, 2011


It's very weird, it looks like it's orbiting something in in Earth's plane. Like a secret planet the government doesn't want us to know about.
posted by Brandon Blatcher at 8:35 AM on July 29, 2011 [1 favorite]


No it's not very cool.
That's one fucked up orbit. More like a kid brother, it's all over the road, so-to-speak.
posted by djrock3k at 8:41 AM on July 29, 2011


In case anyone else is disappointed by the post framing, it's in L5.

This differs from 3753 Cruithne, which is not co-orbital with Earth.
posted by Eideteker at 8:52 AM on July 29, 2011


And it's more like a little cousin.
posted by Eideteker at 8:55 AM on July 29, 2011


Eideteker: "In case anyone else is disappointed by the post framing, it's in L5."

According to Wikipedia's summary of the original publication in Nature, it oscillates around L4 with a period of about 395 years
posted by Plutor at 9:00 AM on July 29, 2011 [1 favorite]


Yeah, I just saw the animation. The article led me to believe it was following Earth. My apologies.
posted by Eideteker at 9:01 AM on July 29, 2011


Aw, look at it, all running off ahead and going in circles. We should formally name it Yotsuba.
posted by cmyk at 9:01 AM on July 29, 2011 [1 favorite]


This thing's orbit is inclined more than 20 degrees from the ecliptic, yet it's described as "sharing Earth's orbit." So what exactly does "sharing an orbit" mean?

It's sharing our orbit in a vague sense that its orbiting the sun at about the same distance we are. It would be more accurate to describe the object as being in/near one of Earth's Lagrange points. The picture of the Jupiter Trojans makes it look like the Lagrange points can be more like Lagrange areas, in that if an object is sort of close to the point it can be sort of stable in that position.

What I don't get from the animation is that it looks like it is orbiting our orbit. Is it orbiting the L4 point? Is that a thing that happens?


There have been a couple probes sent out to Lagrange points, and that's where the James Webb Space Telescope will go if it ever flies.

I think James Webb is going in the L2 point, which is a hell of a lot closer to Earth than this little guy.
posted by cirrostratus at 9:03 AM on July 29, 2011 [1 favorite]


We should check if it is hollow. And filled with a group of humans waiting to repopulate Earth when the debt ceiling debate results in planetary civil war.
posted by oneironaut at 9:06 AM on July 29, 2011


I imagine it's fairly tricky but no more difficult than going to the moon.

The way we went to the Moon was to use a long engine burn to put the spacecraft into a very eccentric orbit around the Earth, with a perigee of about 500km and an apogee well beyond the moon. However, the orbit was such that, as the spacecraft approached the Moon's orbit, the Moon would be there, and the Moon's gravity would alter the orbit from an eccentric Earth orbit to a hyperbolic lunar one, with a perilune around 100km.

In most cases, the orbit was even more clever -- since it was hyperbolic, you needed to burn to actually lower your apolune below infinity and enter lunar orbit, and if you didn't, you'd sling around the Moon. If you entered that orbit just right, it would sling you right back to Earth in what was called a Free Return Trajectory. The Apollo missions weren't launched into such trajectories, but close to them, a little bit of foresight that helped to save Apollo 13. The normal abort would have been to use the CSM engine (the SPS) to quickly lower the apogee of the TLI orbit and get back to Earth quickly, but because of the explosion, they couldn't risk using the SPS, and the engine they did have, the LM descent stage, didn't have the Δv they needed. It did have enough to change the TLI orbit into free return trajectory, and so they looped around the Moon and came back to Earth.

This isn't going to work for something at the L4/L5 points in the Earth/Sun system. You're going to need to get into a solar orbit -- which means a full Earth escape orbit -- and then you're going to need to change that solar orbit to match 2010 TK7's solar orbit, and you're not going to have much gravitational assist from the object to help you stop when you get there -- certainly nothing like we did with the Moon and Earth in Apollo. So, you're going to need a lot of ΔV and a lot of time. You can trade, somewhat, between them -- the more ΔV you have, the less time you'll need.

To move the same mass from here to 2010 TK7 as we did to the moon -- close to 35,000kg for the CSM/LM combination -- you will need vastly more ΔV, which means either vastly more fuel or vastly higher Isp.

Not easy. Putting a small probe over there, of course, would be much easier -- one of the fundamental implications of Tsiolkovsky's rocket equation is that the less mass you need to put at the target, the easier the whole system becomes to build.
posted by eriko at 9:09 AM on July 29, 2011 [17 favorites]


We should check if it is hollow. And filled with a group of humans waiting to repopulate Earth when the debt ceiling debate results in planetary civil war.

That would be nice, but it's probably just filled with reptilians.
posted by cirrostratus at 9:09 AM on July 29, 2011


From the 2nd link, frm NASA: "It's as though Earth is playing follow the leader," said Amy Mainzer, the principal investigator of NEOWISE at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Earth always is chasing this asteroid around."

The planet Earth isn't chasing anything. I know it's a cute metaphor, but it is misleading.

here on earth itself, the chasing of things never stops.
posted by longsleeves at 9:43 AM on July 29, 2011


The planet Earth isn't chasing anything. I know it's a cute metaphor, but it is misleading.

I know, right?

It's Asteroids, NASA, not Pac-Man!
posted by Sys Rq at 11:20 AM on July 29, 2011


It's at L4. We're chasing it.


Quick calculations:
~150m radius, 1.4M m3
Density ~1500kg/m3 (if similar to some more closely observed asteroids)
Mass ~= 2.1 billion kilograms, likely rich in Fe and/or H2O

This is a very happy discovery for people who dream of an aggressive space program. Lagrange points are useful places to be in space, and this is heaps of mass that we don't need to launch from earth. Unleash the robot miners!

(now let's hope there's also something at L1. That would be even happier news - that's a great place to drop a solar observatory)
posted by justsomebodythatyouusedtoknow at 11:27 AM on July 29, 2011 [1 favorite]


longsleeves: " The planet Earth isn't chasing anything. I know it's a cute metaphor, but it is misleading."

As justsomebodythatyouusedtoknow points out, the Earth is chasing it in a very real way. It orbits our L4 Lagrangian point, about 60 degrees "ahead" of Earth's orbit. I suppose you could make the argument that this is still just a metaphor, that both bodies just happen to be where they are because of the various gravitational forces and inertias. But you could make analogous arguments to claim that orbiting is just a metaphor.
posted by Plutor at 11:44 AM on July 29, 2011


Are we pushing it? Or is our L4 pulling it? What's the right/more correct way to think about it?
posted by Eideteker at 12:05 PM on July 29, 2011


We are actually pushing it. A stable Lagrange point is a region of space where the closer you are to the L point, the more powerfully you are attracted to that point. Accordingly, you can orbit a stable Lagrange point even though there isn't a physical object at its center.

The Lagrange point is actually a feature of the Earth-Sun system. The Earth and Sun would do what they do regardless of whether the asteroid is there, but if either the Earth or the Sun were to suddenly disappear the asteroid would either fly off or go looking for a human city to vaporize.

This asteroid is in a particularly wild Lagrange orbit, which suggests that there may be some other resonance issues with other planets keeping it from settling in.
posted by localroger at 1:07 PM on July 29, 2011 [1 favorite]


I wonder if the wild orbit points to some clue about the formation of the moon. Maybe if we find some more of these asteroids, we can gather some more data!
posted by Eideteker at 1:21 PM on July 29, 2011


Dammit--
can we start giving new planets names that don't sound like a serial # for a laptop? Christ.
posted by herbplarfegan at 2:48 PM on July 29, 2011


eriko - I would pay a lot to watch a 90 minute documentary (with good animations) based on your comment.
posted by benito.strauss at 3:05 PM on July 29, 2011


herbplarfegan, this isn't a name, it's a provisional designation. It was the 185th minor planet reported during September 1-15 of 2010. No doubt it will eventually be named.

Sometimes discoverers propose names right away and they are used in the media, prior to IAU adoption, but that doesn't seem to be the case here. The proposed names aren't always accepted.

Accordingly, you can orbit a stable Lagrange point even though there isn't a physical object at its center.

It's important to realize that this is true of any two objects in an orbital relationship. The Earth doesn't orbit the Sun; it orbits the barycenter (a nominal mathematical location) of the Sun-Earth gravitational attraction system. For practical purposes, this is the same as the center of the Sun, but the existence of the L4 and L5 points illustrates very graphically how it doesn't need to actually be the center of the larger object. In the Earth-Moon pair, the barycenter is "merely" 1707 km beneath the Earth's surface. In the case of two objects of much more equal mass -- pretty rare, but some examples exist -- the two objects will be found to be orbiting a point essentially in open space between them. Waving hands and oversimplifying, this is how the L4 point functions for the three-body problem of the Earth-Sun-TK7 triad.

I'm sure somewhere out there are charts or animations showing how this works.
posted by dhartung at 3:36 PM on July 29, 2011 [1 favorite]


The problem with saying that the earth is 'chasing' the asteroid is that it implies the earth's orbit is somehow affected by the asteroid. It is, but in a really, really, really minuscule, barely detectable way. It's just a bad way of thinking about what's happening.
posted by empath at 5:13 PM on July 29, 2011


(now let's hope there's also something at L1. That would be even happier news - that's a great place to drop a solar observatory)

There is, and we put it there, and funny enough, it is a solar observatory! It's SOHO the winner of the "You gotta be kidding me, that thing still works?" award. Launched in 1995, went into operation on a two year mission in 1996, and it's still running.

Nearby is ACE, the Advanced Composition Explorer. It's been hanging around L1 for almost as long.

Technically, they're not exactly at L1 -- staying at L1 precisely is actually somewhat hard, like balancing a bowling ball on top of a hill. It's unstable, so both craft actually use more complicated orbits near or around the L1 point. SOHO is in a halo orbit near L1, but closer to Earth, and ACE is in a lissajous orbit around L1 itself.
posted by eriko at 5:34 PM on July 29, 2011 [2 favorites]


Jupiter has lots. Mars has some, too, as does Neptune. Turns out Earth's got a trojan asteroid of its own.

What about Uranus? Glad to hear about Mars.
posted by Joe in Australia at 2:14 AM on July 30, 2011


dhartung: "It's important to realize that this is true of any two objects in an orbital relationship."

Actually, L4 and L5 are only stable if the ratio of the two masses (in this case, Earth and Sun) is at least 24.95. (Cite: pages 7-8 of this paper.) This is true for Earth-Sun, Jupiter-Sun, and by a very small ratio, Moon-Earth. L4 and L5 are not particularly stable, for, say, Charon-Pluto.
posted by Plutor at 8:00 AM on July 30, 2011


What about Uranus?

[unfunny joke re: ointment]
posted by Sys Rq at 9:19 AM on July 30, 2011


I just meant that Earth is "not chasing it" in the sense that it is not trying to catch it. It is merely following it.
posted by longsleeves at 1:36 PM on July 30, 2011


So it's more like the beginning of a conga line then?
posted by A dead Quaker at 9:13 AM on July 31, 2011


EXACTLY.
posted by longsleeves at 9:26 AM on August 2, 2011




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