STEREO Spacecraft To Explore Earth's L4 and L5

Hugh Pickens writes "Launched on October 25, 2006, NASA's twin Solar Terrestrial Relations Observatory (STEREO) spacecraft are about to enter the L4 and L5 Lagrangian points, special points in our orbit around which spacecraft and other objects can loiter because the gravitational pull of earth and the sun balances the forces from the object's orbital motion. (The spacecraft won't linger at the Lagrangian points; they are just passing through.) 'These places may hold small asteroids, which could be leftovers from a Mars-sized planet that formed billions of years ago,' said NASA Project Scientist Michael Kaiser. STEREO will look for asteroids with a wide-field-of-view telescope. 'If we discover the asteroids have the same composition as the Earth and moon, it will support Belbruno and Gott's version of the giant impact theory. The asteroids themselves could well be left-over from the formation of the solar system.' L4 and L5 are also good places to observe space weather. 'With both the sun and Earth in view, we could track solar storms and watch them evolve as they move toward Earth. Also, since we could see sides of the sun not visible from Earth, we would have a few days warning before stormy regions on the solar surface rotate to become directed at Earth,' says Kaiser."

Comments

May hold?

[palindrome]

'These places may hold small asteroids, which could be leftovers from a Mars-sized planet that formed billions of years ago,'

Can we not confirm the existence of these using telescopes on Earth or in orbit?

Re:May hold?

[aicrules]

Possibly, but the solar storm monitoring wouldn't be as effective.

Re:May hold?

[Bakkster]

Since the L4 and L5 points don't move relative to our perspective, any objects we would see there would move very little compared to the background of stars. Movement across a series of telescope images is the usual method for detecting small objects in our solar system, and it can't be used for these locations.

To detect objects here, you would need to look at images taken over a series of months and centered on the points to find objects that didn't move with the rest of our perspective. This would probably need to be done by a space telescope, since by the time a ground based telescope could see the points, the sun is already rising or still setting. Even then, the objects are only half lit by the sun, due to our angle of viewing, so they would be especially dim. In addition, sending a spacecraft to the area would allow the sattelites to determine the composition of the asteroids to see if they came from an Earth collision or are leftover from the solar system's birth.

Re:May hold?

[Hynee]

Since the L4 and L5 points don't move relative to our perspective, any objects we would see there would move very little compared to the background of stars.

They'd move as fast as the sun does through the background stars, for obvious reasons! That's ~1 deg/day.

Re:May hold?

[ATestR]

Actually, the L4 and L5 points would move at the same rate as the moon, since they are the gravitationally stable points created by the moon and Earth (60 degrees ahead and behind the moon on its orbit). And last time I looked at the moon, it does move against the background stars.

Re:May hold?

[Hynee]

OK, I'll continue.

To detect objects here, you would need to look at images taken over a series of months and centered on the points to find objects that didn't move with the rest of our perspective.

Months would do it, so too would hours! 2.5 min / hour.

This would probably need to be done by a space telescope, since by the time a ground based telescope could see the points, the sun is already rising or still setting.

They would set and rise at most 4 hours after the sun, plenty of time for 1x 1 hour exposure a day.

Even then, the objects are only half lit by the sun, due to our angle of viewing, so they would be especially dim.

Half-lit by the sun is no problem, this would only give them +0.75 Magnitudes (dimmer by a factor of 2).

In addition, sending a spacecraft to the area would allow the sattelites to determine the composition of the asteroids to see if they came from an Earth collision or are leftover from the solar system's birth.

You can still get composition information from asteroid spectra, they can put them into groups of composition types from that. If the spectra hasn't been observed before, it's best to have a sample.



I don't know what the problem with observing these points is, maybe the asteroids are likely too small.

Re:May hold?

[Bakkster]

That's a lunar L4 and L5. These satellites are headed to the solar L4 and L5.

Re:May hold?

[drerwk]

The L4 and L5 of TFA are the ones formed between the Earth and Sun - not the Earth and Moon.

Re:May hold?

[AaxelB]

If I may add, the two points are also really far away. I thought they were somewere within the orbit of the moon, but they're actually just as far away as the sun. (This picture cleared things up nicely.) We could probably tell whether asteroids are there, but for the reasons you mentioned we couldn't find out anything more useful.

Re:May hold?

[Geirzinho]

While the Earth-Moon system has lagrangians of its own, STEREO will pass through L4 and L5 belonging to the Earth-Sun system. STEREO left the Earth-Moon system only a few days after launch.

http://en.wikipedia.org/wiki/Lagrangian_point#Lagrangian_point_missions

Re:May hold?

[AaxelB]

Actually, the L4 and L5 points would move at the same rate as the moon, since they are the gravitationally stable points created by the moon and Earth (60 degrees ahead and behind the moon on its orbit). And last time I looked at the moon, it does move against the background stars.

This spacecraft is visiting the Sun-Earth Lagrangian points, not the Earth-Moon ones. The Sun-Earth L4 and L5 are just as far away as the sun, along the earth's orbit, so they'd appear to move just like the sun.

Re:May hold?

[Bakkster]

Yeah, I guess it's not quite as difficult as I thought. My additional guess would be that size and distance considerations makes it difficult enough that nobody has put quite enough effort into it. If the region of asteroids is large, it might be difficult to balance looking at a large enough area while still being able to see small objects. If STEREO does see something, it'll likely be small.

Re:May hold?

[v1]

afaik, all the L points are NOT static. The points exist where equilibrium of gravity from all nearby major sources is, and since all these sources are in motion relative to each other, the L points must also move.

For example, the location of the lagrange point between earth and moon is affected by the sun's gravity. It's not enough necessarily to pull anything out of it, but since it's moving, relative to what's IN it, (asteroids, satellites, whatever).

What I don't understand is why things tend to collect there. I can understand that once something arrives there, it would be easy for it to stay there, but the L point is just that, a point, not a region. A single asteroid that found itself exactly centered at L5 (ignoring tidal effects of the asteroid) and with zero relative momentum to L5's movement through space, could stay there. But L5 moves as the planets and satellites orbit. Not a lot, but some. And I don't see any factor that would cause an object that had left L5 (or more correctly, L5 had moved) to become attracted to moving back to L5. It's like a steel ball in between two magnets. If you put the ball in precisely the L point of where their fields meet, it can stay there. But one tiny nudge in the wrong direction (any point NOT on the perpendicular bisector of its location) would cause one magnet to attract it more than the other could counter, and the ball would slowly start to creep, and would soon accelerate and fly to the magnet. Why is this not an issue with the lagrange points? Only objects on the perp bisector of that L point would tend to move to the L point.

Re:May hold?

[mabhatter654]

because the small things still have gravitational force between them. Which at the point is exactly zero. So as long as the small objects don't move around much THEIR center of gravity stays on the point and they'd orbit it.

Re:May hold?

[v1]

Although mutual attraction would account for multiple objects in the L point staying near each other, there's no specific force attracting things TO the center of the L point. (beyond the gravity of objects already there, which unless they're massive, is pretty small) Beyond that, the areas anywhere except exactly in the L point only work to take you AWAY from the L point. This would seem to suggest that only one thing can maintain its position at any given L point, since only one thing can be precisely at the center of the L point. (tho maybe several things can collect together there in a lump?)

The traditional drawings I've seen of them show several satelites collecting in a cloud of sorts at a given L point. That doesn't seem to make much sense, the only way they could stay there is if they were touching? wouldn't work too well for satellites. Also having debris collect all around your surface would not be good either.

If one body managed to get to the L point, it could help attract other objects to the L point where they could lump together, but that still does not explain what keeps the mass IN the L point. Even a very weak influence from the outside would pull it ever so slightly away from the center (matter of millimeters even) and then it would not be experiencing even attraction anymore and would be pulled away from the L point?

Re:May hold?

[dwye]

Actually, it depends on which L4 and L5 one writes. The O'Neill space colonies were going to be at the Earth-Moon L4 and L5 points, whereas this is looking at the Sun-Earth ones, the equivalent of Jupiter's Trojans, about 93 million miles away (about 150 million km, according to unix's units prgm).

So you were right and wrong at the same time.

Re:May hold?

[OolimPhon]

Seems to work for Jupiter.

Re:May hold?

[camperdave]

That's a lunar L4 and L5. These satellites are headed to the solar L4 and L5.

Of course they are talking Sun-Earth Lagrange 4 and 5 (SEL4,SEL5), where do you think the figure of 1 degree per day came from SEL4 and SEL5 move with Earth along its orbit. 365 days to complete 360 degrees = approximately 1 degree per day.

Aliens

[Anonymous Coward]

I am 99% certain that this is the secret rendezvous where the Italians receive their coded instructions from their space alien masters. A U.S. space visit to this secure site may touch off a world war! But we have let the Italians control our Space and our moon for too long. I do not wish for war, I prefer peace, as every GOD-fearing American does. But when evil threatens our Galaxy and our homes and families, America mus stand ready for its historic duty to free our Solar System from the clutches of the Italo-Alien conspiracy.

Loiter?

[PinkyDead]

Get off my Lagrangian points you young hoodlums!

Re:Loiter?

[Anonymous Coward]

You so fat, you ain't got love handles - you got Lagrangian points!

Russell's teapot

[Nick Fel]

If its out there, the atheist community isn't going to be happy.

Re:Russell's teapot

[Anonymous Coward]

Na that'd be fine - as long as it isn't in orbit between Earth and Mars we're still right.

Re:Russell's teapot

[Limburgher]

On the contrary, it would simply provide evidence to back up a simple, intentionally ludicrous, hypothesis. Now, if they find God up there. . . I know, I know, WHOOOOOOSH. . .

Blasting Peter Gabriel?

[sprior]

So your telling me that NASA is parking the worlds most expensive STEREO in the only free parking spots in the solar system? Next you're gonna tell me they used it to blast "In your eyes"...

Re:Blasting Peter Gabriel?

[necro81]

"The light, the heat
I am complete"

Re:Blasting Peter Gabriel?

[Ioldanach]

Maybe they're rickrolling the solar system?

Re:Blasting Peter Gabriel?

[Lumpy]

Nope they are blasting Depeche Mode, Zig Zig Sputnik, and some Flock of seagulls music.

Come on, NASA guys dont like Peter Gabriel, not hip enough....

Re:Blasting Peter Gabriel?

[Limburgher]

Nah, it's for an upcoming Disaster Area reunion.

Re:Blasting Peter Gabriel?

[mabhatter654]

it's OK, we have a backup.

I wonder, how.

[SharpFang]

AFAIK, Lagrange points are points of -unstable- balance, that is any object placed there that has even minimal speed will proceed to move out and gain speed doing so; only maneuver thrusters would allow a satellite to "linger" there pushing it back when it slips out, and I wonder what cosmic odds would it take for a passing meteor to -stop- there, as in, hit a meteor with exactly the same momentum coming from opposite side at exactly that location...

Re:I wonder, how.

[hcpxvi]

That (the lagrange points being unstable equilibria) is true of L1, L2 and L3 (all on the Earth-Sun line, L1 between Earth and Sun, L2 outside the Earth's orbit and L3 round the other side of the Sun). L4 and L5, OTOH, are stable equilibria and junk can collect there. The equivalent points for Jupiter have observable collections of asteroids in them.

Re:I wonder, how.

[fredrik70]

actually 4 and 5 are stable, from wikipedia:
In contrast to the collinear Lagrangian points, the triangular points (L4 and L5) are stable equilibria (cf. attractor), provided that the ratio of M1/M2 is greater than 24.96.[5][6] This is the case for the Sunâ"Earth and, by a smaller margin, the Earthâ"Moon systems. When a body at these points is perturbed, it moves away from the point, but the Coriolis effect bends the object's path into a stable, kidney beanâshaped orbit around the point (as seen in the rotating frame of reference). However, in the Earthâ"Moon case, the problem of stability is greatly complicated by the appreciable solar gravitational influence.[7]

source

Re:I wonder, how.

[east coast]

IANAAP but I think that is only true for L1-L3. IIRC L4 and L5 would be relatively stable as long as a body had the correct momentum when it entered them.

Re:I wonder, how.

[Anonymous Coward]

Just about everyone of my professors at U.T. have declared that if they see any cite to Wikipedia, the paper, assignment, whatever, will automatically receive a failing grade.

Reason? Because while the articles may cite legitimate sources, they are almost always contaminated by the ignorance and/or bias of the author(s) and/or simply misinterpreted.

Friends don't let friends cite Wikipedia.

Re:I wonder, how.

[fredrik70]

utter rubbish, in an informal environment like this wikipedia is fine. Indeed you should not use it in papers and such, that' splain silly, but for a quick lookup of fact, together with a quick check if the content seems unreasonable or not, it's fine

Re:I wonder, how.

[jeepien]

You are just as likely to receive a failing grade if you sign your paper Anonymous Coward.

So your point was, what?--rules for college assignments should apply to slashdot?

Re:I wonder, how.

[pwfffff]

But but but it's tainted with lieeesssss!!!!!11

Re:I wonder, how.

[Anonymous Coward]

http://map.gsfc.nasa.gov/mission/observatory_l2.html

problem solved. next time you can be un-lazy about it and find your own non-wikipedia sources.

Re:I wonder, how.

[Anonymous Coward]

So for Slashdot, information "contaminated by the ignorance and/or bias of the author(s) and/or simply misinterpreted" is fine?

That explains quite a bit.

L1,2,3 are different from L4,5

[Anonymous Coward]

L4 and L5 are stable, means that a force pushes objects back in the direction of those points regardless of the direction, because they are a local potential minimum.

L1, L2, L3 are indeed unstable, but there exists an orbit around those points, which is stable.

Re:L1,2,3 are different from L4,5

[kmac06]

Actually L4 and L5 are local potential maxima (in a rotating reference frame, maybe? It's been a while since I took mechanics), but orbits around these points are kept stable by some combination of the Coriolis force and gravity.

No Such Lagranimals

[DynaSoar]

"The asteroids themselves could well be left-over from the formation of the solar system."

No way. The Lagrange points are theoretical solutions to the 3 body problem. The Earth-Sun system is not 3 body. The Earth's relationship with the moon is such that their common center is outside the Earth. Fluctuations in the gravity field of the co-orbiting the Earth-moon would guarantee no permanently stable solution.

The L4 and L5 points are not gravity wells. They are the tops of gravity hills (see the top map at http://en.wikipedia.org/wiki/Lagrange_point ). The slightest perturbation will result in a body at those points to orbit the point and eventually be thrown out. We have satellites at Lagrange points now and they are operated in that way. They orbit the L point, and have station keeping motors to keep them orbiting them.

The above is doubly applicable if the theorized collision scenario occurred. The moon supposedly came from the collision of the Earth and a Mars sized object. Such a collision would preclude their being any L points that remained stable throughout, making it impossible that there should be asteroids remaining in such points since the beginning of the solar system.

Re:No Such Lagranimals

[kill-1]

First of all, the Lagrange points are only the solution of a special case of the three body problem (m3 is negligibly small). Then, L4 and L5 actually are stable. The arrows in the Wikipedia article "indicate the gradients of increasing potential". Note the word "increasing".

Re:No Such Lagranimals

[AikonMGB]

First: The Earth's relationship with the Moon is such that their barycentre is inside the Earth, about 1700 km below the surface.

Second: L4 and L5 are potential minima, meaning the gravitational potential field increases as you move away from these points. Although the term "well" is misleading, it is certainly more applicable than "hill". It is this increasing potential that leads to the Lyapunov stability of L4 and L5 in the restricted three-body problem. The definition of this kind of stability is that if you are perturbed from equilibrium some small delta less than epsilon, then you will stay within that epsilon band.

Third: The Earth-Sun Lagrange points currently occupied by satellites are L1 and L2, for perpetual sunlight and perpetual shadow respectively. L1, L2, and L3 are all unstable, hence the necessity for station-keeping of these satellites. As far as I am aware, there are no satellites currently occupying L4 or L5.

Fourth: Large Impact Theory is just that, a theory. One of the objectives of this mission is to determine if there are small asteroids at L4 and/or L5, which could either lend support to or detract support from this theory. Regardless of whether this event happened or not, the L4 and L5 points still exist for any restricted three-body problem. Case in point: Jupiter-Sun L4 and L5 are filled with the Trojan asteroids.

-Aikon

Earth's L4 and L5

[hammarlund]

When I read the headline I thought if this worked out that there might be help for my L4 and L5 back problems.

Re:Earth's L4 and L5

[NoobixCube]

The earth is getting pretty old, even if you believe the Christians (what do they think, 6000 years?). I'd say it needs some lumbar support by now.

Get another acronym

[Anonymous Coward]

In space, no one can hear your STEREO

missing link

[Takichi]

The team is inviting the public to participate in the search by viewing the data and filing a report at: >

There's a missing link in the article for where you can help out. The link meant to posted is:

Re:missing link

[Anonymous Coward]

Try this article: http://science.nasa.gov/headlines/y2009/09apr_theia.htm

I think the link should probably be to here: http://sungrazer.nrl.navy.mil/index.php?p=lagrange_campaign

Alright I'll sacrifice myself

[Yvan256]

The new STEREO spacecraft is an improved version of MONO. The next spacecraft, scheduled to be released in 10 years, will be called SURROUND.

Sorry, I'll be here all week.

Re:Alright I'll sacrifice myself

[Anonymous Coward]

I winced.

all I could think of

[jaimz22]

yeah I know it's off topic but all I could think of when I saw the headline was homeboys in outer space http://en.wikipedia.org/wiki/Homeboys_in_Outer_Space/

Missing Planet

[Jokerz17]

"These places may hold small asteroids, which could be leftovers from a Mars-sized planet that formed billions of years ago"


So... Mars?

'Secrets' in L4/L5 (and risks)

[ghostlibrary]

As a researching using STEREO data, I wrote a piece on some of the logistics of this, and what we may find.
http://scientificblogging.com/daytime_astronomer/secrets_l4l5_gravity_wells

The summary is: we've already seen a bit in an earlier roll so we know there's stuff there, we lose use of the in-situ to explore L4/L5 so we have to balance that with our core science, there's a higher risk to the detectors due to dust, but what the heck, we have to pass through it anyway. We may find any of: dust, the moon's progenitor, and earth-killer, more dust.

La Grange?

[Ranhert]

I finally figured out what ZZ Top was singing about. Earth's and the Sun's gravitational limbo land.

Given the probable mass and relative speeds...

[mmell]

These places may hold small asteroids

which will turn the STEREO spacecraft into interplanetary techno-confetti upon impact.

This surprised me...

[argStyopa]

"These places may hold small asteroids..."

Really? We don't KNOW?

Checking wiki, apparently we're not even sure of what's in the L4/L5s in the Earth/Moon system. A Japanese probe failed to find the expected Kordylewski clouds.

I'm well aware of the vasty nature of space, but I guess I'm sometimes startled about how ignorant we are about our own very local neighborhood...

Re:This surprised me...

[RoboRay]

Considering that the L4 & L5 points are 60 degrees around our orbit of the sun, I wouldn't call it "our own very local neighborhood." They're as far away from earth as the sun.

Re:This surprised me...

[RoboRay]

Oh, I missed that you were referring to the lunar Lagrange points, rather than the Earth's (as discussed in the article. Never mind.

Thank God they put these out there

[drewsup]

Sorry, I just say Knowing, I'm still scared shitless..LOL NOT!

STEREO

[reidiq]

Powered by THX Dolby Surround Sound.

Mars-sized?

[guspasho]

"which could be leftovers from a Mars-sized planet that formed billions of years ago"

I wonder which planet that could be!

My God!

[MJMullinII]

It's full of stars!

The other Earth..

[Fishbulb]

Who knows, maybe they'll see our Antichthon!

I learned about Lagrange points from a game.

[tekshogun]

Does anyone remember Independence War and Independence War 2? The first one is almost 11 years old and the second is almost 8 years old. They used Lagrange points for a type of FTL travel. It was a cool game and being I was still in high school, I didn't know much about that level of astrophysics.