STEREO Spacecraft To Explore Earth's L4 and L5 66
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."
May hold? (Score:2, Interesting)
'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?
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Re:May hold? (Score:5, Informative)
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? (Score:4, Informative)
They'd move as fast as the sun does through the background stars, for obvious reasons! That's ~1 deg/day.
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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.
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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 [wikipedia.org]
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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.
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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 collec
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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.
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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 a
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Seems to work for Jupiter.
Re:May hold? (Score:4, Insightful)
Months would do it, so too would hours! 2.5 min / hour.
They would set and rise at most 4 hours after the sun, plenty of time for 1x 1 hour exposure a day.
Half-lit by the sun is no problem, this would only give them +0.75 Magnitudes (dimmer by a factor of 2).
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.
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So you were right and wrong at the same time.
Loiter? (Score:5, Funny)
Get off my Lagrangian points you young hoodlums!
Russell's teapot (Score:3, Funny)
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Blasting Peter Gabriel? (Score:3, Funny)
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"...
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I am complete"
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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? (Score:4, Funny)
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it's OK, we have a backup.
I wonder, how. (Score:1)
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...
L1,2,3 are different from L4,5 (Score:4, Informative)
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.
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Re:I wonder, how. (Score:5, Informative)
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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 se
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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
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But but but it's tainted with lieeesssss!!!!!11
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So your point was, what?--rules for college assignments should apply to slashdot?
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No Such Lagranimals (Score:2)
"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 h [wikipedia.org]
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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 (Score:5, Informative)
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 [wikipedia.org].
-Aikon
Earth's L4 and L5 (Score:1)
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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 (Score:2, Funny)
In space, no one can hear your STEREO
missing link (Score:1)
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:
Alright I'll sacrifice myself (Score:2)
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.
Missing Planet (Score:1)
So... Mars?
'Secrets' in L4/L5 (and risks) (Score:4, Informative)
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 [scientificblogging.com]
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? (Score:2, Funny)
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... (Score:1)
which will turn the STEREO spacecraft into interplanetary techno-confetti upon impact.
This surprised me... (Score:2)
"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...
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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.
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Oh, I missed that you were referring to the lunar Lagrange points, rather than the Earth's (as discussed in the article. Never mind.
STEREO (Score:1)
Mars-sized? (Score:2)
"which could be leftovers from a Mars-sized planet that formed billions of years ago"
I wonder which planet that could be!
My God! (Score:1)
It's full of stars!
The other Earth.. (Score:2)
I learned about Lagrange points from a game. (Score:1)