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."

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: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?

[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.