Astroblog: Is this an L4 asteroid?

Sunday, March 22, 2009

Is this an L4 asteroid?

UPDATE: No, it's not an L4, it's 234 Barbara. See here for further explanation.

On March 12 and 18 the Stereo Ahead craft and the Stereo Behind craft respectively did a 180 degree roll to image the L4 and L5 Lagrangian regions.

The Lagrange points are gravitationally stable points where researchers believe asteroids can accumulate. There are around 1000 asteroids in Jupiter's Lagrange points (but apparently none at Saturn's Lagrange points). The Earth's Lagrange points lie close to the Sun, so imaging them from Earth is pretty hard, and we have no real idea what lurks there. However, the Stereo spacecraft are about to pass the Lagrange points on September and October this year (see this orbit animation). This month though the two spacecraft were rolled to image the Lagrangian points for about 6 hours.

So what was revealed. Not much. I've gone through both the 12 March and 18 March images, and there is nothing really outstanding, so the area imaged didn't contain any really big rocks. There were 2 asteroidal candidates in each sequence, however, trying to exclude know asteroids has hit a snag. I have no idea what I am looking at.

According to me, Stereo A was looking at Pisces, and a 180 degree roll should make it look at the Virgo/Leo border. However, comet Al reckons it should be looking at a different segment of Pisces. My spherical geometry is sufficiently rusty that I have no idea which of us is right, and trying to match up features with both most likely frames is a nightmare.

Nonetheless, this object looks sufficiently interesting, its faint, but not a "Hot Pixel", and best of all, it is nowhere near the asteroidal and cometary candidates I can find in both alleged stereo A fields. Here's an animation of the object (bottom lefthand section of the image). It still could be a known object, I just have to spend a decent batch of time trying to work out where the actual field is. Also, as the area was only imaged for about 6 hours, there is not much time to establish an orbit. Lagrange asteroids should be moving very slowly with respect to the Stereo craft, and more or less in the ecliptic plane (similar to my 4 objects) so picking them up will be hard.

Here's the image coordinates of my best candidates. Top left of the image is 0,0


Best candidate
                       X       Y       Density Slice
20090312_060901_s4h1A   90      194     294     1
20090312_064901_s4h1A   90      194     387     2
20090312_072901_s4h1A   89      194     403     3
20090312_080901_s4h1A   89      194     455     4
20090312_084901_s4h1A   88      193     812     5
20090312_092901_s4h1A   88      193     331     6
20090312_100901_s4h1A   87      193     402     7
20090312_104901_s4h1A   87      192     236     8

Next best
20090312_060901_s4h1A 329 313 665 1
20090312_064901_s4h1A 329 313 553 2
20090312_072901_s4h1A 328 313 658 3
20090312_080901_s4h1A 327 313 706 4
20090312_084901_s4h1A 326 313 606 5
20090312_092901_s4h1A 326 313 505 6
20090312_100901_s4h1A 325 313 684 7
20090312_104901_s4h1A 324 313 808 8

20090318_164901_s4h1B 664 565 2527 1
20090318_172901_s4h1B 664 565 1506 2
20090318_180901_s4h1B 663 565 2679 3
20090318_184901_s4h1B 663 565 1502 5
20090318_192901_s4h1B 662 565 2712 6
20090318_200901_s4h1B 661 565 2022 7
20090318_204901_s4h1B 661 566 1752 8

20090318_164901_s4h1B 993 547 7 1
20090318_172901_s4h1B 993 546 766 2
20090318_180901_s4h1B 992 546 939 3
20090318_184901_s4h1B 992 546 813 5
20090318_192901_s4h1B 991 546 1313 6
20090318_200901_s4h1B 990 546 1275 7
20090318_204901_s4h1B 990 546 632 8

hot pixel
                       X       Y       Density Slice
20090312_060901_s4h1A   379     135     1322    1
20090312_104901_s4h1A   379     135     1357    8