Hubble Photo of Sedna Suprises Astronomers

waynegoode writes "Soon after the announcement of the discovery of Sedna, the solar system's furthest object and planet wanna-be, the Hubble Space Telescope was pointed at it to answer some of the many questions its discovery generated. The photos were released today and are surprising for what they don't show--a moon. Astronomers were certain it had a moon because of its slow rotation. "I'm completely baffled at the absence of a moon," says Michael Brown, Sedna's discoverer. Story and photo at Universe Today, hubblesite and NASA press release."

Comments

Re:Quality?

[d60b9y]

I may not be a lawyer ;-) but I have just finished a Ph.D. in astonomy and I've worked with Hubble images (included ACS images) before.

NaSa are wonderful at using Hubble to produce pretty publicity images. I'm not saying that the images of nebulae etc. are not without scientific justification, only that NaSa are very good at presenting them to the public.

These images are more typical of the data taken by Hubble on a day-to-day basis; single filter images (presented in black and white) of faint objects pushing down close to the detection limit of the instruments.

Dr.Mike Brown gives four possible explanations..

[EqualSlash]

Dr.Brown one of sedna's discoverers gives out the following expanation at his site

We can think of 4 possibilities for why we do not see a moon around Sedna.

• (1) Perhaps we got extremely unlucky and the moon is hiding directly behind Sedna. This possibility is unlikely (about 1 in 100 chance), but can't be ruled out completely.
• (2) Perhaps the moon is fainter than expected. We think that the moon has to be quite large to explain the very slow rotation of Sedna, so we think that it should be bright. But it is possible that it is large but has a very dark surface and so is difficult to see. We believe that many objects (other than Sedna!) in the outer reaches of the solar system should be quite dark, so perhaps this suggestion is not unreasonable.
• (3) Perhaps the moon is gone! It is possible that there once was a moon which slowed the rotation of Sedna but now the moon is gone. Moons can get destroyed by impacts with other large objects in space or they can be stripped away by close encounters with other planetoids. While we can't rule out this possibility, we do not think it is very likely.
• (4) Perhaps our circumstantial evidence is misleading us. There are 2 ways that we can think of for this to have happened: Perhaps the brightening and faintening that we think we see are not real. Measurements in science are never perfect, and perhaps some of these imperfections have, by bad luck, led us to believe that we are measuring Sedna's rotation when we are really not. From our understanding of the measurements, we can estimate that there is about a 1 in 20 chance of this type of bad luck. We thus think it is unlikely, but, again, we can't rule it out. Perhaps the measurement is real, but we are being fooled. Imagine that you look at a clock once every twenty-five hours. How fast would you think the hands were turning? The first day the clock would say noon. The second day 1pm. The third day 2pm. You might think the clock only moved 1 hour per twenty-five hours. Perhaps the same thing is happening with Sedna: Our measurements were made approximately every 24 hours, so if Sedna rotates every 25 hours, then every time we look it appears to have only rotated a little, and we think it takes 24 days to make a full rotation. This possibility cannot be ruled out with the current data, though it would require the unusual coincidence that Sedna's rotation period would have to be unusually close to the earth's rotation period!