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opli
2004-May-13, 11:45 AM
What elements, substances or conditions might be the cause of Sedna appearing to be red and having a highly reflective surface?

(I'm finding the popular artist's depiction of Sedna a little bit distracting when it comes to the actual look and makeup of this planetoid. It's kind of become what I picture in my head when I think of Senda, but I feel it may be misleading.)

Kullat Nunu
2004-May-13, 01:41 PM
What elements, substances or conditions might be the cause of Sedna appearing to be red and having a highly reflective surface?

As far as I know, it a still a mystery. We still don't know how Sedna formed (in situ or thrown out from nearer the Sun).

Distant minor objects tend to be quite dark, but larger planetoids are all brighter than usual KBOs. Pluto is an extreme case, but it may be due to its atmosphere (ices condendsing on its surface).

Many KBOs are quite red, including Pluto and Triton, which is almost certainly a captured KBO. None is as red as Sedna, though, and it may present a completely different population of minor objects (i.e. not a KBO at all).


(I'm finding the popular artist's depiction of Sedna a little bit distracting when it comes to the actual look and makeup of this planetoid. It's kind of become what I picture in my head when I think of Senda, but I feel it may be misleading.)

Well, if Sedna's diameter is about 1,500 - 1,600 km it is almost certainly a round object. With an albedo greater than 0.2 its surface is brighter than the Moon's. Distance from the Sun makes it naturally look darker. I think surface should be cratered, because where it formed, it subjected to meteor bombardment anyway (unless it has melted).

Any surface markings are yet to be detected, it is possible that the surface is not uniform.

That satellite in the illustration seems not be real.

Otherwise, I see not problem with the illustration. It is still much more accurate than most illustrations made on Pluto.

Padawan
2004-May-13, 08:14 PM
Do you guys have a link to the illustration?

Kullat Nunu
2004-May-13, 08:32 PM
Do you guys have a link to the illustration?

From Spitzer's homepage (http://www.spitzer.caltech.edu/Media/releases/ssc2004-05/ssc2004-05b.shtml).

Well, it seems to be less illuminated than I remembered...

Anyway, it is a strange press release, as Spitzer Space Telescope didn't detect Sedna.

opli
2004-May-13, 11:12 PM
I should have mentioned that I'm mostly looking for speculation. Any ideas?

Brady Yoon
2004-May-14, 12:57 AM
From intuition, I would think KBO's are mostly white because they are mostly ice. Why are KBO's red?

AK
2004-May-14, 12:56 PM
From intuition, I would think KBO's are mostly white because they are mostly ice. Why are KBO's red?

If KBOs were white, they'd be much higher albedo objects than they are. For a while it was thought that most of them are as black as soot, but apparently that perception is/was incorrect. Nevertheless, most known KBOs are still exceptionally dark.

As for why Sedna is red, not a clue.

weatherc
2004-May-14, 01:53 PM
From intuition, I would think KBO's are mostly white because they are mostly ice. Why are KBO's red?

When astronomers speak of bodies being made mostly of ice, they don't always mean water ice. Icy bodies can be made of mixtures of ammonia ice, methane ice, and many other kinds of ice.

From what I can tell, if astronomers are speaking of a body that is made of water ice, they will actually use that term specifically, as opposed to just using the term "ice."

Swift
2004-May-14, 01:55 PM
I have a vague memory that red might be hydrocarbons. I think one of Jupiter's or Saturn's moon's is also reddish (not counting the sulfur on Io) and it was postulated that the interaction of UV and methane could create higher-molecular weight hydrocarbons that would produce a reddish color. How that mechanism might work on Sedna, I have not a clue.

SiriMurthy
2004-May-14, 07:26 PM
I Don't intend to stray off-topic, but I wonder what would be the size of the Sun if I were to stand on the surface of Sedna? Would our Sun look as big as Venus from Earth? A little bigger?

Crazieman
2004-May-14, 09:42 PM
I remember articles saying that the Sun from Sedna could be blocked by the head of a pin held at arms length. Likely - bigger than Venus, but not by much.

daver
2004-May-14, 11:09 PM
I remember articles saying that the Sun from Sedna could be blocked by the head of a pin held at arms length. Likely - bigger than Venus, but not by much.

Sedna's perhelion is 76 AU, its aphelion is 990 AU. Venus is close enough to 1/100 the sun's diameter.

So, at perihelion, the Sun is roughly the size of Venus (Venus at its closest is about twice the angular diameter from us as the Sun from Sedna at its closest; Venus at its farthest from us is about half the angular diameter as the Sun from Sedna at perihelion). Venus from us is about 10x the angular diameter of the Sun from Sedna at aphelion.

SiriMurthy
2004-May-20, 03:29 AM
I remember articles saying that the Sun from Sedna could be blocked by the head of a pin held at arms length. Likely - bigger than Venus, but not by much.

Sedna's perhelion is 76 AU, its aphelion is 990 AU. Venus is close enough to 1/100 the sun's diameter.

So, at perihelion, the Sun is roughly the size of Venus (Venus at its closest is about twice the angular diameter from us as the Sun from Sedna at its closest; Venus at its farthest from us is about half the angular diameter as the Sun from Sedna at perihelion). Venus from us is about 10x the angular diameter of the Sun from Sedna at aphelion.

76 AU and 990 AU! That's one heck of an elliptical orbit! Thanks for the explanation.