# A planet beyond Pluto? **URL:** \ **Category:** Factual Questions\ **Created:** [December 2, 2003, 2:32pm UTC](https://boards.straightdope.com/t/a-planet-beyond-pluto/216495 "2003-12-02T14:32:16Z")\ **Posts on this page:** 8\ **Page:** 2
**Author:** ![Cervaise](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cervaise/32/16693_2.png) [@Cervaise](https://boards.straightdope.com/u/Cervaise)\ **Post date:** [March 15, 2004, 9:50pm UTC](https://boards.straightdope.com/t/a-planet-beyond-pluto/216495/21 "2004-03-15T21:50:58Z")
> [@Engywook](#): > > Yeah, but isn’t Charon so large compared to Pluto that the two bodies can be said to orbit each other? Don’t all paired bodies orbit one another, technically speaking? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [March 15, 2004, 10:00pm UTC](https://boards.straightdope.com/t/a-planet-beyond-pluto/216495/22 "2004-03-15T22:00:50Z")
> [@Cervaise](#): > > Don’t all paired bodies orbit one another, technically speaking? Pairs Schmairs - _everything_ orbits its collective centre of mass. It’s just that when the common centre of mass of the local system under consideration lies very close to one particular body (like the sun, in the solar system), then it is convenient shorthand to say that the other objects orbit that object. ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [March 15, 2004, 10:43pm UTC](https://boards.straightdope.com/t/a-planet-beyond-pluto/216495/23 "2004-03-15T22:43:26Z")
> [@](#): > > _aswonke wrote:_ > according to Mike Brown, an astronomer quoted in the Washington Post, “Sedna is so far out that from its distance the sun could be completely blocked out with the head of a pin, he said.” That quote bothered me. First, if you’re talking about an eye that’s a point receiver, any size of the Sun can be blocked out with the head of a pin if you hold it the right distance. Second, your pupil is larger than the head of a pin, so even a point souce (like Rigel) can’t be blocked if you hold the pin close to your eye. I was surprised to see such a sloppy description in the popular media. > [@](#): > > _dtilque wrote:_ > I’ve been in a cave with the lights off, and I can say without question it’s going to be brighter than that. Currently, Sedna is some 90 AU away from the sun. Since light decreases as the square of the distance, the sun will be only 1/8100 as bright as it is here on Earth. Or a bit brighter, allowing for the fact that the sun is seen through the filter of the atmosphere here on Earth. At any rate, that’s not very bright and I’d definitely bring a flashlight. I was in a cave with the lights off Friday morning, and I agree that it was really, really dark. According to [this site](http://lightingdesignlab.com/articles/metrics_quantity/metric_quantity.htm), the eye adapts from about 10,000 footcandles of light intensity on a sunny day to about 0.01 footcandles on a moonlight night. On Sedna, it would be somewhere around 1 footcandle. You wouldn’t be able to read by it, but you should be able to keep from tripping over a Sedna-rock. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [March 16, 2004, 12:53am UTC](https://boards.straightdope.com/t/a-planet-beyond-pluto/216495/24 "2004-03-16T00:53:05Z")
Pluto is definitely a Kuiper belt object; the question is just whether “Kuiper belt objects” and “planets” are mutually exclusive. And Pluto isn’t even necessarily the largest of the KBOs, just the largest thus far discovered. I’ve seen speculation that some as-yet undiscovered KBOs might be as much as ten times Pluto’s size. I was annoyed about that pinhead comparison, too, but in this case you can’t blame the popular media. NASA’s own press release, which the newspapers ought to be able to rely upon, used that same quote. As for spacesuits, I suspect that the Apollo spacesuits already have enough insulation on the soles of the boots. The biggest difference between the Moon at night and a satellite of an outer planet is that many of the outer satellites have atmospheres, which would conduct heat away from the body of the suit. But both on the Moon and on, say, Titan, you’d be walking on a very cold solid surface, so the Apollo suits already had to take that into account. ---
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [March 16, 2004, 1:16am UTC](https://boards.straightdope.com/t/a-planet-beyond-pluto/216495/25 "2004-03-16T01:16:35Z")
> [@Carnac the Magnificent!](#): > > Here’s a question for you: If a team of NASA astronauts were today standing on this planetoid (whatever), would the ambient light be enough for them to see surface features unaided, or are we talking midnight-in-a-coal-mine dark? Since there probably isn’t much atmosphere, if any, I imagine there’d be plenty of starlight, with the sun appearing as just another bright star. ---
**Author:** ![LemonThrower](https://avatars.discourse-cdn.com/v4/letter/l/d2c977/32.png) [@LemonThrower](https://boards.straightdope.com/u/LemonThrower)\ **Post date:** [March 16, 2004, 1:38am UTC](https://boards.straightdope.com/t/a-planet-beyond-pluto/216495/26 "2004-03-16T01:38:03Z")
If Pluto is not considered a planet, then Johnny will be Made to Stay Up Nights, but he’ll never Propose. On the other hand, if Sedna and Pluto are planets, then Johnny just might propose something that starts with an “S”. I guess he’ll blame it on Mary’s Velvet Eyes. ---
**Author:** ![umop\_ap\_sdn](https://avatars.discourse-cdn.com/v4/letter/u/dbc845/32.png) [@umop\_ap\_sdn](https://boards.straightdope.com/u/umop_ap_sdn)\ **Post date:** [March 16, 2004, 1:54am UTC](https://boards.straightdope.com/t/a-planet-beyond-pluto/216495/27 "2004-03-16T01:54:51Z")
Let’s look at this in terms of magnitude. The Sun’s apparent magnitude from Earth is -26.72. 1/8100th of that intensity equates to a magnitude of about -16.95. For comparison, the full Moon’s apparent magnitude is about -12. That’s several tens of times dimmer. So the Sun would still be far brighter than any other object in the sky, and let’s just say that if you can see at all under a full moon, you’ll probably have little trouble reading by sunlight on Sedna. ---
**Author:** ![bup](https://avatars.discourse-cdn.com/v4/letter/b/6bbea6/32.png) [@bup](https://boards.straightdope.com/u/bup)\ **Post date:** [March 16, 2004, 3:36am UTC](https://boards.straightdope.com/t/a-planet-beyond-pluto/216495/28 "2004-03-16T03:36:56Z")
> [@bienville](#): > > …I remember news reports of Science discovering a tenth planet in our Solar System (I realize we have folks posting from lots of different location: I’m referring to the Solar System that has Earth in it). I know “Solar System” is used in the media to mean any planetary system, but “Solar System” has “Sol” right in it, so it should go without saying that it’s ours. _Somewhat_ more seriously, I don’t see why the light on Sedna would be any darker than a moonless night here (I’m on earth). [Previous page](https://boards.straightdope.com/t/a-planet-beyond-pluto/216495.md?page=1)