I noticed the other "Planet X" thread in Babbling and it got me thinking. Are the instruments that we have today too powerful not to detect something as large as a Earth sized hypothetical "planet X"?
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I noticed the other "Planet X" thread in Babbling and it got me thinking. Are the instruments that we have today too powerful not to detect something as large as a Earth sized hypothetical "planet X"?
Order of Kilopi
"The" other thread?Originally Posted by banquo's_bumble_puppy
I believe you have been here long enough to know all the planet X nonsense and all the variants that exists. Which brings me to the point that I think that your question is rather vague since it doesn't indicate the "flavor" of planet X.
Also; you should be very familiar that this discussion exists. In absence of relating your question to it, I can only assume you haven't gone there.
Yet, for Planet X to be here in less then a decade, it can't be farther than a billion or so kilometers away. Even at that distance, it would be one of the brightest objects in the sky.
...
Also, a giant planet has giant gravity. Neptune was discovered because of its gravitational effects on Saturn and Uranus. Planet X, if it were anywhere near the inner solar system (and in truth, even a long way out), would pull on those planets...
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I'm not talking about the planet X of doom, I'm talking about a hypothetical Kuiper belt object that just happened to be as big as the Earth....could something that large remain undetected?
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There are a number of tools that could observe distant objects orbiting the Sun, and for an Earth-sized lump of soot covered charcoal and ice, the question isn't so much whether it could have gone undetected, but how far away it would need to be to remain undetected till now. I suspect that if such an object were 1000 AU or more away and superimposed against the Milky Way, we wouldn't have picked it up yet. We mostly aren't looking for things that move THAT slowly.
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Agreed. So there could be several undetected Earth-sized (by volume) planets inside the inner circumference of the Oort cloud 50 or so thousand AUs from the sun. They could even be located such as to not disturb the orbits of smaller objects out there; however, I believe it to be unlikely.We mostly aren't looking for things that move THAT slowly.
Can we know, due to the low detectability of "unlit" planets ad snowballs, whether objects presumed to populate the Oort cloud are homogeneously permeating the interstellar space throughout the MW at density levels approximating, within a couple of orders of magnitude, that presumed for the MW?
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I think the presumption is that objects in the Oort cloud have very elongated orbits, and return to the inner Solar system for brief visits every once in a great while. The distribution of the source of the very long-term comets is our indicator of the density and isotropy of the Oort cloud.
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Order of Kilopi
don't we need to find another "planet IX" before we can move onto "planet X"?
last i heard, we were down to "Planet IIX" (or is tha "planet VIII"- i never did quite grasp that numbering system..) since Pluto got demoted..
or is the "X" just a generic label for a planet that has no name?
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Perhaps X was referring to 'the unknown' as opposed to some Roman numeral. I think your input here was a bit off topic.
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I never thought about the X being a roman numeral, but it did make sense until last year.
Back to the original question. I don't see why an Earth sized object in the Kuiper Belt can't exist undetected. The KB is such a vast volume that I would think many such objects could exist, especially ones that are in the line of sight of the Milky Way. Perhaps there are many such objects. I would think that such an object around 200 or 300 AU would not perturb any object that we currently know about. The Oort cloud is so far away, that I don't know how we could possibly detect anything smaller than a Brown Dwarf from that distance. A previous statement about Oort cloud objects having eccentric orbits could be a matter of sampling bias. The only ones we know about have eccentric orbits, but perhaps the vast majority of the others are circular.
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The current notion of how the Oort cloud objects got there is that they were ejected from the inner Solar System. Once that happened, it would be difficult to circularize a significant number of their orbits.
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hehe planet x. my science book this year was published in 1998 or something and they mentioned it, they said that there is no such thing as planet x.
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Well, if we will discover some such body, would it get the planet status or KBO status?
Order of Kilopi
First we would have to determine the properties of such body and it's relation to other bodies before we can make that determination.
But; Just being a KBO in itself would probably disqualify it anyway.
it must be in orbit around the Sun
it must be large enough that it takes on a nearly round shape
it has cleared its orbit of other objects
Order of Kilopi
If we use "KBO" as narrowly defined, we can say, with a very high degree of confidence, that there are no Earth-sized (classical belt or resonant) KBOs - they'd be pretty easy to detect, and it's hard to imagine how any could have escaped the many searches that have been conducted over the past few decades.
For SDO (scattered disc objects) the situation is less certain, but only Earth-sized ones with aphelia > 100 au (say), presently more distant than ~100 au (say), and with albedos < 0.04 (say) would likely have escaped detection ... or not; anyone care to calculate the apparent magnitude of an 'Earth' with albedo 0.04 at a distance of 100 au?
Several techniques have been used to indirectly estimate to total mass in the (classical) KB; AFAIK, this total mass is well below 1 Earth mass (it's only a few percent of an Earth mass, IIRC).
For the SDO, these techniques provide similarly less tight constraints on unseen Earths ... but again the conclusion is that it's unlikely there are any.
However, the further out you go, the greater the chance an Earth-like object lurks undetected ... but Sedna was detected; what would an 'Earth' in Sedna's orbit look like? How easy would it be to see such an object?
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Sedna is near its perihelion, and is traveling about 40% faster than other objects that distance away. This makes it a bit more likely to have been found than an Earth-sized object the mean distance that Sedna would have (90 vs 700 AU).
BTW, if transported to 200 AU from the Sun, the Moon would would have a visual magnitude of 33 (undetectable by modern visual wavelength instruments). The Earth would be about 27 or 28 (maybe a little brighter because of a fresh layer of Oxygen snow).
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Apparent magnitude is not the key to discovering these objects. It's possible that something well within the reach of our telescopes has escaped detection. For an object to be detectable, it must have fast motion against the background stars.
Consider the example of Eris (aka Xena or 2003 UB313). It is something like the 4th brightest object in the Kuiper Belt, yet it was something like the 500th KBO discovered. This is because it is currently near aphelion; its great distance causes it to move very slowly against the background stars. Mike Brown's detection scheme had the computer discard anything that moved slower than about 1.5 arcseconds per hour to reduce false positives, and make the data manageable. Eris, while very bright, is currently at about 97 AU from the Sun. It moves slower than this threshold, rendering it undiscoverable by this detection scheme. But the discovery of Sedna, moving slightly faster than this threshold because of its current distance of about 90 AU, encouraged Brown to lower the threshold, which enabled him to find Eris.
Keep in mind that the majority of Sedna's orbit is much further than Sedna's current position. And since things travel much slower at aphelion than perihelion, anything in a Sedna-like orbit would spend the majority of its time much further from the Sun than Sedna's current position. And the appearent brightness dims as approximately 1/d4.So the answer to your question depends heavily on where in its Sedna-like orbit the Earth-like object is.
It's additional orbital speed is actually of little help. The vast majority of motion we detect is not Sedna's orbital motion, but its parallax as viewed from Earth's orbit.
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Well, there exists some evidence that KBO cuts off sharply. If this cutoff really exists, this may be caused by planetary-sized body that, yes, cleared its orbit and throw away too near KBOs long ago.
Order of Kilopi
Planet X was first proposed by Percival Lowell back in the early teens. At the time there were only eight planets, so X never stood for ten. A true Planet X would be an object whose existence was inferred from its grativational effect on known objects, like Neptune's was.
The closest thing I've heard to a modern Planet X in the classical "Lowellian" sense has been some work done a few years back that looked at the frequency of comets from the Oort cloud and claimed that they were biased from a specific region, and that something large out there must be purturbing them.
http://www.blackwell-synergy.com/doi...1.2002.05649.x
The Kuiper cliff is also an intriguing possibillity for another Planet X
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Well, wouldn't that mean that Percival went to his grave convinced he'd found Planet X?
Shouldn't we come up with a new name for this putative planet?
Order of Kilopi
Percival Lowell went to his grave before his Planet X had ever been found. He was a fairly broken man at that point; he was a pacifist and World War One had destroyed much of his idealism. He desperately wanted Planet X to be real, so that people would start to take him seriously after all his Martian-talk, but he never saw Pluto found. His wife, who was, by all accounts, a fairly hideous human being, probably contributed her fair share to his death as well.
I like Planet X. It's a useful term for a planet hypothesised via gravity. Just because it wasn't what Lowell imagined doesn't mean it's not still out there.
Last edited by parallaxicality; 2007-Aug-30 at 11:12 AM.
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The irony is that Lowell never realized that he actually had found "planet X" ("X" represented the unknown, not a number). After Pluto was discovered by Clyde Tombaugh in 1930, astronomers reviewed Lowell's photographic plates from around 1915, and found that Pluto actually appeared on some of them. Unfortunately, Lowell didn't recognize it for what it was. In retrospect, he has made significant scientific contributions, as the Lowell Observatory, which he established in 1894, has played a major role in both astronomical research and education.
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Hmm. and I always assumed that when people discussed some hypothetical "Planet X" that they were referring to some undiscovered earth-lke planet sharing our orbit around the sun - but on the opposite side of the sun. Although the idea's been debunked, I think it still pops up from time to time.
Would be neat, though, no? Damn, that mean old science -- eliminating mystery and romance in the process of banishing ignorance!! Oh well...
...one man's yin is another man's yang.
Order of Kilopi
You're thinking of Counter-Earth, aka Antichthon:
http://en.wikipedia.org/wiki/Counter-Earth
Order of Kilopi
An emphatic "yes!"
As has been pointed out, the object's proper motion, if minimal over weeks or months, would appear as a stationary object. I think Anderson of JPL stated as much regarding the IRAS survey.
Where the telescope ends, the microscope begins. Which of the two has the greater view?
Order of Kilopi
antoniseb, tony873004, or anyone else: what's would the visual magnitude of an Earth (with or without fresh oxygen snow) be, at a distance of 100 au?
For moderately elliptical orbits, with aphelia of 100 au, approx (OOM) what proportion of the time would an object fall below a 1.5"/hour threshhold?
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My back-of-the-envelope attempt:
I can't find a magnitude for Earth, so let's substitute Venus for Earth since it is about the same size, and has a readily available visual magnitude. Venus at superior conjunction is about magnitude -3.8. From Wikipedka: "Venus is always brighter than the brightest stars, with its apparent magnitude ranging from −3.8 to −4.6." I'm assuming that its least bright at superior conjunction, when it presents a full face from a distance of 1.72 AU. At 100 AU, it is (1.72/100)^2 = 0.00029584 times as bright, as brightness falls off as an inverse square. The formula to convert brightness to magnitude is
M1-M2=-2.5 log(b1/b2)
and rewritten to solve for M2 is
M2=2.5 log(b1/b2)-M1
Where:
M2 is Venus' magnitude at 100 AU
M1 is Venus' magnitude at 1.72 AU = -3.8
b1 is Venus' brightness at 1.72 AU = 1 (unitless because b2 is a ratio relative to this)
b2 is Venus' brightness at 100 AU = 1/(100/1.72)^2=1/3380
2.5 * log10(1/1/3380)-(-3.8) =
2.5 * log10(3380)+3.8 = 12.6
So Venus at 100 AU would be about mag 12.6. I'm guessing a fresh oxygen snowy Earth would be about the same albedo as Venus, so that's also my back-of the-envelope guess for Earth.
Venus' albedo is 0.65, Earth's is 0.367, making it about 56% as bright as Venus
2.5 * log10(1/0.56)+3.8 = 13.22
So Earth, at its current albedo would be about mag 13.22 from 100 AU.
Accounting for the size difference between Venus and Earth would make the answer a little more accurate, and Earth a little brighter.
I don't know the formula for distance as a function of time. And distance is what makes the biggest difference in appearent motion. The orbit you're describing is basically the orbit of Eris (~40-90 AU). Things tend to linger at aphelion as their orbital velocities are lower, and Eris is right around this 1.5"/hour threshold at 90 AU. A quick Order of Magnitude guess, I would say perhaps 20 to 50% of the time it is travelling slower than this threshold. I can do a numerical model and get a more exact answer if you like, but you have to pick an eccentricity or perihelion distance.
Order of Kilopi
Assume an Earth at ~100 au is around 12-13 mag.
How likely is it that such an object would have escaped detection?
Extremely unlikely, I think; even HIPPARCOS would have picked it up, not to mention any one of dozens of spectroscopic surveys ... it may well occupy a quite unique place in broadband colour space too ...
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That's a good point about Hipparcos.
Wikipedia says:
...The final Hipparcos Catalogue (120,000 stars with 1 milliarcsec level astrometry)...120,000 stars is all stars down to about mag 9 according to http://www.stargazing.net/David/cons...manystars.html . About 3 million stars would have to be considered to reach mag ~12-13 according to the same web site....The Hipparcos and Tycho data have been used to create the Millennium Star Atlas: an all-sky atlas of one million stars to visual magnitude 11...
So at mag 12-13, our hypothetical Earth is about 1 to 2 magnitudes dimmer than stars cataloged by Hipparcos or Tycho.
I'm not too familiar with Hipparcos, and the Wikipedia article doesn't go into much detail, but I believed it snapped images spaced 6 months apart in an effort to look for parallaxes in the milliarcsecond range. Even if these surveys included stars as faint as mag 12-13, our hypothetical Earth probably moved several minutes of arc in that time frame. In searching for ants, they may have failed to see the elephant. Realistically, it may have been discarded as an asteroid, many of which are in this magnitude range and would fail to remain within a few arcseconds over a 6 month period. Just my guess...
Last edited by tony873004; 2007-Aug-31 at 05:06 AM.
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My apologies, I was forgetting that Percy was well on the way to his maker when Clyde managed to pluck a diamond from the very very rough.
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Sorry, but you've made an important mistake here. If you move Venus to a distance of 100 AU from the Sun, and then observe it from Earth, there are _two_ factors involved:
a) it receives less sunlight because it is farther from the Sun, by factor (0.72/100)^2
b) the reflected sunlight spreads out over a very large surface before it reaches
the Earth, so becomes dimmer by factor (1.72/99)^2
So, rather than falling off as one-over-r-squared, the apparent brightness of a planet reflecting sunlight falls off as one-over-r-fourth; it's similar to a reflected radar beam in that way.
Ignore the niceties, and use a factor of (1/100)^2 for each term. This makes the apparent brightness of distant-Venus dimmer by about 10^(-8) than the real Venus, which is 5+5+5+5 = 20 magnitudes. So the apparent magnitude would be closer to 20 than to 12, making the detection of this hypothetical object much more difficult. It would probably not appear in the Palomar Sky Surveys, and possibly not even in the recent Sloan Digital Sky Survey. As for 2MASS ... probably not, but I'm not an expert with those near-IR surveys.
In other words, it would take a dedicated search with pretty big telescopes (and small fields of view) to find it; in other words, one of the current KBO search programs.
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