With the recent discoveries of near-planet-sized objects out beyond Neptune, it makes you wonder just how much junk is floating around out there.
Usually, when you see some big stuff, it means there’s probably lots of little stuff. For example, asteroids collide and shatter. You get a few big pieces, but lots and lots of little shrapnel. Also, little guys can stick together to make bigger guys, and it takes a lot of little ones to make a big one. So if we see a handful of big objects, we kindof expect to see lots of smaller ones.
So a good thing to wonder is, how many little iceballs are wandering remote space outside Neptune’s orbit?
The cool thing about astronomers — and there’re lots of cool things to choose from, because we are so very, very cool — is that when we wonder about something, we can go and take a look to check it out.
That’s just what a team of astronomers did. They created TAOS: the Taiwan-America Occultation Survey to look for Kuiper-Belt Objects (KBOs), those chunks of ice orbiting in the distant solar system.
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| Diagram of how an iceball can be seen, courtesy TAOS. |
The concept is actually pretty simple. Take a telescope, point it at a likely patch of sky, and start taking pictures. When a KBO passes between us and a star, we’ll see the star dim for a short time, then brighten again. By making some assumptions (how many stars are in the image, the distribution of KBOs, how quickly they move, etc.) you can figure out how many KBOs are out there by measuring how many times the stars dim and brighten. You can even tell how big they are, too; TAOS is sensitive to KBOs from 3 – 28 km (2 – 17 miles) across.
What they found is rather surprising: after 200 hours of observing, they didn’t see a single event! Not one star appears to have been occulted (blocked) by a KBO. This means there are much fewer of them out there in that size range than previously thought.
Why? It’s too early to say. Maybe the small ones at that distance have all stuck together to form bigger objects. Maybe the small ones are sensitive to some force or event than bigger ones, making them preferentially go away (dropped into the inner solar system, or flung farther out than the survey can find them). Right now, all we know is that our back yard isn’t as crowded as we first thought. The thing to do now is to make longer observations, more sensitive observations, expanding the survey and see over what total size range and what distance range this emptiness seems to hold.
I’m not sure myself what implications this has. I’ve often wondered if there is another more massive planet out in the distant solar system — very far out, like 5 times Neptune’s distance from the Sun. Nothing we’ve seen seems to preclude that, but we have no evidence for it either. Studies like TAOS help; they provide pieces of the puzzle that we need to put together so that we better understand our own neighborhood.
October 3rd, 2008 at 12:59 pm
I’m sure you simplified the method they use for the blog a bit. It would seem to me that so many other factors would play into this, that one really needs to better understand the predicted observation versus what they really see. Would a 3 km chunk of something really make a noticeable effect of the magnitude they are expecting on a bright star? Also, that’s quite a bit of cosmic billiards they are dealing with. 200 hours seems a rather small sample size. I’m going to assume they were observing in the ecliptic the whole time, or were some of those hours outside by a significant margin?
Like you said, too early to tell really. And I guess i don’t have enough data to really make a fully coherent reply, and I just like getting posts in early.
October 3rd, 2008 at 1:27 pm
@ Larian LeQuella
I bet you use “Talk It, Type It” software!
October 3rd, 2008 at 1:32 pm
this is cool stuff. I’d really like to know what’s causing that, and it would be too cool if there was another giant planet somewhere out there… though I bet if they discovered one, the Planet X’ers would go insane.
October 3rd, 2008 at 1:33 pm
There was a survey of small Kuiper Belt objects using the Hubble Space Telescope. The research team expected to see several dozens of KBOs, instead only 3 were found. Looks like the region really is empty of small objects.
October 3rd, 2008 at 1:49 pm
@Ivan,
Nope, I just type stream of consciousness! Sometimes i don’t even make sense to myself!
October 3rd, 2008 at 2:25 pm
It’s Pluto getting even
October 3rd, 2008 at 2:44 pm
@Jadehawk
How can they go insane? That would require them to start from a different place than insanity.
October 3rd, 2008 at 3:07 pm
For those of you who want to participate, you can join IOTA the International Occultation Timing Association, and do real science yourself!
http://www.occultations.org/ is the website!
Phil:
From the headline of the post I thought at first you were going to put an observatory in your “empty back yard”!!! You should do this anyway! TLA would get a charge outta it fer sher!
I’m one of the guys (guy #2 to be exact) who got the Explora Dome project going. You too can afford a domed observatory in your back yard. Now if only the neighbors don’t mind….
Rich
October 3rd, 2008 at 3:45 pm
DGKnipfer:
good point; replace “go insane” with “go from insane but passive to completely berserk”, that should make more sense.
October 3rd, 2008 at 7:11 pm
# GregW Says:
It’s Pluto getting even
Speaking of Pluto, I loved Thursday’s Adam @ Home:
http://wpcomics.washingtonpost.com/feature/08/10/02/ad081002.gif
J/P=?
October 4th, 2008 at 5:50 am
I dunno if you guys (Phil, too) know her, but author C.J. Cherryh has a carefully built “history” in her Merchanter series, in which the flight controllers at orbiting stations use occultation as a detection method. It makes some sense if you can build the automation and afford the ’scope coverage and processor time, since you’re not getting a radar return worth anything off small and distant objects, and man-made stuff can be “stealthed” now.
October 4th, 2008 at 6:04 am
Of course, if they do find any biggies out there, the astrologers are just gonna say “Hah! That’s why Mercuric retrograde isn’t a predictive tool, yet!”.
Nifty. Is there a snowball’s chance in hell this could be refined to look for the Oort Cloud?
October 4th, 2008 at 7:35 am
Has the method been tested by checking any ocultations of Pluto, Eris, Sedna, Haumea (ex-EL-61) Makemake, Varuna, Orcus, Quaoar etc ..?
There’s a lot of space out there and I would’nt think ice dwarf planets the size of Ceres or even Pluto would occult many stars so I’d imagine the odds are against them.
Incidentally if large Kuiper Belt Objects / Trans Neptunean Objects are quite rare doesn’t that add more weight to the fact that Pluto and Eris are in fact proper planets?
(BTW. Does anyone, anywhere ever use the IAU’s dumb “Classical planets” or “Small Solar System Bodies” terms? No, I thought not.)
Given that one of the arguments against Pluto & Eris having full planetary status was that there were heaps of similar objects out there – then does finding that well there’s really NOT – just a handful say five to ten ice
dwarfs or so and maybe only one that’s larger – and that only fractionally – shouldn’t this latest twist in the Kuiper belt evidence rule Pluto back into planetary contention?
I’d say so. I’d suggest the initial IAU definition proposal – the
one incl. Ceres, Pluto and Eris as legitimate planets – was
was right & I’d divide our solarsystem into three zones with representative planetary types :
I) Inner solar system / terrestrial (rocky) planets : Mercury, Venus, Earth & Mars
II) Middle solar system / Gas (& ice) giant planets : Jupiter, Saturn, Ouranos & Neptune.
&
III) Outer solar system / Ice dwarf planets : Pluto, Eris, Makemake, Haumea,
Quaoar, Sedna
Really, what is wrong with adopting a model like that and a broader, more reasonable definition of “planet” than the IAU’s current mess with its debateabtle and logically inconsistent and absurd “Cleared Orbit” criterion?
If it only adds a few more planets then frankly that’s fine with me – I’d happily welcome Eris, Huamea, Makemake, Sedna and Quaoar into planetary ranks at the same time as welcoming back Pluto – and Ceres and Vesta!
PS. What BA? No post from you here on Haumea (ex-2003 EL-61) a fascinating
fast-spinning little egg-shaped TNO 1/3rd Pluto’s mass – joining official “dwarf planet” ranks?
Click on my name above for the Wikipedia link to Haumea if you so desire,
folks.
Planets : the more the merrier!
——————-
“Still there is no rule that says a planet has to be larger than a certain size and despite its smallness, Ceres would certainly have entered the list of planets if Piazzi’s discovery had remained as it was.”
-P.63, Asimov, Isaac, ‘The Tragedy of the Moon’,
Mercury Press, 1973.
October 4th, 2008 at 11:44 am
This reminds me of an article years ago, when I still read ASTRONOMY. They recruited dozens of amateur astronomers to time the occultation of a star by an asteroid, then plotted the times and locations–AND GOT A DISC! It was Soooo Kewl!
October 4th, 2008 at 1:44 pm
@ Chas – I have friends who do this all the time. IOTA is an organization that announces occultations and predicted paths, then dozens of dedicated (one might say obsessive) amateurs grab their scopes, video equipment and GPS time inserters and hit the road to catch some photons. A few years back one path went right through Toronto, and they used the 72″ David Dunlap Observatory scope, which caught a rare grazing occultation (the star winked out twice). If enough people can successfully time it, they can determine the shape, and better refine the orbit. Sometimes a small companion (sometimes called a “satelloid”) can also be detected in this way.
A youtube search for “asteroid occultation” will pull up dozons of hits. But these are main belt asteroids, much closer in than KBO’s. I wonder if KBO occultations would be so fast they might be indistinguishable from atmosperic effects.
October 4th, 2008 at 2:25 pm
A couple of years ago there was an announcement of apparent trans-neptunian occultation events in x-ray observations of Scorpius X-1. I’m afraid I can’t offer any details since Nature mag has taken the information hostage and won’t release it without a ransom payment.
http://www.nature.com/nature/journal/v442/n7103/full/nature04941.html
October 4th, 2008 at 10:12 pm
I’ve been snooping around on the net, and learned that someone has decided that all but a small percentage of the x-ray events I mentioned above are instrument errors.
http://lanl.arxiv.org/abs/0805.1579
The initial interpretation of the observations was in line with the old estimates of the number of smallish KBOs, so the new interpretaion is in line with both the TAOS results and Hubble results cited by Kullat Nunu.
October 6th, 2008 at 12:24 am
Phil says:
“What they found is rather surprising: after 200 hours of observing, they didn’t see a single event! Not one star appears to have been occulted (blocked) by a KBO. This means there are much fewer of them out there in that size range than previously thought.
“Why? It’s too early to say. Maybe the small ones at that distance have all stuck together to form bigger objects. Maybe the small ones are sensitive to some force or event than bigger ones, making them preferentially go away (dropped into the inner solar system, or flung farther out than the survey can find them). Right now, all we know is that our back yard isn’t as crowded as we first thought.”
WHAT is “rather surprising”? I’m never sure exactly what that “what we previously thought” stuff is. Everybody in pop-science reporting invokes it, as if there must always be a pre-established solid consensus on matters nobody really knows about from any observational or experimental data. Whatever we supposedly “previously thought” comes about from theoretical suggestions. Yet it becomes “what we previously thought” every time somebody writes about it (invariably for the FIRST time in pop science articles) in light of new OBSERVATIONAL or EXPERIMENTAL info that becomes available which doesn’t resonate with the theoretical ‘consensus’ allegedly already in place.
How “crowded” can we expect it to be out in the “Kuiper belt”? Certainly, it is obvious there’s LOTS of room out there. And theoretical studies have long since already suggested that the belt-like distribution of objects in the so-called “Kuiper BELT” would be significantly more diffused out of the ecliptic than objects that are distributed even in the asteroid belt, which aren’t distributed in a crisply narrow range of inclinations either. Those and similar theoretical studies that stretch back all the way to Jan Oort’s own studies and earlier suggest that the departures of inclinations from the ecliptic increase with distance, so that the Kuiper “belt” insensibly becomes a “cloud” farther out with relatively little “memory” of their ecliptic heritage. It’s relatively simple to show that chaotic gravitational stirring will do that.
If that’s all more or less correct, the population density of objects that must be distributed into a more diffuse configuration that departs from the ecliptic can easily account for the apparent “expected lack” of occultations by smaller objects when staring at a particular x-ray source (of course, along the ecliptic, which is an entirely suitable target, since one would still expect some residual concentration along it). Mind you, the SAME NUMBER of objects CAN be out there, except they aren’t as concentrated along the ecliptic plane as “previously thought”.
Doesn’t that make at least as much sense as concluding that those smaller objects (by the zillions) are NOT there just because we haven’t detected any occultations of smallish objects over a POINT SOURCE after a mere 200 hours? After staring at a point source for only a little over 8 days (not to mention the sporadic quality of the data)? Is the latter conclusion really more justified than the possibility that we have chosen to accentuate the research against a spurious notion of a distribution confined to a more crisply-defined “belt”? With no mention of OTHER theoretical considerations that have demonstrated how lower mass objects tend to be more dynamically scattered than more massive objects within the same regime?
This sort of thing is rampant in science reporting, especially in astronomical reporting, and it’s been getting rapidly worse over the last decade or so. Almost every article that utilizes the “what we previously thought” gag contributes to the public’s misconception of science, as a vessel of knowledge that already has a fixed picture of the way things are. No mention is ever made that scientists view ALL conclusions as provisional, and ALWAYS subject to ammendment, confirmation or refutation by new information that might come along.
This horrible “journalistic habit” is tantamount to fixing within the public a mindset of certainty that only a religion could love.
October 6th, 2008 at 12:42 pm
Wouldn’t an easier and more reliable approach be to use the Arecibo radar or one of the other planetary radars. Emit a high energy radar beam and see what reflects back? I know Arecibo has been used to bounce radar beams off Venus, Mars, asteroids, etc. but I don’t know if it would be effective out past the orbit of Neptune since the strength of the reflected signal falls off as the inverse fourth power of the distance.
So choose a patch of sky, maybe 1 degree on a side and sweep it with a radar beam to see what’s out there. That might give you a pretty good census of how many objects exist out there per unit area of sky.
October 7th, 2008 at 9:03 am
[...] The back yard is empty | Bad Astronomy | Discover Magazine "What they found is rather surprising: after 200 hours of observing, they didn’t see a single event! Not one star appears to have been occulted (blocked) by a KBO. This means there are much fewer of them (2 – 17 miles across sized object) out there in that size range than previously thought." (tags: space science Astronomy asteroid solarsystem) [...]