evidence for a 9th planet

[Ryujin]

Most of that dense starfield is just that - a starfield, not a collection of known objects. Something less than 1% of the stars in that dense starfield have been cataloged.



Now, note that I also spoke about occultation of "bright" stars. That's because there are actually lots of stars in the catalog. Too many. Like, a bit short of 950 million in the Guide Star Catalog. There is no way you're going to watch to see which of 950 million stars got occulted. It doesn't matter how impressive your computer power is. The fact of the matter is that we are not *constantly watching* 950 million objects. We are not taking nightly catalogs of the entire sky that resolves each star. We have not even taken nightly catalogs of the regions we suspect the planet is in, because we had no reason to. The data you'd want simply has not been collected.

Specifically bright stars, however, get a bit more attention, but there are far fewer of them, and that leads to the problem that in all likelihood, none of those *just happen* to be in the path.

In addition, as I've been writing I've been realizing - we are talking about a thing that has an orbital period of 10,000 to 20,000 years. That means, since the time of Galileo, it has gone across an arc of *at most* 14 degrees of sky - a smidge less than the distance across the sky the Sun or Moon moves in an hour. In the time that we've had really serious telescopes and major catalogs such that we might have seen the occultation, it has gone more like 1 degree of sky - the distance the Sun or Moon moves in about 4 minutes (plus a little bit for parallax).

So, not a lot of opportunity for occultation.

Not having data on the stars in question would certainly be an issue. Not 'constantly watching' 950 million objects does not preclude them being in arcs that are being actively viewed. True, the swept arc caused by our movement with respect to a proposed object might not get anywhere near something we'd see in our lifetimes, or many multiples thereof.

 

[Umbran]

Not 'constantly watching' 950 million objects does not preclude them being in arcs that are being actively viewed.

"Not precluded" does not translate into "has a good probability that we were looking in the right place at the right time".

True, the swept arc caused by our movement with respect to a proposed object might not get anywhere near something we'd see in our lifetimes, or many multiples thereof.

The arc length thing isn't about *our* movement. It is about *its* movement - the proposed thing is *way* out there, and so covers only a small bit of sky each ear. To first approximation on these scales, we can consider the Earth to be stationary.

 

[Ryujin]

"Not precluded" does not translate into "has a good probability that we were looking in the right place at the right time".

The arc length thing isn't about *our* movement. It is about *its* movement - the proposed thing is *way* out there, and so covers only a small bit of sky each ear. To first approximation on these scales, we can consider the Earth to be stationary.

Actually it's about the movement of both. It's the way that we determine if something is relatively close, or at interstellar distances. In a 10K+ year orbit is nothing, compared to something that's 50LY away. The movement of the nearer object, compared to the stellar background, is significantly different.

 

[Umbran]

Actually it's about the movement of both. It's the way that we determine if something is relatively close, or at interstellar distances. In a 10K+ year orbit is nothing, compared to something that's 50LY away. The movement of the nearer object, compared to the stellar background, is significantly different.

It is about both *if* they are close together and/or moving large angular distances relative to one another over the time in question. They aren't. Planet Nine is expected to have an orbit that is highly elliptical, but with a semi-major axis of about 700 AU. The Earth's is 1 AU. The movement of the Earth is, as I said, small potatoes here.

Let me try it this way. Lay a football player down on the ground. Now, put the football *seven football fields away*. When looking at the football, it doesn't matter much if you're standing at the player's head or feet. The football looks like it is pretty much in the same place.

It is actually probably worse than this - Planet 9 is expected to have a semi-major axis of 700 AU, but an aphelion distance of 1200 AU. And, just statistically, it is more apt to be out at aphelion. So, put the football *more than half a mile away*. Now, stand at the player's head or feet and look at the football. Is that football going to seem to move much against the more distant background? No.

 

[MechaTarrasque]

If aliens from that planet come asking to borrow Godzilla and Rodan, don't trust them. I have seen that movie before....

 

[tomBitonti]

Some text from The TAOS paper:

The detected rate of TNO occultation events depends on the actual occurrence rate and the detectability. Relevant parameters include: (1) The surface number density (our goal) and angular size distribution of TNOs. (2) The surface number density and angular size distribution of background stars. Both these depend on the Galactic line of sight. With our current instrument setup, the 5 Hz observations reach about R=14 mag, which gives within the 3 deg2 field of view typically several hundred to a few thousand stars in a target field. A dense field would be favorable for occultation but would create images too crowded for analysis. The angular size of a star can be estimated, for example, by its optical and infrared colors (van Belle 1999). Most stars have an angular size less than 0.1 milliarcsecond (mas). For reference, a TNO at 50 AU with an angular size of 0.1 mas has a physical diameter of ∼ 4 km. Items (1) and (2) together specify the probability of area overlap (geometric consideration for occultation), plus the diffraction effect (King et al. 2006; Lehner et al. 2006) ...

Also

Fig. 2 shows the occultation of the star TYC076200961 by the asteroid (286) Iclea observed on 6 February 2006. TAOS observed this predicted event successfully with 3 telescopes. Iclea is known to have a diameter of 97 km, and the TAOS system detected the event readily.

Figure 2. A showcase data of the star TYC076200961 (mV ∼ 11.83 mag) occulted by (286) Iclea (mV ∼ 14.0 mag at the time) on 6 February 2006 observed by 3 TAOS telescopes. Data were taken at 4 Hz, and the duration of the event was estimated to be ≈ 5.75 s.

For the larger planet, are we still in the realm of single star occultations? Is the proposed planet big enough to occult more than one star at a time?

Thx!
TomB

 

[Umbran]

For the larger planet, are we still in the realm of single star occultations? Is the proposed planet big enough to occult more than one star at a time?

The planet is larger, but much, much, much farther away. I think someone suggested it be about 4x the size of the Earth. At a distance of 700 AU (give or take - it could be as close as 200, or as far away as 1200, with current proposal), it would subtend an angle of about 6.8755e-9 Degrees

287 Iclea mentioned above, at a distance of about 3 AU (give or take, depending on orbital positions - it could be from about 2 to about 4 AU) , would subtend an angle of 1.2383e-8 Degrees

(This, if I have my factors of 10 correct, a common disclaimer I use )

So, the asteroid will look larger than Planet 9.

 

[tomBitonti]

Thanks!

Found this while searching on the topic:

http://www.icranet.org/download/ESOP/Slides/andrei.pdf

"International Program of Stellar Occultations by Trans-neptunian Objects
The Contribution of the Aosta Valley Astronomical Observatory"

But just more background.

Thx!
TomB

 

[freyar]

For the larger planet, are we still in the realm of single star occultations? Is the proposed planet big enough to occult more than one star at a time?

Only pretty big-looking objects in the sky can occult multiple stars at once. Think the sun or moon or maybe the naked-eye-visible planets in a very dense star field.

The big difference between the TAOS project and looking for planet 9 is that TAOS is just looking at a large set of stars and seeing how many occultations occur. That tells us about the count of the trans-Neptunian objects. However, an occultation doesn't necessarily tell us how far away the occulting object is, etc, etc, so you'd have to follow up any occultation you see with a search for the occulting object.

I think the way to search for this is to look for a dim object that moves compared to the background star field. It is in fact close enough that (assuming Umbran's numbers for its proper motion) its parallax throughout the course of the year will be the biggest effect.

 

[Janx]

Can math help us here? As I understand it, newton's math helped us find some planets. If I recall Pluto was predicted with math. Sedna as well.

When we say predicted though, what does that mean?

In the sense of, did all it do was say, based on the known planets orbits, we did math, and predict an orbit out here for Planet Y that is yet unknown.

Or, was it precise enough to say: next tuesday, if you set your telescope to X/Y/Z you should see planet Y, because I did math and it says its there?

If the latter, then this is just a matter of looking where the math says. Seems like it would be a done deal then.

Otherwise, if they are saying there's a planet yay big on this 10,000 year orbit. Go look out where along that track it might be. That's pretty hard.