IPB

Welcome Guest ( Log In | Register )

7 Pages V  « < 3 4 5 6 7 >  
Reply to this topicStart new topic
Researchers Find Evidence Of Distant Outer Planet
JRehling
post Apr 12 2016, 11:40 PM
Post #61


Senior Member
****

Group: Members
Posts: 2013
Joined: 20-April 05
Member No.: 321



The lack of innovation has been discussed and largely rebutted here:

http://www.unmannedspaceflight.com/index.php?showtopic=7842
Go to the top of the page
 
+Quote Post
dtolman
post Apr 13 2016, 11:18 AM
Post #62


Junior Member
**

Group: Members
Posts: 76
Joined: 20-April 05
Member No.: 291



With the electric-ion engines we have now - isn't the issue just finding a powersource that we can pair up with it to provide thrust for the necessary length of time?
Go to the top of the page
 
+Quote Post
nprev
post Apr 13 2016, 11:39 AM
Post #63


Senior Member
****

Group: Admin
Posts: 8009
Joined: 8-December 05
From: Los Angeles
Member No.: 602



MOD NOTE: Let's please stay on topic.


--------------------
A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
Go to the top of the page
 
+Quote Post
AJAW
post May 2 2016, 02:52 PM
Post #64


Newbie
*

Group: Members
Posts: 4
Joined: 17-July 15
Member No.: 7604



Two relevant things:
First, Mike Brown and Konstantin Batygin comment on the Malhotra, Volk & Wang ArXiv e-print here:

http://web.gps.caltech.edu/~mbrown/papers/ps/findp9.pdf

(Near the end of the paper.) Their final relevant sentence is this: “Thus, it appears that no useful constraint on the orbit or position can be drawn from this method.”
I’m not qualified to evaluate the arguments, but from their blog postings I’ve formed the impression that Brown & Batygin are very competent and cautious scientists and I’m biased in their favour. smile.gif

The second thing is something that I discovered when I was fortunate enough to attend the British Astronomical Association one-day meeting on Robotic exploration of the Solar System on the 30th
April. (Incidentally James Canvin of UMSF gave a great talk on “Amateur use of Solar System spacecraft data”.) What attracted my notice Planet Nine-wise was a talk by Prof. Mark McCaughrean
on ESA’s Solar System exploration programme. (He is the Senior Science Advisor in the Directorate of Science & Robotic Exploration at ESA.) When talking about the Gaia astrometry mission,
he mentioned that the gravitational lensing effects of the sun and planets have to be removed as part of the data processing – the sun’s effects are practically 360 degree, and those for Jupiter are
very large, but I believe they do it for all the planets.

After the talk, I asked him if they could potentially detect the gravitational lensing effects of Planet Nine. He thought that they probably could – if they already knew where it was! smile.gif
However, he thought that the volume of the data and the small signal would make it very difficult to extract without knowing where to look.

He was answering after just a few seconds thought, and I still wonder if there might be some hope in this method – after all, we should be able to calculate roughly what the lensing signal
would look like, and it’s moving, so Gaia, with multiple observations of the same patches of sky, should have observations with and without the planet, at multiple locations that have a
roughly predictable separation from each other. But I don’t know anything about the signal to noise ratio, or the data set. For a billion stars, I guess it’s pretty big!

Can anyone give a more informed opinion on this?
Go to the top of the page
 
+Quote Post
Phil Stooke
post May 2 2016, 03:41 PM
Post #65


Martian Cartographer
****

Group: Members
Posts: 7333
Joined: 5-April 05
From: Canada
Member No.: 227



This would make a good test of the laser propulsion and data collection technology promoted recently for Alpha Centauri, as Explorer 1 already noted.

Phil


--------------------
... because the Solar System ain't gonna map itself.
Go to the top of the page
 
+Quote Post
Gerald
post May 2 2016, 04:00 PM
Post #66


Senior Member
****

Group: Members
Posts: 1927
Joined: 7-December 12
Member No.: 6780



For visual magnitude 14 stars, GAIA should see displacements of about 10 micro arcseconds (muas).
If my calculation is correct, that's pi/(180° x 1e5 x 3600) = 4.848e-11 in radians.
The Schwarzschild radius for a 1e25 kg mass (about twice the mass of Earth) should be 2GM/c˛ = 14.8 mm. Use this to calculate the gravitational deflection angle, and resolve the equation to the radius r = 0.0148 m / (2 x 10 muas) = 0.0148 m / 4.848e-11 = 153122 km = 1.02e-3 a.u. (astronomical units).
For a mass at 1000 a.u. distance that's an apparent angle (in radians) of about 1.02e-3 a.u./1000 a.u = 1.02e-6.
With a FOV of 0.66° and 1966 pixels, we get an angle (in radians) of (0.66° x pi / 180°)/1966 = 5.86e-6 per pixel.
Hence the displacement of background stars of magnitude 14 by a 1e25 kg mass at 1000 a.u. distance would be detectable using mag 14 stars within a radius of about 1/5 pixel around the CCD position of the (theoretical) image of the mass.
This would be extremely difficult. For a larger mass at closer distance it would look more realistic.
Go to the top of the page
 
+Quote Post
fredk
post May 2 2016, 07:39 PM
Post #67


Senior Member
****

Group: Members
Posts: 3798
Joined: 17-January 05
Member No.: 152



QUOTE (Gerald @ May 2 2016, 05:00 PM) *
This would be extremely difficult.

Taking the number density of mag 14 and brighter stars to be optimistically 1000/deg^2, from here, that corresponds to a density of roughly 1e-4 stars per Gaia pixel, according to Gerald's numbers. So at any instant it's almost certain that there would be no stars close enough to a putative planet to be detectable with Gaia.

At 1000 AU, the object would have a period of roughly 32 000 yr, so would move roughly 360 deg/32 000 = 0.01 deg/yr in our sky. (Parallax would be of the same order or less.) This corresponds to roughly 40 Gaia pixels per year. So the object would sweep out an area with roughly 40*1e-4 stars per year, ie 4e-3 stars per year. So even accounting for the object's motion, we would not expect any stars bright enough and close enough to be detectable. We'd have to wait hundreds of years before a bright enough star happened to pass close enough.

So yes, this would be difficult, even if you knew exactly where the planet was!
Go to the top of the page
 
+Quote Post
AJAW
post May 2 2016, 08:31 PM
Post #68


Newbie
*

Group: Members
Posts: 4
Joined: 17-July 15
Member No.: 7604



Thanks for the info. The size of the gravitational lens is indeed small.
I have two questions:
Why are we talking about mag 14 stars? Gaia can go down to about mag 20.5, there ought to be a lot more of those stars.
Also, why twice the mass of the Earth? - I thought planet nine might be 10 times the mass of the Earth.
Go to the top of the page
 
+Quote Post
fredk
post May 2 2016, 09:34 PM
Post #69


Senior Member
****

Group: Members
Posts: 3798
Joined: 17-January 05
Member No.: 152



According to the reference Gerald cited, at 20th mag the astrometric accuracy is 20 times worse than at 15th mag. So to see a lensing effect the star'd have to be 20 times closer to the planet, ie confined to an area roughly 400 times smaller, than for 15th mag stars. But we might expect only roughly a few hundred times as many stars down to 20th as down to 15th mag, so it doesn't help to push to fainter magnitudes, even when you consider the planet's motion. And pushing the planet's mass up 5 fold gets you out about 5 times farther, which still won't likely give you a star close enough.

Also the motion of a star due to variable deflection as the planet passes near by might just be degenerate with the star's proper motion. Ie, if you only observe for a short enough time how do you know if the star's position is being deflected by lensing, or the star just has a different proper motion? If you observe for long enough with enough samples, you could distinguish them in principle.
Go to the top of the page
 
+Quote Post
AJAW
post May 2 2016, 10:03 PM
Post #70


Newbie
*

Group: Members
Posts: 4
Joined: 17-July 15
Member No.: 7604



Thanks fredk. Pity about the accuracy change. One factor in our favour (but unlikely to be big enough) is that the sky areas most likely to contain planet nine are densely populated - a nuisance for
most searches but an advantage with this one.

If Gaia is aiming to get proper motions for all the stars it looks at (with 70 observations of each one) I guess we could distinguish that from the lensing effect, if there is any.
Go to the top of the page
 
+Quote Post
TheAnt
post Jun 1 2016, 05:09 PM
Post #71


Member
***

Group: Members
Posts: 495
Joined: 12-February 12
Member No.: 6336



Planet 9 might literally be out of this world.

A study by Univ of Lund, Sweden have shown that planet 9 (if it will be shown to exist) might have originated elsewhere, and been adopted by our solar system.
This is obviously one elegant way of explaining the remote and elongated orbit of this world, but also offer one opportunity to have a space probe visit an exoplanet in the not too distant future.
"Theft behind planet 9 in our solar system."
Go to the top of the page
 
+Quote Post
jasedm
post Jun 1 2016, 06:57 PM
Post #72


Member
***

Group: Members
Posts: 614
Joined: 22-January 06
Member No.: 655



No expert in celestial mechanics me, but my initial reaction is to think this is putting the cart before the horse - the planet has yet to be 'discovered' - it's posited from observational data of established Kuiper belt objects. A bit of a stretch therefore imho to infer an extra-solar origin of a body whose existence has not yet even been confirmed.

Happy to be shot down in flames for my opinion though..... wink.gif

[MOD NOTE: THANK you!!!]
Go to the top of the page
 
+Quote Post
JRehling
post Jun 1 2016, 08:27 PM
Post #73


Senior Member
****

Group: Members
Posts: 2013
Joined: 20-April 05
Member No.: 321



Planet Nine should perhaps be given the provisional name Phlogiston… wink.gif
Go to the top of the page
 
+Quote Post
JohnVV
post Jun 1 2016, 08:44 PM
Post #74


Member
***

Group: Members
Posts: 829
Joined: 18-November 08
Member No.: 4489



or
plan 9 from planet 9
(been playing with " plan9 from bell labs" )
Go to the top of the page
 
+Quote Post
HSchirmer
post Jun 1 2016, 11:29 PM
Post #75


Member
***

Group: Members
Posts: 296
Joined: 24-July 15
Member No.: 7619



QUOTE (jasedm @ Jun 1 2016, 06:57 PM) *
No expert in celestial mechanics me, but my initial reaction is to think this is putting the cart before the horse - the planet has yet to be 'discovered' - it's posited from observational data of established Kuiper belt objects. A bit of a stretch therefore imho to infer an extra-solar origin of a body whose existence has not yet even been confirmed.

Happy to be shot down in flames for my opinion though..... wink.gif


No, you are accurate.
"That isn't right, heck it isn't even wrong." Wolfgang Pauli

The youtube editing produces jumbled logic -
"there isn't enough material that far out to form an ice giant " (yes)
"so Planet 9 must have been captured at that distance from another star" (eh, no)

The video editing seems jumbled, it avoids the science questions: Where it did form? If if formed close to a star, then how did it get that far away in the first place?
Postulating that it formed around a different star simply displaces the question of how would it get from the snowline area to the outer fringe of a solar system.
That problem exists whether it formed around the sun, or around another nearby star.

Looking at the paper's abstract, things look a little better.
I think they are arguing that getting an ice giant from the inner solar system into an outer solar system elliptical orbit would disrupt the kuiper belt.
However, if the ice giant is captured from another star, it might stay far enough away to have an elliptical orbit without shredding the kuiper belt.
Go to the top of the page
 
+Quote Post

7 Pages V  « < 3 4 5 6 7 >
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 18th December 2017 - 03:26 AM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.