The quest for the REAL NINTH PLANET, Something for number-crunchers Options

[karolp]

I was wondering: if there really was a "jupiter" or an "earth" lurking in the far reaches beyond Neptune, would we be able to detect it with present technology? The current limiting magnitude record is magnitude 28.2 (that of Comet Halley in 2003 seen by the VLT telescope).



So here it goes: what magnitude would be a) Earth b) Jupiter at: 100 AU, 200 AU and 1000 AU respectively?



I am looking forward to the results of your calculations.

[Greg Hullender]

I think you'll find most of what you want in here:

http://www.ifa.hawaii.edu/~jewitt/papers/2004/J2004.pdf

The Pan-Starrs project is supposed to find asteroid threats to the Earth, but as a side-effect it ought to find remote objects too. For example, another Pluto out to 320 AU and another Jupiter out to 2140 AU. (That's between 2 and 12 light-days.) Thsoe are the distances where these bodies would be Magnitude 24 objects.

Here's the Science Goals section of the Pan Starrs site:

http://pan-starrs.ifa.hawaii.edu/public/sc...lar-system.html

Does anyone know how likely this is to actually be built?

[Jyril]

The prototype telescope (PS-1, first of the four telescopes) has already achieved the first light meaning the project is 1/4 complete.

I've got the impression that it has got the funding it needs. The final location is still open. It's either Haleakala or Mauna Kea. The latter, although better, may not be selected because of environmental and cultural reasons (the indigenous Hawaiians are against building telescopes on their holy ground).

[Greg Hullender]

Should we be concerned that the project is 1/4 complete even though they haven't picked a location for it yet? :-)

[djellison]

Given the 'neigbourhood' clause of the IAU definition - anything they find out at those ranges will not be classified as a planet.

Doug

[AndyG]

<W>hat magnitude would be a) Earth Jupiter at: 100 AU, 200 AU and 1000 AU respectively?
I am looking forward to the results of your calculations.

My calculator says (though I need to turn 200AU and 1000AU into light hours and light days, respectively):

Earth
100AU - Earth 16.1, Jupiter 10.6
200AU - Earth 19.2, Jupiter 13.7
1000AU - Earth 26.1, Jupiter 20.6

All under 28.2 - but that's a lot of sky to look around, and at 1000AU the orbital period is vast. An object at 1000AU would only move about 0.11 arcsec per day.

Andy

[Guest_Myran_*]

Neat tool AnyG.
I see you used the albedo for Earth and Jupiter in that comparision, but yes one Jupiter sized object would have a hard time escaping visual detection (not to mention the effects caused by its gravity) and even one the size of Earth seems unlikely unless perhaps at the largest distance out to 1000 AU.

I dabbled around with that tool and got a magnitude between 18 - 28 perhaps as high as 30 for a really dark Mars sized chunk which corresponds with my own guesstimate that one object of that size might be hiding there in the Kupier belt.

[edstrick]

We should note that it's now pretty clear the classical Kuiper belt extends out to only some 52 or 54 <I think> AU. Scattered disk objects go out further, but they're not in billions-of-years-stable orbits. There are almost certainly no classical KB objects as big as Mars, though there could be scattered disk objects in the aphelion parts of their orbits far enough out to be too faint to have been spotted yet. The REAL possibility is finding large objects beyond the KB and never part of it, except at best during the very formation of the solar system.. things like Sedna, at perihelion, 70 AU in an orbit that goes out to.. was it 250 or so AU?

[AndyG]

Neat tool...

Many thanks. Next time I edit it I'll fix the typoes! But the maths is fine. I put it together to get an idea of the relative brightness of extrasolar planets (though the calculation is for an orb fully lit by a star, which would therefore be lost in a sun's glare) and found it works fine for our planets/dwarf planets/objects-by-other-names at opposition.

Incidentally, now that Voyager's at 100AU, I see Earth is less than magnitude 6. Or rather, I wouldn't see it. "No longer visible to the naked eye". That puts a sense of perspective on just how far away that is!

Andy

[ugordan]

Incidentally, now that Voyager's at 100AU, I see Earth is less than magnitude 6. Or rather, I wouldn't see it. "No longer visible to the naked eye". That puts a sense of perspective on just how far away that is!

Interestingly, Venus' magnitude comes out at 4.6 which ought to be visible, if you neglect the 0.4 degree maximum angular separation from the Sun. You could just barely cover the Sun with the thumb and see a tiny speck of light right near it

[David]

The REAL possibility is finding large objects beyond the KB and never part of it, except at best during the very formation of the solar system.. things like Sedna, at perihelion, 70 AU in an orbit that goes out to.. was it 250 or so AU?

Woeful understatement. Sedna's aphelion is 975 AU.

[AndyG]

Interestingly, Venus' magnitude comes out at 4.6 which ought to be visible, if you neglect the 0.4 degree maximum angular separation from the Sun. You could just barely cover the Sun with the thumb and see a tiny speck of light right near it

You get Jupiter and Saturn thrown in, too: at mags 4.3 and 5.9 (that last would be fairly tough - even though the nearest street lights are some way off!)

But I think oddest of all is the Sun...it's a speck. The size of a pinhead at 15 metres, yet still 45 times brighter than a full Moon. So for human eyes at Voyager, the shadows would be extremely sharp and well-defined, colour vision would be just present - but on the verge of fading to neutral greys; and you'd be leaving a system seemingly comprising two gas giants and a high albedo planet ...

Brrr!

Andy

[alan]

My calculator says (though I need to turn 200AU and 1000AU into light hours and light days, respectively):

Andy

I believe the absolute magnitude is defined wrong. It is how bright an object would appear at 1 AU from the sun and 1AU from the observer. This should depend only on the diameter and the albedo of the object. It should not change when you change the distance X from star.

[Guest_Myran_*]

alan wrote: believe the absolute magnitude is defined wrong. It is how bright an object would appear at 1 AU from the sun and 1AU from the observer.

Oops, you're right about absolute magnitude there alan.

[hermes]

Hi. I'm new here. I'm working on a school project about pluto. The teacher asks me to design a space trajectory for a spacecraft to travel to pluto and return to earth. I have no ideas what to do. Please help me...