Hey /sci/, I know jack shit about astronomy. How come we can

Yes. its much more distant and its not lit by a lightsource like our sun. we only discovered it because cassini recieved EM signals from the planet X

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>>8059597
Galaxies radiate light. Planets ... well ok planets do to but at a much much lower frequency and power.

https://en.wikipedia.org/wiki/Stefan–Boltzmann_law

That's the energy everything radiates at according to temperature. Apply that to any planet you want in the solar system. Remember the Sun's energy drops off significantly with distance because of the inverse square law. A planet at that distance will receive very little solar energy and emit extremely little.

Compare that to Earth for example. Earth is 1 AU (by definition) and receives 1380 Watts per meter squared. Pluto for instance is 39.5 AU. According to the inverse square law how many Watts per meter will Pluto receive light from the sun? You can then plug in to the energy balance equation to calculate at what temperature it emits light.

Compare that to stars. The sun's blackbody radiation curve is phenomenal when compared to the Earth. It radiates energy at 5778 kelvin (Earth radiates at about 285 K) and it's a SMALL STAR.

Long story short. Stars are huge radiators of energy, planets are not.

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>>8059608
Eh, sorry, here's a simpler energy balance equation that removes the greenhouse effect. In this case we can probably ignore it because Icy bodies like Pluto and further Kuiper Belt Objects will have no significant atmosphere.

It's also already solved for T

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My apologies I had to go grab my old advanced meteorology textbook. I didn't want to get things wrong.

You're also going to want Wein's Law and for the inverse square law use ... I don't know how to use the equation form here.

Use s = s0*(r0/r)^2

Wien's law is the graphic

>>8059638
So, for an object of Pluto's distance you get

S = 0.884 Watts per meter squared

Pluto's albedo is .4-.6 object at Pluto's distance is going to emit light in radio waves at a temperature of 36 K assuming an albedo of .5 (Nasa puts this number at 37K pretty good for our equation)
http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html

And it will radiate at 80 meters (visible light is between 400 and 800 nanometers) putting it way out in radio waves.

Since we put the albedo at .5 that means 50% of that .884 watts is bouncing back in our face. Not much to work with. Barely perceptible by telescope.

Now think of an object 3x as far and you start to see the problem real fast.

>>8059600
> we only discovered it because cassini recieved EM signals from the planet X

No. The Cassini was not used in the discovery. It was used to try and find it's gravitational influence but the results were null.

>>8059674
You don't look for emission from the planet you look for it in reflection in optical light. Pluto was discovered with photographic plates not radio antennas. The reason this is hard is reflected falls off with distance to the fourth power.

Someone on here once said that its like the difference between seeing a lighthouse a few miles away at night and trying to see an ash spec right in front of your face.

>>8059597

Stars emit light
Planets don't

/thread

>why is it easier to see collection of millions of stars than a sliver of reflected light of a single star

>>8061677
Pretty handy huh? This scientist can declare that he "found a planet" but it's impossible to ever verify. I swear half the "discoveries" by scientists these days are untestable bullshit

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>>8061712
>it's impossible to ever verify
No it's fucking not. There are two simple ways to test it, firstly by finding more TNOs to test the model and secondly by direct search. It's not invisible, if we knew where to point the telescope it would be quite detectable, most of it's orbit is already ruled out from surveys.

Just because YOU don't know how to test something doesn't mean it's untestable. It's probably bullshit but it's falsifiable.

I am really sick of people who know nothing about anything and yet feel qualified to declare modern science is a sham. Fuck off.

>>8059597
Not an expert either. But basically, yeah. It's just really far away. So it's harder to detect. Especially when it's in such a clustered area of space that's just full of stuff. It basically means that it's not just sitting there in the open. It seems like just another piece of space rock.