Do Planets Generate Their Own Light?

[DB]

Do planets have actual lumosity or are they just lit up by stars? Might be a stupid question but I am just wondering.

Thnx

 

[The Bob]

Do planets have actual lumosity or are they just lit up by stars? Might be a stupid question but I am just wondering.

Thnx

Personally I do not know but I assume they might have because of some of the chemical reactions that happen on some of them (like the Great Spot on Jupiter). I don't know, to be honest, but I would say yes.

Sorry.

The Bob (2004 ©)

 

[turbo]

Personally I do not know but I assume they might have because of some of the chemical reactions that happen on some of them (like the Great Spot on Jupiter). I don't know, to be honest, but I would say yes.

Sorry.

The Bob (2004 ©)

Well THIS particular planet is certainly luminous! It's a big pain in the butt, and I'm glad I live in a thinly populated place.

http://www.pha.jhu.edu/~atolea/second/page1.html

 

[russ_watters]

Its virtually all reflected from the sun.

 

[Nereid]

If you had IR eyes, you'd still see the planets ... and some (most in some cases) of that IR would be from the planet itself.

You can tell how much of the light (or IR) that you see from a planet is 'native' vs reflected by looking at the planet at night ... i.e. looking at the side of the planet that is not facing the Sun. We can do this - from Earth - for Mercury and Venus, but not for the others. Do you know why DB?

Also, even if the Earth had no cities, fishing fleets, etc, it would still be quite visible 'at night' from out in space ... at least some of the time. Do you know why?

Finally, things like aurorae and lightning are 'local' in origin, so ... (But Mercury is pretty dark 'at night', why?)

 

[Chronos]

That's Nereid. Always handing out homework.

 

[Orion1]

Giant Jupiter...

Jupiter radiates twice as much heat as it receives from the Sun. No other planet comes even close to doing this. This fact is the key to understanding Jupiter's complex and beautiful cloud circulation pattern. There must be some internal energy source, perhaps the energy remaining from Jupiter's collapse from a primordial gas cloud 20 Mkm across to a protoplanet 700,000 km across, 5 times the present size of Jupiter. This catastrophic phase of collapse theoretically started, when the temperature grew sufficiently high to break up hydrogen atoms. The rapid phase may have taken only 3 months to occur, following the 70,000 years it had previously taken to shrink from a more diffuse cloud. Jupiter is undoubtedly still contracting.

The heat emanating from the interior of Jupiter produces huge convention currents. The bright zones are rising currents of gas driven by this convection. The belts are falling gas; the tops of these dark belts are somewhat lower (about 20 km) than the tops of the zones and are about 10 K cooler.

Earth-based infrared observations measure temperatures only 100 K to 200 K in the uppermost atmosphere far above Jupiter's clouds. Yet Pioneer's data at other infrared wavelengths reveal that at a pressure of one-half that of the Earth at sea level, the temperature of supposedly frigid Jupiter reaches a boiling 400 K.

Infrared radiation refveals Jupiter's temperature in the upper atmosphere to be very cold because of the planet's great distance from the Sun, about 133 K (-220 F), on both the sunlit and nighttime sides. At a lower level, the poisonous clouds are warmer. Gaps in the clouds have revealed still lower haze layers with even higher temperatures of around 250 K (-9 F).

Jupiter's infrared thermal radiation is generated by the heat of the planet itself. This figure turns out to be about twice as much energy as Jupiter absorbs from the Sun!. Theorists believe Jupiter is slowly contracting, releasing gravitational energy as heat and radiation. This radiation was most intense when Jupiter formed and has declined ever since to the low level observed today. According to some theoretical models, the core may be over twice the size of Earth and have a temperature around 30,000 K.

Jupiter's Luminosity and Intensity are calculated by reference (3) as:
L_j = 1.05 * 10^17 W - wrong!
$$I_J = \frac{L_J}{4 \pi dr_c^2}$$ - wrong!
$$dr_c$$ - Cassini-Jupiter surface range
I_j = 9.83 * 10^(-5) W/m^2 - wrong!

$$L_J = \frac{L_\odot}{4} \left( \frac{r_j}{r_t} \right)^2$$
$$I_J = \frac{L_J}{4 \pi r_J^2}$$
$$r_J$$ - Jupiter radius
$$r_t$$ - Sol-Jupiter distance

Luminosity based upon reference 3 equation and information:
$$L_J = 8.122*10^{17} W$$
$$I_J = 12.678 W*m^{-2}$$

However, Arxiv information reference 4:
$$L_J = 8.363*10^{17} W$$
$$I_J = 13.054 W*m^{-2}$$


Reference:
Contemporary Astronomy (Jay M. Pasachoff, 1977)
The Cosmic Voyage (William K. Hartmann, 1992)
http://www.nap.edu/html/oneuniverse/energy_solution_12.html
http://arXiv.org/abs/astro-ph/9506055

 

[DB]

We can do this - from Earth - for Mercury and Venus, but not for the others. Do you know why DB?

Also, even if the Earth had no cities, fishing fleets, etc, it would still be quite visible 'at night' from out in space ... at least some of the time. Do you know why?

Yes, we can only see the sides of Mercury and Venus oposing the sun because they are in front of us in the solar system.

As for why we can see Earth at night from space, I am assuming it's due to the light of the stars, the light reflected from planets behind us, the moon at the right position would reflect some light on the dark side of the planet.

So know I'm thinking that rock planets generally do not emit their own lumosity, but gas planets can, due to their (as The Bob said) chemical reactions.

 

[DaveC426913]

Inasmuch as they are not at absolute zero, all things, including plants and rocks emit heat, and woud be visible (at least against a background of empty space) if you could see in the IR band.

Now, the *origin* of that heat is mostly from the Sun, although a certain percentage is due to the Earth's internal molten core.

As for actually emitting its own EM radiation, Jupiter is the only planet in our Solar System that actually emits more than it absorbs from the Sun. It is a pretty strong emitter of radio frequencies.

But none of the planets are luminous in the *visible* band, unless you count local, discrete events such as aurorae and lightning.

 

[DaveC426913]

You can see the back of Mars if you look at just the right time. But you need to lean waaaaaay out, and a mirror on a stick helps too.

:-)