# Temperature in the space between planets of our solar system?

Gold Member

## Main Question or Discussion Point

I know that the overall temperature of the universe is microwaves at 3 Kelvin or so from the Big Bang, but is this mostly for deep space? Or is this pretty much the temperature in our solar system also, assuming a coordinates some distance away from any of our planets but still within our solar system? For example, since we are close to a star that puts out a significant amount of energy, it seems that within our solar system and between the planets, space around our neighborhood should be higher. I tried to look for a map of temperature verses distance from sol but I couldn't find one.

Related Astronomy and Astrophysics News on Phys.org
DrClaude
Mentor
Since the planets are more or less in equilibrium with the Sun (neglecting residual heat when the planet formed, radioactivity, ...), the temperature of the planets is a pretty good indicator of the temperature at different distances from the Sun. One has to be careful though to take into account the greenhouse effect, especially for Venus and the Earth.

Nasa has a nice picture: http://solarsystem.nasa.gov/galleries/solar-system-temperatures

Last edited:
DrClaude
Mentor
One could also calculate the temperature of a blackbody in equilibrium with the Sun as a function of the distance between the two.

Last edited:
Gold Member
Perfect! I went through the calculations on that map, everything works. All good here.

Ken G
Gold Member
And be aware that the solar wind is at a much higher temperature than that, since it is not in radiative equilibrium like the planets are. So it depends on what you mean by the "temperature of the space," but it does sound like you mean the average radiation temperature.

Gold Member
Yes, I did mean the average radiation temperature. But I didn't think about the solar wind. I know the solar wind happens every few days, and bigger storms on the order of weeks. Does the solar wind significantly increase the temperature between the planets? Is it something easy to calculate for a ballpark calculation? If you know of a good source, I'd like to know. I know it could also vary depending on the distance from the sun, and I would be interested in how the solar wind temperature depends on sun distance.

Ken G
Gold Member
The solar wind fills the interplanetary space with warm plasma, so although there are periods where it increases during storms, it's always there. The density is just very low, so you wouldn't feel it if you stuck your hand in it. The temperature does drop with distance due to the expansion that comes with spherically spreading out. It starts out at millions of Kelvin, but by the time you get to Earth it is already down to thousands. I'm sure there's a fine Wiki on the solar wind.

Gold Member
I'll look at the solar wind in a moment, but I did think of one other thing based on the above comment. I calculated that at 0.86 Au away from the sun, the temperature due only to the incoming radiation of the sun would be 300 Kelvin or so, roughly room temperature. I used the formula on Wiki of

T = (L(1-A)/(16*Pi*Steph_sigma*(D^2)) to the one-fourth power

Where A = 0, L = sun power of 3.846(10 to the 26 power) at 0.86 Au.

Does this mean that at 0.86 Au, an astronaut would pretty much feel they were at room at room temperature or is this some kind of particle energy thing? Would they feel they were at the right warmth without needing any special heaters or coolers? Or would the effective temperature the astronaut feel actually be much colder than this? If the later, what formula would I use to calculate what temperature a person in between the planets would feel?

I'll neglect solar wind for this moment right now.

Chronos
Gold Member
The temperature of the interplanetary medium is around 100,000oC. But, its density is extremely low [about 5 particles per cc] in the vicinity of earth, so it actually would feel quite chilly. The equilibrium temperature in a shaded area near earth [the temperature a thermometer would measure] is not much more than 2.7oC, or about the same as the CMB temperature. In direct sunlight the equilibrium temperature could be as high as about 120o C. For further discussion see http://www.madsci.org/posts/archives/1998-05/893698682.Es.r.html

Gold Member
Just a quick clarification.

"is not much more than 2.7oC, or about the same as the CMB temperature. In direct sunlight the equilibrium temperature could be as high as about 120 C."

Do you mean Kelvin or Celsius here? "same as CMB temperature" seems to imply Kelvin. 2.7 Celsius (~275 Kelvin) is much higher than CMB. Also the same as the 120 C, whether you mean Celsius or Kelvin.

Chronos