Why does the signal from Curiosity on Mars take 14 minutes?

[Syntarsus]

Just wondering why the signal from Mars curiosity takes so long. I assume electro-magnetic waves travel at light speed in space. The Sun is only 8 light minutes away so I assume Mars is currently closer than that so wondering why all those extra minutes.

[Tinker1947]

There diverted to orbiting satellites then relayed to Earth, i do believe...

[ronin]

Not sure where Mars is in relation to us at present but could easily be 14 minutes away from us.

It will be somewhere in it's orbital path and not at it's closest point that occurred August 2009. At it's closest it is just over 3 minutes, at its furthest around 22 minutes (eccentric orbit). So any number inbetween is possible.

[GlassWalker]

Just had a look, Mars is currently further away from us than the sun.

[JamesF]

According to Stellarium the distance to Mars is 1.65 AU. 1.65 x 8 is 13.2, so there's your fourteen minutes, near enough. Have to admit though that I don't know whether Stellarium is quoting the distance to the Earth or distance to the Sun.

James

[Stephen]

On the 6th of August, Mars and Earth will be 238M Km apart.

Speed of EM wave approximately 300,000 Km/s

v = d / t

t = d / v

t = 238,000,000,000 / 300,000,000 (converted both to metres for simplicity)

t = 794s

t = 13.2m (as stated above)

I should add Mars is now WAY behind us in an orbital sense.

[JamesF]

Where did you get the distance from out of interest Stephen?

James

[JB80]

Here are a couple of videos which may help.

And a link but it isn't working for me possibly due to heavy traffic.

http://www.jpl.nasa.gov/video/index.cfm?id=1100

[Syntarsus]

Thanks for all the replies. 1.65 AU - all makes sense now. So my assumption of its proximity was the error.

[Stephen]

Where did you get the distance from out of interest Stephen?

James

Random Google relating to Mars and Curiosity

[Ronnie67]

Hey I could have done that on my calculator

[George Jones]

Thanks for all the replies. 1.65 AU - all makes sense now. So my assumption of its proximity was the error.

More on what ronin and other folks wrote.

Proximity depends on the relative geometry of Mars, Earth, and the Sun. Right now, this is as in the figure below, which shows that the current distance between Mars and Earth is greater than the distance between the Earth and the Sun.

At opposition (which might be the situation you had in mind), Earth is directly between Mars and the Sun (they're on the same side of the Sun), and the distance between Earth and Mars is less than the distance from Earth to the Sun, so the time taken for a signal is less than 8 minutes.

At conjunction, the Sun is direcly between Earth and Mars (they're on opposite sides of the Sun), and the distance between Earth and Mars is more than twice the distance from Earth to the Sun, so the time taken for a signal is more than 16 minutes.

Right now, the situation is between conjunction and opposition, and hence the 13 minutes.

This can all be seen from the diagram below.