Mars has been colonized, close to a million people are now living above (and below) the martian soil, every few months a ship from Earth arrives with more resource for expansion and more settlers, currently the travel is one way until the martian space elevator will be completed in the near future.
Everything is going well until one day the "blackout" happens, all communication to Earth & the sister colonies on the moon stopped, pointing what telescopes the Martian settlers did have to Earth show no signs of life - no lights in the dark sides of the planet, no signals of any kind in any of the electric spectrum that the settlers have equipment to measure and as the months pass no new ships arrive.
It's as if one day everybody on Earth and Earth orbit just vanished.
What caused the "blackout"?
- The settlers don't know if anyone is alive, causes which would keep people alive on Earth yet unable to communicate with Mars or use anything that shows sign of life to settlers outside the planet is acceptable.
- Ideally Earth should remain intact, I would prefer answers where the settlers are guessing but never know for sure what happened on Earth.
- Tech level is near future - 100 years to the future is a good benchmark.
- Whatever the "blackout" is it should have no affect on Mars.
- I can handwave the lunar colonies using Earth to relay communication with Mars do to the small size of the lunar colony so it's possible the "blackout" to affect Earth only and not the moon - however satellites around the earth should still be affected as even automatic transmissions from them stopped.