Why this cosmic phenomenon means NASA can't communicate with Mars

Placing a long-distance call to a robot on another planet is already complicated enough. But it becomes nearly impossible when a nearly 864,400 mile-wide star is in the way.

On Saturday, Mars entered solar conjunction. This means the Sun is wedged between the Earth and the Red Planet for a period of about two weeks. During that time, the radiation from the star interferes with radio signals between Earth and Mars.

In order to avoid any dropped calls between mission control and ongoing Mars missions, NASA is keeping communication with Perseverance and other Martian explorers to a minimum.

NASA will stop sending commands to most of its missions from October 2 to October 14, a period called the “solar conjunction moratorium.” Some missions will be offline until October 16, depending on the angular distance observed from Earth between Mars and the Sun.

In the meant time, the space agency has set up its rovers, orbiters, and landers alike with a list of simple commands to carry out while they’re on the other side of the Sun.

What is the Mars solar conjunction?

The solar conjunction takes place every two years.

Mars takes 687 days to complete one orbit around the Sun, while a speedier Earth takes 365 days. During their orbit around the star, Mars and Earth will end up on opposite sides of the star for a period of about two weeks.

For those two weeks, the two planets are invisible to one another.

What happens to NASA missions when Mars is in conjunction?

NASA uses a global network of antennas known as the Deep Space Network (DSN) to send commands for its missions to carry out in space or on other planets. DSN uses radio frequency transmissions that travel through large antenna systems with specialized receivers.

But with the Sun in the middle between Earth and Mars, the hot gas being emitted by the star interferes with the radio signals being sent between the two planets.

During that time, NASA will refrain from sending commands to its missions in order to avoid “unexpected behavior” from the spacecraft, according to NASA. The agency states:

“No one attempts to send new instructions to Mars during solar conjunction. It's impossible to predict what information might be lost due to interference from charged particles from the Sun, and that lost information could potentially endanger the spacecraft. Instead, prior to solar conjunction, engineers send two weeks' worth of instructions and wait.”

How NASA prepares for the Mars solar conjunction — Ahead of the Mars mission blackout, NASA engineers prepared a list of simple commands and sent them over to ongoing missions on or around the planet.

“Though our Mars missions won’t be as active these next few weeks, they’ll still let us know their state of health,” Roy Gladden, manager of the Mars Relay Network at NASA’s Jet Propulsion Laboratory in Southern California, explained in a statement. “Each mission has been given some homework to do until they hear from us again.”

The Mars missions will continue to gather data, but will not be receiving any new commands from NASA until mid-October.

• NASA’s Perseverance mission will spend the next two weeks taking weather measurements on Mars, looking for dust devils and recording Martian sounds with its microphone.
• Perseverance’s companion, the Ingenuity Helicopter, will remain stationary at its location 575 feet away from the rover while communicating its status weekly to the Perseverance rover.
• Meanwhile, Perseverance’s predecessor, the Curiosity rover, will take weather and radiation measurements, and look for dust devils with its host of cameras.
• The InSight lander will continue to hunt for marsquakes from its stationary position.
• NASA’s three orbiters, Odyssey, Mars Reconnaissance Orbiter, and MAVEN, will continue relaying data back to Earth, as well as gathering their own science during the next two weeks.

If any data sent during this period is evaluated as corrupted, that data can usually be retransmitted. Mission controllers also accept that “some data will be lost” during this period.

After the period of moratorium ends, Perseverance, Curiosity, and InSight will continue to beam their data to Earth, including any new images they captured during the time of solar conjunction. The difference this time and before October 14 is that NASA will be there to receive it.