There's quite some activity happening around Mars. The China National Space Administration (CNSA) has been collecting data from its first-ever rover, Zhurong, currently located on the surface of Mars since May 14. The rover has been exploring the region around its landing site in Utopia Planitia and gathering important information on the Red Planet's surface and interiors.
However, it can not get this data back to Earth on its own. Instead, it requires the help of orbiters such as the European Space Agency's (ESA) Mars Express. Why?
Rovers like the Zhurong do not carry the equipment they would need to transmit data directly to Earth because this would take up too much valuable space that is needed for space experiments. They are instead equipped with small, short-range radios similar to what the spacecraft orbiting Mars, such as ESA’s Mars Express, have.
Rovers use these radios to send their data up to Mars's roaming orbiters, which then forward it back to Earth where scientists eagerly await to receive it and analyze it. And it's (relatively) common practice to share orbiters for information relaying purposes when the rover's preferred orbiter is not around.
So far, Zhurong has used the Chinese Tianwen-1 orbiter with which it arrived to send information to Earth. But starting in November, ESA’s Mars Express will undertake five tests in which it will attempt to listen to Zhurong and send the information it captures back to ESA’s ESOC Operations Centre in Darmstadt, according to an ESA blog.
There's a catch though: Due to an incompatibility between the two radio systems, the Zhurong rover cannot receive the frequencies used by Mars Express. Luckily though, it is capable of transmitting a frequency compatible with Mars Express.
How will this work?
When Mars Express reaches the space above Zhurong’s landing site in Utopia Planitia, it will turn on its radio and simply listen and record any incoming data. Once it has accumulated all the information it can gather, the spacecraft will turn to face Earth and relay the data across space to ESOC. ESOC will then share the data it receives with the Zhurong team for processing and analysis.