They are doing research to see if humans can live on Mars.
They are doing some studies on Mars to see if humans can exist on that planet.
この場合、次のような言い方ができます。
ーThey are doing research to see if humans can live on Mars.
「彼らは人類が火星に住めるか研究を行っている」
to do research「研究を行う」
to live on Mars「火星に住む」
ーThey are doing some studies on Mars to see if humans can exist on that planet.
「彼らは人類が火星で生存できるかの研究を行っている」
to do some studies「研究を行う」
to exist「生存する」
ご参考まで！
They are researching if humans are able to live on Mars.
"彼らは火星に人類が住めるように研究を行っています"
- They are researching if humans are able to live on Mars.
- They are conducting research to see if humans will be able to live on Mars.
- Research is being done to see if people are able to live on Mars.
カナダ 
アメリカ合衆国 
