A study of data from Curiosity published in September found the rover had detected only trace elements of methane in the atmosphere.
"Remember that it (Curiosity's methane reading) is for a single spot.
One point doesn't make it a story for the whole planet," top Indian space scientist Jitendra Nath Goswami told AFP.
NASA, which will launch its Maven probe on November 18 to study why Mars lost its atmosphere, is helping ISRO with communications.
Clouds of methane have previously been identified by telescopes on Mars, but the gas has never been confirmed by a mission there.
Methane on Earth is mostly produced by micro-organisms, so a positive reading would suggest some form of life on a planet that scientists believe was once covered with water.
Updated II "It's lift off," said a commentator on state television as the red-and-black rocket launched into a slightly overcast sky on schedule at 02:38pm (0908 GMT) from the southern spaceport in Sriharikota.
The 350-tonne