Lewis David Kaplan and his team detected the signals of water vapor and carbon dioxide in the spectrogram of Mars in 1964,[25] as well as carbon monoxide in 1969.[26] In 1965, the measurements made during Mariner 4's flyby confirmed that the Martian atmosphere is constituted mostly of carbon dioxide, and the surface pressure is about 400 to 700 Pa.[27] After the composition of the Martian atmosphere was known, astrobiological research began on Earth to determine the viability of life on Mars.