LOS ANGELES, Oct 25 (Reuters) - An orbital NASA instrument designed mainly to advance studies of airborne dust and its effects on climate change has proven adept at another key Earth-science function - detecting large, worldwide emissions of methane, a potent greenhouse gas.That study, NASA's Earth Surface Mineral Dust Investigation, or EMIT, will help scientists determine whether airborne dust in different parts of the world is likely to trap or deflect heat from the sun, thus contributing to warming or cooling of the planet.Circling Earth once every 90 minutes from its perch aboard the space station some 250 miles (420 km) high, EMIT is able to scan vast tracts of the planet dozens of miles across while also focusing in on areas as small as a soccer field."Some of the (methane) plumes EMIT detected are among the largest ever seen - unlike anything that has ever been observed from space," said Andrew Thorpe, a JPL research technologist leading the methane studies.Scientists estimate the Turkmenistan plumes collectively spew methane at a rate of 111,000 pounds (50,400 kilograms) per hour, rivaling the peak flow from the 2015 Aliso Canyon gas field blowout near Los Angeles that ranks as one of the largest accidental methane releases in U.S. history."