Searching for signs of life

Answers to astrophysics’ biggest questions. As it travels through space at 186,000 miles per second, light provides images on delay: The naked eye views the moon as it was 1.3 seconds ago, Jupiter as it was 40 minutes ago, and Andromeda— the nearest galaxy to ours—2.5 million years ago. Space telescopes are often compared to time machines, collecting light emitted billions of years ago. Scientists believe Webb will be vital for studying the end of the Dark Ages—the period between the Big Bang and the formation of stars. That could reveal insights about the “dark matter” that makes up about 80 percent of the universe’s mass. Webb can see back about 150 million years farther than Hubble, and thus may provide glimpses of the formation of the first stars, solar systems, and galaxies, says Caitlin Casey, an assistant professor of astronomy at the University of Texas at Austin. “With Webb,” she says, “we’re going right up to the edge of the observable universe.”

Recent breakthroughs in astronomy have established that most stars have orbiting planets, which means our galaxy probably hosts billions of these “exoplanets.” Planets around other stars are too distant and dim to image clearly, but Webb can use its enormous capacity to gather infrared light to search the atmospheres of exoplanets for circumstantial evidence of extraterrestrial life, such as the presence of water, oxygen, carbon dioxide, methane, and other chemicals. One planetary system that Webb will study is about 40 light-years away: a small star called TRAPPIST-1, orbited by seven Earth-size planets—three of which orbit in the zone where temperatures could be mild enough for liquid water to form. Researchers are particularly excited to measure the methane and carbon dioxide in the fourth planet’s atmosphere. “We all want to find another Earth, don’t we?” said Kevin Stevenson, an astronomer at the Johns Hopkins Applied Physics Laboratory. “Webb will provide us the first opportunity to really answer that question.”