Image: John Watson

John Mather: ‘I never expected to see individual stars in the dawn of time’

The Nobel prizewinning physicist describes his work on Nasa’s James Webb, the most powerful telescope in history
January 25, 2023

John Mather knows what it is like to be Galileo. The Italian scientist saw a new world of mountains on the Moon and satellites in orbit around Jupiter when he turned the most powerful telescope of his day on the heavens in 1610. In the past six months, Mather has glimpsed a new world of galaxies and stars beyond anything seen before with the most powerful telescope of our own day: Nasa’s James Webb Space Telescope. “I never expected to see individual stars in the dawn of time,” he tells me over video call. “The telescope has far exceeded our expectations and we are beyond ecstatic.”

The successor of Nasa’s Hubble Space Telescope, the James Webb was launched on Christmas Day 2021. With its 6.5-metre mirror made of 18 hexagonal segments, it is floating around the “Lagrange-2” point, 1.5m kilometres from Earth, shielded from solar heat by a tennis-court-sized sunshade.

It has been a long journey for the James Webb and for Mather, its senior project scientist. Mather, who grew up in Virginia, discovered his passion for astronomy when, aged eight, he was taken by his parents to the New York Hayden Planetarium. “At the time, 1953, Mars was at its closest and there was a lot of excitement about whether we would see its canals, purportedly built by a Martian civilisation,” he says. “Sadly, they were an illusion.”

Mather studied physics at university and as a graduate student worked on a balloon-borne experiment to observe the “afterglow” of the Big Bang in which the universe was born 13.82bn years ago. This led to him becoming one of the driving forces behind Nasa’s Cosmic Background Explorer satellite, for which he shared the 2006 Nobel prize in physics.

He was invited to become the project scientist of the James Webb in 1995. The job involved concentrating on the science, rather than the engineering, and, in Mather’s description, providing the world with a “vision of why it is important to do things… It was obvious to me that this was the most important thing I could possibly work on.”

He did not know it would be 26 years until the James Webb’s launch and that, at $10bn, it would come in 20 times over budget. Mather admits it was “scary” when they thought they might not get the money and the time to finish. It was also scary when, in 2017, Hurricane Harvey hit Houston, where the telescope was being tested in a giant vacuum chamber. “Despite the high winds and 48 inches of rain, to our relief the telescope and the team survived,” he says.

Surprisingly, the launch of the James Webb—which involved effectively putting a bomb under the telescope—did not stress him. “I knew we had carried out all the necessary tests,” he says. “When you’ve done everything you can, you might as well enjoy the launch.” He was proven right. And although, once the telescope reached orbit, there were 344 steps in the unfurling of the mirror and sunshade, and each had to go to plan or the project would fail, everything worked perfectly.

Mather’s great hope is to see the first stars to be born after the Big Bang and to better understand the composition of the atmospheres of planets around other stars. But a telescope is just as likely to find things that no one anticipated. For the 20,000 people involved in the project, this is the most exciting prospect.

At 76, Mather remains as enthusiastic as the eight-year-old wowed by New York’s planetarium. In addition to the James Webb, he is involved in a project to put a 100-metre opaque disk in space to blot out the light of individual stars so ground-based telescopes can directly see their planets, which are some 10bn times fainter. “I am so busy,” he says. “I don’t think a quiet retirement is for me. That would be so boring.”