Russ Walker has not been out at night to see the NEOWISE comet, although his home in the Santa Cruz Mountains is well above the fog line. At 89, he says he doesn’t get out much anymore, but he’s still awestruck by it. “It’s a beautiful comet,” Walker says. “The photos I’ve seen are just incredible.”
Walker also has some insider knowledge that makes him appreciate this comet even more. He was part of a team of roughly 20 astronomers who were responsible for developing and launching WISE then relaunching NASA’s NEOWISE – that’s Near-Earth Object Wide-field Infrared Survey Explorer. The telescope was active from 2009-11, then decommissioned, then reactivated in 2013.
“They kind of ran out of money and stopped,” Walker says. “But we left it in good condition in orbit, and you can’t bring it down anyway. It was very expensive to build and put up there, but it’s really continuing to pay off.” It’s taken some 10.3 million images of near-Earth objects, according to NASA.
So WISE, which was originally limited by its super-cold solid hydrogen coolant system, revived with a different search capability – and discovered the NEOWISE comet, which won’t be visible from Earth for another 6,800 years.
“We wanted to use WISE to try to measure as many near-earth asteroids as we could. We discovered over 100,000 of those; comets were fewer and farther between, probably only about 20.” (Per NASA, it discovered 21 comets.)
Throughout his career, Walker (now retired) specialized in studying comet trails – not to be confused with comet tails, which are made of particles roughly equivalent to cigarette smoke. He looked at the “big chunks – particles the size of marbles to golf balls” that might give some insight into what the comet was made of, the material it shed as it went around the sun. “It’s really a sample of what our solar system is made of primordially,” Walker says.
He worked for about 15 years at the Monterey Institute for Research in Astronomy, where director Bruce Weaver has also been occupied by what comets leave behind, though his focus is different. Weaver practices astronomical spectroscopy, collecting information about the molecules of celestial bodies – things like temperature and chemical composition. The chemical composition of a comet is interesting to him if it’s a comet that’s made of primordial material before our solar system was formed, but that applies to only about one-third of comets; another third are fully ejected; and another third, including NEOWISE, “are heavily processed by having passed by the sun dozens or hundreds or thousands of times.” That means NEOWISE no longer serves as something like a fossil record of what was out there before Earth.
So scientifically, Weaver isn’t so interested in this comet – it’s already been modified by our planet’s existence. “I’m not interested in it scientifically, but as a tourist I think it’s great,” he says, talking about being a tourist of the sky.
The spectroscopy of comets – the part that interests Weaver – has illuminated some surprises about their composition. “They were primarily thought to be dirty ice balls, but when the spectrum came up, it was more like an icy dirt ball,” he says.
MIRA’s mission is in part to help regular people get more out of stargazing, in addition to supporting astronomical research. “People look up and say, ‘Wow that’s gorgeous, that is so cool, and it would be even cooler if I understood it a little bit better,’” Weaver says.
For Walker, the night sky was always interesting, but it was his time serving in the U.S. Air Force from 1954-57 that truly sold him on astronomy. “Back in that time we were worrying about hydrogen bombs and things,” he says. “The inside of a hydrogen bomb is very much like the inside of a star. That’s where I got interested in astronomy.”