Before Ralph McNutt embarked on his doctoral studies, he had never been east of the Mississippi River. But soon after the young Texan arrived at the Massachusetts Institute of Technology (MIT) in the fall of 1975, he found himself on a journey to the edge of the Solar System—and beyond. While looking for a research assistant, he ended up in the office of plasma physicist Herbert Bridge, a prominent figure in space science who oversaw a covert effort to dismantle and ship Harvard University’s cyclotron to New Mexico for the Manhattan Project. World War II. Bridge evidently saw a familiar spark in McNutt and invited him to work on the plasma detector for Voyager, the epic mission to the outer planets that began in 1977. “I said, ‘Where do I sign up before you change your mind?'”
Now this veteran of Voyager, one of NASA’s greatest scientific triumphs, wants to launch his own passion project. McNutt and colleagues at the Johns Hopkins University Applied Physics Laboratory (APL) unveiled a concept for the Interstellar Probe (IP), a $3.1 billion mission to pick up the science gauntlet that the two Voyager probes dropped a decade ago after they left the heliosphere. , the zone of the Sun’s influence. Few expected the spacecraft to survive this long, yet their fascinating observations, which continue to trickle in, have disproved many beliefs about the outer limits of the Solar System. “A lot of our preconceived notions didn’t work very well,” says McNutt.
Voyager’s data is so enigmatic that some prominent researchers say the probes have yet to reach interstellar space, perhaps because the boundaries of the heliosphere extend farther than generally thought. A view from the perch of the Earth will not solve the matter. “The only way to see what our aquarium looks like is to be outside and look in,” says McNutt. “We need to get modern instruments up there,” adds Lennard Fisk, a space physicist at the University of Michigan (UM), Ann Arbor. “In that sense, Interstellar Probe would be revolutionary.
Now McNutt must convince a jury of his peers. His team delivered an IP concept study to the Decadal Survey of Solar and Space Physics, a community-based exercise led by the National Academies of Sciences, Engineering, and Medicine that sets the field’s priorities for the next 10 years. The panel is expected to begin deliberations next month and deliver its verdict in 2024. A thumbs up for IP would go a long way toward securing NASA support for the probe, which would ideally lift off in 2036. The timing would allow it to rendezvous with Jupiter and its strong gravity, which would throw the probe into interstellar space. It arrived about 16 years later, in half the time Voyager took.
Chinese scientists are proposing a similar mission called Interstellar Express, which could launch around the same time. Buckle up, enthuses Jim Bell, a planetary scientist at Arizona State University, Tempe, and past president of the Planetary Society. “It’s a space race to the edge of the Solar System!”One of the challenges for McNutt and his colleagues is selling a mission that will last at least 50 years and require three or more generations of scientists. More daunting may be winning hearts and minds in space physics, dominated by experts in space weather solar flares and coronal mass ejections that can wreak havoc on satellites and power grids. “People are too afraid that one big project will suck up all the funding for the rest of the science we want to do,” says APL space physicist Pontus Brandt, principal scientist of the IP mission concept study. But Merav Opher, an astrophysicist at Boston University, says expanding the boundaries of the field is important. “It is short-sighted if we continue to fund only space weather.”
“Voyager on steroids,” as McNutt calls the IP, may hit this first hurdle. “It’s a long shot,” says Bell, who has no stake in the project. But IP has a powerful champion in McNutt, says Opher, who calls him “a fantastic mover and shaker.” McNutt’s great mentoring skills will also be important, according to Bell. “You really have to think outside of your own life,” he says.
Interstellar Space was a lifelong endeavor for McNutt, who he says was an “introverted and nerdy kid” with a passion for science fiction. One work that left a deep impression was Robert Heinlein’s A Time for the Stars, whose premise was the Twin Paradox, an early 20th century thought experiment that sought to explain the mind-bending aspect of Albert Einstein’s special theory of relativity. In the novel, a telepathic teenager joins an expedition to find habitable planets around other stars; he spends 4 years on a spaceship that can travel at speeds close to the speed of light. He returns home to find his Earth identical twin at age 71. This premise inspired the 16-year-old McNutt to come up with an interstellar mission as a project for a science fair in Fort Worth, Texas in 1970. He laid out the physical obstacles to such an epic voyage and even created a prototype spacecraft out of poster board, balsa wood and Elmer’s glue.
Voyager on steroids,” as McNutt calls the IP, may hit that first hurdle. “It’s a long shot,” says Bell, who has no stake in the project. But IP has a powerful champion in McNutt, says Opher, who calls him “a fantastic mover and shaker.” McNutt’s great mentoring skills will also be important, according to Bell. “You really have to think outside of your own life,” he says.
Interstellar Space was a lifelong endeavor for McNutt, who he says was an “introverted and nerdy kid” with a passion for science fiction. One work that left a deep impression was Robert Heinlein’s A Time for the Stars, whose premise was the Twin Paradox, an early 20th century thought experiment that sought to explain the mind-bending aspect of Albert Einstein’s special theory of relativity. In the novel, a telepathic teenager joins an expedition to find habitable planets around other stars; he spends 4 years on a spaceship that can travel at speeds close to the speed of light. He returns home to find his Earth identical twin at age 71. This premise inspired the 16-year-old McNutt to come up with an interstellar mission as a project for a science fair in Fort Worth, Texas in 1970. He laid out the physical obstacles to such an epic voyage and even created a prototype spacecraft out of poster board, balsa wood and Elmer’s glue.
In high school, McNutt sought to satisfy his thirst for science. School administrators were “more interested in keeping kids out of school,” but he and several classmates successfully applied for a physics class. A few years later, McNutt got a chance to meet the “father of space travel”: Wernher von Braun, a former Nazi rocket scientist who moved to the United States after World War II and became the chief architect of NASA’s lunar program. Von Braun was giving a talk at Texas Christian University, and McNutt was selected to be on a student panel to ask questions. He asked von Braun if NASA had plans to send humans to Mars by, say, 1990. That wasn’t in the cards, von Braun replied dryly. Instead, he said, the space agency will focus on robotic probes. “I was really irritated,” says McNutt. “I was like, ‘What the hell is wrong with you?’
McNutt came away from the meeting with von Braun’s autograph—now in his basement, along with a science fair model—and a fierce determination to become a space scientist. He had a knack for math—“I used to do slide speed races,” he admits—and majored in physics at Texas A&M University, College Station. At MIT, as a junior member of the Voyager team, he made it to Cape Canaveral for the launch of Voyager 1 in 1977, and vividly remembers a visit two years later to mission control at the Jet Propulsion Laboratory (JPL). Television monitors in the JPL cafeteria were showing the first images of Io, Jupiter’s spectacularly colorful volcanic moon. “It looked like a rotting orange or a pizza pie. I thought, ‘Oh my God, this is so beautiful.'”
Voyager’s revelations about the mysterious outer planets kept coming. And the intrepid probes continued. In the early 2000s, it seemed likely that one or both would reach the heliopause—the boundary between the heliosphere and interstellar space, where the solar wind of the Sun’s charged particles dies out. This exciting prospect was tempered by the fact that the probes were primarily designed to probe Jupiter’s powerful magnetosphere, not the much weaker fields and particles of the interstellar medium. “By today’s standards, the information you can get from the Voyager spacecraft is primitive,” Bell says. Still, McNutt adds, “The fact that we could get something was a lot better than nothing.”
The big surprise came in 2007 when Voyager 2, plunging below the plane of the ecliptic in which the planets orbit, passed the terminal shock: where the solar wind first begins to weaken as it is buffeted by the interstellar gas and dust in which the solar system rolls . over. Voyager 1 passed the shock 3 years earlier, about 94 astronomical units (AU) from Earth. (One AU, the average distance between Earth and the Sun, is approximately 150 million kilometers.) But its plasma detector failed at Saturn in 1980, leaving it unable to measure the deceleration of the solar wind. The models predicted that winds would slow from 1.2 million kilometers per hour to about 300,000 kilometers per hour. But Voyager 2 reached wind speeds of 540,000 kilometers per hour. “People who were going through the shock of the termination were like, ‘WTF?'” says Brandt.
Also puzzling was that Voyager 2 crossed the shock wave a full 10 AU closer to Earth than Voyager 1. After a Voyager team member delivered the report at a conference in Switzerland, “Everybody was like, ‘What’s going on?'” says Elena Provornikova of APL , Head of Heliophysics IP, who was then at the Institute of Space Research of the Russian Academy of Sciences in Moscow. “We immediately started talking about what could cause this asymmetry—what the physics behind it could be.”
For more read: https://www.science.org/content/article/voyager-steroids-mission-probe-mysterious-region-beyond-solar-system
