Back in 1980, a trip to a Lancaster, Ohio, bookstore netted an astronomy book about sending unmanned probes to nearby stars. While I enjoyed the look at exotic starship propulsion systems that might come into use decades or centuries from now, what really fascinated me were the ways we could put together an interstellar mission using today’s technology.
In 1980, no one expected an interstellar mission to be flown anytime soon. Astronomers didn’t even know if planets orbited other stars. They thought so, but they lacked proof. All that has changed.
Our super-telescopes both on the ground and in space have detected hundreds of planets of varying sizes around other suns. Just this year, we learned that a planet orbits a star called Proxima Centauri. It’s a small, red M dwarf only about half as hot as the Sun and 14 percent as wide. It’s one of the stars in a triple-star system known as Alpha Centauri. For those of you who remember your high school science classes, that star system is the closest one to Earth, just over 4 light years away.
Now it’s realistic to contemplate an interstellar mission to a nearby star system. We have a planet we can investigate – if we can cut travel time down to a manageable time period of say 30 to 50 years. NASA’s nuclear-powered Voyagers were launched in the summer of 1977, and are now out beyond the solar system and are still operating. For those of you who are math-challenged, the two planetary probes are into their 39th year of operation.
Based on the Voyagers, unmanned nuclear-powered probes can last for decades. But can we use current or feasible future technology to cut travel time down to three to four decades for a flyby of Proxima Centauri’s planet?
Investors led by a Russian billionaire philanthropist think they can mount a mission to Alpha Centauri within a generation. Yuri Milner is investing $100 million toward a research program to send nanocraft that would reach the planet in about 20 years. The goal is to reach a speed that’s about 20 percent the speed of light, or 37,000 miles per second. The technology isn’t farfetched.
The plan is to develop nano-sized cameras, sensors, maneuvering thrusters and communication equipment for a tiny gram-scale robotic probe. A ground-based kilometer-scale laser would beam 100-gigawatt laser pulses through the atmosphere to multiple probes. Light sails would allow the probes to ride those beams to Proxima Centauri’s planet. In the microgravity vacuum of space, the torrent of photons unleashed by the laser would push the tiny craft to relativistic speeds. The nanoprobes would be launched into Earth orbit by the thousands. Not able to decelerate, they would briefly collect data at Alpha Centauri and beam it back to Earth.
Another interstellar option has always fascinated me – a slingshot gravity assist from Jupiter and our Sun. I first read about it in that book I purchased back in 1980. In researching a solar gravity assist, I’ve learned that a close swing-by of the Sun in combination with a high-thrust burn at closest approach can send an unmanned space probe into interstellar space, but isn’t practical for a flight to the three-star Alpha Centauri system. It would take thousands of years to reach the planet.
The exoplanet, dubbed Proxima Centauri b, has a mass at least 1.3 times that of Earth, meaning it’s potentially rocky. It orbits the star every 11.2 days at a distance of only 0.05 times the Earth-Sun distance, or roughly one-tenth the space between Mercury and the Sun. That places it right in the star’s putative habitable zone.
No one actually has seen the planet, even via a telescope. But they know it exists because they’ve seen its gravity tug on the red dwarf star it orbits. Its year lasts only 11.2 days, an orbit too tight to pick out a planet from the blinding glare of a star. Some are calling it the Earth Next Door and that’s because it could have an atmosphere and water. In 2018, NASA’s James Webb space telescope (JWST) could provide an answer once it’s in space by sampling the star system’s infrared light.
Proxima b is apparently tidally locked like Earth’s Moon, where one side always faces Earth. In the case of Proxima b, one side of the exoplanet always faces its star, awash in permanent daylight, the other side trapped in an endless cold night. If the exoplanet has an atmosphere, it would circulate warmth from the day side to the night side – and prevent water from boiling off into space. A ring of habitability could exist between the day and night sides.
According to Business Insider, “When a rocky planet is warmed up by a star, it absorbs and re-emits light. Yet rocky planets emit a different kind of infrared light than is given off by stars like Proxima Centauri. So instead of trying to photograph a tiny planet in a flood of visible light, JWST may only need to hunt for specific wavelengths of infrared light in the glare.”
So if a ring of habitability turns out to exist on Proxima Centauri b, maybe someday the planet could become mankind’s first colony on a world that orbits a star other than our Sun.
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Mike’s the author of a published fantasy trilogy called Larenia’s Shadow. The novels – The Emperor’s Mistress, Thief’s Coin and Assassins’ Lair – are available for purchase on the websites of Amazon and Barnes and Noble. He’s working on a Civil War adventure/romance novel titled Blessed Shadows Dark and Deep.