the-search-for-extraterrestrial-life-is-going-to-look-at-our-nearest-galactic-neighbor

Scientists are starting to look for life in our galactic backyard.

Alpha Centauri, two stars that at just over four light-years (about 25 trillion miles) away are the closest sunlike stars to our solar system, is the focus of a new effort to find planets that could reveal signs of life. The project centers on building a small space telescope — dubbed TOLIMAN after a medieval name for the star — that will go into Earth’s orbit in about two years and could start detecting planets by about 2025.

Although Alpha Centauri is right next door in astronomical terms, no planets have been detected around its binary star system. If any are found, their atmospheres could be scanned for the “biosignatures” created by extraterrestrial life — a relatively new astronomical technique that could allow scientists to determine by telescope if there’s alien life, especially microbial, on distant planets.

More than 4,000 alien planets have now been confirmed, but they’ve been largely discovered thanks to lucky alignments, said project leader Peter Tuthill, a professor of astrophysics at the University of Sydney. 

“There’s a little bit of a dark secret that astronomers have been keeping,” he said. “We’re not actually very good at finding planets.”

Most of the “exoplanets,” as they’re known, have been discovered by automated systems like the Kepler space telescope, which watches continuously for planets crossing in front of hundreds of thousands of stars.

But finding planets around a particular star system — such as Alpha Centauri — is much more difficult.

To improve their chances, the new space telescope will have a specially etched mirror to create what’s known as a “diffractive pupil” effect — spreading the incoming starlight from a tiny point into a much larger, flower-shaped pattern that can better reveal any of the very slight “wobbles” caused by the gravity of orbiting planets.

The Alpha Centauri system has two stars similar to the sun, orbiting each other at about 20 times the distance between the sun and the Earth, Tuthill said.

Each has its own so-called Goldilocks Zone — where rocky planets are at just the right temperature to have liquid water on their surfaces, which is thought to be necessary for life as we know it to evolve.

In 2016, two planets were discovered around what could be a third star in the system — the red dwarf Proxima Centauri, discovered by telescope in 1915 and slightly closer to us than the other two.

But they’re not thought to be suitable for life because Proxima emits dramatic flares that can be 100 times more powerful than flares from the sun, Tuthill said.

That means the sunlike stars of Alpha Centauri may be our best bet for locating signs of alien life.

“If we found an Earth-mass planet in the habitable zones there, that would constitute a Holy Grail — a true Earth analogue,” he said. “That would potentially be an environment that could have all of the same conditions that we know here on Earth.”

The TOLIMAN project is backed by Breakthrough Initiatives, a space exploration fund based in California.

The group has proposed exploring Alpha Centauri with Breakthrough Starshot, a project consisting of thousands of tiny space probes that can be propelled at very high speeds by lasers on Earth.

In theory, the Breakthrough Starshot “nanocraft” could reach Alpha Centauri in about 20 years — an epic voyage of 25 trillion miles that would take tens of thousands of years with the fastest spacecraft that now exist.

“Alpha Centauri is very close, so if people want to dream visionary dreams about interstellar flight one day, then Alpha Centauri has to be our first  bus stop on the way out into the galaxy,” Tuthill said.

If the TOLIMAN telescope does find any planets, the next step will be to study them with other telescopes to determine the composition of their atmospheres — and perhaps even to find chemical “biosignatures” produced by life.

The latest astronomical techniques for studying the atmospheres of exoplanets only work well with very large planets orbiting close to their star, and studying the atmospheres of Earth-size planets is currently beyond their reach, said astrophysicist Chris Watson of Queen’s University Belfast in Northern Ireland.

But chemicals are being discovered on smaller and more “challenging” planets as scientists find new ways to analyze their data and as new instruments — such as the James Webb space telescope — become available, he said.

Watson, who is not involved in the TOLIMAN project, is part of a team that recently detected hydroxyl radicals — a component of water — in the atmosphere of a planet orbiting a star about 400 light-years from Earth.

Detecting chemicals and possibly biosignatures on Earth-like planets around the stars of Alpha Centauri will be difficult, but “observing the nearest and brightest planetary system is going to provide our most likely route to success,” he said. “The signals will be very faint, and so we will need every photon of light to make it work.” 

Tom Metcalfe

Tom Metcalfe writes about science and space for NBC News.

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