Life really may be unique to Earth: Study shows that even planets in the ‘habitable zone’ are inhospitable

SYDNEY — Astronomers and space fanatics across the glove have long sought to answer the question of whether or not there are other planets like Earth out there. One study may put a disappointing end to that search. Researchers from the University of Sydney say that life really may be unique to Earth, after all.

Prior studies in recent years suggest the universe could be teeming with life. But that is unlikely to be the case, explains the Aussie team. They show that the first weather forecasts from our solar system’s next door neighbor are a massive setback for alien hunters. The discovery has implications for other distant planets, too. It will make it easier to detect their atmospheric conditions.

According to their study, an Earth sized waterworld only 4.2 light years away is inhospitable, despite being in the “habitable zone.” The rocky planet, named Proxima b, is being bombarded with radiation, they say. The planet lies too close to Proxima Centauri, a type of star known as a red dwarf, and the most common.

Unfortunately, the reports from Proxima Centauri are not promising for “finding life as we know it.” Habitable zones closer than Earth’s would rule it out.

“Astronomers have recently found there are two ‘Earth-like’ rocky planets around Proxima Centauri, one within the ‘habitable zone’ where any water could be in liquid form,” says study leader Andrew Zic, in a statement. “But given Proxima Centauri is a cool, small red-dwarf star, it means this habitable zone is very close to the star – much closer in than Mercury is to our Sun. What our research shows is this makes the planets very vulnerable to dangerous ionizing radiation that could effectively sterilize them.”

Alien life is wishful thinking?

They are 25 trillion miles from Earth. It would take thousands of years to get there using current technology. Scientists are hoping to propel tiny spacecraft across the galaxy by lasers at 20% the speed of light, shortening the journey to decades.

Proxima b’s discovery four years ago generated huge excitement. It suggested ET might be right on our doorstep, astronomically speaking, of course. Red dwarfs are much smaller and dimmer compared with our Sun. It was thought a planet can be nearer and still enjoy a climate as benign as Earth’s.

The first analysis of stellar flares and radio bursts on a star outside the solar system turns that theory on its head, however.

“This is probably bad news on the space weather front,” admits Zic. “It seems likely the galaxy’s most common stars, red dwarfs, won’t be great places to find life as we know it.”

Proxima b is about 4.7 million miles from its star, taking about eleven days to complete an orbit. That’s compared to Earth’s 93 million miles and 365 days, respectively.

“Our own Sun regularly emits hot clouds of ionized particles during what we call ‘coronal mass ejections,” explains Zic. “But given the Sun is much hotter than Proxima Centauri and other red-dwarf stars, our ‘habitable zone’ is far from the Sun’s surface, meaning the Earth is a relatively long way from these events. Further, the Earth has a very powerful planetary magnetic field that shields us from these intense blasts of solar plasma.”

Countless exoplanets give astronomers hope for finding another Earth

There are now more than 4,000 known exoplanets, or those revolving around stars beyond the solar system. This has boosted hopes of finding extra-terrestrial life. Recent research suggests half the Sun-like stars in the Milky Way could be home to Earth-like planets. But they make up only seven percent of the galaxy’s stellar objects.

By contrast, red dwarfs such as Proxima Centauri account for 70 percent.

The findings published in The Astrophysical Journal were based on observational data from space and land-based telescopes that captured the phenomenon in “amazing detail.” They show planets around these stars are likely to be showered with stellar flares and plasma ejections. It suggests they suffer strong atmospheric erosion, leaving them exposed to very intense X-rays and ultraviolet radiation.

“Red dwarf radio bursts might happen for different reasons than on the Sun, where they are usually associated with coronal mass ejections,” says Zic. “But it’s highly likely there are similar events associated with the stellar flares and radio bursts we have seen in this study.”

Coronal mass ejections are hugely energetic expulsions of ionized plasma and radiation leaving the stellar atmosphere.

“Understanding space weather is critical for understanding how our own planet biosphere evolved, but also for what the future is,” says co-author Dr. Bruce Gendre, of Western Australia University.

Magnetic fields like Earth’s have never been identified around an exoplanet, and finding them could prove tricky. “But even if there were magnetic fields,” concludes Zic, “given the stellar proximity of habitable zone planets around red dwarf stars, this might not be enough to protect them.”

SWNS writer Mark Waghorn contributed to this report.