Red dwarfs always make me think of the classic British TV science comedy show in the 90’s that was named after them. The stars themselves better little resemblance to the show though. They are small, not surprisingly red stars that can generate flares and coronal mass ejections that rival many of the much larger stars. A team of astronomers have recently used the Chandra X-Ray Observatory to study Wolf 359 and found it unleashes brutal X-ray flares that would be extremely damaging to life on nearby planets.
Red dwarf stars are small, cool, and very long-lived stars that shine with only a fraction of the brightness of our Sun. They have a mass less than half of the Sun’s and their surface temperatures range from 2,500 to 4,000 degrees Celsius. Because they burn their fuel so slowly, red dwarfs can last for trillions of years, far outliving more massive stars. They are common across the cosmos making up about 70-80% of all stars in the Galaxy but despite this they are hard to spot with the naked eye.
Wolf 359 is a one such red dwarf star located about 7.8 light-years away from Earth, making it one of the closest stars to our solar system. It’s still too dim to be seen without a telescope though shining at just one-thousandth the brightness of the Sun. It’s part of the constellation Leo and has a mass only about 12% of our Sun’s, with a surface temperature around 4,000 degrees Celsius. Wolf 359 is a relatively young star, but due to its low mass, it will burn its hydrogen fuel slowly and could remain stable for tens of billions of years.
With the intense radiation emissions from Wolf 359 its very likely that any planets in orbit around it will be unable to maintain a stable life supporting atmosphere. A team of astronomers however have been studying it with NASA’s Chandra X-Ray Observatory and ESA’s XMM Newton. They have found that only a planet that has green house gasses, just like Earth, in its atmosphere could sustain life. Given that red dwarfs are the most prevalent stars in the Universe, astronomers have explored them to find evidence of exoplanets but to date, with little success. The team found evidence for two planets in orbit about Wolf 359 but not all scientists are convinced.
Every star has a habitable zone and its location is determined by the temperature and energy output from the star itself. The outer limits for this zone around Wolf 359 is about 15% of the distance between Earth and Sun. The two yet to be confirmed exoplanets orbit the star outside the habitable zone; one is too close, the other to far.
As they studied the system over 3.5 days, they observed 18 X-Ray flares from Wolf 359. That was just over 3.5 days though and the team propose that more powerful and more damaging flares will occur from time to time. These intense X-ray flares are the chief reason that any planets in orbit must be within the habitable zone and will need an atmosphere rich in carbon dioxide to sustain habitable conditions. It’s unlikely however, that any planet within the habitable zone will be able to keep its atmosphere due to the strength of the wind blowing upon it.
Source : Exoplanets Need to Be Prepared for Extreme Space Weather, Chandra Find
