There’s something menacing about red dwarfs. Human eyes are accustomed to our benevolent yellow Sun and the warm light it shines on our glorious, life-covered planet. But red dwarfs can seem moody, ill-tempered, and even foreboding.
For long periods of time, they can be calm, but then they can flare violently, flashing a warning to any life that might be gaining a foothold on a nearby planet.
To date, 5,250 extrasolar planets have been confirmed in 3,921 systems, with another 9,208 candidates awaiting confirmation. Of these, 195 planets have been identified as “terrestrial” (or “Earth-like“), meaning that they are similar in size, mass, and composition to Earth. Interestingly, many of these planets have been found orbiting within the circumsolar habitable zones (aka. “Goldilocks zone”) of M-type red dwarf stars. Examples include the closest exoplanet to the Solar System (Proxima b) and the seven-planet system of TRAPPIST-1.
These discoveries have further fueled the debate of whether or not these planets could be “potentially-habitable,” with arguments emphasizing everything from tidal locking, flare activity, the presence of water, too much water (i.e., “water worlds“), and more. In a new study from the University of Padua, a team of astrobiologists simulated how photosynthetic organisms (cyanobacteria) would fare on a planet orbiting a red dwarf. Their results experimentally demonstrated that oxygen photosynthesis could occur under red suns, which is good news for those looking for life beyond Earth!
Astronomers have found another Earth-sized planet. It’s about 31 light-years away and orbits in the habitable zone of a red dwarf star. It’s probably tidally locked, which can be a problem around red dwarf stars. But the team that found it is optimistic about its potential habitability.
Astronomers are keenly interested in red dwarfs and the planets that orbit them. Up to 85% of the stars in the Milky Way could be red dwarfs, and 40% of them might host Earth-like exoplanets in their habitable zones, according to some research.
But there are some problems with their potential habitability. One of those problems is tidal locking.
“Go then, there are other worlds than these.” Or so Stephen King said in his famous Dark Tower series. As of yet, none of those worlds are known to be like Earth. But, according to some new simulations by researchers at the National Astronomical Observatory of Japan (NAOJ), finding a genuinely Earth-like world might be in the cards by the decade’s end.
Photosynthesis is probably the most important chemical reaction for life on Earth. It is the process plants use to transform sunlight into energy it can use. Through it, plants can produce carbohydrates they can use (and we can eat when we harvest plants), generating oxygen as a by-product. Photosynthesis is why Earth’s atmosphere is about 20% oxygen. No photosynthesis, no life on Earth as we know it.
As the planets of our Solar System demonstrate, understanding the solar dynamics of a system is a crucial aspect of determining habitability. Because of its protective magnetic field, Earth has maintained a fluffy atmosphere for billions of years, ensuring a stable climate for life to evolve. In contrast, other rocky planets that orbit our Sun are either airless, have super-dense (Venus), or have very thin atmospheres (Mars) due to their interactions with the Sun.
In recent years, astronomers have been on the lookout for this same process when studying extrasolar planets. For instance, an international team of astronomers led by the National Astronomical Observatory of Japan (NAOJ) recently conducted follow-up observations of two Super-Earths that orbit very closely to their respective stars. These planets, which have no thick primordial atmospheres, represent a chance to investigate the evolution of atmospheres on hot rocky planets.
The only known life in the universe lives on a mid-size rocky planet that orbits a mid-size yellow star. That makes our planet a bit unusual. While small rocky planets are common in the galaxy, yellow stars are not. Small red dwarf stars are much more typical, making up about 75% of the stars in the Milky Way. This is why most of the potentially habitable exoplanets we’ve discovered orbit red dwarfs.
Proxima b, the closest exoplanet to our Solar System, has been a focal point of scientific study since it was first confirmed (in 2016). This terrestrial planet (aka. rocky) orbits Proxima Centauri, an M-type (red dwarf) star located 4.2 light-years beyond our Solar System – and is a part of the Alpha Centauri system. In addition to its proximity and rocky composition, it is also located within its parent star’s habitable zone (HZ).
Until a mission can be sent to this planet (such as Breakthrough Starshot), astrobiologists are forced to postulate about the possibility that life could exist there. Unfortunately, an international campaign that monitored Proxima Centauri for months using nine space- and ground-based telescopes recently spotted an extreme flare coming from the star, one which would have rendered Proxima b uninhabitable.