Most stars aren't like the sun.
Some 55 light-years away — which is relatively close by in space terms — scientists have discovered a rocky, Earth-sized world orbiting extremely close to its star (a single orbit, or "year," lasts just 17 hours). The exoplanet, which receives much more solar radiation than Earth and is unlikely to harbor liquid water, orbits the most long-lived type of star, called an "ultra-cool red dwarf." Red dwarf stars are the most common in the universe, and the coolest types of red dwarfs, which are also the dimmest and coolest of stars, are suspected to burn for over 100 billion years.
"When the universe grows cold and dark, these will be the last stars burning," NASA explained.
Our medium-sized sun, in contrast, will shine for some 10 billion years before exhausting its fuel.
The small Jupiter-sized star is called "SPECULOOS-3," named after the Search for Planets EClipsing ULtra-cOOl Stars research project, which aims to learn more about the worlds around these faint objects. This ultra-cool star is some 4,760 degrees Fahrenheit (2,627 Celsius), while the sun's surface is over 10,000 F (5,537 C).
But the nearby Earth-sized planet, called SPECULOOS-3 b, isn't exactly "cool." At such a close distance, it's walloped with radiation.
"Though this particular red dwarf is more than a thousand times dimmer than the sun, its planet orbits much, much closer than the Earth, heating up the planetary surface," Catherine Clark, a researcher at NASA’s Jet Propulsion Laboratory who coauthored the new research recently published in Nature Astronomy, said in a statement. Blasted by solar storms and winds, it might not harbor much of an atmosphere, the space agency said.
Yet some rocky worlds, like a super-Earth found this year, inhabit the "habitable zone" around red dwarfs, meaning a region of space where water exists on the surface. It takes 19 days for this super-Earth (dubbed "TOI-715 b") to orbit its red dwarf — which is still relatively close. (A habitable zone around a red dwarf star can be just one percent the distance Earth is to the sun).
To find this Earth-sized world, scientists employed a number of robotic telescopes around the world to look for a slight dimming of such ultra-cool red dwarf stars, which is caused by a distant world transiting in front. This allows astronomers to measure the size of the world and determine its density. Next, a space observatory like the James Webb Space Telescope — fitted with instruments able to detect the composition of exoplanet atmospheres and surface mineralogy — can further investigate this alien world. Research time on Webb is highly competitive, but NASA noted SPECULOOS-3 b is "an excellent candidate" for further research.
A lot of things have to go right for a planet to be considered habitable, allowing conditions for life to evolve. A planet that harbors an atmosphere, isn't too hot nor cold, and isn't relentlessly blasted with solar radiation, are important factors. Red dwarf stars can indeed emit huge bursts of radiation, but with trillions of red dwarfs in the universe, perhaps some can provide favorable environs for life to persist.
If so, such an exoplanet will certainly have time for potential organisms to evolve. Perhaps 100 billion years.
Topics NASA
