The next closest exoplanet beyond our solar system may sound like a cold, alien and inexorable place, but what if it is not? What if, as new research suggests, are pockets of habitable environments deep beneath the icy surface, provided it can produce heat from its core?
Barnard's Star b is discovered late in 2018 as none of the planets in the solar system. With a mass three times the earth's earth, this enigmatic exoplanet is known as a "super earth", a likely rocky planet that occupies a mass range between the earth and the smaller gas giants, such as Neptune. Exoplanet hunting missions that Kepler has found that the super Earth is common throughout the galaxy, so Barnard's Star b is more than just a curiosity, it can be the key for us to understand how they formed, what they are made of, and most strikingly, why the solar system does not have one.
After a careful search through two decades of Barnard's Star Spectroscopic data, astronomers announced the new world's discovery in November. They found a 233-day "wobble" that indicated that an exoplanet was located at about the same distance where Mercury revolved around our sun, very weakly on its star as it orbited. But since the star is a low-mass and dark red dwarf, the planet's path sets it beyond the star's "habitable zone" and into its "snow line". If Barnard's Star b has any water on the surface, it will freeze and not help support life (as we know).
According to new research presented at the American Astronomical Society's 233rd meeting) in Seattle, Washington, January 1
"Geothermal heating can support" zones of life "below its surface, similar to underground lakes found in Antarctica," said astrophysicist Edward Guinan, Villanova University, in a statement. "We note that the surface temperature of Jupiter's icy moon Europe is similar to Barnard b but due to tidal warming, Europe probably has floating sea beneath its icy surface."
Astrobiologists have long been fascinated with Europe. Though it orbits Jupiter well beyond our sun's inhabited zone and has a very obvious thickening crust, through tidal interactions with the gas giant, the core produces heat that maintains an underground ocean in liquid water conditions. Decades of lunar observations have also shown that the ocean can have sufficient amounts of oxygen and nutrients to support a hypothetical marine ecosystem.
Barnards Star b is much larger than Europe and cannot have the same degree of tidal warming experienced by Jovian moon, but should it have a large and hot iron / nickel core, Guinan and his co-researchers suspect that its geothermal activity might give rise to to primitive life forms.
Unfortunately, we go before ourselves. Barnard's Star b may well be habitable, but at present we know only his mass and orbital around the star. We know nothing about its composition, atmosphere (whether it even has one) or physical size. It will undoubtedly be cold, because the star only generates 0.4 percent of the sun's radiant power, but does it have water ice? Does it have geothermal activity? For now we do not know, but there is hope.
Barnard's Star is just six light years from Earth, so it is conceivable that a future generation of powerful telescopes will have observational power to study the aliens. According to the researchers, such observations will shed light on the nature of the planet's atmosphere, surface and potential.
"The most important aspect of the discovery of Barnard's star b is that the two closest star systems to the sun are now known to host planets," said Angle in the same statement. "This supports previous studies based on Kepler mission tasks, which means that planets can be very common throughout the galaxy, even numbering in tens of billions."
The closest exoplanet to the earth is Proxima Centauri b, a Earth-sized world that orbits its red dwarf star within the inhabited zone, the distance surrounding a star that may allow a planet to have liquid water on its surface. On paper it sounds like a great place to look for extraterrestrial life, but Proxima Centauri is an angry little star, known for its violent spots that would irradiate any planet orbiting too closely. Barnard's Star b circles his red dwarf further away, and if life can find a way under its surface, it can be protected from any ionizing radiation.