For the second time in the past eight years, astronomers examining stars in the Milky Way close to Earth discovered a planet orbiting one of these celestial objects. The first such discovery took place in 2016, when astronomers identified an exoplanet (the name for any planet beyond our solar system) orbiting the star Proxima Centauri in the 4.2-light-years-distant Alpha Centauri solar system. The latest discovery was confirmed earlier this year, when professional stargazers positively identified a small-sized planet circling a lone solar traveler known as Barnard’s star, a red dwarf that can be found 5.96 light-years from Earth.
This planet was found by researchers affiliated with the Europe Southern Observatory (ESO), using a Very Large Telescope (VLT) array installed by the ESO on the summit of Cerro Paranal mountain in the Atacama Desert region of northern Chile.
This extremely sensitive and powerful array of four interconnected telescopes includes an instrument known as the Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO), which can detect tiny gravitational wobbles in the orbit of a faraway star caused by another celestial body orbiting around it. The newly discovered planet caused these wobbles in the motion of Barnard’s star, and further analysis of the orbital path of this planet over a five-year period verified its true identity.
The setting Sun dips below the horizon of the Pacific Ocean, bathing the Paranal platform and the Very Large Telescope in light in this amazing aerial image from the Atacama Desert in northern Chile. (ESO/G. Hüdepohl (atacamaphoto.com)/CC BY 4.0)
While the three-star Alpha Centauri system is the nearest multi-star system to Earth, Barnard’s star is the closest single star (with the exception of the Sun, also a single star). Its red dwarf status is shared by 70% of the other stars in the Milky Way galaxy (there are at least 100 billion stars in our galaxy in total), and if other red dwarf systems also have planets it means the number of planets in the Milky Way in total could approach or even surpass the one trillion mark.
Introducing Barnard’s b, Earth’s Next-Door Neighbor (Relatively Speaking)
This newly discovered planet is estimated to have less mass than the Earth (about half the mass of Venus, to be more exact). It has been given the name Barnard’s b, and it was found to have an orbital path that puts it approximately 1.8 million miles (2.9 million kilometers) from the surface of its sun.
This is only five percent of the distance between our Sun and Mercury. However, the planet does not burn up because Barnard’s star is a red dwarf that produces a surface temperature that is only half that of the Sun. This explains why the temperature on the surface of exoplanet Barnard’s b is much lower than the temperature on Mercury (125° Celsius vs. 430° Celsius), despite being so close to its star.
Despite this huge difference, Barnard’s b is no more capable of supporting life than Mercury.
“Barnard b is one of the lowest-mass exoplanets known and one of the few known with a mass less than that of Earth,” stated study lead author Jonay González Hernández, a researcher from Spain’s Instituto de Astrofísica de Canarias, in a European Southern Observatory press release.
“But the planet is too close to the host star, closer than the habitable zone. Even if the star is about 2,500 degrees [Fahrenheit] cooler than our sun, it is too hot to maintain liquid water on the surface.”
Planet Hunters Celebrate
Astronomers from around the world have been studying Barnard’s star intently for many years, looking for among other things evidence that it might have planets. Its proximity has made it a relatively easy planet to study, and the fact that it is a red dwarf also made it an attractive target for exoplanet hunters.
Because red dwarfs have less mass than other types of stars (Barnard’s star is 80% less massive than the Sun), wobbles in their movements caused by planets are easier to detect.
Another advantage of looking for planets near red dwarfs is the stars’ relatively low production of heat. They have a smaller habitable zone (called the “Goldilocks zone” by astronomers) in comparison to brighter stars that radiate more heat, meaning the search for planets that could have liquid water on their surfaces—and possibly support life—has to cover a less expanse area of space.
Another advantage still is that planets attached to red dwarfs complete their orbits quite quickly (a year on Barnard’s b is only three Earth days long), so astronomers are able to monitor and evaluate the nature of their movements in a shorter period of time.
Interestingly, the conventional theory of planet formation suggests red dwarfs are at a disadvantage when it comes to planet formation. In comparison to hotter stars like the Sun they are less rich in elements heavier than hydrogen and helium, and these elements are believed to be essential to the creation of solid planetary-like bodies.
But as this new research shows, red dwarfs can indeed form planets, regardless of any obstacles that might prohibit such an outcome.
Artistic impression of an exoplanet orbiting a Red Dwarf. (NOIRLab/NSF/AURA/J. da Silva/Spaceengine/M. Zamani/CC BY 4.0)
There May Be Exoplanets Galore in the Barnard’s Star System
All the detailed observations and mathematical calculations that allowed the ESO-affiliated researchers to find this exoplanet are explained in a new article just published in the journal Astronomy & Astrophysics.
As exciting as this discovery was, there may be other thrills coming soon for the exoplanet hunters scoping out the Barnard’s star solar system. As they explain in their journal article, the team of researchers found clues to suggest that there may at least three other planets circling around this modestly-sized red dwarf, and there are hopes that one or more of these planets will be found within the Goldilocks zone.
In the coming months and years the team members will be relying on the ESPRESSO technology to verify the existence of these astronomical bodies.
“We now need to continue observing this star to confirm the other candidate signals,” said study coauthor Alejandro Suárez Mascareño, another researcher from the Instituto de Astrofísica de Canarias.
“The discovery of this planet, along with other previous discoveries such as Proxima b and d, shows that our cosmic backyard is full of low-mass planets.”
If indeed any of these planets are found within the star’s temperate zone, it raises the possibility that they might support some kind of life—although this will likely remain impossible to prove.
Top image: This artist’s impression shows Barnard b, a sub-Earth-mass planet that was discovered orbiting Barnard’s star. Source: ESO/M. Kornmesser
By Nathan Falde
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