By Will Dunham
WASHINGTON (Pawonation.com) – Astronomers have discovered four small terrestrial planets circling Barnard’s Star—one of the nearest stars to us—although their research indicates that none of these planets can support life due to high temperatures, similar to how Mercury functions within our own solar system.
Barnard's star is located approximately six light years from us and stands as the closest solitary star — one not part of a multiple-star system — to our solar system. The only exceptions are the trio of stars within the Alpha Centauri system, which lie around four light-years distant. One light-year represents the distance that light covers in a year, equivalent to roughly 5.9 trillion miles or 9.5 trillion kilometers.
Researchers utilized information gathered from the Gemini Telescope located in Hawaii and the Very Large Telescope based in Chile to verify the existence of the four planets orbiting Barnard’s Star. An earlier study from the previous year, which analyzed data sourced from the Very Large Telescope, suggested evidence for one planet along with potential indications of an additional three planets.
Planets located outside our solar system are known as exoplanets. Some of these orbit around Barnard's Star and rank amongst the tiniest out of over 5,800 exoplanets found since the '90s, as scientists enhance their capability to detect smaller celestial bodies.
Barnard’s Star, found within the boundaries of the constellation Ophiuchus, is classified as a red dwarf—the smallest kind of main-sequence star. With roughly 16 percent of our Sun's mass, it pales in comparison when it comes to temperature. Despite this cooler nature, its planetary system features worlds circling at such proximate distances that their surfaces experience extreme conditions—temperatures akin to those seen on Mercury, which generally do not support known forms of life.
"Essential for livability is the existence of liquid surface water," stated Ritvik Basant, a doctoral student in astronomy at the University of Chicago and principal author of the study released this week in the Astrophysical Journal Letters.
"If a planet is situated too near to its star, any water present would vaporize. Conversely, being too distant would cause the water to freeze. As it happens, all four planets circling Barnard’s Star are positioned too closely to their host, rendering them excessively warm to support liquid water," explained Basant.
This is the sole recognized star hosting a planetary system where all planets are smaller than Earth. The first planet from the star possesses a mass 26% that of Earth, followed by another with a mass 30% of Earth’s. Next comes one weighing in at 34% of Earth's mass, and finally, the most distant among the quartet tips the scales at 19% of Earth's mass. All these orbits are completed within mere days.
To provide some context regarding their masses, Mars possesses roughly 11% of Earth’s mass, whereas Mercury holds approximately 6%.
Each of the four planets follows an almost perfect circular path around Barnard's Star, with their distances being within Mercury’s orbital range from the Sun.
Astronomers define a "habitable zone" as an area around stars where conditions could permit liquid water on a planet’s surface, similar to what we see on Earth. In the case of Barnard's Star, scientists concluded that there are no Earth-sized planets within this habitable region; however, they haven’t dismissed the potential existence of smaller planets elsewhere in the same system.
When seeking extraterrestrial life, researchers focus on discovering planets with similar characteristics to Earth—rocky and temperate—as opposed to gaseous giants. Recent discoveries indicate that there are terrestrial planets circling within the Alpha Centauri and Barnard’s Star systems; however, these do not reside in the habitable zones of their respective stars. The Alpha Centauri system has identified two such exoplanets, which revolve around the red dwarf known as Proxima Centauri.
Several techniques are employed for discovering exoplanets. For their research, scientists utilized what’s known as the “wobble” technique, also termed the “radial velocity.” When a planet orbits around its parent star, it imparts a gravitational pull strong enough to make the star move minutely back and forth. Astronomers observe these subtle movements with telescopes, thereby deducing the existence of an orbiting planet.
Astronomers have sharpened their capability to detect exoplanets via this technique, owing to more advanced instrumentation. Among the roughly 1,100 exoplanets identified with this approach, the farthest one from Barnard's Star is the least massive.
This research highlights the increasing abilities of advanced instruments in identifying low-mass planets. The four recently detected planets circling Barnard’s Star are all smaller than Earth, an area that has been scarcely investigated outside our solar system. This represents a crucial advancement in the quest for Earth-sized worlds located in the habitable regions around Sun-like stars, according to Basant.
(Reported by Will Dunham, Edited by Rosalba O’Brien)
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