Small rocky planet detected in orbit about nearby Barnard's star

Barnard's star is a red dwarf, the smallest type of regular star and much smaller and less luminous than our sun. At about six light years away, it is the closest single star - one not orbiting with other stars - to our solar system. It is, in cosmic terms, in our neighborhood.

Because of this, scientists eager to study nearby potentially habitable worlds are excited by the discovery of the first confirmed planet orbiting Barnard's star, a rocky one with a mass about 40 per cent that of Earth.

While this planet, orbiting very close to Barnard’s star, has a surface temperature too high to be suitable for life, the researchers found what they called "strong hints" of three other planets around Barnard's star that might be better candidates.

The confirmed planet, called Barnard b, has a predicted diameter about three-quarters that of Earth, so about 6,000 miles (9,700 km).

"It is one of the least massive planets ever found," beyond our solar system, said astronomer Jonay González Hernández of the Instituto de Astrofísica de Canarias in Tenerife, Spain, lead author of the study published this week in the journal Astronomy & Astrophysics, opens new tab.

Among planets in our solar system, only Mars and Mercury are smaller.

Barnard b, with a surface temperature around 275 degrees Fahrenheit (125 degrees Celsius), orbits Barnard's star in just three Earth days at a distance 20 times closer than our solar system's innermost planet Mercury is to the sun.

Planets beyond the solar system are called exoplanets. Scientists searching for exoplanets that possibly could harbor life look at those residing in the "habitable zone" around a star, where it is not too hot and not too cold, and liquid water can exist on the planetary surface.

The researchers used an instrument called ESPRESSO on the European Southern Observatory's Chile-based Very Large Telescope to detect this planet.

The three other potential planets orbiting Barnard's star all apparently are rocky and smaller than Earth, ranging from 20-30 per cent of Earth's mass. The hope is that at least one of these may be in the vicinity of the habitable zone.

If confirmed, this would be the only known star with a multi-planet system entirely comprised of planets smaller than Earth.