Evrim Yazgin
Cosmos science journalist
An often-overlooked type of star could have planets in the habitable zone and harbour life, according to new research.
Stars are categorised by surface temperature as well as other physical factors such as mass, luminosity and radius. Astronomers identify surface temperature variation in stars by dividing them up into 7 groups, identified by different letters.
Our Sun, for example, is a G-type star known as a yellow dwarf. G-type stars have surface temperatures between 5,300 and 6,000 kelvin (K).
F-type stars fall right in the middle of the spectrum. They are larger and hotter than our Sun. They are yellowish white in colour and have surface temperatures of 6,000–7,600K.
A new study published in the Astrophysical Journal suggests these stars are good candidates to host planets which may have life.
“F-type stars are usually considered the high-luminosity end of stars with a serious prospect for allowing an environment for planets favourable for life,” says co-author Manfred Cuntz, a professor at the University of Texas at Arlington (UTA). “However, those stars are often ignored by the scientific community.”
When looking for exoplanets which may hold life, astronomers look for rocky worlds which sit in the “habitable zone” around their host star. This is the point at which liquid water can be found on the surface. This is sometimes called the “Goldilocks zone” – not too hot, not too cold.
“Although F-type stars have a shorter lifetime than our sun, they have a wider habitable zone,” Cuntz adds. “In short, F-type stars are not hopeless in the context of astrobiology.”
The team looked at 206 F-star systems with information about their planets. From there, the team identified 18 systems where planets spent at least part of their orbits in the habitable zone.
One planet, HD 111998, known as 38 Vir, is in its star’s habitable zone year-round. The system is 108 light-years from Earth.
“The planet in question was discovered in 2016 at La Silla, Chile,” Cuntz says. “It is a Jupiter-type planet which is unlikely to permit life itself, but it offers the general prospect of habitable exomoons.”
“In future studies, our work may serve to investigate the existence of Earth-mass planets and also habitable exomoons hosted by exo-Jupiters in F-type systems,” adds lead researcher Shaan Patel, a doctoral student at UTA.
