No Earth-like planets around red dwarf stars due to missing Jupiters, study finds

Jupiter is a gas giant that played a central role in the development of the early Solar System and also life on Earth. What does its absence around red dwarfs imply?
Tejasri Gururaj
Exoplanets and red dwarf
Exoplanets and red dwarf


Red dwarfs are the smallest and the most common type of stars in the universe. Their mass reaches up to 0.5 times the mass of the Sun, their surface temperatures stay below 4000 degrees Celsius, and they are red in color.  

Given their abundance in the universe, astronomers have spent many decades studying them and exploring habitable worlds in their systems. However, astronomers now believe that red dwarfs may not be a host to Jupiter-like planets. 

How does this relate to the search for habitable worlds? Well, scientists believe that Jupiter played a crucial role in the evolution of our Solar System, setting the stage for Earth's habitability.

The research team comprised scientists from the Center for Astrophysics | Harvard & Smithsonian, Williams College, and the University of Cambridge. 

How did Jupiter impact the formation of the Earth?

Jupiter is the heaviest planet in the Solar System, with a mass greater than the combined mass of all the planets in our Solar System. It played a pivotal role in forming our Solar System and Earth. 

According to astronomers, early in the history of the Solar System, Jupiter underwent a migration, moving from the outer regions of the Solar System towards the Sun, exerting a strong gravitational force that impacted the structure of the entire Solar System.  

During this migration, Jupiter's gravitational pull scattered icy bodies, such as comets, causing a collision with planets in the inner Solar System, including the Earth. It is believed that these collisions delivered substantial amounts of water and other organic (carbon-based) molecules, which were vital for life to emerge on Earth. 

Examining red dwarfs for signs of Jupiter-like worlds

In the current study, astronomers examined 200 small red dwarfs using a method known as the radial-velocity technique, which helps scientists detect and characterize exoplanets. 

They found no Jupiter-like planet was observed in the 200 systems they studied, indicating that these heavy plants occur in less than 2 percent of low-mass red dwarf planetary systems.

The absence of Jupiter-sized planets around red dwarfs suggests that more material is available for more minor rocky planets to be formed. The abundance of rocky planets around red dwarfs has been observed before, with the red dwarf system TRAPPIST-1 hosting seven rocky worlds!

While the presence of rocky planets and the absence of Jupiter-like ones do not necessarily eliminate the potential for habitable life in red dwarf systems, it does raise the possibility of extraterrestrial life that we are unaware of.

"We're excited to see what exactly that means as we forge ahead in remotely exploring the planets in our cosmic neighborhood," said lead researcher Emily Pass in a press release.

The research is soon to be published in The Astronomical Journal.

Study abstract:

Cold Jovian planets play an important role in sculpting the dynamical environment in which inner terrestrial planets form. The core accretion model predicts that giant planets cannot form around low-mass M dwarfs, although this idea has been challenged by recent planet discoveries. Here, we investigate the occurrence rate of giant planets around low-mass (0.1-0.3M) M dwarfs. We monitor a volume-complete, inactive sample of 200 such stars located within 15 parsecs, collecting four high-resolution spectra of each M dwarf over six years and performing intensive follow-up monitoring of two candidate radial-velocity variables. We use TRES on the 1.5 m telescope at the Fred Lawrence Whipple Observatory and CHIRON on the Cerro Tololo Inter-American Observatory 1.5 m telescope for our primary campaign, and MAROON-X on Gemini North for high-precision follow-up. We place a 95%-confidence upper limit of1.5% (68%-confidence limit of 0.57%) on the occurrence of MPsini>1MJ giant planets out to the water snow line and provide additional constraints on the giant planet population as a function of MPsini and period. Beyond the snow line (100 K <Teq<150 K), we place95%-confidence upper limits of 1.5%, 1.7%, and 4.4% (68%-confidence limits of 0.58%, 0.66%, and 1.7%) for 3MJ<MPsini<10MJ, 0.8MJ<MPsini<3MJ, and 0.3MJ<MPsini<0.8MJ giant planets; i.e., Jupiter analogs are rare aroundlow-mass M dwarfs. In contrast, surveys of Sun-like stars have found that their giant planets are most common at these Jupiter-like instellations.

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