Astronomers find a planet too big for its star
“We discovered a planet that is too massive for its star,” said Penn State astronomer Suvrath Mahadevan, one of the leaders of the study published this week in the journal Science. The star, called LHS 3154, is relatively close to us, about 50 light years from Earth.
A star barely capable of nuclear fusion
The star, LHS 3154, is considered a dim star compared to our sun. “It is barely a star,” said Princeton University astronomer Guðmundur Stefánsson, the study’s lead author. “It has a mass just above the cutoff of supporting hydrogen fusion to be considered a star.”
A planet with an extremely close orbit
The planet, LHS 3154 b, orbits at about 2.3% of Earth’s orbital distance from the sun, circling its star every 3.7 days. It is much closer even than our solar system’s innermost planet, Mercury, is to the sun.
A planet similar to Neptune
The planet, LHS 3154 b, is believed to be similar in size and composition to Neptune, the smallest of our solar system’s four gas planets. Although the researchers were unable to measure its exact diameter, they estimate it to be about three to four times that of Earth.
Unlikely to support life
Due to its probable Neptune-like composition and close proximity to its star, LHS 3154 b is unlikely to support life. Neptune lacks a solid surface and has a dynamic atmosphere mainly composed of hydrogen and helium, atop a mantle mostly consisting of slushy ammonia and water, and a solid core.
Raising questions about planet formation
The discovery of LHS 3154 b raises questions about how planets form around low mass stars. Previously, it was thought that such stars could only form small terrestrial planets similar in mass to Earth. This finding challenges that assumption.
Using advanced technology for discovery
The researchers used the Habitable Zone Planet Finder (HPF), an instrument built by a team led by Suvrath Mahadevan, to detect the subtle wobble in the host star caused by the planet’s gravitational effects during its orbit. HPF is installed on the Hobby-Eberly Telescope at the University of Texas’ McDonald Observatory and is designed to find planets that orbit relatively cool stars and have the potential for liquid water on their surfaces.
“As we build new instruments, and as our measurement precision increases, we see the constant stream of surprises,” Mahadevan said. “We built HPF to detect terrestrial planets around these cool stars. This discovery is another example of how much we still have to learn about planets and planet formation.“
