The researchers say the planet, named 55 Cancri e, whips around its star in just 18 hours, Postmedia reported Monday.
"You could set dates on this world by your wristwatch," the University of British Columbia's Jaymie Matthews said.
There's little chance of life on the planet, he said, given that the surface temperature is believed to be close to 4,900 degrees Fahrenheit.
Still, astronomers said, the planet may have retained an atmosphere due to its strong gravity.
"It's so exotic, it's like the poster child for rocky super-Earths," Matthews said.
Observations indicate the planet's diameter is only 60 percent larger than Earth's, but it is eight times more massive.
"In fact, 55 Cancri e is the densest solid planet known, anywhere," the astronomers said.
And it's not all that far from Earth, with its home star, 55 Cancri A, visible to the naked eye.
That makes 55 Cancri e a "unique laboratory to investigate the story of how planets form and evolve," the researchers said.
MAVEN now orbiting Mars