The confirmed discovery of exoplanets revolutionized our understanding of the universe. Among the thousands of confirmed exoplanets, HD 20794 d in particular, recently attracted attention for a unique characteristic – an eccentric orbit that moves in and out of the parent star’s habitable zone. Astronomers are studying this planet to gain insights into habitability beyond Earth.

In a recent SETI Live discussion, senior astronomer Franck Marchis explored the significance of this planet with Nicola Nari, lead author of a new paper published in Astronomy & Astrophysics.

What is HD 20794 d?

Nari refers to HD 20794 d as a super-Earth, with a mass larger than Earth but smaller than ice giants like Neptune. The planet orbits a G-type star, similar to our Sun, and is located just 20 light-years away, making it a relatively close subject for study.

Discovery and Detection

Unlike direct imaging techniques, HD 20794 d was discovered using the radial velocity method. This method detects small wobbles in a star’s motion caused by the gravitational pull of orbiting planets. The discovery was made possible by two advanced instruments:

• HARPS: A high-precision spectrograph located in La Silla, Chile.

• ESPRESSO: A more advanced spectrograph installed on Chile's Very Large Telescope (VLT). These instruments, used over a period of more than 20 years, allowed astronomers to confirm the presence of HD 20794 d alongside two other planets in the same system.

The Orbit and Its Implications

One of the most intriguing aspects of HD 20794 d is its highly eccentric orbit. Marchis explains, "This planet moves in and out of the habitable zone, meaning the temperature could vary dramatically, possibly up to 100 degrees Celsius between its closest and farthest points from the star."

Nari added, "The flux of light from the star changes by a factor of seven throughout the orbit, making it a natural laboratory for studying planetary habitability."

What’s Next?

HD 20794 d does not transit its star, making atmospheric characterization challenging. However, future advancements in adaptive optics and next-generation telescopes could provide new insights despite that challenge.

HD 20794 d is a compelling target for astronomers studying exoplanet habitability. Its eccentric orbit and proximity to Earth make it a valuable laboratory for understanding the conditions that might support life beyond our solar system. As technology advances, this intriguing super-Earth may help answer one of humanity’s biggest questions: Are we alone in the universe?

Watch the video below to learn more about this exploration or find Super-Earth Laboratory: Using HD 20794 d to Understand Habitability on our YouTube channel.