A newly-discovered exoplanet super-Earth’s unusual orbit through hot and cold conditions tests the limits of tolerability for any known lifeforms, according to European astronomers.
Billions of exoplanets await discovery, even after 7,000 of them were discovered in the last three decades. With advancing equipment and an increasing sample size, many exoplanetologists are moving from discovery to investigating these distant planets’ characteristics.
Decades On The Exoplanet Quest
Super-Earth HD 20794 d, a find 20 years in the making, was discovered by an international team including the University of Geneva (UNIGE) and the NCCR PlanetS. For two decades, astronomers analyzed data from sources including two European Space Agency installations, The ESPRESSO spectrograph at the Very Large Telescope in Chile and the HARPS spectrograph at the La Silla Observatory, also in Chile, to identify the super-Earth.
The researchers took advantage of an algorithm named YARARA, recently developed at the UNIGE. Noise in the data made pulling out planetary signals exceedingly challenging for years, until YARAHA helped cut through it to reveal the discoveries hidden within the information collected.
“We analysed the data for years, carefully eliminating sources of contamination,” explained Michael Cretignier, a post-doctoral researcher at Oxford University, co-author of the study and developer of YARARA during his PhD at UNIGE.
Exoplanet HD 20794 d
HD 20794 d is a rocky globe in a three-planet solar system larger than Earth. Like Earth, it orbits a G-type star. The planet’s 19.7 light-year distance makes it a relatively close neighbor on a universal scale. That closeness makes it easy to look out of our cosmic window and observe the super-Earth’s strong light signals generated by an unusually bright star.
“HD 20794, around which HD 20794 d orbits, is not an ordinary star,” explains Xavier Dumusque, Senior Lecturer and researcher in the Department of Astronomy at the UNIGE and co-author of the study. “Its luminosity and proximity make it an ideal candidate for future telescopes whose mission will be to observe the atmospheres of exoplanets directly.”
Planetary Systems and Habitable Zones
The consensus is that every star in our galaxy likely holds a planetary system in its orbit. Today, astronomers tend to focus on two kinds of exoplanets: those that are easy to characterize and those with unusual features to test hypotheses about cosmic incongruencies.
HD 20794 d is a planet in the latter group. The exoplanet’s elliptical orbit weaves in and out of its star’s habitable zone, the region where conditions exist allowing liquid surface water, a precondition for life as we know it.
For those G-type stars like HD 20794 or even our Sun, that habitable zone is a ring extending between 0.7 to 1.5 astronomical units out from the star. Any closer than that, the water would boil off into steam, and any farther, it would be locked in ice.
Earth and Mars reside in our Sun’s habitable zone, while HD 20794 d makes a 647-day orbit. That makes its orbit slightly tighter than Mars’s by about 40 days, yet it follows an elliptical orbit instead of a circular one like Earth or the red planet. This leaves the planet skimming the closest survivable proximity to its star at 0.75 AU to arching beyond the theoretical limit of habitability at 2 AU. If water exists on the planet, it will experience both liquid and frozen states every year on its skewed orbit.
Continuing The Exoplanet Investigation
Discovering the super-Earth gives scientists a new Exoplanet lab to model and test their hypothesis due to its cosmically novel orbit. The team hopes to include the ANDES spectrograph, which the agency expects to come online later this decade at the European Space Agency’s Extremely Large Telescope, yet again in Chile.
The more advanced data from ANDES should help, but genuinely discerning whether life exists not the exoplanet will require transdisciplinary advances, which the new Centre for Life is pursuing in the Universe (CVU) at the UNIGE’s Faculty of Science.
The paper “Revisiting the Multi-Planetary System of the Nearby Star HD 20794” appeared on January 28, 2025 in Astronomy and Astrophysics.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.