New 'super-Earth' just 20 light-years away is our best chance yet to find alien life

Over the past thirty years, astronomers have identified more than 7,000 planets outside of our solar system – a remarkable leap since the first exoplanet discovery in 1995. Yet, researchers estimate that countless more remain undetected in our galaxy alone. 

In this context, a team of scientists has confirmed the existence of a potentially habitable super-Earth named HD 20794 d. 

The study represents a key step in exoplanetology’s ongoing shift from merely detecting planets to investigating their features, particularly conditions that might support life.

Significance of this super-Earth

Exoplanetary science has advanced significantly since Michel Mayor and Didier Queloz discovered the first planet orbiting a star other than our Sun in 1995. This achievement earned them the 2019 Nobel Prize in Physics. 

Today, it is broadly accepted that most stars have at least one orbiting planet. Scientists are now concentrating on more nuanced questions, such as identifying characteristics that make a world amenable to life. 

In this regard, the confirmation of super-Earth HD 20794 d introduces a planetary system that could allow scientists to test their theories of planetary formation, climate models, and the processes tied to biological emergence.

HD 20794 d in the habitable zone

A super-Earth is a planet that is larger than Earth but smaller than gas giants like Neptune. HD 20794 d occupies a system that includes two other planets, all revolving around a G-type star (similar to our Sun) at a distance of approximately 19.7 light-years.

Study co-author Xavier Dumusque is a senior lecturer and researcher in the Department of Astronomy at the University of Geneva (UNIGE)

“HD 20794, around which HD 20794 d orbits, is not an ordinary star,” noted Dumusque. “Its luminosity and proximity makes it an ideal candidate for future telescopes whose mission will be to observe the atmospheres of exoplanets directly.”

Among the planet’s most intriguing features is its eccentric orbit, causing HD 20794 d to oscillate between the inner edge of its star’s habitable zone at 0.75 astronomical units (AU) and extending outwards to 2 AU. 

Such an orbital path could allow for periods in which surface temperatures might be suitable for liquid water, although the planet’s distance from the star varies significantly over the course of its 647-day year.

Exploring the habitable zone

In astronomy, the habitable zone describes the span around a star where conditions could permit liquid water to persist.

For stars like the Sun or HD 20794, this zone typically lies between 0.7 and 1.5 AU, encompassing the orbits of Earth and Mars in our solar system. 

HD 20794 d completes its orbit just shy of two Earth years, placing it well within reach of conditions that might harbor life.

According to the researchers, the planet’s oscillation into and out of the habitable zone provides an exciting scenario for studying how planetary climates evolve and whether they can sustain liquid water.

If liquid water exists, the planet’s elliptical orbit would likely cause it to freeze at greater distances, then thaw as it approaches the star – offering a natural laboratory to examine how temperature fluctuations affect potential habitability.

How we found super-Earth HD 20794 d

Confirming the discovery of exoplanet HD 20794 d demanded two decades of meticulous observations using the world’s most sophisticated instruments.

Among them are ESPRESSO and HARPS, high-precision spectrographs that are critical in detecting subtle signals from exoplanets. 

The researchers also used YARARA, an advanced data-reduction algorithm developed at UNIGE, to filter out noise that had previously concealed any signs of the planet.

“We analyzed the data for years, carefully eliminating sources of contamination,” explained Michael Cretignier, a postdoctoral researcher at Oxford University and co-author of the paper. 

YARARA enabled the team to isolate the signals of HD 20794 d from the background noise. The result is a clearer understanding of the planet’s orbit and an emerging picture of what could be a potentially life-supporting environment.

What happens next?

Because of its location and the brightness of its star, HD 20794 d stands out as a target for upcoming observational campaigns and missions. 

Scientists plan to employ telescopes such as the ANDES spectrograph on ESO’s Extremely Large Telescope (ELT) to probe its atmosphere, looking for biosignatures like oxygen or methane.

If these molecules are detected, they could indicate biological processes similar to those on Earth.

In the meantime, the Center for Life in the Universe (CVU) at UNIGE’s Faculty of Science is already investigating this planet’s habitability.

The experts are integrating diverse scientific disciplines to explore conditions that might allow life to arise and flourish on exoplanets.

Why does any of this matter?

Exoplanet HD 20794 d offers a revealing case study of a super-Earth occupying a shifting seat at the edge of its star’s habitable zone. 

The research expands the horizon of exoplanetary science, reinforcing the notion that the universe may contain abundant worlds capable of supporting life.

Each exoplanet discovery brings us closer to understanding the processes that give rise to habitable environments.

While multiple barriers remain – most notably, the need for more advanced observation techniques and sustained interdisciplinary collaboration – HD 20794 d stands as a powerful reminder of how far exoplanet exploration has progressed. 

The study is published in the journal Astronomy & Astrophysics, 

Video Credit: © Gabriel Pérez Díaz, SMM (IAC)

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