Goldilocks Zone Serves Up Another Super Earth
November 9, 2012

Habitable Super Earth Found Relatively Close By

[ Watch the Video: New Habitable Zone Super-Earth Found in ExoSolar System ]

John P. Millis, Ph.D. for — Your Universe Online

Mankind´s fascination with the possibility of life on other worlds has been a mainstay of science fiction for more than a century. But it wasn´t until the last decade that we possessed the technology to begin searching in earnest for habitable planets outside of our solar system.

While the tally of new worlds has seen a surge recently — growing to well over 800, thanks to the deployment of increasingly advanced instrumentation and more sensitive analysis techniques — locating a true Earth-like planet has remained elusive.

However, new research suggests that we may have stumbled across the first potentially habitable planet orbiting around a Sun-like star.

The Habitable Zone

When searching for a habitable world there are several factors that need to be considered: Is it possible for the planet to sustain water on its surface? Does the planet have a tenable atmosphere? Is the temperature in a reasonable range for the existence of life?

The answer to these questions depends on the planet´s size and position relative to its host star. While the specifics differ from one solar system to the next, the area around a star where a planet could exhibit the necessary characteristics is known as the habitable zone.

Mikko Tuomi, from the University of Hertfordshire, recently spoke with redOrbit and shared that while we have previously found planets orbiting in the habitable zone, “they have been detected orbiting low-mass red dwarf stars that are very different from the Sun; and the rest of the observed planets are either too massive, too hot or too cold for liquid water to exist on their surfaces.”

A New Super-Earth

Analyzing data from the HARPS spectrograph, part of the European Southern Observatory (ESO), Tuomi and his colleagues were able to isolate the presence of three large, rocky worlds orbiting the star HD 40307, located a mere forty-four light-years from Earth.

The planet with the outermost orbit from its parent star could possibly support liquid water on its surface — a necessity for the proliferation of life. This new super-Earth, dubbed HD 40307g, is at least seven times the mass of Earth and has a similar orbit to Venus.

Researcher Guillem Angla-Escude, from the University of Goettingen adds, “The star HD 40307, is a perfectly quiet old dwarf star, so there is no reason why such a planet could not sustain an Earth-like climate.” The team also speculates that since the planet is far enough from its star to mitigate the effects of tidal locking — the phenomenon that, for instance, keeps the Moon in lock-step with Earth — that they expect the planet to experience a distinct night and day as the planet rotates about its axis. This would help create a more Earth-like environment on the surface, and increase the chances for life.

New Techniques for Detection

The existence of planets around HD 40307 is not a complete revelation, as three worlds had already been discovered. However, these planets orbit too close to the star to possibly support life.

Previous efforts were not able to resolve the presence of the outermost planets, known as ℠e´, ℠f´, and ℠g´. (The star itself is often designated as ℠a´, while the planets are given letters, with the closest planet assigned ℠b´ and so on.) Since the farther the planet is from the star the more difficult they are to detect, new methods had to be developed to find them.

“We applied newly developed statistical methods capable of constraining smaller signals that previously used analysis methods,” explains Tuomi. “This, coupled with an improved treatment of the stellar spectrum, i.e. the ability to spot and exclude variations and spurious periodicities caused by stellar activity, enabled the detection. So, our team has been developing the statistical methods that enabled this discovery.”

Could HD 40307g Actually Support Life?

There is a temptation here to get excited about the possibility of life on a planet so close to Earth, but there is a caution: Simply because a planet could support life, does not mean that life exists. Furthermore, while HD 40307g appears to lie in the “habitable zone”, where things like an atmosphere and liquid water could exist, we can´t predict with much accuracy if these things are present.

“With the current detection methods, we cannot observe the atmospheric, physical and geochemical properties of the planet,” says Tuomi. “We can only speculate at the moment, and I would rather leave the speculations for others.”

The researchers will be publishing their findings in the journal Astronomy & Astrophysics.