Artist's impression shows HD 85512b, an exoplanet orbiting the sun-like star HD 85512 in the southern constellation of Vela.ESO

Sept. 12, 2011 — Drawing comparisons between our planet and worlds orbiting other stars can be misleadingor even controversial — but more often than not, exoplanet-hunting scientists are simply trying to put these alien worlds into perspective.

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Whether NASA's Kepler space telescope has spotted an exoplanet's shadow, or ESO's High Accuracy Radial velocity Planet Searcher (HARPS) has spotted the wobble of a star caused by the gravity of an orbiting world, very few details about these exoplanets present themselves.

Let's face it, a world called "HD 85512b," with a mass of 3.6 Earths, and an orbital period of 54 days hardly evokes thoughts of anything even vaguely familiar to our planet. But with these few characteristics, astronomers using HARPS have deduced that although it's more massive than Earth, HD 85512b has a few potentially Earth-like qualities.

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Most critically, HD 85512b orbits its star just within its habitable zone. Although we have no clue whether this alien planet has any water on its surface, if it did, there's the possibility that it may exist in a liquid state. In fact, astronomers predict a temperature of 25 degrees Celsius (77 F) at the top of HD 85512b's atmosphere — a temperature that isn't so alien to us Earthlings. However, the predicted temperature at the top of the atmosphere will likely be entirely different from the temperature on the surface.

A comparison of three stars that are known to have planets orbiting them. The top row shows a selection of planets from the solar system and their relative positions to the sun's habitable zone.ESO

Now that we know HD 85512b is out there, follow-up work is needed to further refine the exoplanet's orbit. Also, further work will be needed to understand what this world is made of. Is it a rocky, truly Earth-like world? Does it have an atmosphere? If it does, is the atmosphere thick like Earth's; as suffocating as Venus'; or, as tenuous as Mars'? Does the atmosphere contain organic compounds?

The star HD 85512 as imaged by the Digitized Sky SurveyESO

These questions (and many, many more) will be pursued by astronomers using the increasingly sophisticated suite of exoplanet-hunting instrumentation to derive whether HD 85512b is not only a "super-Earth," but whether it could be considered an Earth-like super-Earth.

Until then, we know that there is a preponderance of small worlds in our galaxy, it's only a matter of time before a true Earth-like exoplanet emerges from the dark.

The neighborhood surrounding the star HD 85512 as imaged by the Digitized Sky SurveyESO