Sun's Twin Discovered -- the Perfect SETI Target?

Analysis by Ray Villard
Thu Apr 26, 2012 01:53 PM ET

There are 10 billion stars in the Milky Way galaxy that are the same size as our sun. Therefore it should come as no surprise that astronomers have identified a clone to our sun lying only 200 light-years away.

Still, it is fascinating to imagine a yellow dwarf that is exactly the same mass, temperature and chemical composition as our nearest star. In a recent paper reporting on observations of the star -- called HP 56948 -- astronomer Jorge Melendez of the University of San Paulo, Brazil, calls it "the best solar twin known to date."

His team combined observations from the Very Large Telescope (VLT), Keck Telescope, and Hobby Eberly Telescope to characterize the star and look for planets. Though fast orbiting large planets weren't found it still begs the question: could HP 56948 have a twin solar system too?

The majority of planetary systems discovered to date make our solar system look like the exception and not the rule. For example, the sun-like star 55 Cancri, only 41 light-years away, has a mix of close-in hot Jupiters, followed by terrestrial planets an then more Jupiters.

In some systems the planets are in much more elliptical orbits than found around our sun. Epsilon Eridani for example has a planet that swings as close to the star as Venus is from our sun, and then climbs out to the orbital radius of Jupiter.

The good news is that astronomers have not detected the short-period wobble of HP 56948 that would indicate a hot Jupiter was tugging on it. This leaves the inner few million miles around the star safe territory for the presence of one or more terrestrial planets. Earth-mass worlds would pull so weakly on the star that they have not yet been detected.

But the chemical composition of HP 56548 has unusual amounts of aluminum, calcium, magnesium, and silicon -- by the same ratio as our sun has. In our solar system these elements are found locked away in interplanetary dust, meteorites and rocky planets like Earth.

This means terrestrial planets could exist around HP 56548. In fact, there is a reasonable chance that the star's planetary system has a solar system architecture with the massive outer worlds staying beyond the "frost line" where ices condense to form bloated worlds. And, a family of terrestrial planets huddled close to the star.

Simply put, the nearby presence of a twin star potentially offers a fascinating experiment in parallel evolution. Assuming that HP 56548 has at least one inhabitable planet, has life arisen and successfully evolved to higher forms over 4 billion years? If not, why not?

If 4 billion years is the typical time for the emergence of intelligent beings, then there is a civilization now orbiting HP 56548. If we dare to extrapolate even further, a technological civilization should have developed astronomy, which is at the root of modern physics. Their astronomers should have located our sun as easily as we found their star. They then might have been compelled to undertake a program of both monitoring and transmitting radio message to our solar system.

That said, it would not be surprising if SETI observations of the star came up empty handed. The system may not have an Earth-sized planet in its habitable zone. Even if there is one it may not be Earth-like with oceans and plate tectonics. And, even if there is a world flourishing with multi-cellular life, it may not have progressed to an intelligent species. Or, it has a civilization but it is not as technologically advanced as ours.

Keep in mind that any alien astronomers on such a planet would be studying Earth as it appeared in the early 1800s. That information, encoded in light, is just arriving at HP 56948 now. Our radio and television signal leaking into space won't reach the star for another 130 years. In the absence of such an electromagnetic signature extraterrestrials may overlook Earth and scout elsewhere.

They nevertheless would speculate, as we are, whether our sun offers and abode for intelligent life. But the quarantine imposed by the physics of time and space keeps us forever apart.

Image credits: ESO, NASA

Tags: Alien Life, Extrasolar Planets, SETI, Stars