But in the early universe, as Loeb speculates in a paper published in Astrobiology late last year, everything would have been a habitable zone. 10 to 20 million years after the Big Bang, the universe was still bathed in that warm gas we saw in the CMB, but it had cooled down to a temperature that would keep water liquid no matter where it was relative to its star. The ambient temperature of the universe would provide enough heat to turn an ice giant like Neptune into a water giant. That’s why Loeb has dubbed this era the “habitable epoch.”
It would have been a weird time for life to evolve, though. Many of the building blocks of life on Earth, like carbon and metals, exist only because of the massive stellar explosions called supernovas which signal the deaths of stars. In a universe where so few stars had been born, even fewer would have died. This was a period when solid matter was an anomaly, before most of the elements on the periodic table existed.
Stars would have been few and far between. “Life might have been more isolated than it is today,” Loeb said. “Now we are members of a galaxy, with tens of billions of stars not far away.” Still, Loeb said, the rare stars and planets would form hotter, more energetic regions in the sea of warm gas. There would be energy to kick-start life forms and liquid water would slosh across the surface of planets with atmosphere. Also, the relative isolation of these worlds would have protected them from threats like cosmic radiation and asteroid bombardment—two dangers that have nearly extinguished life on Earth more than once.
Would this life have been intelligent? “No,” Loeb said. “I’m talking about very simple organisms like algae.” Because the universe was changing so quickly, species would only have about a million years to evolve on a planet before the warm gas clouds around it cooled enough to change the environment radically. Still, a million years is enough time for a single-celled creature to evolve. And another simple species, more adapted to the colder world, could evolve to take its place. But could a humanlike civilization arise in one of those evolutionary windows? The odds are slim—consider that it took roughly 65 million years for the small, fluffy mammals of the Tertiary period to evolve into modern humans.
Astronomers working at the European Southern Observatory (ESO) in Chile have discovered seven planets orbiting the star Gliese 667C.
Two exoplanets have been discovered in the star’s habitable zone, which has just the right range of distance where liquid water can exist on a planet’s surface.
A super-Earth is an extrasolar planet with a mass higher than Earth’s, but substantially below the mass of the Solar System’s smaller gas giants Uranus and Neptune, which are both more or less 15 Earth masses.
The term super-Earth refers only to the mass of the planet, and does not imply anything about the surface conditions or habitability.
Astronomers at the European Southern Observatory in Chile found out that 40 per cent of red dwarves are orbited by super-Earths. Red Dwarfs are by far the most common type of star in the Milky Way galaxy, so there might be tens of billions of such planets in our galaxy alone.
If you really hate living here on Earth the next best place to be is just a hop, skip, and a jump away!
But research to appear in Astronomy and Astrophysics has found three more - among them a “super-Earth” seven times our planet’s mass, in the habitable zone where liquid water can exist.
Many more observations will be needed to confirm any other similarities.
But the find joins an ever-larger catalogue of more than 800 known exoplanets, and it seems only a matter of time before astronomers spot an “Earth 2.0” - a rocky planet with an atmosphere circling a Sun-like star in the habitable zone.
HD 40307, which lies 42 light-years away, is not particularly Sun-like - it is a smaller, cooler version of our star emitting orange light.
But it is subtle variations in this light that permitted researchers working with the Rocky Planets Around Cool Stars (Ropacs) network to find three more planets around it.
Data from NASA’s Cassini spacecraft have revealed Saturn’s moon Titan likely harbors a layer of liquid water under its ice shell. The finding appears in today’s edition of the journal Science.
“Cassini’s detection of large tides on Titan leads to the almost inescapable conclusion that there is a hidden ocean at depth,” said Luciano Iess, the paper’s lead author and a Cassini team member at the Sapienza University of Rome, Italy. “The search for water is an important goal in solar system exploration, and now we’ve spotted another place where it is abundant.”
This artist’s concept shows a possible scenario for the internal structure of Titan, as suggested by data from NASA’s Cassini spacecraft. Image credit: A. Tavani
The evidence is tidal. Saturn’s powerful gravity stretches and deforms Titan as the moon moves around the gas giant planet. If Titan were composed entirely of stiff rock, the gravitational attraction of Saturn should cause bulges, or solid “tides,” on the moon only 3 feet (1 meter) in height. Instead, the data show Saturn creates solid tides approximately 30 feet (10 meters) in height. This suggests Titan is not made entirely of solid rocky material.
Thanks largely to the Kepler space telescope, astronomers have discovered more than 2,000 planets orbiting distant stars — not half bad considering that until recently we knew of only eight planets in the entire universe, all of them in the immediate neighborhood. The point of Kepler isn’t simply to rack up numbers, though: the ultimate goal is to find worlds similar to Earth — places where there’s a chance that alien life might have taken hold. Those planets could then get a closer look as a new, more powerful generation of telescopes comes on line.
But the search for life across interstellar space will still not be easy, and even the most advanced telescope on the drawing boards will have to work hard to suss it out, so it will be key to choose the best possible targets. That’s the reasoning behind a new paper in the journal Astrobiology in which environmental scientist Dirk Schulze-Makuch, of Washington State University, along with nine other colleagues, has proposed a new planet-classification scheme to make the sifting process easier.
Actually, they’ve proposed two schemes, designed to let observers slice their searches in two different ways. The first and crudest of their methods is something they call the Earth Similarity Index, or ESI. That’s just what it sounds like: it’s a measure of how closely an alien world matches Earth in terms of size and temperature. The temperature is important because biologists say liquid water is an essential ingredient for life as we know it: nutrients can dissolve easily in water in order to circulate to every part of an organism. Blood, after all, is essentially just water with stuff dissolved in it.
The size of the planet, meanwhile, is important because … well, actually, it’s not clear why. It’s true that if a planet is too small, like Mars, it might not have enough gravity to hold on to its atmosphere. Mars itself once did have a blanket of air, but it was probably blasted away by barrages of incoming asteroids billions of years ago. And if the planet is too big, gravity might have pulled in too much of an atmosphere, which would create crushing pressure at the surface. A world four or five times as massive as Earth might well be habitable, but anything bigger than that could cause problems. Still, since Earth is the only place we know harbors life, the ESI favors planets as much like ours as possible.