Tag Archives: exoplanets

Well, when I say “Earth-like”…

… I certainly don’t mean “capable of supporting life of the sort found on Earth, or even recognisably similar at a glance”. Yeah, it’s another (albeit milder) sexing-up-science-headlines post! The Kepler telescope has confirmed the discovery of the first “Earth-like” exoplanet, says COSMOS Magazine (who, in fairness, are a good science publication), while Wired picked the more honest “definitively rocky”. Basically, “Earth-like” in this context means “not a gas planet”; from the Wired piece:

… the starquake measurements make astronomers even more certain that Kepler-10b is a ball of rock. COROT-7b’s host star is magnetically active, Batalha says, making it difficult to tease the planet’s gravitational pull from the star’s own magnetic jitters. Some measurements of the planet’s mass leave room for other interpretations of the planet’s composition, like a planet that is more than half water.

Kepler-10b, on the other hand, is denser than the Earth, meaning it is probably made up of rock and iron.

Unfortunately, the new rocky world is hot enough to melt iron. It orbits its star once every 0.84 days, meaning the planet is 23 times closer to its star than Mercury is to the sun. At such a close orbiting distance, the planet shows the same face to the star at all times, the same way the moon always shows the same face to the Earth. Temperatures on the daytime side of the planet would reach 2780 degrees Fahrenheit, as hot as some red dwarf stars.

So: in a totally different orbital zone to Earth, with no day/night transition like Earth’s, no atmosphere like Earth’s, and a temperature that ensures there isn’t and probably never was any biosphere like Earth’s. But hey, it’s made of rocks – just like Earth!

Look, I’m pretty much a lifelong space geek, and I think this is an awesome discovery. But this journalistic upselling of new discoveries just cheapens them, y’know?

Have we found the first habitable exoplanet?

This story’s pretty much everywhere today, though the headlines would probably be more accurate (if more cumbersome and less exciting) if they said that researchers have located the first exoplanet confirmed to be in an orbit around its parent star that would permit the possibility of liquid-phase H2O on its surface, and to have sufficient mass to hold on to a “substantial” atmosphere.

(Kinda takes the magic out of it, this whole accuracy thing… but it’s still pretty awesome when you think about it. Or it is for me, anyway.)

The new planet is one of six orbiting the star Gliese 581, a red dwarf 20 light-years from Earth. Two of the planet’s siblings, dubbed planets C and D, have also been hailed as potentially habitable worlds. The two planets straddle the region around the star where liquid water could exist — 581c is too hot, and 581d is too cold. But 581g is just right. The discovery will be published in the Astrophysical Journal and online at arxiv.org.

The new planet is about three times the mass of Earth, which indicates it is probably rocky and has enough surface gravity to sustain a stable atmosphere. It orbits its star once every 36.6 Earth days at a distance of just 13 million miles.


Gravity dictates that such a close-in planet would keep the same side facing the star at all times, the same way the moon always shows the same face to Earth.

That means the planet has a blazing-hot daytime side, a frigid nighttime side, and a band of eternal sunrise or sunset where water — and perhaps life — could subsist comfortably. Any life on this exotic world would be confined to this perpetual twilight zone, Vogt says, but there’s room for a lot of diversity.

“You can get any temperature you want on this planet, you just have to move around on its surface,” Vogt said. “There’s a great range of eco-longitudes that will create a lot of different niches for different kinds of life to evolve stably.”

The inevitable disclaimer here is that although it looks like Gliese 581g could support some sort of life, whether it actually does is still something of a cosmological crapshoot with unknown odds. However, the relative ease with which we’ve found it suggests there may be many more planets in similar situations, which raises the chances of us humans not being the only gang in town after all. Those odds are still pretty long, of course… but hey, we can dream, right? Question is, will we find ’em and meet ’em before time runs out?

The first watery exoplanet?

An alien coastline?I’ll wager you’ve caught at least a hint of this story already: astronomers reckon they’ve located the first serious candidate for a water-bearing exoplanet:

… new calculations – made possible by the discovery of “[Gliese 581] e” – show that the larger planet is squarely within the so-called “habitable zone,” neither too far nor too close to the star around which it orbits to support life.

“Gliese 581 d is probably too massive to be made only of rocky material, but we can speculate that it is an icy planet that has migrated closer to its star,” said co-author Stephane Udry, a professor at Geneva University, in Switzerland.

“It could even be covered by a large and deep ocean – it is the first serious ‘waterworld’ candidate,” he said.

A waterworld, eh? As Gareth L Powell put it, maybe we should dispatch Kevin Costner immediately

More seriously, a wet Gliese 581 d is only a possibility as yet, but it’s a possibility that shifts the odds on there being life elsewhere in the universe. When (or perhaps I should say “if”) we manage to confirm the presence of liquid-phase water on other planets, we’ll have to concede that the likelihood of life evolving elsewhere is not as remote as was once thought… which will doubtless be immensely upsetting to some people, but makes me feel pretty good. [image by Paulo Brandão]