Exoplanet

So, news not of one newly discovered exoplanet, but two – in the past fortnight. First was this:

The rocky world, called Speculoos-3b, is 55 light years from Earth and was detected as it passed in front of its host star, an ultra-cool red dwarf that is half as hot as the sun and 100 times less luminous.

The newly discovered world, described as “practically the same size as our planet”, swings around the red dwarf once every 17 hours, making a year on the planet shorter than a single Earth day.

But while the years are short on Speculoos-3b, the days and nights are never-ending. “We believe that the planet rotates synchronously, so that the same side, called the day side, always faces the star, just like the moon does for the Earth. On the other hand, the night side hand, would be locked in endless darkness,” said Michaël Gillon, an astronomer at the University of Liège in Belgium and lead author on the study.

And then yesterday:

An Australian university student has co-led the discovery of an Earth-sized, potentially habitable planet just 40 light years away.

Shishir Dholakia, a PhD candidate in astrophysics at the University of Southern Queensland, is part of an international team that published the discovery in the Monthly Notices of the Royal Astronomical Society.

He described the “Eureka moment” of finding the planet, which has been named Gliese 12b.

“We did the back-of-the envelope calculations,” he said. “We worked out it’s probably Earth-sized, it’s probably temperate, and that it’s really, really nearby. In the span of a day we were like, ‘Oh, we have to write this up. This is something really cool.’

I’ve long been fascinated by exoplanets, that is planets orbiting around other stars than our Sun. What is of particular interest is that I’m more than old enough to remember when there were no known planets outside the, then, 9 in our solar system. 

The first that was discovered was in 1992 (though another was detected four years earlier and then confirmed only twenty one years ago) and I’ve got to be honest, I don’t remember that. It must have passed me by. Next thing I know is eight or ten have been discovered and the numbers just keep ticking upwards. As of this month 5,662 planets in over 4,000 systems. And keep in mind at one point no-one was certain whether any other solar system had planets, or even whether those in this solar system were a fluke of some kind and/or vanishingly rare. 

As it happens the first evidence came as far back as 1917. But even more amazing is the fact that planets have been detected in other galaxies. 

Here’s an interesting one, an Earth sized planet in a system just 40 light years away. Just. A hop and a skip away in the context of the Universe. Except. With current technologies it would take a very long time to get there. I’ve read some calculations that suggest to go 40 light years would take in or around 700,000 years.

Which makes the following understatement:

“It’s only 40 light years away, and this might not mean that we can actually get to it any time in the near future, but it does mean that we can point the largest space telescopes in the world at it, and understand what its atmosphere might be like,” Dholakia said.

That last is important. 

As to the number of Earth-sized planets in the galaxy, well, there’s likely to be lots. Habitability is a longer shot. 

A review in 2015 identified exoplanets Kepler-62f, Kepler-186f and Kepler-442b as the best candidates for being potentially habitable.^[204] These are at a distance of 1200, 490 and 1,120 light-years away, respectively. Of these, Kepler-186f is in similar size to Earth with its 1.2-Earth-radius measure, and it is located towards the outer edge of the habitable zone around its red dwarf star.

When looking at the nearest terrestrial exoplanet candidates, Proxima Centauri b is about 4.2 light-years away. Its equilibrium temperature is estimated to be −39 °C (234 K).^[205]

Earth-size planets

See also: Earth analog

• In November 2013, it was estimated that 22±8% of Sun-like^[a] stars in the Milky Way galaxy may have an Earth-sized^[b] planet in the habitable^[c] zone.^[8][117] Assuming 200 billion stars in the Milky Way,^[d] that would be 11 billion potentially habitable Earths, rising to 40 billion if red dwarfs are included.^[10]
• Kepler-186f, a 1.2-Earth-radius planet in the habitable zone of a red dwarf, was reported in April 2014.
• Proxima Centauri b, a planet in the habitable zone of Proxima Centauri, the nearest known star to the solar system with an estimated minimum mass of 1.27 times the mass of the Earth.
• In February 2013, researchers speculated that up to 6% of small red dwarfs may have Earth-size planets. This suggests that the closest one to the Solar System could be 13 light-years away. The estimated distance increases to 21 light-years when a 95% confidence interval is used.^[206] In March 2013, a revised estimate gave an occurrence rate of 50% for Earth-size planets in the habitable zone of red dwarfs.^[207]
• At 1.63 times Earth’s radius Kepler-452b is the first discovered near-Earth-size planet in the “habitable zone” around a G2-type Sun-like star (July 2015).^[208]

And life?  

Future telescopes might even pick up signs of photosynthesis – the transformation of light into chemical energy by plants – or even gases or molecules suggesting the presence of animal life. Intelligent, technological life might create atmospheric pollution, as it does on our planet, also detectable from afar. Of course, the best we might be able to manage is an estimate of probability. Still, an exoplanet with, say, a 95 percent probability of life would be a game changer of historic proportions.

Now that would be something.