The rate of scientific progress is often hard to measure. But in certain circumstances, the data is unambiguous and easy to measure, creating a trend. And when that happens, the futurologists aren’t far behind, extrapolating and predicting the way things will be.

The most famous example is Moore’s Law, which predicts that the density of transistors on integrated circuits doubles every two years or so. This trend has continued for more 40 years and looks set fair for at least another 10.

Today, we’re introduced to another data set that makes possible a bold prediction about the future. Samuel Arbesman from Harvard Medical School in Boston and Gregory Laughlin at the University of California, Santa Cruz, point out that astronomers have been discovering extrasolar planets at an increasing rate since 1995.

The discoveries follow a well understood pattern, the first extrasolar planets being necessarily massive, many times the size of Jupiter, and so easier to spot. As techniques have improved, however, astronomers have found smaller planets, some just a few times more massive than Earth.

There’s an additional factor to take into account for a planet to be habitable–the surface temperature which must support liquid water for life as we know it to take hold. And that, of course, depends on the size of the star, the planet’s distance from it and the conditions on the surface, such as the amount of greenhouse effect.

Astronomers have found superhot gas giants and snowball-like Neptunes. And here too, the trend is toward the discovery of a planet in the habitable zone. (Some would argue that Gliese 581 d falls into this category although it is not Earth-like in size).

There’s no real dispute among astronomers that the discovery of an Earth-like planet is on the cards. The only question is who’s going to find it and when.

Now Arbesman and Laughlin have taken this data and projected it forward to see when an Earth-like planet is likely to crop up. The results have a heavy-tailed distribution in which there is a 66 per cent probability of finding the other Earth by 2013, a 75 percent probability by 2020 but a 95 percent probability by 2264.

However, they say the median date of discovery is in early May 2011, which for various reasons is the date they emphasis in their paper.

That’s a brave call. The biggest player in this business is the team behind the Kepler space telescope which was launched in March last year specifically to find extrasolar planets. The team released its first data in June and this is currently being analysed. The first set of candidate planets are due to be announced in February next year.

Many astronomers expect this set to include a habitable Earth-like planet. But according to Arbesman and Laughlin, they’ll have to wait a little longer. “Because of the limited time base line of the mission to date, the Kepler planet candidates to published in February 2011 may be too hot to support significant values for H [their habitability metric],” they say.

Which means that somebody else is line to take this prize. That’s not so far-fetched. Various new techniques have made Earth-bound telescopes almost as sensitive as Kepler and certainly on the verge of finding Earth 2.0.

The importance of such a discovery is hard to under-estimate. The idea of Earth 2.0 orbiting another star could have a major impact on the global psyche and provide the focus for an international effort to characterise this place. We’re going to want to know more. Whoever makes this announcement is likely to become a well known face on the global stage.

And all this to happen in early May 2011, at least according to Arbesman and Laughlin. Put the date in your diaries.

Ref: arxiv.org/abs/1009.2212: A Scientometric Prediction of the Discovery of the First Potentially Habitable Planet with a Mass Similar to Earth