So How often do we think we are going to see the headline announcing the discovery of the “First Earth-Like Planet” ? The latest example (CoRoT-7 b) came just as the New Year arrived. It turned out to be a firey world with temperatures ranging between -210 to 2000 degrees centigrade because it is tidally locked with its star. That’s not what most of us would consider Earth-Like. It earned its dubious title by being a rocky planet not very different in size than Earth.
Even as the news broke the sense of deja-vu was overwhelmingly strong. The previous “First Earth-like planet” (Gliese 581g) had been discovered just four months previously. This one is in the Goldilocks zone of its star meaning that it is at the right distance for liquid water to form on the planet. However, water would only actually form if it was rotating to give the surface an even temperature, but this one is probably tidal locked too.
Looking back through the news archives it is no surprise to find that news of the first Earth-like planets first appeared as far back as 1998 when just a handful of exoplanets were known. since then there have been a number of candidates, hopefully with each one being a little bit more Earth-like than its predecessor, although it is also the case that some of these discoveries later turn out to be errors.
At viXra log we confidently predict that the next collection of such headlines will hit us when the next major update from the Keplar mission is released on February the first, if not before. The pre-release of info about CoRoT-7 b may however signal that nothing much better has been found. In any case we can be sure that planets described as more and more Earth-like will be appearing for many years to come.
So what do we really think should be counted as an Earth-like planet? The data we get from Keplar and other observations should tell us about the planet’s size, mass, and distance from its star. From this information we can infer its average temperature, whether it is likely to be tidally locked, the strength of its surface gravity. Then from this we can make a guess about whether it could support liquid oceans of water, and an atmosphere of the right density as well as whether it has a molten iron-rich core. the latter is important because it could give the planet a magnetic field that protects it from radiation.
If “Earth-like” means a planet could support an ecosystem like ours it will need to be in the Goldilocks zone of a star that is not too dim so that it does not tidally lock and liquid water can exist. It will also need to have a size and density reasonably close to Earth’s. That will ensure that it can retain its atmosphere without it becoming too dense. It also means that large land based animals will not be hindered by excess gravity and the molten core will not solidify to remove the magnetic field as it did on Mars.
It follows form these considerations that the star around which the planet orbits must also be like our Sol. If it were less bright the planet would need to get nearer and would be tidally locked. Bigger stars tend not to last long enough to provide a stable environment in which life can evolve. Other types of star may be too variable in brightness, or may have regular deadly flares that could strip any nearby planet of its atmosphere, even with the protection of a magnetic field.
Taking these things into consideration, the parameters that we can currently measure of exoplanets and the stars they orbit need to be very close to those of Earth and our Sun.
Apart from these considerations, an important feature of our planet is its large moon. Without it there would be no tides and these have surely been very important in promoting the evolution of live. The Moon is also said to keep our planet’s rotation axis stable. If it were otherwise we might suffer catastrophic changes in climate that would ruin the atmosphere of our planet. There may be an outside chance that Kepler could see the presence of such a moon as the system transits in front of its star.
Even if a star meets these requirements it really just makes it potentially Earth-like. The planet also needs to have the right chemical mix of elements in the right quantities to make oceans and an atmosphere that would support rather than poison life. Will we ever be able to detect their presence?
After Keplar has made a long (hopefully) list of potentially Earth-like exoplanets the next step will be to examine them more closely using other observatories. The best hope of being able to do this in the foreseeable future lies with the James Webb Space Telescope that is due for launch in 2014. The JWST will have spectrometers sensitive enough to see the slight differences in a systems spectra when planets pass behind their stars. It will even have a special camera with a spot that can block out the light from a star so that some planets can be seen away from the glare. This should certainly be good enough to work for the gas giants but it may require the next generation of space telescope to be able to do the same for smaller (potentially) Earth-like planets.
In the long term the prospects for finding truly Earth-like planets can only get better. Just how fast depends on technological and economic developments that are hard to predict. Ultimately there is no reason why we should not be able to determine the chemical composition of the atmospheres of Earth-sized exoplanets and if they have the right proportions of oxygen and nitrogen we will know that Earth-like plant and animal life must be present. Perhaps we will even be able to see the tale-tale signature of chlorophyl or other molecules that can only be produced in quantity by vegetation. That’s if such planets even exist nearby.
In any case one thing is for sure: Headlines telling us of the “First Earth-like Planets” are going to be around for some time.