There is so much over enthusiastic hype about this planet today, I thought could do with a bit of more sober reporting of the results, interesting though they are. Much of that speculation derives from just one phrase in the press release I think, where they say:  "Today, and thousands of discoveries later, astronomers are on the cusp of finding something people have dreamed about for thousands of years -- another Earth." The idea of what that means by "another Earth" for astronomers who know the capabilities of Kepler, is rather different from what most of the general public would think of when you say "another Earth".

Kepler is great for getting an idea of what proportion of stars have planets, and what types of stars typically have planets, because it focuses on a small patch of the sky, using transit method, looking at lots of stars likely to be far away. However it can't tell much about these planets, except the diameter of the planet and its orbital period, and spectral type of its parent star. Anything else such as its mass is informed guesswork.

So, anyone with that background knew in advance that this announcement could only tell us things like that, and understood the press release accordingly. Just from knowing that it was a Kepler press release. Unless just through luck it happened to find some nearby star, that is, but typically you expect them to be distant stars, at their closest, hundreds of light years away, so far away any light signal due to the planet's atmosphere or surface would be very faint indeed and hard to analyse.

But now that it's found that some G type stars have planets like Earth - that means that perhaps it gets a bit more likely that we will find similar planets around some of the nearby G type stars, maybe even Alpha Centauri, or Tau Ceti or some such. 


There are many much closer potentially habitable exoplanets already known  - the one NASA just announced is the one labelled "New" here::

The Habitable Exoplanets Catalog - Planetary Habitability Laboratory @ UPR Arecibo - organized by distance from Earth.


And this new exoplanet is not even the one most similar to Earth found so far if we show those same planets organized by their "Earth similarity index" then it is sixth in this ranking.

HEC: Graphical Catalog Results - Planetary Habitability Laboratory @ UPR Arecibo - organized by similarity to Earth.


The main thing that's notable about it is that its sun is very similar to our sun. Which given that our sun seems to have been pretty much ideal for life on Earth, may be a good sign. 

But then on the other hand, might be that there are other stars that are also good stars for life, is hard to reason very far with a sample size of just one known inhabited star to date. The smaller and more numerous red and orange dwarfs also seem to have a lot of promise for habitable worlds, and because there are so many of them, could easily be that the best places to look for life are around, e.g., orange dwarfs (or red dwarfs), or whatever. We just don't know at present.


And note - that we know nothing about this planet except its size and orbit. Don't really know its mass - that's a guess. Amongst other possibilities:

  • It could be a tiny version of Jupiter - a miniature gas giant with no solid surface.
  • Its oceans could have boiled away like Venus. Like Venus it could have a dense atmosphere and a surface temperature of hundreds of degrees centigrade.
  • It could be a snowball planet, just solid ice on the surface to depths  of tens or hundreds of kilometers (which might or might not have a habitable ocean beneath it but we'd have no way of knowing either way by observation from Earth with present day technology).
  • Could be a bare rock with no water or atmosphere at all.
  • It could be an ocean world, but with no continents or shallow regions, everywhere hundreds of kilometers deep oceans, with the floors of the oceans covered in thick layers of dense ice (if the ocean is very deep then you get a form of ice that sinks rather than floats) - so insulating the water from minerals and rocks making it rather unlikely that life evolves according to modern ideas.
  • Or it could be a world with shallow oceans and continents, and an atmosphere of some sort, not necessarily an Earth like atmosphere, with or without life.
  • Or a second Earth closely resembling our planet geologically.
  • Or, even a planet with life and multicellular life closely resembling Earth life.
There's no evidence yet to suggest the last of those possibilities is more likely than any of the others, or indeed to assign it a probability at all, we just don't know enough to say anything with any assurance there.

The chance that it is a rocky body rather than a miniature gas giant type planet they estimate as between  49% and 62% - that's based on statistical analyses of nearby rocky planets (around red and orange dwarf stars).  such as this one.The Mass-Radius Relation for 65 Exoplanets Smaller than 4 Earth Radii

For the paper and the calculations: Discovery and validation of Kepler-452b: a 1.6-r⊕ super earth exoplanet in the habitable zone of a G2 star and short scientific summary: Kepler telescope identifies new ‘habitable zone’ planet,  and see also (abstract)

But is early days yet. We don't have much chance of finding out a lot about it at that distance, but given that there are likely to be many planets like that closer to Earth, other searches and telescopes will probably let us study those ones and eventually find answers to questions like that for the closer stars, especially e.g. after the launch of a giant telescope to the Sun Earth L2 position - pointing away from the sun especially designed to help with the search for habitable worlds (the James Webb telescope).

If close enough for spectroscopic observation we can look at its atmosphere and detect e.g. if there is oxygen, methane etc in its atmosphere. And also spectroscopic observation of its surface also and distinguish e.g. if it has oceans or ice, or even maybe detect organic chemicals produced by life e.g. whatever is its equivalent of chlorophyll if it has it. Eventually there are methods that may be able to pick out the larger permanent surface variations also such as ice caps and continents (based on the spin which lets us see different parts of it at different times).

There are many nearby planets that may well be habitable.  List of nearest terrestrial exoplanet candidates

And even restricting search to sun like stars, quite a few nearby G stars.


Even Alpha Centauri, closest G type star known to Earth, only 4.24 light years away, only a little further than Proxima Centauri, the closest known star to Earth, could have planets in its habitable zone.

These authors in a 2008 paper raised the possibility that we could detect those planets: Page on

And there is a search underway to try to find them: The Mt John University Observatory search for Earth-mass planets in the habitable zone of α Centauri


Once we find many of these planets, and are able to study them in detail, surely many of them will be Venus like, or ice covered worlds, or mini gas giants or in other ways not easy for life to inhabit - and perhaps some will be habitable but not have life on them. All telling us a lot about the possibilities for solar systems like ours.

In short this is one significant step along the road to detecting habitable exoplanets - as to whether this particular one is habitable, nobody knows, and maybe the chances aren't that great that it is (depending on how easy it is for a habitable planet to arise around a G type star) but the evidence suggests its one example of a large population of planets around sun like stars - and so with so many planets this increases the chances that we may be able to detect one, or indeed most likely many such planets close enough to study - not just like Earth but also orbiting a sun-like G class star. 


And - whether they are Earth like to the extent of having life on them or not, they are also of interest as planets in solar systems like ours, so telling us things about past and future and alternative present for evolution of planets in our own solar system.

BTW they said that the age of 6 billion years is correct to about +- 2 billion years. So - though probably older than our solar system, it's still within the bound of possibility that it is younger. If older, it could also give us an idea of some of the possibilities for future evolution of planets in a solar system similar to ours, though this particular planet is five times more massive than Earth.


Not unless they beam a signal at us. Or do mega-engineering, create huge obviously artificial structures in space.

If they are just going about their own thing, and have efficient technology that doesn't leak much, or they don't have technology, we'd never know.

Even if they have technology and actively try to communicate with us, they would need to be very dedicated to send signals into space for hundreds of millions of years continuously in hope that someone spots them eventually - and if they only do it as a short term project for a few centuries or millennia, it would be an amazingly lucky chance to spot them just at the moment when they do the transition, over periods of many billions of years.


With a close by star, then we could spot the way that life makes a difference to the atmosphere, or even e.g. spectroscopic signatures of some prevailing chemicals in its vegetation (or whatever the equivalent is), e.g. chlorophyll. This would be a very delicate measurement, but we have already made spectroscopic observations of the atmospheres of some nearby gas giants, so not beyond our capability, to get started on learning about the composition of the atmospheres of nearby Earth like stars, especially with next generation telescopes such as James Webb.

We have even managed reflection spectroscopy - not just how light is affected as it passes through a gas giant's atmosphere - but also the spectrum of the surface of the planet, for a "hot Jupiter"

First visible light spectrum from exoplanet observed


But - that's just searching for life. As for intelligent life - even for nearby stars could easily miss intelligent life.

We could even have intelligent life in our own solar system in the oceans of any of the moons or dwarf planets that are thought to possibly to have liquid ocean interior shells below the ice - and again - we'd never know, not yet, and they wouldn't know about us if non technological as is quite likely in such a situation (so far we have no way to see into these oceans, and if non technological they would probably have no way to know even that there is a universe outside of their ocean and no way of getting out of it - to them, their ocean would be the entire universe almost certainly).

There would be no sign at all of a civilization in the ocean of an icy moon around an exoplanet, there wouldn't even be any sign of life at all at that distance if the planet or moon is covered by a layer of several kilometers of ice - so there's a strong observer bias here - we can only spot very limited types of civilizations and types of life. Civilizations with radio signals or such like if not too far away - and forms of life that make changes to the atmosphere or the surface of their planets which can be noticed by spectroscopy from a long way away.

We could spot a civilization which transmits or leaks radio signals if it is really close. If close enough, just a few tens of light years away, chances are they've spotted us already. 

At 1400 light years away, not likely to detect them unless they get into mega-engineering in a big way or leak huge amounts of radio energy etc . But it might be that as ETs get more advanced, they leak less energy and are more efficient in how they use it so harder to detect.

As for them contacting us, they would see Earth as it was 1400 years ago - no matter how sensitive their detectors, they wouldn't know that we have developed radio technology but might be able to detect life on our planet, and so we might be a target of their radio transmissions or optical laser transmissions if they do happen to have a very long term probably hundreds of millions years long ET contact program directed towards all the known nearby potentially habitable planets just on the off-chance that technological species eventually evolve on them.


If they just broadcast to us, say, for a century, out of billions of years - we'd have to be amazingly lucky to evolve to the point where we can detect them during that very century when they try to contact us (or rather, tried to contact us exactly 1400 years ago to the nearest century). 

Or we have to wait for hundreds of millions of years before we contact them. So - especially if you try to contact a civilization about a particular star - then if you do make contact, one or the other of you has to be very patient, and either broadcast, or listen, for a very long time. Or one of you has to be very noisy in the radio or optical spectrum or do mega-engineering in a big way.


It's a very interesting announcement, but so far anyway, more for its promise for what we might be able to find out about other planets as an example of a population of planets, rather than as an individual planet itself. As for the planet Kepler 452B, the main things that made it interesting for us at this stage is that 

  •  it just happened to have its orbit tilted at the right angle so that we could detect it by the transit method,
  • it was in the part of the sky that Kepler focused its attention on
  • its sun is very similar to our sun, so suggesting possibility of finding Earth like planets in the habitable regions around nearby sun like stars.
But whether this particular planet is of any more interest to us than any of the probably thousands of other nearby similar planets, only time will tell.
(based on a couple of my answers on Quora where many people have been asking about what this announcement means, see my answers to: Is there a way to detect if there is intelligent life on Kepler-452b? and How much can we learn about the new Kepler planet?)