Kepler mission announces two exoplanets in the habitable "zone"

The planets are the right temperature and size to support liquid water.

The Kepler mission, a NASA project to find and profile planets outside of our solar system, has announced the discovery of two potentially habitable exosolar planets.

The planets are part of a system, Kepler-62, which is thought to contain five roughly earth-sized planets. The biggest is almost twice earth's size; the smallest slightly more than half.

That alone is notable, because the normal way the Kepler mission identifies planets is by measuring the gravitational they exert on their star. A big enough planet will pull the star slightly closer to the earth when it's on one side, and slightly further when it's on the other. That causes a minute fluctuation in the brightness of the star, measured from our planet, which the Kepler orbital observatory can sense.

But only the largest gas giants have such an effect, and while they are noteworthy finds in themselves, they aren't habitable. To find smaller planets, the mission looks at stars which have other fluctuations in light – due to planets passing in front of them. They then have to model every possible reason why those fluctuations could occur, and hope that they find that the most likely cause is exoplanets traversing the star.

The planets which they've found this way aren't just earth sized, though. Two of them, each measuring around 1.5 times the size of earth, are roughly the same distance away from their star as we are. Their orbits take a third and two thirds of an earth year each, but, because their star is less bright than our sun, they receive 1.2 and 0.4 times the light, respectively, that we do.

That will equal one hot planet and one cold one – but either of them might be in the so-called "habitable zone", where liquid water can exist. And liquid water is the only universal prerequisite we know for life.

The authors note that their method cannot tell if the planets are even rocky, as opposed to gas giants, let alone whether they actually have an atmosphere or water. But they are some of the best candidates we've found to date.

And crucially, we've found them fast. The Kepler telescope has been in orbit for around half its expected life, but it's already produced a vast amount of data to crunch. It's discovered almost 3,000 possible exoplanets, and has already found one that could have water. If the hit rate stays high, there could be many more.

Johannes Kepler, the 16th century astronomer for NASA's mission is named. Image: Hulton Archive/Getty Images

Alex Hern is a technology reporter for the Guardian. He was formerly staff writer at the New Statesman. You should follow Alex on Twitter.

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Scientists have finally said it: alcohol causes cancer

Enough of "linked" and "attributable": a new paper concludes that alcohol directly causes seven types of cancer.

I don't blame you if you switch off completely at the words "causes cancer". If you pay attention to certain publications, everything from sunbeds, to fish, to not getting enough sun, can all cause cancer. But this time, it's worth listening.

The journal Addiction has published a paper that makes a simple, yet startling, claim: 

"Evidence can support the judgement that alcohol causes cancer of the oropharynx [part of the throat], larynx, oesophagus, liver, colon, rectum and [female] breast"

So what's especially significant about this? 

First, scientists, unlike journalists, are very wary of the word "causes". It's hard to ever prove that one action directly led to another, rather than that both happened to occur within the same scenario. And yet Jennie Connor, author of the paper and professor in the Preventive and Social Medicine department at the University of Otago, New Zealand, has taken the leap.

Second, alcohol not only causes cancer of one kind – the evidence supports the claim that it causes cancer at seven different sites in our bodies. There was weaker evidence that it may also cause skin, prostate and pancreatic cancer, while the link between mouth cancers and alcohol consumption was the strongest. 

What did we know about alcohol and cancer before?

Many, many studies have "linked" cancer to alcohol, or argued that some cases may be "attributable" to alcohol consumption. 

This paper loooks back over a decade's worth of research into alcohol and cancer, and Connor concludes that all this evidence, taken together, proves that alcohol "increases the incidence of [cancer] in the population".

However, as Connor notes in her paper, "alcohol’s causal role is perceived to be more complex than tobacco's", partly because we still don't know exactly how alcohol causes cancer at these sites. Yet she argues that the evidence alone is enough to prove the cause, even if we don't know exactly how the "biologial mechanisms" work. 

Does this mean that drinking = cancer, then?

No. A causal link doesn't mean one thing always leads to the other. Also, cancer in these seven sites was shown to have what's called a "dose-response" relationship, which means the more you drink, the more you increase your chances of cancer.

On the bright side, scientists have also found that if you stop drinking altogether, you can reduce your chances back down again.

Are moderate drinkers off the hook?

Nope. Rather devastatingly, Connor notes that moderate drinkers bear a "considerable" portion of the cancer risk, and that targeting only heavy drinkers with alcohol risk reduction campaigns would have "limited" impact. 

What does this mean for public health? 

This is the tricky bit. In the paper, Connor points out that, given what we know about lung cancer and tobacco, the general advice is simply not to smoke. Now, a strong link proven over years of research may suggest the same about drinking, an activity society views as a bit risky but generally harmless.

Yet in 2012, it's estimated that alcohol-attributable cancers killed half a million people, which made up 5.8 per cent of cancer deaths worldwide. As we better understand the links between the two, it's possible that this proportion may turn out to be a lot higher. 

As she was doing the research, Connor commented:

"We've grown up with thinking cancer is very mysterious, we don't know what causes it and it's frightening, so to think that something as ordinary as drinking is associated with cancer I think is quite difficult."

What do we do now?

Drink less. The one semi-silver lining in the study is that the quantity of alcohol you consume has a real bearing on your risk of developing these cancers. 

On a wider scale, it looks like we need to recalibrate society's perspective on drinking. Drug campaigners have long pointed out that alcohol, while legal, is one of the most toxic and harmful drugs available  an argument that this study will bolster.

In January, England's chief medical officer Sally Davies introduced some of the strictest guidelines on alcohol consumption in the world, and later shocked a parliamentary hearing by saying that drinking could cause breast cancer.

"I would like people to take their choice knowing the issues," she told the hearing, "And do as I do when I reach for my glass of wine and think... do I want to raise my risk of breast cancer?"

Now, it's beginning to look like she was ahead of the curve. 

Barbara Speed is a technology and digital culture writer at the New Statesman and a staff writer at CityMetric.