Will we ever find life on planets around other stars? STEPHEN LEWIS spoke to a York astrophysicist who thinks we will - and quite soon

HELLO? Is there anybody out there?

It's one of the most profound questions we can ask as an intelligent, thinking species: are we alone in the universe?

At the moment, we just don't know. But we are getting closer to an answer.

One of the keys to answering the question lies in whether there other planets out there that would support life.

It is still possible that one day we might find simple life in the waters below the icy crust of Jupiter's moon Europa, or else on Titan, Saturn's giant moon.

But University of York astrophysicist Dr Emily Brunsden believes we're actually far more likely to find life on a planet circling another star entirely.

There are plenty of planets out there, we know that. The problem is that even the nearest star - Proxima Centauri - is so far away that it would take a fast jet travelling at 2,000mph more than a million years to get there.

Because they're so far away, planets around these distant stars are very hard to see. The very first 'exoplanets' as they're called, weren't confirmed until 1992.

But in recent years, using increasingly sophisticated telescopes and techniques, the discoveries have been coming thick and fast. As of this March, scientists had confirmed the existence of almost 4,000 planets orbiting stars far away from Earth.

We can't actually see them directly, says Dr Brunsden, who recently gave a public talk in York entitled Fantastic Planets and How To Find Them.

Instead, we use powerful telescopes to look at the stars themselves, and see if we can work out from their behaviour whether they have planets orbiting them.

York Press:

Stargazer: Dr Emily Brunsden

There are various methods for doing this (see panel below).

But the bottom line is that, as our instruments improve, we are getting better and better at finding planets around other stars.

By studying the effect they have on their star we can even tell quite a lot about them, says Dr Brunsden: how big they are; how far away they are from their sun, so how hot they are; what their gravity is, and so how much we'd weigh if we lived there - and even if they have liquid water, something that would be vital for life as we know it.

So far, some of the planets we've found are quite extraordinary. "Some seem to have come straight from science fiction," Dr Brunsden says.

Imagine living on a world with three suns, or where the jungles and grass are all red; where it is always night, or where you weigh twice as much as you do now, and you begin to get the idea.

NASA has produced a series of great 'travel' posters - in the style of old railway posters - imagining what some of these planets would be like.

"Relax on Kepler-16b, the 'land of two suns' where your shadow always has company," says one poster, showing a man in a spacesuit gazing up at two suns in the sky. Actually, you wouldn't be likely to do much relaxing on Kepler-16b. It's almost certainly huge - about as big as Saturn - so that the weight would crush you: and it's probably mainly made of gas and freezing cold, too. But, like Luke Skywalker's planet Tatooine in Star Wars, it really does have two suns - so it would at least have that spectacular double-sunset.

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SHINE ON: The delights of Kepler 16b. Image: NASA

Then there's Kepler-186f, 'where the grass is always redder on the other side', says the NASA poster. This is actually thought to be a rocky, Earth-sized planet that could have liquid water on its surface. But its star is much cooler and redder than our sun. And because the star gives out a lot of red light, the NASA poster imagines that if there was any plant-life on the planet it might all be red, rather than green as here...

One of the most exciting recent discoveries, however, was the Trappist-1 system. Trappist 1 is a cool red star about 40 light years from Earth - quite close in cosmic terms, only ten times as far away as our nearest neighbour, Proxima Centauri.

Remarkably, scientists found evidence that it had no fewer than seven Earth-sized planets orbiting closely around it. "These seven rocky worlds huddle around their small, dim, red star, like a family around a campfire," the NASA travel poster says. "Any of them could harbour liquid water."

The NASA poster shows Trappist-1e, which scientists think is the most likely to be in the 'habitable zone' around its star, where the temperature is just right to allow water to exist in liquid form. It shows a dark night sky with six red planets looming above, looking like red versions of our moon - the other six planets in the Trappist-1 system.

York Press:

SPACE TRIP: A poster imagining the night sky from the surface of Trappist-1e. Image: NASA

We still don't know whether these or any of the countless other planets out there waiting for us to find them have life of their own, Dr Brunsden admits.

But we are getting closer to finding out.

She herself is an astero-seismologist. She studies the make-up of stars by looking at the wavelengths of light they give off. This information gives clues to the way a star changes and develops through its life cycle of billions of years.

Dr Brunsden isn't directly involved in the search for planets around other suns herself - but she does work closely with scientists who do, including from NASA. And techniques similar to her own can be used to measure the make up of the atmospheres of these distant planets.

You can tell from the colours of the light that a star gives off what gases it contains. And when a planet passes in front of a star, you can tell from the way it changes the star's colour whether the planet itself has a gas atmosphere - and even what that atmosphere could be made up of.

We know that on Earth, life affects the atmosphere, leading to an increase in certain gases such as oxygen, methane and carbon. These are the 'bio-signatures' of life as we know it - and that means we can look for this same bio-signature on distant planets.

Dr Brunsden is almost certain that there is life out there somewhere.

"We live in a galaxy of 100 billion stars, and there are 100 billion galaxies in the universe," she says. "The universe is really big."

We haven't found that evidence of life on planets around others stars yet, she admits. "But my opinion is that we will get a bio-signature really soon."

That bio-signature may be from only a very simple life-form. It is very unlikely to be a sign of intellignt life.

But the very fact that there is life out there at all would greatly increase the likelihood that somewhere out in the stars like dust, there is intelligent life too.

Which would mean we aren't alone after all...

Dr Brunsden hopes to repeat her 'Fantastic Planets and How to Find Them' talk at the University of York's Pint of Science event from May 14-16.


There are several techniques that astrophysicists use to find planets around other stars.

One is the transit technique. As they circle their stars, planets inevitably sometimes come between their star and us. When that happens, the light of the star dims slightly. Only by a tiny amount, because compared to a star even the largest planet is very small. But enough to be detected by sophisticated instruments. That tiny dimming is a telltale sign of a planet.

Another technique involves looking for evidence that stars are wobbling, which can again be a sign that a star is orbited by a planet or planets. The wobble changes the colour of the star's light very slightly, causing something called a red shift or a blue shift, another telltale sign.

Scientists have already discovered many different types of planets around other stars. Some are giant balls of gas like Jupiter. These are the easiest to find, because they are so big - especially planets called 'Hot Jupiters', giant gas planets which orbit very close to their stars. Because they are so big and close to their star, they have more of an effect on it, so it is easier to spot them, Dr Brunsden says.

But scientists are also now finding other kinds of planets - including rocky 'Super Earths' with a gravity two times what we have here, and other planets that are about the size of our own Earth - like the extraordinary family of 7 planets orbiting Trappist-1.