Luke Skywalker gazed at a twin sunset

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Many planets may have double suns

 

In the film Star Wars, Luke Skywalker gazed at a twin sunset from his

desert homeworld

 

 

Enlarge Image

 

The dual suns that rise and set over Luke Skywalker's homeworld in

the film Star Wars may be more than just fantasy, according to data

from Nasa.

In a classic scene from the 1977 movie, the hero gazes into the

distance as two yellow suns set on the horizon.

 

Nasa's Spitzer Space Telescope has found that planetary systems are

as common around double stars as they are around single stars, like

our own Sun.

 

Details of the research have been published in the Astrophysical

Journal.

 

The number of potential sites for planets has just increased

enormously

 

David Trilling, University of Arizona

 

In the study, a team of researchers used an infrared camera on the

Spitzer telescope to search for so-called dusty discs around binary,

or double, stars.

 

Dusty discs are made from the leftover debris of planet formation.

 

 

" We knew the stars would be there, the question was whether there was

a planet to be the place where you could stand and see these

sunsets, " said Karl Stapelfeldt, a scientist at Nasa's Jet Propulsion

Laboratory (JPL) in Pasadena, California.

 

" The inference is getting stronger now that there must be such

planets based on what Spitzer has found. "

 

The presence of planets in dusty discs is thought likely, but is by

no means certain.

 

 

Click here to see which binary systems might have planets

" In our Solar System, asteroids collide with each other and produce

showers of dust and that is, we assume, what we're seeing in these

other discs - the dust produced by the collision of two bigger

bodies, " lead author David Trilling, from the University of Arizona,

told BBC News.

 

" We can infer that there are bigger bodies like asteroids. The next

logical leap is that if there are processes that formed these bigger

bodies like asteroids, those same processes may also have formed

planets. "

 

 

Planets could be commonplace around binary stars

The team looked for dusty discs in 69 binary systems between about 50

and 200 light-years away from Earth.

 

The data show that about 40% of double systems had dusty discs -

slightly higher than the frequency for a similar sample of single

stars.

 

This finding suggests that planetary systems are at least as common

around these binary stars as they are around single stars like our

Sun.

 

In systems where stars are 50-500 astronomical units (50-500 times

the distance from the Earth to the Sun) apart, dusty discs circle one

of the pairs of stars.

 

Close-knit stars

 

But the researchers found no discs in binary systems where stars were

3-50 astronomical units (AU) apart.

 

In these double systems, Dr Trilling suggests, gravitational forces

may kick debris out into deep space, preventing the formation of

planets.

 

 

Nasa's Spitzer infrared telescope

 

 

More details

 

When the team looked at even more closely spaced binary stars -

positioned at three to zero astronomical units distance - they were

surprised to find that dusty discs were common, occurring in about

60% of cases.

 

In these systems, a dusty disc circles both stars, rather than just

one. Any planets orbiting these close-knit star systems would

experience sunsets similar to the one depicted on the fictional

desert world of Tatooine in Star Wars: Episode IV - A New Hope.

 

" The number of potential sites for planets has just increased

enormously, because now we know these multiple star systems may be

commonly associated with planetary formation, " said Dr Trilling.

 

Habitable zones

 

Dr Trilling said that if planets did exist in dusty discs around

these binaries, they might be at distances where the conditions could

be hospitable for life.

 

" The Luke Skywalker picture is science fiction. But I don't see

anything that's astronomically incorrect about it, " said the

University of Arizona researcher.

 

" With some of our systems, you could play with the geometry, put a

planet there, get the temperatures right and make it look just like

[Tatooine]. "

 

 

" Of course, we don't know anything about planets in these systems -

it's all imagination - but it looks fine. "