How starlight could help map alien worlds thousands of light years away

How starlight could help map alien worlds thousands of light years away
How starlight could help map alien worlds thousands of light years away
  • New software inspired by technique used to spot hidden military bunkers in satellite photos of Earth
  • It analyses starlight reflecting off a distant planets to calculate the mix of features that might combine to create a specific hue
  • However telescopes powerful enough to carry out the process on worlds beyond our solar system do not yet exist

[dropcap]A[/dropcap]stronomers are developing a system to use reflected starlight to create maps of alien planets that show oceans, land and even clouds.

Developed by planetary scientist Nicolas Cowan and presented this month at a meeting of the American Astronomical Society in Long Beach, California, it is inspired by a technique originally developed to distinguish between natural surfaces – such as forests – and unnatural ones like military bunkers in satellite images of Earth.

The software can take a point of reflected starlight from an exoplanet, and analyse it to extract the unique signals required to form a rough map.

Distant jewel: This EPOXI mission image shows what an Earth-like exoplanet might look like from afar
Distant jewel: This EPOXI mission image shows what an Earth-like exoplanet might look like from afar

Because there is currently no telescope powerful enough to directly photograph a faraway rocky planet, Dr Cowan tested the software on images of Earth taken from a distant vantage point inspace byNasa’s Deep Impact spacecraft as part of the EPOXI mission.

‘The object of this experiment was to see whether we could identify the colours of surfaces on Earth, [and tell] how many major surfaces are there, and what they look like,’ said Dr Cowan, who works at Northwestern University in Evanston, Illinois.

Dr Cowan‘s technique – called ‘rotational unmixing’ – analyses the changing colour of starlight reflecting off a distant, spinning exoplanet to calculate the mix of planetary features – such as land or ocean – that might combine to create a specific hue.

The technique is similar to being in an otherwise dark room with a muted television and analysing the light reflected on the opposite wall to figure what is playing on the TV.

‘You’re not seeing the picture, but you’re seeing the reflection of the picture and learning something about what’s going on there,’ said Eric Ford, an astronomer at the University of Florida in Gainesville, who was not involved in the study.

When Dr Cowan‘s software was applied to EPOXI images of Earth, it was able to extract reflectance signatures corresponding to three major surface types.

‘The analysis told us there were three important features,’ Dr Cowan said, ‘and their spectra look an awful lot like land, ocean, and clouds.’

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