IT'S the planetary equivalent of a family portrait. An image snapped from Earth reveals the chemical contents of four worlds at once – the first result in a push to characterise whole solar systems, not just individual planets.
The portrait, of the star HR 8799 and its four massive planets, is spectral, meaning it splits the light from planets into its constituent wavelengths to reveal molecules in their atmospheres. This in turn gives clues about how life-friendly they may be.
Previously, only a handful of planets had had their spectra measured, and most were worlds that crossed in front of their stars, or transits, as viewed from Earth, meaning only individual planets have been clocked in one go.
By contrast, Project 1640, an international collaboration named after the wavelength of infrared light at which it works best – 1640 nanometres – uses advanced imaging techniques that block the light from stars. This leaves only the light from planets, including ones that don't transit, and means light from all the planets in a system can be detected simultaneously.
The 1640 team used the Hale telescope at California's Palomar Observatory to capture the HR 8799 system. But more spectra are coming. The project has begun a three-year campaign to survey 200 stars within 150 light years of our solar system.
This article appeared in print under the headline "Planetary portrait"
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