New Worlds mission: Hunting for alien life using a starshade

An artist’s impression of the New Worlds mission. Image Credit: Jay Wong

The question of whether life exists on other planets is one that scientists frequently ponder, but have so far failed to answer. Hoping to change this is the New Worlds mission that, while still in the early phases of development following years of research, is likely to bear fruit in the near future.

One of the problems with observing extrasolar planets is the amount of light emitted by the parent star they orbit. When scientists use a telescope to look deep into space, they find the brightness of these stars drowns out the light from the orbiting planets. They still see the more-intense glow of larger planets, but the smaller ones are virtually impossible to spot. Since those tinier planets are, like Earth, more likely to contain signs of life, it means experts risk missing potential life-supporting worlds.

Dr Webster Cash, of the University of Colorado at Boulder, has devised a method to combat this problem. He proposes using a starshade, effectively a large blocker spacecraft that would be placed between the telescope and the target star. It would prevent light from the star reaching the telescope that would, in effect, be cast within a shadow. Just as a ball heading your way from up high on a bright day is better seen if you hold your hand to block the sunlight, so the planets orbiting their parent star are brought into view when the brighter light is blocked.

In 2013 NASA created a mockup of the starshade. The initial plan had been to produce a round disc, but this caused a problem with diffraction. When light from the parent star hits a round circle, it will diffract around the edge. Not only does this give a halo-like glow but it also drowns out the dimmer light of the smaller extrasolar terrestrial planets being sought, because it remains so bright.

Could the New Worlds mission help us to find a planet like Earth? Image Credit: NASA

The idea is to make the starshade look like a series of slit petals, each one sitting around the inner disk. Since the perimeter shape of the object the light is hitting governs diffraction, this design controls the way the light waves of the star behave, drastically cutting diffraction. Because the starshade will be tilted when put into space, the light from our own Sun will not disrupt the telescope’s view of the extrasolar planetary system either.

Although the proposal is to fly the starshade and the telescope into space in formation, it’s more likely that the telescope will be sent up first and the starshade will follow at a later date. The team behind it is conscious of cost – with a budget of around £1.8 billion ($3 billion) – so it’ll either work with an existing collector, such as the James Webb Space Telescope, or a four-metre (13-foot) telescope likely to be built in the future.

This won’t be an easy mission, as the starshade will be sent to space in a folded state before unfurling. It also needs to be aligned with a telescope around 200,000 kilometres (124,000 miles) away. With little room for error and the need to maintain alignment, so much could go wrong. If the mission enables scientists to see planets they’d otherwise miss, enabling them be to analysed for water vapour, carbon dioxide and oxygen, the big question of the universe could be answered soon.