It has captured images of stars coalescing out of glowing clouds of dust, peered back more than 10bn years to study the early universe, pinpointed the remnants of supernovae explosions and helped physicists uncover some of the cosmos’s deepest secrets. The Hubble space telescope, which celebrates its 25th birthday next month, has been, if nothing else, an astronomical workhorse of unprecedented effectiveness. Yet its greatest achievement has less to do with hard science and much more to do with our appreciation of our own place in the universe.
Thanks to the space telescope, which was launched by Nasa on the shuttle Discovery, we can see the unbelievable richness, colour and grandeur of the universe: newborn stars glittering through thick columns of interstellar dust, or luminous galaxies whose light has taken billions of years to reach us.
These visions excite contradictory responses. There is a sense of empowerment in knowing our species is capable of revealing the wonders of the universe in such an effective way. Humanity has clearly come a long way in running such a complex machine so far from home. On the other hand, these images of incredibly remote galaxies, each filled with billions of stars like our own sun, are as effective a demonstration of human insignificance as you could get. We are the denizens of a small planet “in the uncharted backwaters of the unfashionable end of the western spiral arm of the galaxy”, as Douglas Adams once put it. The Hubble has made this abundantly clear, albeit in glorious, rich hues.
In terms of public relations, the Hubble has also been a soaraway success, not just for Nasa but for science in general. Manned space missions usually only make headlines today when things go wrong – toilet troubles on the International Space Station being a major media favourite. Certainly, everyday life in orbit now looks humdrum and banal. By contrast, the Hubble has generated breathtaking visions of other worlds in an unabated stream since its launch in 1990, and in peering with such clarity into the universe from its orbit outside the blurring effects of Earth’s atmosphere, it has done more than any other spacecraft – or any other scientific instrument, for that matter – to generate intrigue and excitement about the universe.
An indication of the Hubble’s impact can be gauged by the public outcry that erupted over Nasa’s decision to scrap the agency’s last servicing mission to the telescope, announced after the destruction of the shuttle Columbia in 2003. In the end, the cancellation was reversed and the shuttle was saved for a further decade’s use – though at some cost: the final servicing mission to the Hubble cost more than $1bn.
That mission was carried out by the crew of the shuttle Atlantis in 2009, shortly before the entire US space shuttle fleet was grounded. The instruments fitted to the telescope were expected to give it a further five years’ life. That deadline has now passed, and the great telescope is today operating on borrowed time, though most engineers believe it could easily work for another five years. Nevertheless, its gyros, which guide the great instrument, will eventually fail and controllers on Earth will no longer be able to guide the telescope. The Hubble will drift in space for years before it falls back to Earth, probably between 2030 and 2040, and burns up in the atmosphere.
It will not be the end of the concept of the orbiting observatory, however. Nasa’s next-generation instrument, the James Webb space telescope (named after a former Nasa administrator), should then be in orbit. It will not return the same glittering images as the Hubble, however. It is designed to collect infrared radiation, not visible light, from stars and galaxies, because it was conceived to explore the deepest, most distant parts of the universe. Astronomical objects move faster from us the more distant they are – and the faster they speed from us, the more their observed light is shifted to the red end of the electromagnetic spectrum, until it moves from visible into infrared. Thus, if we want to probe the farthest depths of the universe, and understand the cosmos’s early formation, we need to study objects moving away from us at colossal speeds – stars and galaxies that generally can only be seen in the infrared part of the spectrum.
We should not despair at losing those glorious optical images like those provided by the Hubble, however. “The Hubble was designed to fly in space and study stars without the atmosphere blurring its images,” says Britain’s astronomer royal, Lord Rees. “But since its launch, astronomers have devised ingenious ways to remove much of that blurring in ground telescopes. As a result, the giant telescopes now being built in Chile and Hawaii will produce exceptionally sharp optical images.”
These huge instruments will also have mirrors that will be more than 10 times the diameter of the Hubble’s, and so will be able to peer even further into space and generate even more breathtaking images of the cosmos. The space telescope’s legacy will live on, in other words.
