Hubble turns 30
Jenny Winder looks at how the telescope has revolutionised our view of the Universe over the last three decades
How our understanding of the Universe has expanded
Thirty years ago Earth launched a telescope into space that has gone on to change the way we look at the Universe around us – the Hubble Space Telescope. It’s appropriate that the telescope should be named after Edwin Hubble – the scientist who showed us our Universe is expanding – for no other mission has enriched or revolutionised our knowledge of the cosmos, nor captured the imagination of the world quite like Hubble.
The project was decades in the making. The idea of launching a telescope into space, bypassing the distortion caused by Earth’s atmosphere, was first suggested by Herman Obert, a German rocket scientist in 1923. In 1946, American astronomer Lyman Spitzer began lobbying for the project, ▶
▶ but it was not until 1969 that NASA officially took up the proposal and published a report on the scientific advantages of what was then called The Large Space Telescope. The first working group was held in 1974 and $36m of funding was finally approved by Congress in 1978. The European Space Agency then came on board, contributing extra funding and expertise.
The path to the launchpad was far from smooth, however. The telescope was meant to be launched onboard a Space Shuttle in 1983, but problems with the mirror meant the project slipped increasingly behind schedule and over budget. Eventually a launch date of September 1986 looked possible, only for the Challenger disaster in January that year to halt all Shuttle flights. Delayed for another four years, the budget increased to an eye-watering $4.7bn.
Getting off the ground
Elsewhere, budget constraints meant the original plan of having a 3m mirror had to be reduced to 2.4m. This would be capable of accommodating five scientific instruments at once. At launch these were the Wide Field and Planetary Camera (WFPC), Goddard High Resolution Spectrograph (GHRS), High Speed Photometer (HSP), Faint Object Camera (FOC) and Faint Object Spectrograph (FOS).
Space Shuttle flights resumed in 1988 and finally on 24 April 1990, Space Shuttle Discovery mission STS-31 lifted off from the Kennedy Space Center and the following day Hubble Space Telescope launched into a geocentric orbit about 550km above Earth, where, travelling at a speed of 28,00km/h, it orbited once every 97 minutes.
As soon as the first images were received it was obvious there was a serious problem with the optics. Instead of sharp pin point images, stars were surrounded by fuzzy halos. This was a devastating blow. Though the telescope could still carry out some observations of bright objects, any faint observations
were impossible. By analysing the images, the Hubble team soon discovered that a microscopic error on the outer edge of the primary mirror meant the mirror was polished too flat.
On any other telescope, this would have been terminal, but Hubble had been designed to be maintained and upgraded in space using the Space Shuttle. While this couldn’t replace the primary mirror, a second-generation camera for Hubble, the Wide Field and Planetary Camera 2 (WFPC2) was already in development and, with the aid of some corrective optics, NASA hoped to compensate for the flaw in the mirror.
The first servicing mission by Space Shuttle Endeavour launched in December 1993. As well as installing the new optics, the team replaced the solar arrays, four gyroscopes, two magnetometers and other electrical components as well as upgrading the onboard computers to keep the telescope running as long as possible.
Hubble under threat
By January 1994 the first pin-sharp images to be received showed that the ambitious and perfectly executed mission had worked. NASA had snatched victory from the jaws of defeat.
Subsequent service missions have been carried out periodically during Hubble’s lifetime. However, in 2003, all services were thrown into doubt when the Space Shuttle Columbia broke up during re-entry. NASA decreed that all future Shuttle missions must have the capability to dock with the International Space Station (ISS) as a safety precaution. As Hubble was on a different orbit to the ISS, this would not be possible.
There was an outcry from both astronomers and the public and a sustained campaign was mounted to rescue Hubble. Finally in 2006, NASA gave the
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Many of Hubble’s images have become cultural icons, appearing on everything from album covers to coffee mugs
go ahead for a final servicing mission and not a moment too soon. In 2008, the main data-handling unit on board the telescope failed, leading to a month-long black out of all scientific data.
In May 2009, Atlantis flew the last service mission. It replaced the primary data-handling unit repaired two other instruments. Wide Field Camera 3 (WFC3) and Cosmic Origins Spectrograph (COS) were installed and a Soft Capture Mechanism (SCM) was also put in. This would allow a future mission, either crewed or robotic, to perform a safe controlled deorbit when Hubble finally reached the end of its mission.
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Pioneering science
Thoughout the last three decades, Hubble has played a role in investigating almost every area of astronomy. The telescope has found new star-forming regions and informed our knowledge of planetary formation. It has looked at galaxies that formed when our Universe was just three per cent of its current age and informed us that a black hole lies at the heart of most galaxies. It has helped to determine the size and mass of our Milky Way Galaxy, created a 3D map of dark matter, helped to characterise dark energy, pinned down the rate that our Universe is expanding and measured the age of the Universe to 13.7 billion years. In 2016 Hubble data revealed the oldest and farthest known galaxy, GN-z11, which is 32 billion lightyears away, meaning we see it as it was 400 million years after the Big Bang.
In 2001 Hubble was able to measure the elements present in the atmosphere of the exoplanet HD 209458b and in 2008 took the first ever visual image of an exoplanet (Formalhaut b). It was the first telescope to determine the true colour of an exoplanet and created the most detailed weather map of one. It found evidence of two asteroids colliding for the first time and observed the disintegration of another. Hubble discovered Pluto’s moons Styx, Hydra and Nix and in 2015 located five new Kuiper belt objects when it was used to find a target for the New Horizons mission. In 1994 it witnessed the impact of comet Shoemaker-Levy 9 on Jupiter. It has found jets of water vapour erupting on the surface of Jupiter’s moon Europa and, by measuring the aurorae on Ganymede, determined there must be a 100km-deep subsurface ocean beneath the 150km ice crust. Hubble even caught the
first predicted appearance of a supernova in a distant galaxy cluster, and earlier this year Hubble discovered that the Sombrero Galaxy, M104, had undergone mergers with other galaxies in the past. And these are just a few of the discoveries Hubble has made out of a catalogue of hundreds.
In its 30 years, Hubble has carried out several major observation campaigns, the largest being the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). This used Hubble to take deep images of over 250,000 galaxies, exploring the evolution of the early Universe from less than a billion years after the Big Bang. The telescope looked at five different areas of the sky, studying them in the many wavelengths available to it and other survey telescopes.
In 2006, the Cosmic Evolution Survey (COSMOS) used Hubble, alongside many other major telescopes, to study a two square degree patch of sky, 17 times larger than any of the CANDELS regions. Over two million galaxies were detected, covering 90 per cent of the age of the Universe. Another project, the Hubble Deep Fields Initiative, used gravitational lensing to study high-redshift galaxies that are ▶
▶ around 10 to 50 times fainter than any of the ones previously studied.
One particular set of images, Hubble’s Deep Field Observations, includes, perhaps, some of the most astonishing images ever produced. In December 1995, Hubble took 342 exposures over 10 consecutive days of the same tiny patch of sky in the constellation of Ursa Major – an area covering roughly one 24–millionth of the entire sky.
In 1998 a similar area of the Southern Hemisphere in the constellation of Tucana was imaged in the Hubble Deep Field South.
In 2004 the Hubble Ultra-Deep Field covered a small area in the constellation of Fornax containing 10,000 galaxies. It was the most sensitive astronomical image in visible wavelengths ever made until 2012 when the Hubble eXtreme Deep Field was released – covering just a portion of the Ultra-Deep Field.
Keeping track
With so much information to keep track of, the Hubble Heritage Project was founded in 1998 and the following year ESA launched its Hubble Information Centre. These select, process and release images and news bulletins and it is these images that have inspired the public and been hailed for their “outstanding contributions to the public understanding and appreciation of astronomy”.
Many of Hubble’s images have become cultural icons, appearing not just in science books, but on everything from album covers to coffee mugs. No other mission has opened our eyes to the variety, complexity and downright beauty of space.
Thirty years on, Hubble is still working productively and estimated to be operational well into 2030 or 2040. Over the three decades of its life Hubble has taken over a million observations and the data it has generated has been published in more than 16,000 peer-reviewed scientific papers, which are referenced on average at a rate of 150 times a day. In 2017 the American government announced it was considering further servicing missions to extend the life of this iconic telescope that has expanded our view of the Universe.