One of the best: In January 2002, a dull star in an obscure constellation suddenly became 600,000 times more luminous than our Sun, temporarily making it the brightest star in our Milky Way galaxy. The mysterious star, called V838 Monocerotis, has long since faded back to obscurity. But observations by Hubble of a 'light echo' from that explosion around the star have uncovered remarkable new features.
Credit: NASA/Hubble
Put into orbit at an altitude of 600 km by the space shuttle Discovery on 25 April 1990, Hubble has transmitted more than 750,000 spectacular images and streams of data from the ends of the universe, opening a new era in astronomy.
But the telescope, the fruit of a collaboration between the U.S. space agency, NASA, and the European Space Agency (ESA), had a troubled start and did not become operational until three years after its deployment.
It had to be fixed because of a flaw in the shape of its mirror, a sensitive operation that was not carried out until 1993 in the first shuttle-borne service mission, which installed corrective lenses to fix it.
From that time on Hubble has transmitted stupefying images of supernovas – gigantic explosions that mark the death of a star – and revealed that there are mysterious black holes in the centre of virtually all galaxies.
See a slideshow of some of Hubble's most spectacular images here.
Thanks to these observations, delivered with 10 times the clarity of the most powerful telescopes on Earth, astronomers have been able to confirm that the universe is expanding at an accelerating rate and also calculated its age with greater precision as an estimated 13.7 billion years.
The universe's acceleration is the result of an unknown force dubbed dark energy that constitutes about 70% of the substance of the universe and works against the force of gravity. The rest of the universe is composed of about 5% visible matter and about 25% dark matter.
Among the other discoveries credited to Hubble include that the process of formation of planets and solar systems is relatively common in our galaxy, the Milky Way, and the detection of the first organic molecules in the atmosphere of a planet orbiting another star.
Hubble has also observed small proto-galaxies that were emitting light when the universe was less than a billion years old, the farthest back in time that a telescope has been able to peer so far.
The two new instruments that will be installed by astronauts on the shuttle Atlantis this week will enable Hubble to look out in time as far as 600 to 500 million years after the universe's birth in the Big Bang, according to NASA.
"If we are successful, [Hubble] will be more powerful and robust than ever before and will continue to enable world class science for at least another five years and overlap with [its successor] the James Webb Space Telescope," said Ed Weiller, associate director of NASA's research programs.
Closer to home, Hubble has observed radical changes in the direction of Saturn's winds and revealed that Neptune has seasons. The telescope has also examined mysterious lightning flashes on Jupiter and taken astonishing pictures of Mars.
This list of startling scientific discoveries has made Hubble "truly an icon of American life," said Weiller. "I maintain that if the average American knows only one science project, one science instrument, I bet it's Hubble," he said.
Jean-Louis Santini is a writer for the AFP news agency.
