Comets may have plunged to Earth when it was a hot, rocky, barren and inhospitable place and formed the oceans, David Jewitt told his HKU audience.
He explained how three icy comets observed orbiting among the rocky asteroids between Mars and Jupiter may be of the same type that collided with the Earth, providing its water. The observations were made last year using the Gemini North Telescope on Mauna Kea, with the results published in Science Express in March.
The 'main-belt comets', discovered by Professor Jewitt and graduate student Henry Hsieh, differ from other comets in that they appear to have formed in the warmer inner solar system inside the orbit of Jupiter rather than in Kuiper belt.
Professor Jewitt said the existence of the comets could mean that asteroids and comets were more closely related than previously thought and could have contributed to the formation of the Earth's oceans.
Earlier this year, another scientist visiting HKU suggested that life itself could have come from space.
Max Bernstein, deputy chief of the space science and astrobiology division at Nasa's Ames Research Centre, told a lecture audience that cosmic dust entering the Earth's atmosphere via asteroids and meteorites from 'giant chemical factories' formed in dense icy clouds in the universe could have provided the material that led to life.