"Inanimate, wheeled, one-armed boxes roaming another planet have done something no human has ever managed," Science reported in this week's edition.
Opportunity and Spirit found unmistakable proof of Martian water -- rippled sediments that were once at the bottom of a shallow sea, and rock that once was so water-soaked that "it had rotted," the journal said.
"Their finds mark a milestone in humankind's search for life elsewhere in the universe," Science said.
The rest of Science's 2004 "breakthroughs of the year" are:
2. LITTLE PEOPLE: The discovery on the Indonesian island of Flores of fossils from a species of tiny humans who stood about 3 feet tall and had a brain less than a third the size of modern humans. The diminutive hominid lived about 18,000 years ago, which suggests that Homo floresiensis shared the Earth with Homo sapiens, or modern people. Science said some described the find as "the biggest discovery in a half-century of anthropological research."
3. CLONED EMBRYOS: The cloning of human embryos by South Korean researcher Woo San Hwang and his colleagues. The work was not an attempt to genetically duplicate a human. Instead, the researchers hoped to make embryonic stem cells for research purposes. Although many other mammals have been cloned, the work was the first to demonstrate that cloning techniques would work with human cells.
4. NEW GAS: US and Austrian scientists created a new form of condensate, an ultracold gas that slips into a quantum state where a group of atoms act as a single superatom. The achievement was notable because it used fermions, a class of atoms with a nuclear structure that makes it difficult to create a condensate.
5. THE VALUE OF TRASH: Scientists discovered that "junk DNA," the base pairs between known genes in the human genetic structure, aren't junk after all. Several research teams have found that DNA between genes helps determine how vigorously and often the genes are activated, and shapes the coding for protein production.
