Top 10 Discoveries of the Decade

A countdown that begins in space and ends at Earth's poles.

10. Pluto-Sized Eris Rocks Solar System

In January 2005, Mike Brown and his team at Palomar Observatory, Calif. discovered 136199 Eris, a minor body that is 27 percent bigger than Pluto. Eris had trumped Pluto and become the 9th largest body known to orbit the sun. In 2006, the International Astronomical Union (IAU) decided that the likelihood of finding more small rocky bodies in the outer solar system was so high that the definition "a planet" needed to be reconsidered. The end result: Pluto was reclassified as a dwarf planet. Pluto acquired a "minor planet designator" in front of its name: "134340 Pluto." Mike Brown's 2005 discovery of Eris was the trigger that changed the face of our solar system, defining the planets and adding Pluto to a growing family of dwarf planets.

9. T. rex Tissue Dug from Bone

In 2005, Mary Higby Schweitzer and her colleagues reported in Science the discovery of what appeared to be soft tissues -– blood vessels, bone matrix and other cells –- inside the fossilized femur of a small T. rex. Since then, the bones have revealed amino acids that resemble those of modern chickens, firming the link between dinosaurs and birds. Schweitzer's discovery comes in a decade of other stunning revelations about the soft parts of dinosaurs. In 2004, one of the few mummified dinosaurs ever found -- an amazingly well-preserved 66-million-year-old hadrosaur with intact, mostly mineralized skin -- was excavated from a ranch in North Dakota. Then, in June 2009, researchers announced they had isolated molecules related to soft skin tissues from that hadrosaur.

8. Dark Matter's Existence Confirmed Directly

In the summer of 2006, astronomers made an announcement that helped humans understand the cosmos a little better: They had direct evidence confirming the existence of dark matter -- even though they still can't say what exactly the stuff is. The unprecedented evidence came from the careful weighing of gas and stars flung about in the head-on smash-up between two great clusters of galaxies in the Bullet Cluster. Until then, the existence of dark matter was inferred by the fact that galaxies have only one-fifth of the visible matter needed to create the gravity that keeps them intact. So the rest must be invisible to telescopes: That unseen matter is "dark." The observations of the Bullet Cluster, officially known as galaxy cluster 1E0657-56, did not explain what dark matter is. They did, however, give researchers hints that dark matter particles act a certain way, which future research can build on.

7. New Human Ancestors Emerge

In 2002, researchers in northern Chad unearthed the 6- to 7-million-year-old skull of Sahelanthropus tchadensis -- known as Toumai. Only skull bones have been discovered, so it's not confirmed whether Toumai walked upright on two feet. But other Toumai remains make a stronger case that it greatly extends the human family timeline. Then along came Ardi. In 2009, the nearly complete skeleton of Ardipithecus ramidus, a.k.a. “Ardi,” in northeastern Ethiopia bumped the famous “Lucy” as the earliest, most complete skeleton of a human ancestor ever found. The 4.4-million-year-old Ardi could walk on two legs, but was also a skilled tree-climber. Her teeth suggest she ate many different types of food. And scientists theorize that males and females may have paired off at this time, significantly boosting survival, since females could intensify their parenting while males provided food. If the studies prove true, Ardi marks the closest we have come to discovering the last common ancestor of chimpanzees and humans.

6. Alien Planets Seen Directly

The first alien planets -- called exoplanets -- were being detected in the early 1990s, but not directly. In 2000, astronomers detected a handful by looking for a star's "wobble," or a star's slight dimming as the exoplanet passed in front of it. Today we know of 400 exoplanets. In 2008, astronomers using the Hubble Space Telescope and the infrared Keck and Gemini observatories in Hawaii announced that they had "seen" exoplanets orbiting distant stars. The two observatories had taken images of these alien worlds. The Keck observation was the infrared detection of three exoplanets orbiting a star called HR8799, 150 light-years from Earth. Hubble spotted one massive exoplanet orbiting the star Fomalhaut, 25 light-years from Earth. These finds pose a profound question: How long will it be until we spot an Earth-like world with an extraterrestrial civilization looking back at us?

5. Humans Meld with Machines

Cyborgs are becoming reality. In the last decade, much progress has been made with people controlling robotic limbs and computers with their minds. In 2000, researchers at Duke University Medical Center implanted electrodes in monkeys’ brains and then trained them to reach for food using a robotic arm. Such a neurochip could one day restore motor function in paralyzed patients. A team from the MIT Media Lab Europe developed a non-invasive method for picking up brain waves and, in 2004, used those signals for the first time to control the movements of a video game character. Robotic limbs operated with nerve signals debuted in 2001 at the Rehabilitation Institute of Chicago. There, Jesse Sullivan, a double amputee, used the method to control both of his robotic arms. And in 2009, amputee Pierpaolo Petruzziello learned to control a biomechanical hand connected to his arm nerves with just wires and electrodes. Petruzziello became the first person to make complex movements -- finger wiggling, a fist, grabbing objects -- with a robotic limb, using just his thoughts.

4. Stem Cells Found in New Sources

In 2001, President George W. Bush cut federal funding to scientists working with embryonic stem cells -- found in a tiny, hollow ball of about 70-100 human cells that could become anything in the human body -- because of ethical concerns. Embryonic stem cells were one of the most promising medical advances in years, with the potential to cure diseases from diabetes to cancer to genetic disorders, and more. In 2007, scientists from Kyoto University and the University of Wisconsin-Madison, working separately, essentially turned back the clock for adult skin cells, allowing these mature cells, which were preprogrammed to become skin, to act like embryonic stem cells. The adult cells became pluripotent cells, or cells that could end up being virtually any other kind of cell. These pluripotent adult cells solved two big problems. Ethical concerns and financial restrictions could be avoided, and doctors could ultimately use cells with a person's own DNA to grow replacement organs that a patient would be less likely to reject.

3. Mars Surface Gives up Signs of Water

In 2008, NASA's Mars Phoenix lander touched down on the Red Planet to confirm the presence of water and seek out signs of organic compounds. Eight years before, the Mars Global Surveyor spotted what appeared to be gullies carved into the landscape by flowing water. More recently, the Mars Exploration Rovers have uncovered minerals that also indicated the presence of ancient water. But proof of modern-day water was elusive. Then Phoenix, planted on the ground near the North Pole, did some digging for samples to analyze. During one dig, the onboard cameras spotted a white powder in the freshly dug soil. In comparison images taken over the coming days, the powder slowly vanished. After intense analysis, the white powder was confirmed as water ice. This discovery not only confirmed the presence of water on the Red Planet, it reenergized the hope that some kind of microbial life might be using this water supply to survive.

2. Human Genome Mapped

Coiled up inside every human cell sit 23 molecules that, if unwound and placed end to end, would stretch about three feet. Those molecules, known as chromosomes, contain all the instructions necessary to build an entire human being. It took more than 10 years and an international collaboration of scientists, but the year 2000 saw a rough draft of the entire human genome, followed by a completed version in 2003. The publicly funded Human Genome Project and its private competitor, Celera Genomics, constitutes one of the largest scientific endeavors in history, one that revealed in intimate detail just what makes up a human being. With the information from individual genome maps, scientists can uncover new clues about everything from a person's body odor to mental disease. Since decoding the human genome, dozens of other species have had their genomes sequenced, including pigs, dogs, bees, mosquitoes, puffer fish, chimpanzees, yeast, corn, and rice. With these maps in hand, scientists can and will discover new ways to heal diseases or improve crop yields.

1. Glaciers Melting Fast

When the 21st century began, scientists studying Earth’s climate thought the gigantic ice caps on Greenland and Antarctica would melt slowly around the edges and lag behind the overall global warming of climate. But this past decade, the warmest on record, proved the climate modelers wrong. Glaciers have been melting much faster than ever expected and researchers have been trying to understand why. The uptick in melting ice has not been restricted to the Arctic and Antarctic. Europe’s glaciers are now thought to be entering their final decades. The famous snows of Kilimanjaro and other low-latitude mountains could disappear completely. The thick, perennial sea ice of the Arctic is fast disappearing, which will likely bring ice-free summers to the Arctic Ocean. There are global consequences to this melting. Rising seas will make more cities and islands vulnerable to catastrophic flooding like that which nearly killed New Orleans. Mountain glaciers around the world bring fresh water to billions. Any way you slice it, an Earth with less ice is a less hospitable planet.