AUSTIN, Texas — Scientists are beginning to sort out the stellar ingredients that produce a type 1a supernova, a type of cosmic explosion that has been used to measure the universe’s accelerating expansion.

IN THE deserts of an alien planet, the famously neurotic C-3PO from Star Wars had a talent that today’s robots sadly lack: hiking through sand dunes. That could soon change, though, as humanoids learn how to balance when the going gets soft.

It was a year that began with natural disasters and ended with a bevy of discoveries, including Earth-like planets orbiting nearby stars and signs that the Higgs boson may actually exist.

The first part of 2011 was dominated by natural disasters. La Nina caused flooding across large parts of Australia, and resulted in Cyclone Yasi, one of the largest tropical storms to cross the Australian coast.

Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System (after Eris) and the tenth-most-massive body observed directly orbiting the Sun. Originally classified as the ninth planet from the Sun, Pluto was recategorized as a dwarf planet and plutoid due to the discovery that it is one of several large bodies within the newly charted Kuiper belt.

Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus (Ancient Greek: Οὐρανός), the father of Cronus (Saturn) and grandfather of Zeus (Jupiter). Though it is visible to the naked eye like the five classical planets, it was never recognized as a planet by ancient observers because of its dimness and slow orbit. Sir William Herschel announced its discovery on March 13, 1781, expanding the known boundaries of the Solar System for the first time in modern history. Uranus was also the first planet discovered with a telescope.

Chemists have tangled themselves a complicated knot: a molecule whose 160 atoms loop over one another like a five-pointed star.

The molecule’s design, called a pentafoil, is the most complex knot synthesized from building blocks other than DNA. Knowing how to make a pentafoil, its discoverers say, could lead to ways to make materials lighter, stronger or more flexible than before.

On December 5, astronomers introduced a newly discovered planet that seemed habitable for extraterrestrial life. The faraway world is an exoplanet, or planet outside our solar system, called Kepler-22b. It looks E.T.-friendly because its temperature is neither too hot nor too cold for liquid water, which is essential to life as we know it. The planet orbits its star at just the right distance, sometimes called the “Goldilocks” zone.

Odd as it sounds, adding wishy-washy members to a group can wrest control from a strongly opinionated minority and make collective decisions more democratic. At least that’s what happened in an experiment with schooling fish and three kinds of computer simulations described in the Dec. 16 Science.

His appearance was reminiscent of a squirrel with large, sharp teeth so paleontologists have found fossils of this species, now extinct, have dubbed “Cronopio dentiacutus’. This is a small mammal that lived with the dinosaurs about 96 million years in the territory now occupied by the Patagonia Argentina.

Scientists have confirmed that some fossils found in the state of Minas Gerais correspond to a sloth-foot tall, who lived during the Holocene, 10,000 years ago.

“It’s an incredible discovery and of great value to science, it is a prehistoric mammal opens up new and more extensive opportunities to study,” said geologist Carlos Borges, director of the Dinosaur Museum in the city of Uberaba.