Atom & Cosmos

Planets walk crooked after cloud crashes
Cloud fender benders in crowded stellar nurseries may explain why some planets are born with off-kilter orbits. While the solar system is pretty orderly — all the planets circle the sun in the same direction and the same plane — planets circling distant stars can follow highly elliptical, tilted orbits or even dance backwards compared to their suns’ rotations. German and British astronomers suggest in an upcoming Monthly Notices of the Royal Astronomical Society that this diversity might come about in the systems’ infancies, when their stars are still huddled in clusters. Encounters between gas clouds and the disks that later form these systems could cause all these peculiarities and even speed up planet formation. —Camille M. Carlisle

Pulsar planet is way dense
Astronomers have discovered the densest exoplanet yet, orbiting a whirling dead star. Although the first exoplanet system ever found orbits one of these spinning stellar cores, which are called pulsars, no other pulsar planets have been spotted since that first discovery in 1992. The new exoplanet is comparable in size to Jupiter but is 20 times denser, making it about five times denser than Earth, an international team reports online August 25 in Science. The researchers suggest that the planet may be made of carbon and oxygen instead of the hydrogen and helium that are found in run-of-the-mill gas giants like Jupiter and Saturn. That suggests that the planet may be an über-lightweight dead star called a white dwarf that was transformed into a planet when the pulsar stole mass from it. —Camille M. Carlisle

Six Earthy exoplanets
Scientists have created rap sheets for six planets beyond the solar system, orbiting three distant stars. One of the stars hosts a planetary system containing three super-Earth planets that are heavier than Earth but lighter than gas giant planets like Jupiter. Another harbors a 3.6-Earth-mass planet within its habitable zone, a team of scientists from Europe reports in a paper posted August 17 on arXiv.org. That planet, HD 85512b, is the subject of a second paper posted to the arXiv on the same date. In that paper, a second team suggests that the planet could be habitable if clouds cover more than half its surface. Super-Earths are predicted to be frequent around solar-type stars, but are more difficult to detect than larger, Jupiter-mass planets. —Nadia Drake

Earth not so special
A new analysis of recent telescope observations has burst the idea that the Earth occupies a special spot in a gigantic cosmic bubble. The work counters proposals to explain the apparently accelerating expansion of the universe without a mysterious force known as dark energy. Such proposals reject the Copernican principle, which holds that the Earth occupies a typical location in the cosmos. If instead the Earth occupies a sparsely populated bubble, galaxies within it would zip away rapidly, pulled by the gravity of the denser stuff outside, mimicking a universe expanding at an accelerating rate. But such galactic motion should leave detectable imprints in microwave radiation left over from the Big Bang. Telescopes in Chile and Antarctica find no such evidence, astrophysicists from China and the United States report in the July 22 Physical Review Letters. —Devin Powell