Atom & Cosmos

The right mix of dark matter to build a galaxy, plus Kleopatra’s twins and an electric Encaledus in this week’s news

Dark recipe for galaxies
When it comes to dark matter, the mass equivalent of 300 billion suns is the Goldilocks number — just the right amount for making a galaxy teeming with stars. A new report spotlights the role that dark matter, the invisible material that accounts for more than 80 percent of the matter in the cosmos, plays in pulling in gas and stars to form the earliest galaxies. Too little dark matter and a developing galaxy peters out; too much and gas won’t cool efficiently to form a single large galaxy, Asantha Cooray of the University of California, Irvine, and his colleagues report in the Feb. 24 Nature. —Ron Cowen

Electric Enceladus
Plumes of water vapor and heat emanating from below the surface of Saturn’s moon Enceladus could be powered by electric current, a previously overlooked source of power for the features. The current would be generated by Enceladus’ interactions with Saturn’s magnetic field. Although the current would provide no more than 0.25 percent of the observed heat, it might prevent or at least slow the refreezing and sealing of cracks from which the plumes vent into space, Kevin Hand of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and his colleagues calculate in an upcoming Journal of Geophysical ResearchPlanets. Ron Cowen

 
Kleopatra’s moons
Just as Cleopatra, the queen of Egypt, gave birth to twins, so has Kleopatra the asteroid. Planetary scientists have discovered that the asteroid has two moons, each about 8 kilometers across, spawned in the past 100 million years. The moons were most likely created when a chunk of space debris sideswiped Kleopatra, spinning up the asteroid and causing it to shed material, a French-American team reports in the February Icarus. By tracking the orbits of the newfound moons, the team measured the density of Kleopatra and found that the asteroid is a loosely bound amalgam of metal and rock. —Ron Cowen

Organic delivery
Comets may have seeded the atmospheres of both Earth and Saturn’s moon Titan. Spanish researchers base their proposal on the similar abundances of nitrogen and organic compounds in the atmospheres of the two bodies — even though Titan resides in a much colder part of the solar system. Titan could have incorporated icy, cometlike bodies rich in nitrogen and organic compounds from its immediate neighborhood during formation, while comets could have delivered the material to Earth a few hundred million years later, after the planet had formed. The researchers make their case in an upcoming Planetary and Space Science paper posted online at arXiv.org on February 22. —Ron Cowen

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