Atom & Cosmos

Dead stars may actually be a good place to hunt for life, plus organic-free asteroids and watery comets in this week’s news

Life among dead stars
Dead stars may be some of the best, yet often overlooked, places to find Earth-sized habitable planets. Eric Agol of the University of Washington in Seattle considers a group of dead stars known as white dwarfs — the final stage of sunlike stars. A subset of white dwarfs would be surrounded by habitable zones — regions where water on a solid planet would be liquid — lying extremely close to the stars. Because white dwarfs are no bigger than Earth, it should be easy to spot an Earth-sized planet in the habitable zone passing in front of one of the stars, Agol notes in a paper that will appear in an upcoming Astrophysical Journal Letters. —Ron Cowen

Casting doubts on rocky life
Most carbon-rich asteroids in the early solar system couldn’t have harbored life, even though some of them retained liquid water and moderate temperatures at their centers for 24 million years, geologists from the University of Colorado at Boulder calculate. The rocks lacked the abundant organic building blocks deemed necessary for life and the heat needed to drive chemical gradients. The results do not preclude the existence of conditions favorable for life on large asteroids such as Ceres and members of the Themis family, which may have had longer-lived reservoirs of water and a greater storehouse of internal heat, the team reports in an upcoming Icarus. —Ron Cowen

Comet water
Planetary scientists have discovered indirect evidence that grains from Comet Wild 2 that were sampled by the Stardust spacecraft formed in the presence of water, a key ingredient for life. Eve Berger of the University of Arizona and her colleagues base that finding on several types of iron sulfides found in the grains. The sulfides are most likely the products of a chemical reaction that involved water at low temperatures, the team reports in an upcoming Geochimica et Cosmochimica Acta. The discovery suggests that iron sulfides from the inner solar system traveled to the comet-forming region early in the solar system’s history. —Ron Cowen

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