Scientists have long been puzzled about what makes Mercury’s surface so dark. The innermost planet reflects much less sunlight than the Moon, a body on which surface darkness is controlled by the abundance of iron-rich minerals. These are known to be rare at Mercury’s surface, so what is the “darkening agent” there?
New information about the way mature stars spin indicates that one recently developed method for determining a star’s age needs to be recalibrated for stars that are older than our Sun, as spin rate is one of the few windows into stellar ages. This has implications for our own solar system, as our own Sun might be on the cusp of a transition in its magnetic field.
The main-belt asteroid (493) Griseldis, that lies between the orbits of Mars and Jupiter, was probably hit by another object last March. The results were reported on 12 November at the 47th Annual Meeting of the Division for Planetary Sciences of the American Astronomical Society near Washington, DC.
For more than 30 years, scientists have argued about a controversial hypothesis relating to periodic mass extinctions and impact craters on Earth caused by comet and asteroid showers. Now scientists conclude that these events show a cyclical pattern over the studied period, with both impacts and extinction events taking place every 26 million years.
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