What do we define as urban green space?

When do we define a piece of nature in the city as a park? And when is something a tree or shrub? It may seem obvious, but in scientific literature the definitions vary quite a bit. That makes comparisons difficult. Environmental ...

How did the Butterfly Nebula get its wings? It's complicated

Planetary nebulae form when red giant stars expel their outermost layers as they run out of helium fuel—becoming hot, dense white dwarf stars that are roughly the size of Earth. The material that was shed, enriched in carbon, ...

Long-lived lakes reveal a history of water on Mars

The northern hemisphere of Mars is divided into two broadly distinctive areas: the smooth northern lowlands and the pockmarked southern highlands. The region of Arabia Terra sits along the transition between these two regions ...

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