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More than 200 years ago, mathematician Joseph-Louis Lagrange predicted the existence of what became known as Trojan asteroids small bodies that can stably share the orbit of a planet if they remain near triangular points 60° ahead of or behind it in its orbit. Jupiter has thousands of Trojans; Mars and Neptune have some too. Now Earth is shown to have a Trojan. A search of data collected by NASAs Wide-field Infrared Survey Explorer (WISE) satellite revealed the asteroid 2010 TK7 as a strong candidate, and subsequent optical observations confirm its status as a Trojan companion of Earth, oscillating around the L4 (leading) Lagrange triangular point. The cover imagines 165 years of motion of 2010 TK7 seen from a vantage point outside of, and above, Earths orbit. Cover image: Paul Wiegert.
Regulators must look past visceral disgust about human–animal hybrids. Strict but sensible rules are needed for research on hybrid embryos and chimaeric animals that could produce therapies.
International agreements are not enough. Interlinked national and regional tools are also needed to reduce carbon emissions, say Mark Maslin and Joanne Scott.
As sesquicentennial celebrations commemorate the discovery of Archaeopteryx as a historical symbol of evolution and the oldest fossil bird, new work shakes the dinosaur family tree — and our view of this icon. See Article p.465
Shining light on an antiproton masquerading as an electron in a helium atom is a rich source of physics. An approach that brings this technique to unprecedented precision will allow new tests of matter–antimatter symmetry. See Letter p.484
Dust and glowing hydrogen obscure the Carina complex at visible wavelengths. An X-ray study, combined with infrared surveys, provides knowledge of newly formed stellar associations and past supernova explosions in this system.
Magnesium binds to enzymes and nucleic acids and is essential for their activity. It emerges that this ion can also function as a signalling molecule with a crucial role in the immune system. See Article p.471
Wave energy has long been proposed to be a source of the hot solar corona and fast solar wind. Direct measurements made by spacecraft have finally established that coronal waves are ubiquitous and can have the required energy. See Letter p.477